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Logo for the Journal of Rehab R&D
Vol. 36 No. 1, January 1999
Pages 35 — 40

A method of residual limb stiffness distribution measurement

William M. Vannah, PhD; David M. Drvaric, MD; Jeffrey A. Hastings; Joseph A. Stand, III; David M. Harning, CPO

Abstract--A method of recording a residual limb indentation stiffness map was developed for possible use in calculating prosthetic socket rectifications. The method was tested to determine its repeatability. A hand-held, pencil-like instrument was used, with an air-driven piston which indented the tissue 10 times per second. The indentor tip contained an electromagnetic digitizer element, and this element sensed position and orientation 120 times per second. The examiner moved the instrument around the limb; sampling was variable in density, and typically concentrated on critical areas. An interactive visual display of sampled data quality was used to guide sampling. The resulting indentation maps typically contained 4000 locations, in a cylindrical coordinate system, with sampling locations spaced every 3.2 mm vertically, and every 0.087 radians tangentially. The behavior of the system was characterized using six test subjects. The recorded indentations ranged from 1.5 to 21 mm. The largest range of indentations (i.e., worst disagreement) recorded at a single location was 5.4 mm. The average standard deviation on repeated measurement averaged 0.67 mm (or 7 to 15%, relative to the indentation). Many of the structurally-significant anatomical features of the limbs were visible; including the patella and patellar tendon, fibular head, shin, biceps femoris tendon, semitendinosus, and popliteal area.

Key words: artificial limbs, computer-aided design, indentor tests, orthosis, prosthesis, