[25] EFFECT OF THE BANKART LESION ON ANTERIOR JOINT STABILITY GLENOHUMERAL MUSCLE FORCES
Thay Q. Lee, MS; Patrick J. McMahon, MD
Orthopaedic Biomechanics Laboratory, PACT, VA Medical
Center, Long Beach, California, 90822; Department of
Orthopaedic Surgery, University of California, Irvine,
Irvine, CA 92717; email: tqlee@pop.long-beach.va.gov
Sponsor: Department of Veterans Affairs, VA
Rehabilitation Research and Development Service, Washington,
DC 20420
(Project #A880-RC)
PURPOSE--The objective of this project is to biomechanically assess the contribution of two common shoulder injuries to glenohumeral instability: tear of the origin of the inferior glenohumeral ligament (the Bankart lesion) and joint effusion.
METHODOLOGY--To study the effect of the Bankart lesion and joint effusion on glenohumeral joint kinematics and kinetics requires a building of a custom shoulder loading apparatus that utilizes a six-axes load cell, six degrees of freedom (DOF) electromagnetic tracking device, four differential variable reluctance transducers (DVRT) and a video digitizing system (VDS). Using this device, we will simulate the shoulder muscles and static joint restraints in the joint position of instability to measure: the joint compression force, the position of the humeral head on the glenoid, and the strain in the inferior glenohumeral ligament.
PROGRESS--The shoulder testing apparatus has been designed and built. This device permits the application of each individual muscle forces in the shoulder while permitting simultaneous measurement of the glenohumeral joint compression force and kinematics. The joint compression force is measured with the six-axes load cell and the glenohumeral joint kinematics is measured with the magnetic tracking device. In addition, the strain distribution in the inferior glenohumeral ligament (IGHL) has also been determined.
PRELIMINARY RESULTS--Thirteen fresh frozen cadaveric glenohumeral joints were used to determine the strain distribution in the IGHL. Two were positioned at 60° of abduction, externally rotated, and then frozen for histological analyses. The remaining 11 joints were used for biomechanical testing of the IGHL with the humerus abducted 60° and then externally rotated. The histology results showed that the anterior band of the IGHL has two attachments at the glenoid insertion site: the labrum and, the anterior glenoid neck. The results from the biomechanical testing showed that eight (73 percent) of the b-l-l-b complexes failed at the glenoid insertion site (representing the Bankart lesion), one (9 percent) at the humeral insertion site, and two (18 percent) at the anterior band midsubstance. The results also demonstrated that most of the strain occurs at the insertion sites, with failure occurring most often at the glenoid insertion.
FUTURE PLANS--Fresh frozen full upper limb specimens will be mounted by rigidly attaching the scapula on the shoulder testing apparatus. The muscles simulated are those active in abduction of the joint: deltoid (middle and upper portions), supraspinatus, subscapularis, and the infraspinatus/teres minor. The scapula will be positioned in 30° of abduction and muscle force will be applied to the tendons of the simulated muscles until the shoulder joint reaches 90° of abduction. The force in the infraspinatus/teres minor muscles will then be increased for maximum external rotation. Glenohumeral joint motion will be measured with a six DOF magnetic tracking device. Three DVRTs and continuous VDS will be used to determine in-situ strain in the IGHL. The IGHL will then be tested in tension to determine the in-situ stress. For the measurement of the resultant glenohumeral joint compression force, a six-axes load cell will be used. The intracapsular pressure in the joint will then be increased and the test repeated, then a Bankart lesion will be surgically created and the test repeated again. At the completion of joint motion each glenohumeral joint will be dissected and the center of curvatures for the humeral head and the glenoid will be determined.
[26] BIOMECHANICS OF THE PATELLOFEMORAL JOINT AND PERIPATELLAR RETINACULUM
Thay Q. Lee, MS
Orthopaedic Biomechanics Laboratory, PACT, VA Medical
Center, Long Beach, California, 90822; Department of
Orthopaedic Surgery, University of California, Irvine,
Irvine, CA 92717; email: tqlee@pop.long-beach.va.gov
Sponsor: Department of Veterans Affairs, VA
Rehabilitation Research and Development Service, Washington,
DC 20420
(Project #A881-RC)
PURPOSE--The purpose of this study is to quantify the structural and mechanical properties as well as in-situ stress and forces in the peripatellar retinaculum. This study is designed to quantitatively assess the functional role of the peripatellar retinaculum in addition to determining the effects of lateral patellar retinaculum release, tibial torsion, and complete transverse patellar fracture.
METHODOLOGY--Fresh frozen human cadaver knees will be used with an Instron machine and a custom patellofemoral joint loading jig that permits the measurement of strain in the peripatellar retinaculum while controlling the knee flexion angle, degree of tibial torsion and tension in the quadriceps muscles (rectus femoris/vastus intermedius as well as vastus medialis and vastus lateralis). The mean strain in the peripatellar retinaculum will be measured using six differential variable reluctance transducers (DVRT), and the surface strain will be measured using the video digitizing system (VDS). To determine the in-situ stress and forces in the peripatellar retinaculum, the in-situ strain is first measured in intact knees. The peripatellar retinaculum is then isolated for tensile testing to determine both the structural and mechanical properties. The results will then be correlated to compute in-situ stress and forces in peripatellar retinaculum.
PROGRESS--The patellofemoral joint (PFJ) loading jig has been built. This jig allows 5 degrees of freedom (DOF) at the femur and 3 DOF at the tibia. Muscle loading can be accomplished through stainless steel clamps, an adjustable pulley system and lead weights. This custom jig permits independent application of all knee extensor muscle (rectus femoris/vastus intermedius, vastus lateralis, vastus medius, iliotibial band) forces in its anatomic/physiologic orientation at any knee flexion angle. This jig also permits simultaneous measurement of the patellofemoral joint contact pressures and kinematics using Fuji pressure sensitive film and a three-dimensional magnetic tracking device, respectively. We have also determined the anatomic/physiologic loading conditions for the in-vitro testing of the patellofemoral joint.
PRELIMINARY RESULTS--We have quantified the PFJ kinematics and contact pressures while considering physiologic/anatomic muscle loading parameters. These loading configurations will be used for the quantification of the in-situ stress in the peripatellar retinaculum. The physiologic/anatomic loading conditions using the individual extensor muscles resulted in a significantly greater peak PFJ contact pressure at 0° of knee flexion and significantly less peak contact pressure at 90° of flexion as compared to the resultant quadriceps tendon loading. Significantly greater joint contact area was observed with the physiologic/anatomic loading condition at 30° of knee flexion. Kinematic differences between the two loading conditions was evident in patella rotation with the physiologic/anatomic loading condition demonstrating increased medial rotation from 0 to 75° of knee flexion. In addition, the resultant quadriceps tendon loading condition resulted in greater patella flexion from 0 to 45° and greater lateral patellar shift at 15° of knee flexion.
FUTURE PLANS--We plan to determine the tissue strain and stress in the peripatellar. This will be accomplished by quantifying the biomechanical properties as well as the in situ forces in the peripatellar retinaculum. We will also quantitatively assess the effects of lateral patellar retinaculum release, tibial torsion, and complete transverse patellar fracture.
[27] THE EFFECT OF HYDROSTATIC PRESSURE ON INTERVERTEBRAL DISC METABOLISM
Scott D. Boden, MD; William C. Hutton, DSc; William A.
Elmer, PhD
Emory University, Department of Orthopaedics, Decatur,
GA 30033; email: whutton@ortho.eushc.org
Sponsor: Department of Veterans Affairs, VA
Rehabilitation Research and Development Service, Washington,
DC 20420
(Project #A834-2RA)
PURPOSE--This 3-year study tests the hypothesis that hydrostatic pressure directly affects the synthesis of collagen and aggrecan (the cartilage specific proteoglycan) by the intervertebral disc cells.
METHODOLOGY--Chondrocytes maintained in a 3-dimensional configuration suspended in an alginate gel will serve as our in vitro biological assay system. Using this culture system and three pressure chambers, our research plan is designed as follows:
PROGRESS--Our experimental system works and the cartilage cells are affected as anticipated. The progress to date is as follows: 12 separate experiments have been completed. The endpoint for each experiment was the amount of radioactive proline and sulfate incorporated into collagen and sulfated proteoglycans (CSPG) respectively in canine intervertebral disc cells cultured under a pressure of 150 lb/in2 compared to cells cultured at atmospheric pressure. For each experiment, the annulus and nucleus were isolated separately from lumbar discs, and their cells were enzymatically released. Cell number was expanded by culturing in 25 cm T-flasks for 8 days followed by a subsequent subculturing of 8 days in a 75 cm T-flask. The cells in the confluent cultures were resuspended in alginate gel at a concentration of 3×106 cells/ml before encapsulation into gelatinous beads. Equal aliquots of beads were transferred to 5 cc syringes containing complete culture medium sealed with a cap at one end and a plunger at the other end. The syringes were placed in a holding device and lowered into a pressure tank. The tank was pressurized at 150 lb/in2 and placed in a 37 °C humidified incubator for 9 days. In some cases the pressure was not applied until day 8 of incubation. For all experiments, radioactive incorporation was carried out for 24 hours between day 8 and day 9 of incubation. After each experiment, the cells were released from the alginate gel, collected and assayed for collagen, CSPG, and DNA. Greater than 98 percent of the radioactive label remained with the extracellular matrix which surrounds the cells.
PRELIMINARY RESULTS--The data showed a significant increase in both proline and sulfate incorporation caused by pressure applied for either the entire 9 days or for only the last 24 hours of the 9-day incubation period. The values (DPM/µg DNA) ranged between 100 and 500 percent above control levels.
FUTURE PLANS--We have completed year 1 of our project. We will now proceed with Experiment 2.
[28] EFFECT OF SURGICAL PROCEDURES ON THE STABILITY OF THE LUMBAR MOTION SEGMENT
Gunnar B.J. Andersson, MD; Avinash G. Patwardhan, PhD;
Raghunath N. Natarajan PhD; Steven A. Lavender, PhD
Rush Presbyterian-St. Luke's Medical Center, Chicago,
IL; Loyola University Chicago, Maywood, IL 60153; Hines VA
Hospital, Hines, IL 60141
Sponsor: Department of Veterans Affairs, VA
Rehabilitation Research and Development Service, Washington,
DC 20420
(Project #A830-RA)
PURPOSE--Many surgical procedures of the lumbar spine require removal of tissue from the motion segment, for example laminectomy and discectomy. When large amounts of tissue are removed, the stiffness of the motion segment is reduced to a degree that there is an abnormal response to an applied load. To compensate for this decrease in stiffness which, in addition to creating pain, may present a risk to neurological structures, fusion surgery is sometimes performed. At the present time, there is a clinical controversy about when a fusion should or should not be performed. The question of whether to fuse or not is important since the fusion procedure increases the morbidity from spinal surgery. Further, when one motion segment is fused the adjacent segments receive increased stress, placing these segments at risk of future injury. The purpose of this research is to quantify the segmental instability resulting from the commonly used surgical techniques of facet and disc resection through a combination of experimental and analytical techniques.
METHODOLOGY--The study will be conducted in three phases. In the first phase, we will perform experiments on human cadaveric lumbar spine specimens to determine the effects of surgical procedures on the load-displacement behavior of lumbar motion segments. The experiments will simulate 18 unique combinations of surgical procedures including unilateral and bilateral facet removal and disc denucleation. Each simulated surgical procedure will be tested under compression, flexion-extension, lateral bending, and axial torsion. In the second phase, we will validate an existing finite element model of a lumbar motion segment by modeling the experimental simulations of facet removal and disc denucleation. In the third phase, we will use the validated finite element model to conduct a detailed parametric study of the effects of surgical procedures on the change in stiffness of the lumbar motion segments. The finite element model will also be used to determine how disc height and facet orientation influence changes in the stiffness of the motion segment caused by different surgical procedures. The simulation results will be analyzed to determine the critical magnitude of surgical resection that causes a large decrease in the stiffness of the lumbar motion segment.
PROGRESS--Based on the results of our preliminary tests, we have completed final modifications to the experimental set up for testing multisegment human cadaveric lumbar specimens. We are conducting experiments to determine the effects of different surgical procedures on the load-displacement behavior of lumbar motion segments as outlined above.
We have developed an improved model of the facet contact to conduct modeling studies of the effect of graded unilateral facetectomy on the flexibility of the lumbar motion segment. In addition, a three-dimensional finite element model of an L4-5 disc-body unit has been developed using serial CT scans. The model predictions for different loading conditions agreed well with the experimental data in the literature. We are now combining the disc-body model with the facet model to develop a model of the complete motion segment which will be used in the final phase of the study.
FUTURE PLANS/IMPLICATIONS--During the next year we will complete remaining experiments on fresh human cadaveric lumbar spines. The validated finite element model will be used to conduct a detailed parametric study of the effects of surgical procedures on the change in stiffness of the lumbar motion segments. The information generated in this study will be used as a basis for developing recommendations concerning when to fuse and when not to fuse.
[29] CONTACT CHARACTERISTICS OF THE SUBTALAR JOINT AFTER LATERAL COLUMN LENGTHENING THROUGH THE ANTERIOR CALCANEUS AND THE CALCANEOCUBOID JOINT
A. McCormack, MD; Hisateru Niki, MD; N. Felten; P.
Kiser; A.F. Tencer, PhD; Bruce J. Sangeorzan, MD
Department of Orthopedics, Harborview Medical Center
Orthopaedic Biomechanics Lab, Seattle, WA 98104; Section
Orthopedics, Puget Sound VA Medical Center, Seattle, WA
98108-1597; email: atencer@u.washington.edu
Sponsor: Department of Veterans Affairs, VA
Rehabilitation Research and Development Service, Washington,
DC 20420
(Project #A553-2RA)
PURPOSE--Lengthening the lateral column of the foot is used to restore the medial longitudinal arch. Dillwyn-Evans advocated lengthening the calcaneus by insertion of a bone graft between the anterior and medial facets, within the talocalcaneal joint. An alternative technique, which places the bone graft at the calcaneocuboid joint is also done. This study was designed to compare the joint contact properties after restoration by either method.
METHODOLOGY--Ten feet were selected after screening. A posterior approach was made into the posterior facet. The entry site for the middle and anterior facet transducer was made medially. The approach to the talonavicular joint consisted of retracting the extensor digitorum longus (EDL) and hallucis longus (EHL) tendons, and cutting the joint capsule superiorly, while preserving the dorsal talonavicular ligament. The soft tissues were otherwise left intact. Pressure film transducers were made of pressure sensitive film, 0.305 mm thick, inserted between the joint surfaces, and imaged along with a set of calibration prints. The imaged films were analyzed for total contact area (>0.5 MPa) and mean pressure. Intramedullary rods were placed into the tibial and fibular shafts. Axial load was applied by a pneumatic cylinder acting through a shaft with a bearing on its end, against a plate connected to the tibial shaft. Fifteen percent of the applied axial load was transmitted into the fibula. Tendon clamps and cables connected 7 tendons of the foot to pneumatic cylinders. The three positions for testing were: heel strike with 6° of plantarflexion, axial force, 68 percent body weight (BW: 700 N); stance with 7° of dorsiflexion, axial force of 82 percent BW, and respective muscle forces; and heel rise with 10° dorsiflexion, axial force of 110 percent BW. Muscle force values were calculated from physiological cross-sectional areas, reported peak forces, and normalized EMG values.
Each foot was tested first in normal state, then after sectioning the spring ligament and cyclic axial loading to create a radiographically documented flatfoot deformity. Five feet were reconstructed by placing a 1 cm thick tricortical bone graft between the cuboid and calcaneus, while the other five were reconstructed by placing the bone graft into a calcaneal osteotomy between the anterior and medial facets, followed by retesting. An ANOVA was used to determine differences between normal, flatfoot, and the two reconstruction techniques.
RESULTS--The contact area of the talonavicular joint decreased significantly with flatfoot (from 410 mm2 intact to 336 mm2) and was not restored by either reconstruction method. In addition, the area of the anteromedial facet of the talocalcaneal joint decreased with the Dillwyn-Evans reconstruction (from 340 mm2 to 248 mm2). The only significant difference was an increase in pressure in the posterior facet with the Dillwyn-Evans procedure (from 2.22 MPa to 2.53 MPa), although there was a trend to higher pressure in the anteromedial facet (from 1.49 MPa to 1.87 MPa).
CONCLUSIONS--Flatfoot decreases talonavicular joint area, which is not restored by either reconstruction. The Dillwyn-Evans procedure decreases anteromedial facet contact area and increases posterior facet pressure. Therefore, lengthening through the calcaneocuboid joint has less effect upon hindfoot joint contact characteristics.
[30] THE EFFECT OF FOOT POSITION ON LOAD DISTRIBUTION BETWEEN THE TALOCALCANEAL AND TALONAVICULAR JOINTS
A. McCormack, MD; Hisateru Niki, MD; N. Felten; P.
Kiser; A.F. Tencer, PhD; Bruce J. Sangeorzan MD
Department of Orthopedics, Harborview Medical Center,
Orthopaedic Biomechanics Lab, Seattle, WA 98104; Section
Orthopedics, Puget Sound VA Medical Center, Seattle, WA
98108-1597; email: atencer@u.washington.edu
Sponsor: Department of Veterans Affairs, VA
Rehabilitation Research and Development Service, Washington,
DC 20420
(Project #A553-RA)
PURPOSE--During gait, load is transmitted from the tibia into the talus, where it is transferred to both the hindfoot and midfoot. Previous study has determined the relative load distribution between the posterior and anterior facets of the talocalcaneal joint; however, the role of the talonavicular joint as part of this mechanism is not known. This information is necessary when determining the effects of foot deformity or fracture on foot function. We tested the hypothesis that load transmission between the calcaneus and navicular, measured by contact pressure and area, would change with foot position.
METHODOLOGY--Ten feet were used. A posterior approach was made into the posterior facet and a medial entry site for the middle and anterior facet. A superior approach was used for the talonavicular joint. Pressure sensitive film transducers, 0.305 mm thick, were made from Superlow and Low Prescale film. After insertion of the film between the joint surfaces and loading, the pressure film was imaged along with a set of calibration prints. The imaged films were analyzed for total contact area (>0.5 MPa), mean pressure, and total force. Axial load was applied by a pneumatic cylinder to intra-medullary rods placed into the tibial and fibular shafts. This allowed axial force to be transmitted with the tibial shaft at an angle to the vertical for each position. Ten percent of the applied axial load was transmitted into the fibula. Tendon clamps and cables connected 7 tendons of the foot to pneumatic cylinders. Muscle forces were calculated from physiological cross-sectional areas, reported peak forces, and normalized EMG values. For stability, one-third of the calculated forces were applied. The scaled forces are listed below.
The three positions for testing were: heel strike (at 5 percent of the gait cycle), with 6° of plantarflexion, axial force of 159 N, achilles 80 N, tibialis anterior 54 N, EHL 8 N, EDL 20 N, and tibialis posterior 32 N loaded over 35 s; stance (at 30 percent gait cycle) with 7° of dorsiflexion, axial force of 191 N, and respective muscle forces, 329 N, 18 N, 0 N, 0 N, 24 N, as well as the peroneus longus 16 N, the flexor hallucis longus 10 N, and the flexor digitorum longus 8 N loaded over 48 s; and heelrise (at 45 percent gait cycle) with 10° dorsiflexion, axial force of 257 N, and muscle forces of 564 N, 10 N, 0 N, 0 N, 92 N, 36 N, 62 N, and 30 N loaded over 80 s. The Kruskal-Wallis test was used to determine significant differences between total talocalcaneal and talonavicular joint force for the three selected positions.
RESULTS--Posterior facet talocalcaneal joint: contact area increased between heel strike and stance as did contact pressure so total force was significantly increased from 685 bN to 932 N. The changes were even larger for stance (932 N) to heelrise (1492 N; p<0.001). Anterior and middle facets talocalcaneal joint: load was unchanged in this joint in different foot positions. Talonavicular joint: joint pressure and force increased between stance (655 N) and heelrise (887 N; p=0.019).
IMPLICATIONS--The increases in joint load between heel strike and heelrise were more likely due to differences in total load applied than due to differences in orientation of the talus since differences in joint angle were small (10° dorsiflexion for heelrise compared with 6° of plantarflexion for heelstrike). High forces in heelrise were due primarily to a combination of higher axial load and larger Achilles force required to create thrust.
[31] THE EFFECT OF RELEASE OF THE POSTERIOR TIBIAL TENDON ON THE KINEMATICS OF THE HIND FOOT
Hisateru Niki, MD; Randal P. Ching, PhD; Bruce J.
Sangeorzan, MD
Department of Orthopedics, Puget Sound VA Medical
Center, Seattle, WA 98108-1597; Harborview Biomechanics Lab,
Department of Orthopaedics, Seattle, WA 98104; email:
rc@u.washington.edu
Sponsor: Department of Veterans Affairs, VA
Rehabilitation Research and Development Service, Washington,
DC 20420
(Project #A553-RA)
PURPOSE--Acquired flatfoot deformity has been attributed to the loss of the tibialis posterior (TP) tendon. However, there has been no study of the effect of TP rupture on hind foot kinematics. This study documents the effect of releasing the tibialis posterior tendon (simulating rupture) on the kinematic positions of the hind foot bones.
METHODOLOGY--The soft tissue was stripped from the tibial shaft of 8 human cadaver specimens exposing the remaining tendons down to the hind foot level. Motion sensors were attached to carbon fiber pins in the calcaneus, talus, navicular, and cuboid. An acrylic rod was inserted into the intramedullary canal to allow for axial loading of the foot.
Simulated axial compressive and tendon loads were applied to each specimen in three different loading positions: heel strike (at 5 percent of gait cycle), stance (at 30 percent of gait cycle), and heel rise (at 45 percent of gait cycle). Nylon cables with tendon clamps were used to connect the tendons to regulated pneumatic cylinders. For this study, this initial unloaded position of the foot was considered to be the "neutral" position.
The basic test protocol for each specimen entailed the collection of the bone position (motion) data in each of three conditions: neutral position (unloaded); loaded (either in heel strike, stance, or heel rise with all tendons loaded); and finally loaded, but with the TP tendon released. The three different foot positions were achieved by applying various axial compressive and tendon loads in appropriate ratios while positioning each foot on an inclined surface. The degree of incline selected for each position included 6° of plantar flexion for heel strike, 7° of dorsiflexion for stance, and 10° of plantarflexion for heel rise. All of the loads applied in this study were scaled to one fourth body weight, which was a limitation imposed as a result using a plastic loading frame.
Data were reported relative to the neutral position. A nonparametric, Wilcoxon Signed Rank paired analysis was used to statistically compare the angular positions of the four bones.
RESULTS--Statistically significant changes in the angular position of the four-bone complex were observed when the TP tendon was released (as compared to all tendons loaded) for all three loading conditions. These changes, however, were generally small in magnitude (less than 1 or 2°), particularly during stance and heel strike simulation. The greatest changes in angular position resulting from unloading of the TP tendon were seen during heel rise. This was not surprising, since the TP tendon is most actively recruited during this phase of the gait cycle. Mean talar (3.6°±1.5, p=0.011) and calcaneal (2.4°±0.7, p=0.011) internal rotation together with talar plantar flexion (1.0°±0.8, p=0.011) was observed when the TP tendon was released. Eversion of the navicular (3.8°±1.8, p=0.011), cuboid (2.4°±1.1, p=0.011), and calcaneus (1.9°±0.8, p=0.011) was also observed at heel rise.
Although directional changes in the hind foot bones associated with TP tendon release were largely consistent with acquired flatfoot deformity, the magnitudes of these changes were much smaller. This suggests that the intact osteo-ligamentous structure of the hind foot is at least initially sufficient to maintain normal alignment following TP tendon rupture. Subsequent cyclical loading (e.g., normal gait) without TP tendon function may, however, progress toward an acquired flatfoot condition. This is consistent with the clinical presentation in which the hindfoot subluxation is delayed by 6 months to 1 year following the rupture. The fact that the most change occurred in heel rise may explain the lack of success of bracing in some patients.
FUTURE PLANS--Future work will attempt to better clarify the position afer repeated cycling without posterior tibial tendon support.
[32] THE EFFECTS OF CALCANEAL LENGTH AND FUSION POSITION ON THE KINEMATICS OF THE HINDFOOT WITH LATERAL COLUMN LENGTHENING AND CALCANEOCUBOID FUSION FOR SYMPTOMATIC FLATFOOT
A.F. Tencer, PhD; A. Sands, MD; Richard Harrington;
Randal P. Ching, PhD; Bruce J. Sangeorzan, MD
Department of Orthopedics, Biomechanics Lab, University
of Washington, Seattle, WA 98104; Puget Sound VA Medical
Center, Seattle, WA 98108-1597; email:
atencer@u.washington.edu
Sponsor: Department of Veterans Affairs, VA
Rehabilitation Research and Development Service, Washington,
DC 20420
(Project #A553-2RA)
PURPOSE--Surgical treatment of symptomatic flatfoot may include calcaneal lengthening through the calcaneo-cuboid joint, which restores the shape of the foot. However, the effect of the procedure on hindfoot kinematics is unknown. Therefore, the kinematics of the hindfoot were measured first in normal cadaveric feet, then measured after simulated lateral column lengthening and fusion in different positions.
METHODOLOGY--An acrylic shaft was placed into the intramedullary canal of the tibia to support the transmitter of an electromagnetic motion transducer and transmit load to the specimen. A carbon fiber pin was placed into holes drilled in the calcaneus, talus, navicular, and cuboid that had been filled with Methacrylate cement. An acrylic mount with a receiver of the motion tracking system was fixed to the pin. The motion tracking system consists of a transmitter defining the global axis system, which is located on the tibial shaft, and a set of receivers. Verification of sensor measurement accuracy ranged from 0.944 to 1.006 in rotation, and 0.996 to 1.045 in translation. Crosstalk (ratio of output in any other direction to known input) ranged from 0.000 to 0.083.
Each foot was moved manually while holding the tibial shaft stationary, into maximum plantar flexion/inversion and dorsiflexion/eversion. Moments were measured by a six axis load cell. After three repetitions, the foot was placed on the floor, the tibia and shaft were oriented vertically, a 150 N axial load applied manually, and the tibia was internally and externally rotated. After testing intact, fusion was performed across the calcaneocuboid joint using one screw with 1) placement of a 10 mm thick tricortical iliac crest bone graft lengthening the lateral column, with the foot in neutral position, 2) with bone graft and the foot in plantar-flexion/inversion, 3) with bone graft and the foot in dorsi-flexion/eversion, 4) without bone graft and the foot in neutral position, and 5) after removal of a 5 mm thick bone section at the calcaneo-cuboid articulation to obtain congruent fusion surfaces, thereby shortening the lateral column, with the foot in neutral position. Data analysis Kinematics after fusion were compared to intact using a repeated measures ANOVA and Fisher's PLSD post hoc statistics, with significance established at p<0.05). In this scheme, each foot acted as its own control.
RESULTS--Kinematics of the hindfoot joints were unaffected by simulated fusion of the calcaneocuboid joint with the foot in neutral position and the lateral column lengthened. When the joint was fused with the foot in plantarflexion/inversion or dorsiflexion/eversion, motion of the talo-calcaneal was significantly affected. For example, when the foot was fused in plantarflexion/inversion, in/eversion decreased from 15.7° (sd=9.5°) intact to 4.7° (SD=6.2°) after fusion, while dorsi/plantar flexion decreased from 9.0° to 3.1° and rotation decreased from 7.0° to 1.4° (p<0.01). Similarly, talo-navicular motion decreased in flexion from 17.3° (SD=10.4°) to 3.4° (SD=6.0°), in version from 34.3° to 9.2°, and in rotation from 27.6° to 7.6°, (p<0.01). There were no significant effects of calcaneal length on any recorded joint motions.
IMPLICATIONS--Calcaneo-cuboid fusion with the calcaneus lengthened and the foot in neutral position has no effect on hindfoot kinematics. However, fusing the foot in other orientations limits talocalcaneal and talonavicular joint motion. When performing arthrodesis, care should be taken to preserve the neutral position of the joint.
[33] ALTERATIONS IN TALAR MORPHOLOGY ASSOCIATED WITH ADULT ACQUIRED FLATFOOT
John Anderson, MD; Richard Harrington; Randall Ching,
PhD; Bruce J. Sangeorzan, MD
Harborview Medical Center, Seattle, WA 98104-2499;
bsangeor@u.washington.edu
Sponsor: Department of Veterans Affairs, VA
Rehabilitation Research and Development Service, Washington,
DC 20420
(Project #A553-RA)
PURPOSE--Talar morphology is complex due to its unique role in coupling the mechanics of the leg and the foot. In acquired adult flatfoot (AAF), there is uncertainty whether the shape of the bone differs or whether joint subluxation is responsible. We compared the talar morphology of 10 control lower extremities without deformity with the tali from 10 patients with AAF using a computerized 3-D reconstruction format to determine whether the talar bone morphology is different in patients with AAF when compared to feet with a "normal" arch.
METHODOLOGY--CT scans with 1.5 mm cuts through the hind foot were made and the scan data containing the tali downloaded by digital tape and processed using computer-aided design (CAD) software to generate 3-D models; these could be rotated to any view and their dimensions measured by software tools that allowed instantaneous readout of the distance between two points. Measurements of talar length, talar width, talar height, and talar head length and width were taken on each model. In order to assess the accuracy of the dimensions taken from the models, a disarticulated cadaver talus was measured directly using dial calipers with a resolution of 0.01 mm and compared to multiple measurements on the CAD model. Statistical analysis using the unpaired t-test was performed.
PROGRESS--The 3-D CAD models built from CT data had an average difference of 3.2 percent compared to direct physical measurements. There were significant differences between control tali and flatfoot tali in talar width (p=0.005), talar height (p=0.001), and head width (p=0.001). Although flatfoot tali tended to be of greater overall length than the control tali, this difference was not statistically significant. The tali from the flatfoot group were narrower in width and shorter in height when compared to overall length, and had heads that were more oval shaped (i.e., less spherical).
IMPLICATIONS/FUTURE PLANS--The shape of the talus is important to hind foot function and is known to be altered in pathological disorders such as clubfoot. The role of bone morphology in acquired adult disorders is less clear. Our results show that talar morphology is different in patients who have an AAF. Whether these patients develop flatfeet as a result of their altered bone morphology or the bone changes in the flatfoot condition occur as a result of stress remodeling is unclear and will require future investigation. The alteration in talar head dimensions may make axis measurements unreliable. Thus, surgical procedures designed to correct AAF should be evaluated based on the shape of the foot, not on radiographic parameters.
[34] DETECTION AND ACCUMULATION OF MICRODAMAGE IN BONE
T. Clive Lee, MB, PhD, FRCSI; Tara L. Arthur, SM; Lorna
J. Gibson, PhD; Elizabeth R. Myers, PhD; Wilson C. Hayes,
PhD
Orthopedic Research Laboratory, Beth Israel Hospital and
Harvard Medical School, Boston, MA 02215; Department of
Materials Science and Engineering, Massachusetts Institute
of Technology, Cambridge, MA 02139
Sponsor: The Fulbright Program; Health Research Board of Ireland; Royal College of Surgeons in Ireland; Natural Sciences and Engineering Research Council of Canada; Maurice E. Mueller Professorship in Biomechanics, Harvard Medical School
PURPOSE--Fatigue damage is a stimulus for bone remodeling. However, if it accumulates too rapidly and the capacity for repair is exceeded, stress fractures result. If the repair mechanism is deficient, as in old age, damage also accumulates and contributes to fragility fractures. To better understand the fatigue behavior of bone in vivo, we must first understand it in vitro. The purpose of this study is to develop methods for detecting microcracks and use them to demonstrate microcrack initiation, propagation, and coalescence during fatigue testing in compression.
METHODOLOGY--The right sixth rib was excised from 10 human subjects from the Harvard Anatomical Gifts Program and cut into six 0.5 cm sections. Each section was randomly assigned to one of six stains: alizarin complexone, calcein, calcein blue, oxytetracycline, xylenol orange, and the accepted standard, basic fuchsin. Using fluorescence microscopy, the number, density, and length of microcracks labeled by each stain was recorded. No significant difference was found between the six stains for any parameter (ANOVA, a=0.05), indicating that they are all equally effective at detecting microcracks. These stains were then used to differentiate between pre-existing microcracks, those sustained in vivo or during preparation, and microcracks caused by fatigue testing in compression. Pairs of waisted trabecular bone specimens were prepared and stained with oxytetracycline for 16 hours at 20 psi pressure to label pre-existing damage. They were then fatigue tested in compression under load control until a 10 percent decrease in initial elastic modulus was achieved. One from each pair was then randomly assigned to a second staining in xylenol orange. The specimens were embedded in methylmethacrylate, longitudinally sectioned, examined using fluorescence microscopy, and microcrack counts made.
PROGRESS--Five pairs of waisted trabecular bone specimens have been tested to date. In addition two pairs were subjected to a three stain procedure: oxytetracycline prior to testing, calcein blue for the first 75 percent of the test, and xylenol orange for the final 25 percent of the test.
PRELIMINARY RESULTS--Preliminary staining with oxytetracycline revealed that pre-existing damage was present in all specimens and was not confined to the machined edges. In the double stain specimens, microcracks were labeled by oxytetracycline, indicating that they existed prior to the test, by xylenol orange, indicating that they were incurred during the test, and by both, indicating crack growth during testing. The density of labeled microcracks was significantly greater in double stain as compared with single stain specimens (paired t-test, p=0.011). Triple staining suggests that microcracks are incurred during the first 75 percent of the test and well as in the final quarter.
FUTURE PLANS--These results indicate that double labeling can be used to differentiate pre-existing microcracks from those incurred by a mechanical test. We plan to use this technique in monotonic testing of bone. The triple stain data suggest that, used in sequence, these fluorescent stains can label crack growth. We plan to use this tool to study microcrack propagation and coalescence in both trabecular and compact bone.
[35] VALGUS-VARUS MOTION OF THE KNEE IN STAIR CLIMBING AND LEVEL WALKING
Bing Yu, PhD; Michael J. Stuart, MD; Thomas Kienbacher,
MD; Eric Growney, BS; Marjorie E. Johnson, PT, MS; Kai-Nan
An, PhD
Orthopedic Biomechanics Laboratory, Mayo Clinic and Mayo
Foundation, Rochester, MN 55905; email: an@mayo.edu
Sponsor: National Institutes of Health, Bethesda, MD 20892; Mayo Foundation, Rochester, MN 55905
PURPOSE--Osteoarthritis is one of the most common knee disorders. Proximal tibial osteotomy is a commonly used intervention for treatment of osteoarthritic knees. Previous studies indicated that the abduction-adduction (A-A) moment at the knee in gait might be an important parameter for patient selection when using the proximal tibial osteotomy in treating knee deformity due to osteoarthritis. Stair climbing is an important functional activity of daily living and may be a more informative evaluation procedure for patients with osteoarthritic knees. The purposes of this study are to determine (a) the maximum A-A moments and the corresponding angles of the knee, (b) the factors contributing to the variations of the knee A-A moments, (c) the range of valgus-varus (V-V) motion of the knee, and (d) the factors influencing the V-V motion of the knee in stair climbing and level walking.
METHODOLOGY--An Expert VisionTM system (Motion Analysis Corp., Santa Rosa, CA) with four video cameras was used to collect kinematic data at a sampling frequency of 60 Hz. A specially designed staircase with four stairs was attached to two of three force plates for measuring ground reaction forces for two of four steps in stair climbing.
Three-dimensional angles and resultant moments of the knee were calculated using the OrthoTrak II System (Motion Analysis Corp.). Analyses of variance with repeated measures were conducted to compare the maximal A-A moments and V-V angles of the knee between ascending, descending, and level walking. Multiple regression analyses were conducted to identify the factors influencing the A-A moment and V-V motion of the knee in stair climbing and level walking. The 0.05 level of confidence was chosen to indicate statistical significance.
PROGRESS--Ten nonimpaired subjects (five males and five females) without any history of lower extremity disorders have been tested. There was generally an abduction moment at the knee during the stance phases of stair climbing and level walking for all subjects. There was no evidence that the maximum abduction moment at the knee in stair climbing was different from that in level walking. The within-subject variation of the knee abduction moment was mainly affected by the variation in the vertical ground reaction force in descending and level walking, and by the variation in the medial-lateral ground reaction force in ascending. The knee V-V angle was a major contributor to the between-subject variation of the knee abduction moment, especially in stair climbing. The maximal V-V angle of the knee was significantly increased in stair climbing in comparison to level walking. The range of knee V-V motion could be over 10°. The V-V angle of the knee essentially was a function of knee flexion angle. Ground reaction forces had little effect on the knee V-V motion. There seemed to be a coupling between knee flexion-extension motion and V-V motion.
FUTURE PLANS--The relationship between the knee abduction moment and the V-V angle and the coupling between knee flexion-extension and V-V motions are the most important findings of this research project to date. These findings support the use of the biomechanical analysis of stair climbing as a clinical evaluation tool for patients with knee osteoarthritis and warrant further studies on the biomechanics of stair climbing and its clinical applications. Different devices will be used to measure the knee flexion-extension and V-V angles to confirm the relationship between knee flexion-extension and V-V motions and the cause of the coupling between these two motions of the knee. Patients with knee osteoarthritis will be tested and compared to the normal data base. The dynamic load on the knee and the knee V-V motion in different functional activities will be compared. A knee model will be developed to estimate the force distribution across the knee in different functional activities.
[36] COORDINATION OF MOVEMENTS WITH MULTIPLE DEGREES OF FREEDOM
Gerald L. Gottlieb, PhD; Qilai Song, PhD
NeuroMuscular Research Center, Boston University,
Boston, MA 02215; email: glg@bu.edu
Sponsor: National Institutes of Health, Bethesda, MD 20892
PURPOSE--The voluntary control of human movement is a complex task involving tens of skeletal joints and hundreds of muscles. In any task, the brain must devise a command to coordinate many muscles, the consequences of which are the activation of motor units, the development of muscle force, and the evolution of movement. This all takes place within several reflex loops that feed back measures of motion and force to many levels of the central nervous system from the spinal cord through the cerebral cortex. How is this complex coordination of so many degrees of freedom achieved?
METHODOLOGY--Our experiments involve asking normal subjects to stand and point on command to a stationary object, located in the same plane as their right arm. Using a motion analysis system, we record the motions of the limb segments and the electromyographic (EMG) patterns of muscle acting about the shoulder and elbow. From these data we can solve the inverse dynamic equations to compute the net muscle torques about both joints. We can then examine the relations between torques, EMGs, and motions. We can also examine the relations of these variables across joints.
PRELIMINARY RESULTS--We have found that examination of the individual joints during a multijoint movement reveals patterns of activation that are very much like those of a single joint movement. This reveals, not that single joint strategies are used for much more complex multijoint movements but rather the reverse, multijoint strategies are conserved and used for simpler, single joint movements because they are sufficient for the task. We have recently proposed that for many of the reaching movements we can perform, there is a simple rule for coordinating the actions of the elbow and shoulder. It is remarkably simple. The central nervous system activates the muscles of the two joints to produce biphasic pulses of torque that are approximately proportional to each other throughout most of the movement.
[37] MECHANISMS UNDERLYING COMPLIANT BEHAVIOR OF THE LIMBS
Gerald L. Gottlieb, PhD; Heather B. Abushanab,
PhD
NeuroMuscular Research Center, Boston University,
Boston, MA 02215; email: glg@bu.edu
Sponsor: National Institutes of Health, Bethesda, MD 20892
PURPOSE--The fact that our limbs generate forces in response to externally imposed displacement is a manifestation of their "compliant" properties. This compliance is essential both to postural stability and to graceful performance of all voluntary motor activity. It is important to understand the mechanisms that are responsible for creating and maintaining compliance.
METHODOLOGY--Compliance was studied in the elbow by imposing perturbations to the limb with a torque motor, using a specially designed manipulandum controlled by a pair of small computers. The forces and the effects of those forces on the motion of the limb were measured and analyzed. Simultaneously, the concurrent electrical activity of the muscles (electromyography) was recorded from the skin with surface electrodes. This allowed us to partition the responses into components that were produced by intrinsic muscle properties, by reflex mechanisms, and by the intervention of higher functions of the nervous system.
PRELIMINARY RESULTS--Experiments show that during sudden perturbations and during rapid movement, limb compliance is primarily due to the velocity sensitive (i.e., viscous) force, producing mechanisms of the muscle's contractile mechanism. During postural maintenance, length sensitive mechanisms are important and presumably are responsible for achieving end point accuracy in spite of the variability in kinematics. These intrinsic muscle mechanisms are supported by rapidly acting reflex mechanisms that can alter the activity of the muscles to oppose the effects of the perturbations. Neither is sufficient, however, to prevent limbs from being displaced by external perturbations. The motor system relies on the corrective actions of higher centers, including conscious ones, to provide a complete and adequate response.
We have also attempted to demonstrate the adaptability of reflex mechanisms that have hitherto been regarded as highly stereotyped in their behavior. We asked subjects to make movements in which they knew that the load might change without warning. After they became used to this condition, we altered the nature of the unpredictable load and we compared the responses. As we had previously shown, subjects react to unpredicted loads with a combination of reflex and preprogrammed reactions. What we found that was new was that the nature of these reflex and preprogrammed reactions depends, not only on the properties of the unexpected load but also on the subject's recent experience with unexpected loads. We interpret this as evidence that not only is voluntary movement a process of planned muscle activation patterns, but it also involves adjustment of reflex mechanisms to better adapt to possible, but not predictable, perturbations.
[38] EVALUATION OF HIP STABILITY FOLLOWING SIMULATED TRANSVERSE ACETABULAR FRACTURES
Kevin A. Thomas, PhD; Mark S. Vrahas, MD; John W. Noble,
Jr., MD; Christopher M. Bearden, BS; Kirsten K. Widding,
MS
Bioengineering Laboratory, Department of Orthopaedic
Surgery, Louisiana State University Medical Center, New
Orleans, LA 70112; email: kthoma@nomvs.lsumc.edu
Sponsor: Orthopaedic Trauma Association
PURPOSE--One of the major goals in managing acetabular fractures is to prevent post-traumatic arthritis. Unreduced fractures involving the weight-bearing portion of the acetabulum lead to post-traumatic arthritis, while fractures outside the weight-bearing area have a better prognosis. However, the portion of the acetabulum which is necessary for normal weight-bearing is not well-defined. Little previous work has examined hip stability following either actual or simulated acetabular fractures. The purpose of this study was to distinguish between fractures requiring open reduction, those treatable with traction, and those requiring even less aggressive treatment to prevent post-traumatic arthritis.
METHODOLOGY--An in vitro cadaveric model simulating transverse acetabular fractures was developed. Custom guides were designed to create precisely reproducible cuts simulating transverse acetabular fractures at 0, 30, 60, and 90° relative to the roof-arc angle. Each proximal femur was potted in a cylindrical fixture, mounted onto an instrumented x-y displacement table and secured to the load cell of a mechanical testing machine. Steinmann pins were inserted into the posterior-superior acetabulum to provide a reference to the sagittal, coronal and transverse planes. Each acetabulum was potted and mounted to the test machine actuator using an articulated fixture which allowed variable flexion and abduction/adduction. The specimens were loaded in compression to 800 N (at 200 N/s in load control).
Simultaneous recordings were made of the applied load, displacement and x-y translation of the femur. Specimens were tested intact and after simulating the fractures in neutral, 10° abduction, and 10° adduction; in turn, each of these positions was tested in fixed angles of 0, 20, 40, 60, and 80°. A specimen was considered stable if no dislocation occurred during the loading to 800 N. To evaluate contact stresses in the hip joint, pressure sensitive film was placed in the joint, and the resulting pattern of loading was correlated with the fracture type and position of the hip joint.
RESULTS--The results demonstrated that transverse fractures into a roof-arc angle of 90° do not affect the weight-bearing position of the acetabulum. Fractures with a roof-arc angle of 60° began to infringe on the weight-bearing area, and those with roof-arc angles of less than 60° are clearly in the weight-bearing region. Hip stability was significantly affected by the roof-arc angle and by the interaction of the roof-arc angle and the angle of hip abduction or adduction.
FUTURE PLANS--Another series of experiments examining different ranges of both flexion angles and roof-arc angles is currently underway to better define the true weight-bearing portions of the acetabulum.
[39] BIOMECHANICAL ANALYSIS OF NONREAMED TIBIAL INTRAMEDULLARY NAILING AFTER SIMULATED TRANSVERSE FRACTURE AND FIBULECTOMY
Kevin A. Thomas, PhD; Christopher M. Bearden, BS; Daniel
J. Gallagher, MD; M. Alan Hinton, MD; Mitchel B. Harris,
MD
Bioengineering Laboratory, Department of Orthopaedic
Surgery, Louisiana State University Medical Center, New
Orleans, LA 70112; email: kthoma@nomvs.lsumc.edu
Sponsor: None listed
PURPOSE--As a continuation of a previous study on the effect of fibulectomy on loading of the tibia, a model was developed to simulate transverse tibial shaft fractures. The model was used to evaluate the patterns of loading across a diaphyseal fracture under various conditions, including the changes in loading after fracture fixation with an intramedullary (IM) nail and the changes due to partial fibulectomy.
METHODOLOGY--Cadaveric lower extremities were instrumented with three pairs of strain gauges on the anteromedial, arterolateral, and posterior aspect of the tibia at about the middle of the tibial shaft. Each pair of strain gauges was separated by approximately 20 mm to allow the simulated fracture to pass between the strain gauges. Using a servo-hydraulic testing machine, loading was applied through the proximal tibia with the ankle and subtalar joints held in neutral flexion-extension and neutral inversion-eversion. Each specimen was tested under six conditions: intact tibia, intact tibia with IM nail, fractured tibia without IM nail and intact fibula, fractured tibia with IM nail and intact fibula, fractured tibia with IM nail after fibulectomy, and fractured tibia without IM nail after fibulectomy.
RESULTS--Creation of the fracture was found to cause significant decrease in the loading across the anterolateral and anteromedial tibia. Placing the IM nail was shown to counter these changes, with an increase in loading across the anterior aspects of the tibia. With an IM nail in place, the effect of fibulectomy was minimal. In the fractured tibia without an IM nail, the effect of a fibulectomy was to increase the loading of the anterior tibia, as was demonstrated in the previous study. The results of this study demonstrate the redistribution of the applied loading after an IM nail is placed across a simulated transverse fracture and explains how the nail can promote healing across the fracture site. There was no benefit to performing a fibulectomy in the presence of an IM nail.
[40] QUANTITATIVE FUNCTIONAL ANATOMY OF THE UPPER LIMB
R.H. Rozendal; F.C.T. Van der Helm; H.E.J. Veeger; K.N.
An
Faculty of Human Movement Sciences, Vrije Universiteit,
1081 BT Amsterdam. Department of Measurement & Control, TUD,
2628 CD Delft; Orthopaedic Biomechanics Lab., Mayo Clinic,
Rochester MN 55905; email: h_e_j_veeger@fbw@vu.nl
Sponsor: None listed
PURPOSE--We are collecting musculoskeletal parameters for the shoulder and arm for biomechanical modelling of the upper limb. Many of the clinical and ergonomical problems in the shoulder are the result of the complex coordination of the muscles involved in the control of shoulder movements and joint stabilization. This complexity of the human shoulder and arm cannot be directly studied, but needs the application of a 3-D biomechanical model. In addition, the 3-D nature of upper limb motion and the covert motions of the scapula require a highly sophisticated 3-D analysis. Quantitative data on the morphology of shoulder and arm are needed as a basis for analysis of the load on the shoulder and arm, based on arm movement registration in wheelchair propulsion, activities of daily living and vocational activities; analysis of the outcome of shoulder arthrodeses; and interpretation of in vivo human palpation data.
PROGRESS--To date, morphological parameters have been collected on the shoulder mechanism as well as the arm. These data comprise 3-D insertion sites of upper extremity muscles, the 3-D orientations of axes of rotation for elbow flexion/extension and pro/supination and the rotation centre of the glenohumeral joint. Also collected were data on muscle morphology such as muscle mass, in a physiological cross sectional area, for the biomechanical model of the shoulder. With the use of the model it is possible to calculate muscle forces, tensions in ligaments, and reaction forces in joints of the shoulder. We are in the process of adding the morphological information of the arm to the model. Parallel to the model development, 3-D techniques for the measurement of upper extremity kinematics have been developed. The program has proven to be useful in the development of a sophisticated 3-D model of the shoulder mechanism that has been applied in the prediction of optimal fusion angles of shoulder arthrodeses after injury of the brachial plexus, in the analysis of the positioning of endoprostheses and operation techniques used, and in the quantification of mechanical load on the shoulder joint in manual wheelchair propulsion. Morphological data on previous research are now available at http://www-mr.wbmt.tudelft.nl/schouder/dsg/dsg.info.html.
[41] GAIT MECHANICS OF THE PARTIAL FOOT AMPUTEE
Mohammad G. Dorostkar, MD
VA Medical Center, Long Beach, CA 90822
Sponsor: Department of Veterans Affairs, VA
Rehabilitation Research and Development Service, Washington,
DC 20420
(Project #A861-RA)
No report was received for this issue.
[42] QUANTITATIVE POSTUROGRAPHY: OPEN-LOOP AND CLOSED-LOOP POSTURAL CONTROL MECHANISMS IN PARKINSON'S DISEASE--INCREASED MEDIOLATERAL ACTIVITY DURING QUIET STANDING
James J. Collins, PhD; Susan L. Mitchell, MD; Carlo J.
De Luca, PhD; Adam Burrows, MD; Lewis A. Lipsitz, MD
NeuroMuscular Research Center, Boston University,
Boston, MA 02215; Hebrew Rehabilitation Center for the Aged,
Boston, MA 02131; email: collins@bunmrg.bu.edu
Sponsor: Department of Veterans Affairs, VA
Rehabilitation Research and Development Service, Washington,
DC 20420
(Project #E720-2RA); Hebrew Rehabilitation Center for Aged
Men's Associates Fellowship Award, Boston, MA 02131
PURPOSE--Idiopathic Parkinson's Disease (IPD) is a common neurodegenerative disease of later life. The clinical hallmark of advanced IPD is postural instability, which can result in significant morbidity due to falls, associated injury, and functional impairment. Despite the morbid consequences of this problem, the postural dyscontrol associated with IPD remains a poorly understood phenomenon. The objective of this study was to use stabilogram-diffusion analysis to gain an increased understanding of these postural impairments.
METHODOLOGY--We obtained clinical data from 22 subjects with IPD and 24 nonimpaired elderly subjects. The two groups were matched for age and gender. The postural stability of each individual was evaluated by using a force platform to measure the movements of the center of pressure (COP) under their feet. The individuals were tested under eyes-open conditions for multiple 30 s trials. The COP trajectories were parameterized according to stabilogram-diffusion analysis. Standard statistical analyses were used to compare the results from the IPD subjects with those from the nonimpaired.
PRELIMINARY RESULTS--We found that the postural control mechanisms in the IPD subjects, compared to the nonimpaired elderly, were characterized by an increase in the effective stochastic activity in the mediolateral direction. We also found that the mediolateral posturographic measures were associated with a history of falls and poor performance on clinical measures of balance. We hypothesize that the increase in mediolateral activity in subjects with IPD may reflect an attempt to maintain potentially stabilizing movements during quiet standing in the face of impaired movement in the anteroposterior direction. This study supports the notion that mediolateral instability is an important posturographic marker of functional balance impairment in the elderly.
[43] QUANTITATIVE POSTUROGRAPHY: A PINNED POLYMER MODEL OF POSTURE CONTROL
James J. Collins, PhD; Carson C. Chow, PhD
NeuroMuscular Research Center, Boston University,
Boston, MA 02215; email: ccc@acs.bu.edu
Sponsor: Department of Veterans Affairs, VA
Rehabilitation Research and Development Service, Washington,
DC 20420
(Project #E720-2RA); National Science Foundation, Arlington,
VA 22230
PURPOSE--The objective of this project was to use techniques of nonequilibrium statistical mechanics to study the time-varying displacements of the center of pressure (COP) under the feet of quietly standing subjects. It had been previously shown by our group that the two-point correlation function (stabilogram-diffusion plot) of the COP trajectory exhibits three distinct scaling regions. A theoretical model which explained these regions was developed.
METHODOLOGY--Guided by the posturographic data and the biomechanical constraints of the human body, a stochastically driven equation to model posture control was derived. This equation considered the upright body to be a stochastically forced "pinned polymer" (i.e., a flexible string under tension). The pinning represents the neuromuscular forces needed to keep the body upright. The stochastic forcing represents the inherent noisiness of the system. The resulting equation is completely solvable analytically.
PRELIMINARY RESULTS--The model reproduces the two-point correlation function of the experimental data. In particular, the scaling exponents and break points between the scaling regions were determined. The model provides a starting-off point for future theoretical analysis of the posture control system, including the connection between static and dynamic posture control.
[44] QUANTITATIVE POSTUROGRAPHY: A QUANTITATIVE ANALYSIS OF STATICS AND DYNAMIC POSTURE CONTROL
James J. Collins, PhD; Carson C. Chow, PhD
NeuroMuscular Research Center, Boston University,
Boston, MA 02215; email: ccc@acs.bu.edu
Sponsor: Department of Veterans Affairs, VA
Rehabilitation Research and Development Service, Washington,
DC 20420
(Project #E720-2RA); National Science Foundation, Arlington,
VA 22230
PURPOSE--The bulk of recent research in posture control at the NeuroMuscular Research Center has concentrated on static posture control. However, many falls are a result of an external perturbation and thus, understanding dynamic posture control could be important. We hypothesize that the two modes of posture control are inherently connected. The objective of this study was to test this hypothesis.
METHODOLOGY--The pinned polymer model provides a theoretical model to analyze posture control. The dynamic response to perturbations can be computed explicitly from the model. The parameters of static posture control obtained from the two-point center of pressure (COP) correlation function (stabilogram-diffusion plot) can be related to the properties of the dynamic response function, which gives the essential information about dynamic posture control. The response function can be obtained by experimentally measuring the COP motion immediately following a perturbation.
PRELIMINARY RESULTS--The shape of the response function calculated from the pinned polymer model is fully determined by the parameters of the two-point COP correlation function. This connection is a result of the Fluctuation-Dissipation Theorem of statistical mechanics. Both quantities can be experimentally measured independently and then compared to the theoretical predictions. Preliminary experimental data support the hypothesis that static and dynamic posture control are fundamentally linked.
[45] CHARACTERIZING POSTURAL STABILITY IN RELATION TO AGE AND SUSCEPTIBILITY TO FALLING
James J. Collins, PhD; Bryce L. Greenhalgh, BS; Carlo J.
De Luca, PhD; Casey Kerrigan, MD; Lewis A. Lipsitz,
MD
NeuroMuscular Research Center, Boston University,
Boston, MA 02215; Spaulding Rehabilitation Hospital, Boston,
MA 02114; Hebrew Rehabilitation Center for the Aged, Boston,
MA 02131; email: collins@bunmrg.bu.edu
Sponsor: Department of Veterans Affairs, VA
Rehabilitation Research and Development Service, Washington,
DC 20420
(Project #E756-4RA); the Whitaker Foundation, Rosslyn, VA
22209
PURPOSE--Older adults exhibit problems in posture and balance. These disorders predispose the elderly to falls, which are their most common cause of trauma and the largest single cause of accidental death. Despite the severity and frequency of this problem, postural instability in the elderly remains a poorly understood phenomenon. The objective of this study was to evaluate the ability of the multisegmental posturographic technique to identify age-related changes in posture control.
METHODOLOGY--We examined 20 nonimpaired young subjects (21-30 years) and 20 nonimpaired elderly subjects (71-80 years). Each subject was instructed to stand in a standardized position on a force platform, which measured the displacements of the center of pressure under the feet. Simultaneously, an ELITE motion analysis system and linear variable differential transformers measured the movements of body segments, and electromyographic (EMG) signals were recorded from five lower-limb muscles. Multiple 60-s trials were conducted on each subject.
PRELIMINARY RESULTS--We found that there were no significant differences between the two groups for the quiet-standing fluctuations at the ankle, knee, and hip. However, we found that the elderly subjects exhibited significantly larger fluctuations at the head and shoulders during quiet standing. In addition, we found that the correlated structure of the organizational strategy utilized by the quasi-static postural control system was diminished in the elderly subjects. Finally, we found that the elderly subjects exhibited significantly greater lower-limb muscle activity during quiet standing. These findings clearly indicate that the multisegmental posturographic technique can be used to quantify the physiological effects of aging on the mechanisms involved in regulating quiet-standing balance.
[46] SYNTHESIS OF A SIMPLE BALLISTIC WALKING MOVEMENT WITH PUSH-OFF
Richard Q. van der Linde, MSc; Dick H. Plettenburg,
MSc
WILMER group, Department of Mechanical Engineering,
Delft University of Technology, 2628 CD Delft, The
Netherlands email: d.h.plettenburg@wbmt.tudelft.nl
Sponsor: Delft University of Technology
PURPOSE--In this project ballistic walking is considered to be the most fundamental, and therefore the most revealing, approach to bipedal walking. Ballistic walking also brings practical advantages, like energy saving properties and simple mechanical realization. These are primary aspects for successful applications in rehabilitation technology. The goal of this research is to obtain a method of synthesis with which a desired three dimensional bipedal walking movement can be constructed. This is to result in an autonomous prototype biped, which is to be robust for small disturbances. Also, concepts for a renewing hip orthosis are to be developed.
METHODOLOGY--Theory and practice support one another in order to form a firm basis of insight. Bifurcation theory gives insight in the influence of system parameters on the dynamics of the mechanical oscillating bipedal system, and stability can be quantified. This analysis is to be performed with the aid of numerical computer force. Experimental setups provide reliable information of all effects of parameter variation with respect to periodicity and stability. This mutual pollination of a theoretical and practical approach provide information which would not be found if both approaches were handled individually.
PROGRESS--A mathematical model of a simple bipedal walking movement is built gradually. Each effect of a model extension is to be studied in order to expose its effect on system behaviour. Simultaneously experiments are performed to verify theoretical validity. These actions build a toolbox which is to result in a method for synthesis of a desired ballistic walking movement.
PRELIMINARY RESULTS--A working prototype biped already has been constructed and is capable of stable three dimensional walking on a horizontal surface. The ballistic walking motion is actuated solely by a periodic push-off, which is active for only one-forth of a step cycle. This makes the specific energy consumption per unit time 6.5 W/kg. Because of the present small step width 3.5 mm, the specific energy per unit distance amounts to 100 W/kg.m. Improvements on step width as well as on robustness for external disturbances are currently in development.
[47] DEVELOPMENT OF A SYSTEM TO AID ORTHOPAEDIC SURGICAL DECISION-MAKING IN CHILDREN WITH CEREBRAL PALSY THROUGH PREDICTION OF POST-SURGICAL GAIT PATTERNS
Alan R. Morris, MASc; Stephen Naumann, PhD; Gabriele
M.T. D'Eleuterio, PhD; John H. Wedge, MD
Human Movement Laboratory, Bloorview MacMillan Centre,
Toronto, ON M4G 1R8 Canada; Institutes for Aerospace Studies
and Biomedical Engineering, University of Toronto, Toronto,
ON L6L 5N8; Department of Surgery, University of Toronto,
Hospital for Sick Children; email:
morrisa@ecf.utoronto.ca
Sponsor: The Easter Seal Research Institute
PURPOSE--Cerebral palsy (CP) is a nonprogressive neurological disorder that has many effects, including a resulting difficulty in walking due to improper control of muscle activity via the central nervous system. Individuals with this disorder tend to have spastic or hypertonic activity of some muscles, improper sequencing of muscle activation, reduced range of joint motion, walking patterns which are more variable than nondisabled persons, and higher energy requirements for walking. In order to compensate for the effects of CP, orthopaedic surgery is used to modify the lengths and/or position of lower-limb muscles and tendons to reduce the exaggerated muscle activity in the hope of uncovering the normal sequence of muscle activity.
In order for the best possible outcome of surgery to be realized, there is a need for physicians to have objective criteria by which to analyze walking patterns and decide on the type of intervention for individual patients. The purpose of this project is to develop a computer software tool that would be used to assist surgeons in planning orthopaedic surgery specific to CP. The software tool will give surgeons the ability to predict the results of their surgery by seeing hypothetical walking patterns from hypothetical surgical decisions.
METHODOLOGY--It is hypothesised that there exist relationships between the presurgical walking patterns, postsurgical walking patterns, and surgical intervention. Identification of these relationships will allow for the prediction of surgical outcomes in the form of a predicted postsurgical walking pattern. Through the use of a combination of quantitative motion analysis, engineering mechanics, electromyography, numerical optimization techniques, simulation of mechanical systems, and computerized artificial neural networks, the development of a system to identify and utilize the relationships should be possible.
Such a system is required to predict the mechanical affects of either lengthening and/or transfer of muscle by a developing a detailed dynamic musculo-skeletal simulation model of walking, and to predict the change in muscle activity patterns that would result due to surgery by developing a computerized model to relate presurgical muscle activation patterns, postsurgical muscle activation patterns and surgical intervention variables. To dynamically simulate walking, a biomechanical model will be developed to include rigid-bodies, 3-DOF linkages, and multiple 1-DOF muscle actuators; this will provide a framework to input muscle activation patterns which drive the system. The second model to predict changes in muscle activation patterns will be developed through a database of individuals with cerebral palsy and electromyography (muscle activation) records of both pre- and postsurgery. A model will be developed based on the use of computational technique known as artificial neural networks; the technique will enable convergence to a model that relates the multitude of variables between surgery and presurgery electromyography (input) and postsurgery electromyography (output).
PROGRESS--The project is just getting under way.
[48] EFFECT OF AN INDUCED LEG LENGTH DISCREPANCY ON GAIT BIOMECHANICS
Alberto Esquenazi, MD; Mike Hatzakis, MD; Mukul Talaty,
MS BME
MossRehab Hospital, Philadelphia, PA 19141; Thomas
Jefferson University Hospital, Philadelphia, PA 19107;
email: aesquena@aehn2.einstein.edu
Sponsor: MossRehab Hospital, Philadelphia, PA 19141
PURPOSE--We seek to better understand the physiologic factors involved in the compensation for the inequality of lower limb lengths, and we are working to document at what levels of leg length inequality does compensation at the hip occur, and what overall changes occur in the mechanics of gait. With this information, pathologic changes that occur in the hips, lower back, and lower limbs due to compensation for leg length inequality may be better understood. This may facilitate inferences on effective treatment options.
METHODOLOGY--Six to 10 nonimpaired subjects with documented normal leg length (using both the ASIS to floor method and ASIS to medial malleolus methods to assure no structural or functional pre-existing pathology) will be tested by completion of the study. Many have studied the clinical assessment of degree of leg length discrepancy, and we choose the ASIS to medial malleolus because it seems to be the most rigorously tested; although some claim that ASIS to lateral malleolus can detect functional leg length inequalities, this technique has not been as well proven in the literature. Two mechanisms of leg length discrepancy are used: 1) a tapered heel (variable thickness with maximum thickness of 1/2 inch at the heel) lift is placed in one shoe, and 2) a full shoe, constant thickness of 1/2 inch lift is placed under the shoe. Each subject is given a chance to accommodate to the test condition before data is recorded. The subject is tested without any orthotic as well. Temporo-spatial foot fall parameters (such as stride lengths and times, stance/swing lengths and times, step lengths, and walking velocity) as well as ipsilateral hip, knee, and ankle kinematics and kinetics are recorded. Upon completion of the test session, the subject is given the partial lift to wear during all activities for 2 to 3 weeks. Each subject is then retested as outlined above in just the heel lift and no lift conditions.
PROGRESS--This is the first year of the study. Several subjects have been tested to date; testing is ongoing.
PRELIMINARY RESULTS--There appear to be statistically significant differences in lower limb kinematics and kinetics of the longer limb. Differences are noted between the lifted limb and same limb when no orthotic is used to induce a leg length discrepancy, as well as between the lifted limb before and after the accommodation period. An insufficient number of subjects has been tested so far to be able to speculate about trends in the methods of compensation.
FUTURE PLANS--The following questions need to be answered: What are, if any, the differences between short term changes and long term changes in the biomechanics of gait in compensation of leg length discrepancy? What is it about leg length discrepancy that leads to pathologic changes in the hip and back? What is the clinical end point for treatment: clinical symptoms, a fixed length discrepancy, or both depending on activity level of patient, or documented changes in biomechanics of the spine or hip?
[49] THE DEVELOPMENT OF A DIRECT ULTRASOUND RANGING SYSTEM FOR THE QUANTIFICATION OF AMBULATION
Dudley S. Childress, PhD; Richard F. ff. Weir,
PhD
Northwestern University, Prosthetics Research
Laboratory, Chicago, Illinois 60611; email:
d-childress@nwu.edu
Sponsor: National Institute on Disability and Rehabilitation Research, Washington, DC 22202
PURPOSE--Following the idea that more may be obtained from less, we have developed an economical single marker direct ultrasound ranging system (DURS) for the quantitative evaluation of ambulation.
METHODOLOGY--The DURS operates by emitting an infrared pulse at a frequency of 22 Hz from a base unit to a transponder worn by the subject. This transponder is triggered by the infrared pulse and emits an ultrasound pulse back to the base unit. The time of flight of light over these distances is essentially instantaneous but the speed of sound is not. The base unit measures the time difference between the emitting of the infrared pulse and the arrival at the base unit of the ultrasound pulse. By calibrating for the speed of sound in air, this time difference is then converted into a measurement of the distance between the base and transponder units. These distance samples are then stored in a computer and processed through a differentiation algorithm to obtain an estimate of the horizontal velocity, in the plane of progression, of the body trunk. From this velocity profile, additional gait parameters such as gait speed, cadence, stride length, and step time can be calculated.
PROGRESS--The prototype DURS completed last year has been extensively modified to further simplify its operation and reduce the number of components required. This new prototype is interfaced with a laptop computer via the serial port. Calibration for the speed of sound is achieved by measuring the air temperature and known distance and adjusting the hardware until this distance registers. The velocity is computed from the distance data using a three-point differentiator, implemented in software. A time averager is also used to smooth the velocity data as the process of differentiation tends to enhance discontinuities and sharp edges.
RESULTS--The velocity profiles obtained from the DURS and the CODA 3 system are very similar. Both devices accurately measure the periodic fluctuation in the forward velocity of the body trunk that results from the rising and falling of the center of mass during normal gait. The gait speed determined with the D.U.R.S. was consistently within 3 percent of the gait speed determined from the CODA 3 system. The new prototype can accurately measure distance out to 13 meters with a mean error over that range of about 1 mm. The distance limitation is now no longer due to hardware and signal strength limitations but rather due to the distance sound can travel within the designated sample interval.
FUTURE PLANS--The software will be improved to incorporate the algorithms for single marker gait being developed at our laboratory by Dr. Richmond Chan. Changes will also be made in the software to further simplify the devices set-up, calibration, and operation.
[50] USE OF JOINT TORQUE, ENERGY, AND POWER IN CLINICAL GAIT EVALUATION
Sheldon R. Simon, MD; Necip Berme, PhD; Tasos
Karakostas; Rajeev D. Puri, MD; S. Mark Kamaleson, MD
The Division of Orthopaedics and the Department of
Mechanical Engineering, The Ohio State University, Columbus,
OH 43210; email: simon.1@osu.edu; berme.1@osu.edu;
karakostas.1@osu.edu;
puri.2@osu.edu;
kamaleson.1@osu.edu
Sponsor: National Institute on Disability and Rehabilitation Research, Washington, DC 20202
PURPOSE--This project evaluates the value of using lower limb joint torque, energy, and power for diagnosing primary motion disorders, making clinical intervention decisions, estimating long-term prognoses, and assessing disability levels. A related measure is musculotendon length. Knowing the behavior of muscle length can help to model the torques, energies, and powers observed.
METHODOLOGY--We first examined the clinical utility of determining mechanical energy during gait analysis studies in subjects with cerebral palsy (CP). Secondly, we launched an investigation into the behavior of muscle length and tension of the lower limbs and how various surgical and bracing treatments affect this behavior, as well as how musculotendon length could be used in the modeling of joint torque, moment, and power.
PROGRESS--To evaluate the clinical usefulness of quantifying lower extremity mechanical energy in determining efficacy of orthopedic interventions in CP, we conducted a retrospective study comparing pre- and posttreatment quantitative gait analysis in subjects with gait abnormalities residing in the sagittal or transverse planes. The pre- and posttreatment studies of each patient were compared to determine treatment efficacy. Joint powers and energies were calculated as described by Winter. These data were evaluated and compared to the other gait data to assess whether complementary or redundant information was being provided.
Using a software package that includes a model of the lower limb and following appropriate modeling of the kinematics of each of the joints of the lower limb, we have determined the kinematic and kinetic information with respect to the musculotendon units of interest at different joint positions. We have assessed the effects of all the input and output parameters of the software package with a variety of experimentation schemes to evaluate the response of the program and identify its limitations. Our sensitivity analysis indicates that the length and force outputs determined for each individual musculotendon unit are the most acceptable variables to be investigated.
We have also been able to modify the kinematic output of our standard laboratory motion data to achieve compatibility with this software package. Such modifications have allowed us to use our already existing database as well as information collected from recent studies in an effort to combine presurgery and postsurgery data to investigate the effects of musculotendon unit lengthening.
RESULTS--When a change in velocity was compared with the change in energy, three groupings emerged: 1) a large change in velocity with a small change in energy, 2) a moderate change in both velocity and energy, and 3) a small change in velocity with a large change in energy. These patient groupings were based on the initial position of the lower limb at heel strike and ability to compensate for abnormal positioning during stance based on examination of motion and EMG data. We found that mechanical energy analysis calculated from routine gait study measurements is complementary to other gait data and useful for determining the efficacy of orthopedic interventions.
We are currently proceeding with the incorporation of motion data from gait evaluations from patients with CP who have decided to undergo different treatment procedures to determine the effects of these treatments also. We currently combine the output of the program to investigate the changes in strength of the affected musculotendon units. Our initial results indicate that surgery, and in particular musculotendon lengthening, has the most dramatic effects. Future efforts are focused on validating this finding with more studies.
[51] REFINEMENT, EVALUATION, AND DISSEMINATION OF A DIAGNOSTIC AND TREATMENT ASSESSMENT EXPERT SYSTEM FOR THE INTERPRETATION OF WALKING DISORDERS LEADING TO DISABILITY
Sheldon R. Simon, MD; Jack W. Smith, MD, PhD; Kathy A.
Johnson, PhD
The Division of Orthopaedics and the Division of Medical
Informatics, The Ohio State University, Columbus, OH 43210;
email: simon.1@osu.edu;
smith.30@osu.edu;
johnson.32@osu.edu
Sponsor: National Institute on Disability and Rehabilitation Research, Washington, DC 20202
PURPOSE--This project involves the continuing development of a diagnostic and treatment expert system for the interpretation of walking disorders leading to disability. Over the past decade, research efforts have been developing tools to objectively assess human gait performance. To assist clinicians, computational methods in analyzing gait could ensure a standardized, high quality level of analysis, decrease the time involved in doing an analysis, provide updates for new techniques, and be part of a tool for instruction regarding gait analysis.
METHODOLOGY--We have been working with a prototype expert system called QUAWDS (Qualitative Analysis of Walking DisorderS) for diagnosing cerebral palsy gait disorders from the multiple sources of raw data that are used by the gait analysis expert. QUAWDS was built using a generic task theory from artificial intelligence to identify and define the subtasks involved in gait analysis: Motion Deviation Identification, Muscle Fault Generation, Muscle Fault Rating, Explanatory Coverage Determination, and Determination of Overall Interpretation. These modules use a combination of associational knowledge (rule-like) and a qualitative model of the physical system.
For this project, we are in the process of isolating the various subtasks in QUAWDS and embedding them as cognitive tools within a user-friendly cooperative problem-solving interface so that a gait analysis expert can easily use any or all submodules of QUAWDS for gait analysis. We are also evaluating QUAWDS performance against human experts to refine QUAWDS to achieve expert level performance.
PROGRESS--We have nearly completed the transfer of knowledge from QUAWDS to cognitive tools to be embedded in a user-friendly system. Currently, there are tools for identifying significant findings with respect to joint angle graphs, range of motion, time and distance data, and EMGs. We have programmed additional functions that can be used to pull information from the AI decision support tools into a report. We have also written code to determine the muscle faults associated with a particular deviation, and we are currently developing the interface to integrate this function into the interface. There are also some smaller related tasks that are being added such as the ability to sort findings according to importance where that importance is based on several factors such as magnitude of deviation, length of time that the deviation occurred, and qualitative factors concerning the finding's relation to other findings detected.
RESULTS--Providing a single place for data to reside for gait analysis is proving to be quite a useful concept for both teaching gait analysis and facilitating clinical report generation. The decision-aid tools that have been provided up to this point seem to be useful and fairly accurate. Another benefit to this line of research is the ability to easily explore other methods of accomplishing subtasks of gait analysis and comparing the results (as we are currently investigating in the case of motion deviation determination). This eventually leads to a better method for performing gait analysis as well as better support for the people currently doing (or learning to do) gait analysis.
FUTURE PLANS--We are working to add new functionality to the system based on other research into the clinical significance of data analysis types for gait analysis. As we determine new categories of findings based on our research into torques, powers, moments, time/distance parameters, and the like, decision-aid tools will be developed and added to the system. These tools will improve both the functioning of the system as well as our understanding of the process of gait analysis.
[52] DEVELOPMENT OF A GAIT INTERPRETATION, INSTRUCTION, AND REPORT GENERATION SYSTEM
Sheldon Simon, MD; Philip J. Smith, PhD; Rebecca J.
Denning, PhD
The Division of Orthopaedics and the Cognitive Systems
Engineering Laboratory, The Ohio State University, Columbus,
OH 43210; email: simon.1@osu.edu;
psmith@magnus.acs.ohio-state.edu;
rdenning@magnus.acs.ohio-state.edu
Sponsor: National Institute on Disability and Rehabilitation Research, Washington, DC 20202
PURPOSE--Both health care and rehabilitation for orthopaedic patients may be improved by taking advantage of the increasingly sophisticated quantitative measures now available for gait analysis. To ensure the effective use of these measures, the goal of this project is to develop a computer-based tutoring and report-generation system. This system can be used to help orthopaedic residents and physical therapists gain experience and skill in analyzing various gait dysfunctions, and to develop more informative patient reports for referring physicians.
METHODOLOGY--The Gait Analysis Instructional Tool (GAIT) tutor and report generation system is currently being developed on a Macintosh computer environment using the C programming language. This environment allows users to easily manipulate multimedia elements such as sound, video, animation, illustrations, and graphical representations. Providing data in these formats will support both the instruction of individuals interested in acquiring the skills of gait analysis and the production of detailed patient reports for those who manage and provide patient care.
PROGRESS--A fully functional prototype of the GAIT system has been developed. This system is being subjected to preliminary formative evaluations using orthopaedic residents and physical therapists and will also be ported to an IBM environment as evaluation results are compiled and the preliminary system design is refined.
The system allows users to enter, review, and annotate data from actual patient cases. This annotated data and accompanying text segments can be incorporated into a detailed report on patient progress. Preliminary interviews with orthopaedic surgeons revealed that in addition to providing a tutoring system for residents, the ability to maintain and manage patient information is an important additional function from the vantage of those who provide patient care.
The system uses data directly from the gait analysis laboratory. The data that can be viewed on-line includes: medical history, physical exam, time/distance data, joint angle graphs, moment graphs, power graphs, force plate graphs, EMGs, Quicktime video, and animated stick figures.
Each screen of data may be annotated in a manner appropriate to the type of data. Text screens provide the capability to change the typeface and color of the text. The colors that are made available have been chosen for saturation and depth so that they are distinctly identifiable when printed on a grayscale printer.
FUTURE PLANS--Following the completion of the current formative evaluation, a formal evaluation study is planned. Following this evaluation, the GAIT system will be distributed for general use as both a case-based interactive learning environment and a patient evaluation and care management tool. Further evaluations will accompany this distribution.
[53] CENTRAL MECHANISMS FOR MOMENTUM GENERATION DURING GAIT INITIATION AND THEIR DEGRADATION WITH NONIMPAIRED AGING
Amy F. Polcyn, MS; James J. Collins, PhD; Casey
Kerrigan, MD; Carlo J. De Luca, PhD; Lewis A. Lipsitz,
MD
NeuroMuscular Research Center, Boston University,
Boston, MA 02215; Spaulding Rehabilitation Hospital, Boston,
MA 02114; Hebrew Rehabilitation Center for the Aged, Boston,
MA 02131; email: collins@bunmrg.bu.edu
Sponsor: National Science Foundation, Arlington, VA 22230
PURPOSE--During gait initiation, the center of pressure (COP) under the feet moves backward and toward the foot which is to be lifted first, before any appreciable movement of the body's center of mass. Although this movement has been shown to be controlled by centrally programmed motor commands, its functional significance has remained unclear. The objective of this project was to determine the functional significance of the initial shift of the COP and to study how the motor control and biomechanical factors involved in gait initiation change with aging. The information derived from this study could eventually be utilized in the development of a clinical technique for evaluating and characterizing posture and movement disorders.
METHODOLOGY--We examined 20 nonimpaired young subjects (18-29 years) and 20 nonimpaired elderly subjects (64-80 years). Subjects initiated walking under three different speed conditions (slow, normal, fast) from a force platform, which measured the ground reaction forces and displacements of the COP under their feet. Simultaneously, an ELITE motion analysis system measured the movements of the body segments, and electromyographic (EMG) signals were recorded from three lower-limb muscles.
PRELIMINARY RESULTS--We found that the functional significance of the initial COP shift is to generate, in a stable manner, the momentum needed for gait initiation. We also found that in nonimpaired older adults, the gait-initiation motor program is expressed less frequently and the momentum-generating capacity of the COP-shift mechanism is significantly diminished. These findings suggest that the central nervous system employs stable, efficient mechanisms for dealing with the inherent instability of upright bipedalism and that the integrity of these mechanisms degrades with aging.
[54] ASSESSMENT OF VARIABILITY IN HUMAN WALKING
E.N. Biden, DPhil
Institute of Biomedical Engineering, University of New
Brunswick, Fredericton, New Brunswick, E3B 5A3 Canada;
email: biden@unb.ca
Sponsor: Natural Sciences and Engineering Research Council of Canada
PURPOSE--The purpose of this project is to expand on existing variability models in gait analysis.
METHODOLOGY--This project has had its primary activity in modeling human walking. During 1994-95, this activity was also applied to other activities. Some of the data were gathered in the Forest Machine Simulator project, and the technology was also applied to upper limb motions during the time the principal investigator was on sabbatical.
The core activity is to develop general purpose "bootstrap" and error estimation models that can be applied to many different types of data. The general purpose bootstrap routines now existing in their original form in FORTRAN and in MATLAB, allow assessment of prediction regions for time series data without resorting to any particular type of analytical model. Bootstrap methods work by taking an original data sample and resampling it to improve the estimate of various sorts of statistical measures. The technique involves taking a group of time series that are to be modeled as the mean and a prediction region around it. The only constraint is that the vectors must be of consistent length. Processing is then done on a time slice basis. The output of the model is a mean value for the group of time series and a boundary around the mean that can be set to enclose any desired fraction of new time series which may come into the study. This has had particular application in gait analysis where the patterns of motion for walking are well defined and an individual being tested can be compared to "normal."
PROGRESS--The new applications in the past year involve applying the same sort of techniques to movements of the upper limb.
Related to this project is a joint effort with the Children's Rehabilitation Centre in St. John's Newfoundland, which will use the bootstrap information along with a modified version of the San Diego Children's Hospital Gait Analysis software to analyze walking data for children.
FUTURE PLANS--The laboratory is currently in the midst of acquiring a VICON Motion Analysis System and will use it in both upper limb and gait studies. The initial objectives are to characterize amputee movement patterns while doing desktop tasks, to assess joystick use in heavy equipment applications, and to assess gait in low tone children undergoing bracing.
[55] MEASUREMENT OF GROUND-FOOT REACTION FORCE TO DETERMINE GAIT ASSYMMETRY USING A COMPUTER-BASED TELEMETRY SYSTEM
Liliwan Ademola Buriamoh-Igbo, PhD; Mathew Ola Bamidele
Olaogun, MS; Abimbola Muhideen Jubril
Obafemi Awolowo University, Department of Electronic and
Electrical Engieering and Medical Rehabilitation, Ile-Ife,
Nigeria
Sponsor: Obafemi Awolowo University, Ile-Ife, Nigeria
PURPOSE--The objectives of this research are: to develop a computer-based data acquisition telemetry system for the continuous monitoring of ground foot forces (GFF) to test this system on nondisabled subjects and on those with pathologic gait and to assess the reliability of the system for clinical use.
METHODOLOGY--The telemetry system is comprised of a mobile and a stationary component.
The Mobile Assembly consists of a pair of instrumented shoes, a force signal processing unit, and an FM transmitter. The instrumented shoes are flat-soled canvas, with force sensors attached to the metatarsal and heel of each sole. The force sensors form part of bridge/amplifier circuits, and their corresponding output sensor is amplified and multiplexed by time: division pulse: width: modulator (PWM). The PWM multiplexed signal is applied to the modulating input of the FM transmitter.
The Stationary Assembly is made up of an FM receiver, signal conditioning unit, frame synchronization and edge detector unit, pulse-width to digit converter, an intermediate memory storage, an RS 232C serial interface, a microcomputer, an analogue processing unit, and a strip chart recorder. The received output is applied to the signal conditioning unit where the pulses corresponding to the transmitted signal is recovered. This PWM multiplexed signal is converted directly to digital output by the pulse-width-to-digit converter. The purpose of the frame synchronization and edge detector unit is to synchronize the receiving end and transmitting end multiplexed signal and for channel identification.
The digital output is first stored in the intermediate storage memory before it is sent to the microcomputer for analysis. The output of the analogue processing unit is applied to the input of a chart recorder to obtain optional and alternative analogue display of the GFF data. This system works with any microcomputer with serial port.
RESULTS--The system has a maximum measurable groundfoot force of 100 kgf. The system has a range of 100 meters, while the bandwidth of each force signal extends beyond 50 Hz. The gait waveform obtained for normal subject was a true representation of well known patterns of GFF.
Pathological waveforms showed deviations from normal ones vis-a-vis the rate of loading and peak force normalized to body weight. In unilateral clinical condition, differences between the waveforms of the two lower limbs is indicative of gait assymetry.
FUTURE PLANS--The research project is ongoing. The next step is to incorporate a GPIB IEEE 488 parallel interface unit into the stationary assembly for faster data acquisition and simultaneous analogue display on the microcomputer during ambulation.
[56] WHEELCHAIR PROPULSION PERFORMANCE IN YOUNG, MIDDLE-AGED, AND ELDERLY
Mary M. Rodgers, PT, PhD; Peter Gorman, MD;
Randall Keyser, PhD; Pamela Russell, PhD
VA Medical Center, Baltimore, MD 21201; email:
mrodgers@physio.ab.umd.edu
Sponsor: Department of Veterans Affairs, VA
Rehabilitation Research and Development Service, Washington,
DC 20420
(Project #B764-2RA)
PURPOSE--The purpose of this 3-year continuation research program is twofold: 1) to investigate how wheelchair performance compares among three different age groups of disabled (lower-limb impaired) wheelchair users; and 2) to test a specific exercise intervention for its effectiveness in reducing potentially injury-producing biomechanical characteristics and excessive physiologic stresses.
METHODOLOGY--Wheelchair users in three age groups of n=20 (20-39, 40-59, and 60-79 years) will participate in this study. Body measurements, muscle strength, neuromuscular assessments, and wheelchair propulsion testing are performed before and following exercise training (stretching, strengthening, and aerobic training three times weekly for 6 weeks). Shoulder, elbow, and wrist joint kinetics (joint moments and joint reaction forces) are calculated from three dimensional motion and handrim force data. Changes with training are statistically tested using paired t-tests and a significance level of 0.05.
PROGRESS--A total of 15 subjects have now completed the study and 5 more have started initial testing; active recruitment of new subjects is continuing. Institutional Review Board approval for additional testing of nonimpaired subjects for database comparisons has been obtained.
PRELIMINARY RESULTS--Fifteen subjects (age 47±11 yrs; weight 80±19 kg; spinal cord lesion level T2-L5 and multitrauma; 12 male, 3 female; wheelchair users for 17±10 yrs) have completed the study. Biceps skinfolds increased (15.2 percent), yet no significant differences were evident in segment girths, body weight, body mass index, or total body fat as determined by a DEXA scan. Eccentric isokinetic strength increased for wrist flexors (54.0 percent), extensors (45.1 percent), and ulnar deviators (47.4 percent). Temporal changes were reflected in a decreased stroke frequency (6.6 percent) and increased contact time (17.7 percent). Kinematic changes included a 13.6 percent increase in elbow range of motion during the entire cycle, with more extension (8.0 percent unfatigued, 9.1 percent fatigued) and less flexion (5.5 percent unfatigued, 7.8 percent fatigued) during contact. The arm position at contact was in more elbow extension (8.4 percent). Maximum shoulder flexion during contact increased (44.3 percent unfatigued, 35.6 percent fatigued) and maximum shoulder adduction decreased (16.5 percent). Maximum trunk forward flexion during contact was increased by 9.9 percent in the fatigued condition. At release, the wrist was extended (3.8°) as opposed to flexed (9.6°); the elbow was more extended (8.1 percent unfatigued, 9.1 percent fatigued); the shoulder was more flexed (40 percent fatigued); and the trunk was more forward flexed (8.8 percent fatigued).
Kinetic changes included a change in the maximum vertical handrim force. Prior to training, vertical handrim force (69.4 N) was highest after fatigue. After training, the vertical force was lower with fatigue (64.8 N). The difference between fresh and fatigued vertical force decreased after training (-6.22 to 4.87 N). The tangential (effective) moment increased by 14.9 percent. Kinematic effects with training were greatest at the elbow, but also evident at the shoulder and trunk. Training induced improvements were evident in the increased contact time, decreased stroke frequency, increased effective moment, and decreased vertical handrim force.
FUTURE PLANS/IMPLICATIONS--Initial findings indicate that specific training for wheelchair users can improve wheelchair propulsion mechanics and decrease the probability of overuse injuries. Further investigation of joint stresses is continuing. Testing and exercise training will continue until the desired sample size is reached (n=60). Data from non-wheelchair users will be collected for comparison.
[57] IN VIVO MEASUREMENT OF VERTEBRAL DISPLACEMENT AFTER LUMBAR FUSION
Thomas A. Zdeblick, MD; David N. Kunz, PhD; Ray
Vanderby, Jr., PhD; David G. Wilson, DVM
Division of Orthopedic Surgery, University of Wisconsin
Hospital and Clinics, Madison, WI 53792; William S.
Middleton Memorial Veterans Hospital, Madison, WI
53705
Sponsor: Department of Veterans Affairs, VA
Rehabilitation Research and Development Service, Washington,
DC 20420
(Project #A738-RA)
PURPOSE--Posterior spinal fusion is performed for a large variety of clinical problems, including spinal trauma with spinal cord injury, degenerative changes of the lumbar spine, tumors, and scoliosis. Spinal instrumentation systems have increased the fusion success rate. However, this increased rate comes attendant with higher risks of device-related osteoporosis, as well as accelerated degeneration of adjacent vertebral levels near a stiff fusion segment. To date, there are no data on the absolute mechanical environment that leads to fusion and/or nonunion of the spine. In this study, we propose to characterize and quantify the biomechanical environment in which a lumbar spine fusion occurs in a goat model.
METHODOLOGY--An implantable transducer system to measure intervertebral motion has been developed. Motion will be measured in vivo and compared in normal, injured, and surgically fused spines. Fusion using bone graft alone and bone graft augmented by rigid or semirigid spinal instrumentation will be compared. The mechanical data will be correlated with radiographic and histologic evaluation of fusion quality and vertebral body density.
In Phase 1, cadaveric goat spine specimens were tested ex vivo to determine displacement across L4-5 using a new transducer system based on Hall-effect devices. The transducers were calibrated by simultaneous measurement of displacement with extensometers. In Phase 2, Hall-effect transducers were implanted across the normal and destabilized L4-5 disc space of live goats. The output of the transducers was measured periodically in a variety of postures, exercises, and manipulated positions for 6 to 12 weeks. The animals were then sacrificed, and the transducer systems recalibrated by testing the excised spine on the MTS machine.
In Phase 3, three experimental treatment groups were similarly studied. Surgery included laminotomy, resection of the facet capsule and the ligamentum flavum, and transducer implantation in all groups. A posterolateral bone graft fusion across L4-5 was performed in Group I. Group II had the fusion augmented with a semirigid pedicle screw device. In Group III, a rigid pedicle screw system was implanted.
PROGRESS AND RESULTS--All 3 phases of the study have been completed. Data have been used to quantify the surgical artifact of the sensor implantation surgery. The passive range of motion of a spinal segment, controlled by osteo-ligamentous structures has been found to be 2 times greater than the motion under normal muscular control in the spine. Destabilizing injury to posterior ligaments increased these ratios by 30 to 100 percent. While the passive characteristics of spinal motion, including neutral zone and range of motion are controlled by osteo-ligamentous limits, functional motion occurs in a portion of that range that is determined by muscular response to neural systems, or the active subsystem of the spinal column. All of the animals with rigid fixation achieved boney arthrodesis, compared 83 percent of the animals in the semirigid group. The stiffness of the fused segments in the semirigid group, however, was greater in all modes of loading, than the fusion with rigid instrumentation. This indicates that rigid instruments improve the rate of fusion, but load stimulation of bone growth with semirigid implants is important to long-term stiffness and strength of the fusion. Muscular control limited intervertebral motion with semirigid implants to a level less than that observed with rigid implants during active exercises, while passive motion allowed by the semirigid system exceeded passive motion allowed by the rigid implants. Muscle action therefore is very important to spinal stability and healing in surgical treatment of the spine.
[58] THE BIOMECHANICAL EVALUATION OF THE EFFECTS OF LOAD CARRYING ON "DYNAMIC" BALANCE CONTROL
James J. Collins, PhD; Ann E. Pavlik, BS; Amy F. Polcyn,
MS; Carlo J. De Luca, PhD
NeuroMuscular Research Center, Boston University,
Boston, MA 02215; email: collins@bunmrg.bu.edu
Sponsor: Liberty Mutual Insurance Company, Boston, MA 02117
PURPOSE--A number of movement-related injuries in the workplace are associated with load-carrying tasks. There is a need to gain an increased understanding of how different load-carrying situations affect the "dynamic" postural control system. There is a related need to develop an objective test for evaluating quantitatively an individual's risk for slipping and falling while carrying a weight. Information derived from such investigations could be used to redesign potentially dangerous work tasks, for instance, by establishing safety limits for the weights to be carried. The objective of this project was to conduct analyses of the effects of load carrying on dynamic balance control.
METHODOLOGY--We completed the development of an experimental protocol for evaluating an individual's ability to initiate walking while carrying different loads, in this case, weighted boxes. With this protocol, a force platform is used to measure the displacements of the center of pressure (COP) under the feet, and an ELITE motion analysis system is utilized to measure the lower-limb kinematics during the gait initiation period. EMG signals are also recorded from selected lower-limb muscles. During the testing, each subject is instructed to stand on the platform for a brief period while holding a weighted box. He or she is then instructed to walk forward off the platform and to continue walking for several steps. Multiple trials are conducted for each load-carrying condition.
PRELIMINARY RESULTS--We examined 10 nonimpaired young subjects (21-30 years) using the above protocol. In this first set of experiments, each was tested under unloaded conditions. We found that in the anteroposterior and mediolateral directions, respectively, the size of the COP shift was highly correlated with the amount of momentum generated. We also found that the size of the backward COP shift was highly correlated with walking speed. We hypothesize that these relationships will change under loaded conditions, indicating that individuals utilize alternative strategies for dynamic balance control while carrying loads. This hypothesis will be tested in a future study.
[59] A MODEL FOR THE "DYNAMIC" POSTURAL CONTROL SYSTEM
James J. Collins, PhD; Ann E. Pavlik, BS; Carlo J. De
Luca, PhD
NeuroMuscular Research Center, Boston University,
Boston, MA 02215; email: collins@bunmrg.bu.edu
Sponsor: Liberty Mutual Insurance Company, Boston, MA 02117
PURPOSE--This project is designed to develop a physiologically based, mathematical model of the "dynamic" postural control system. In our earlier posturographic investigations, we proposed that open- and closed-loop neuromuscular control mechanisms are involved in the regulation of undisturbed, upright stance. The objective of this study was to conduct in numero experiments to test this postural control hypothesis and to explore the functional roles of related neural and biomechanical factors.
METHODOLOGY--The computer model we developed can take the form of a single or multilink inverted pendulum. The joints of each pendulum are constrained by spring-dashpot systems and noisy force actuators. The software package permits the user interactively to set each parameter affecting the modelled system. The computer model is enabled to explore the effects of various control systems, such as: a proportional, derivative, accelerative feedback controller; a variable-gain feedback controller; a sampled data system; and an ON/OFF feedback controller with an error dead-zone. The output of the system consists of the time-varying position of the system's center of mass and center of pressure. In this study, we conducted a series of computer experiments to explore the possible role of physiological noise (e.g., arising from active muscles) in the maintenance of upright stance.
PRELIMINARY RESULTS--We found that with the addition of low levels of noise, the values of active stiffness (arising from activated postural muscles) needed to stabilize the posture model could be reduced. Importantly, high levels of noise destabilized the model, causing it to fall. These findings suggest that physiological noise, under certain circumstances and in certain amounts, can play an important and beneficial role in the maintenance of quiet standing.
[60] SEATED AND RELATED POSTURAL DEVICES FOR ELEMENTARY SCHOOL ENVIRONMENTS
Denise Reid, PhD, OT(C); Steve Ryan, BESc, PEng; Patty
Rigby, MHSc, OT(C); Michael Doell; AOCA; Kubet Weston
The University of Toronto, Department of Occupational
Therapy, Toronto, Ontario M5T 1W5; Bloorview MacMillan
Centre, Toronto, Ontario M4G 1R8; The University of Toronto,
Department of Physical Therapy, Toronto, Ontario M5T
1W5
Sponsor: The Ontario Rehabilitation Technology Consortium funded by the Ontario Ministry of Health
PURPOSE--The purpose of this project is to develop school furniture that uses universally accessible design features. We plan to identify consumer needs and the issues related to posture and school work to design and develop furniture that can be used by most children with or without physical disabilities.
PROGRESS--The first phase is underway and involves applying qualitative methodologies to acquire information regarding the product needs of consumers. The consumer groups include: teachers, teacher assistants, principals, occupational and physical therapists working in schools, educational consultants, parents, and children. We are also reviewing the relevant literature and conducting a comprehensive product search of ergonomically designed school furniture. We have identified two steps for this first phase. In step one, we are conducting nonstructured interviews with a small number of key informants, representing the various groups we have identified. We are exploring their views about school furniture and the needs of the students in relation to the priorities set by the schools and school boards. In step two, we will develop a survey protocol using the relevant variables identified by the key informants and issues discussed in the literature. We plan to create a self-report questionnaire that will be sent to over 200 consumers across Ontario. The survey findings will be analyzed to determine trends and to establish major consumer needs and issues.
FUTURE PLANS--In the second phase of this project, we will focus on developing and evaluating design concepts for two products. The survey findings will be used in two ways. First, they will be formulated into consumer objectives to guide the design process. Secondly, a consumer-based evaluation tool will be developed. We believe that this tool will help consumers to focus on key issues for school furniture design and assess the various features of the design. Consumers will be invited to participate in 3-4 regionally based focus groups to evaluate existing school furniture products using the evaluation tool. These sessions will include consumers from the groups identified above. The issues and opinions raised in the focus groups, combined with the consumer objectives, will be incorporated into preliminary design criteria for this project to provide directions for the development of furniture design concepts and presentation models. The outcomes of the focus groups will also help to examine the validity of the consumer objectives and the items included in the consumer-based evaluation tool. Design concepts and simple models will be taken to consumer focus groups for evaluation. By spring 1997, we will have developed and evaluated models for each of two new classroom products.
[61] ISOMETRIC LENGTH FORCE CHARACTERISTICS OF PENNATE MUSCLES DURING AND AFTER SHORTENING: EXPERIMENTAL AND MODELING RESULTS
Peter A. Huijing, PhD; Dr. Henk J. Grootenboer; Dr. Ir.
Bart Koopman; Drs. Kenneth Meijer; Ir. Bart van der
Linden
Institute of Fundamental and Clinical Movement Sciences,
Faculty of Human Movements Sciences, Vrije Universiteit,
1081 BT Amsterdam; Institute of Biomedical Technology,
University of Twente, 7500AE Enschede, The Netherlands;
email: P_A_J_B_M_Huijing@FBW.VU.NL
Sponsor: Vrije Universiteit, 1081 BT Amsterdam, The Netherlands; Institute of Biomedical Technology, University of Twente, 7500AE Enschede, The Netherlands
PURPOSE--The purpose of this project was to study effects of shortening history on isometric length force curves of pennate muscle and model muscle geometry and its functional effects.
METHODOLOGY--Variables of muscle geometry (i.e., fiber length, aponeurosis length, and fiber and aponeurosis angles) were determined during maximal activition. Isometric length-force curves were determined without previous shortening and after shortening over different length ranges at a number of shortening speeds. A Finite Element (FE) model was constructed that takes into account muscle fiber properties as well as aponeurosis and tendon properties and the mechanical interaction of these variables.
RESULTS--After previous shortening, length-force characteristics of maximally active rat medial gastrocnemius muscle differ very substantially from that determined in fully isometric contractions. Particularly at or over optimum length attained after low speed shortening, muscle force is decreased compared to the fully isometric case. Actual isometric length force properties can be constructed by connecting points of different curves according to shortening history. Negative length-force slopes found in the fully isometric condition are not present at lengths well over optimum length. FE modelling shows that a secondary distribution of fiber mean sarcomere length develops on activation through mechanical interaction of fibers and elastic components. FE modelling could not predict either fully isometric or shortening history influenced length force curves, due to a primary distribution of fiber mean sarcomere length.
IMPLICATIONS--Due to alterations of length-force curves it is not appropriate to consider actual force delivered by a muscle as a result of combination of a fully isometric length force curve and a force-velocity curve.
[62] EVALUATION OF DUAL BAND GRAFTS FOR ANTERIOR CRUCIATE LIGAMENT RECONSTRUCTION
Kevin A. Thomas, PhD; Carlos A. Guanche, MD; T.B.
Edwards, MD; Scott G. Petrie, MD
Bioengineering Laboratory, Department of Orthopaedic
Surgery, Louisiana State University Medical Center, New
Orleans, LA 70112; email: kthoma@nomvs.lsumc.edu
Sponsor: None listed
PURPOSE--The human anterior cruciate ligament (ACL) consists of at least two distinct bands. Techniques currently employed in ACL reconstruction do not attempt to recreate these two bands; instead, a single band of tissue is placed in an isometric position. These procedures do not emulate the natural ACL and restore normal knee kinematics, as evidenced by the degenerative arthritis experienced by some patients after reconstruction. The purpose of this study was to measure the changes in length of the anteromedial (AM) and posterolateral (PL) bands of the intact ACL and to compare these with six different techniques of ACL reconstruction.
METHODOLOGY--Fresh-frozen cadaveric knees were used in this study. To quantitate the changes in length of the bands of the ACL or grafts, miniature displacement transducers were placed in the tissues. Continuous recordings were made of the shortening or lengthening of the ligament or graft tissues, and of the angle of knee flexion over the range of 0-120°. The graft techniques evaluated were either single or double hamstrings or split bone-patellar tendon-bone (B-T-B) graft. Fixation of the graft was by interference screws for the B-T-B grafts and by post fixation for the hamstring grafts. Single or double tunnels for graft placement in the femur or tibia were used, with the tissues tensioned separately at 90° of flexion (AM band) and at 0° of flexion (PL band). The graft techniques included: (1) dual hamstrings with two femoral and two tibial insertions; (2) dual hamstrings with one tibial and two femoral insertions; (3) dual hamstrings with one femoral and two tibial insertions; (4) dual hamstrings with one femoral and one tibial insertion; (5) single hamstrings graft with one femoral and one tibial insertion; and (6) split B-T-B graft with one femoral and two tibial insertions.
RESULTS--Testing of the ACL reconstructions employing single tunnels at both ends all revealed lengthening of the AM and PL bands of the graft tissues from full extension to 120° of flexion. Similarly, grafts employing double tunnels at only one end also lengthened with knee flexion. The technique employing double femoral and double tibial tunnels most closely reproduced the behavior of the intact ACL. The double bundle, double tunnel technique of ACL reconstruction may be a step toward recreating the complex behavior of the natural ACL. This procedure may restore more normal knee kinematics without adding significant technical demands to the current ACL reconstruction procedures.
Go to TOP.
Last revised Wed 05/26/1999
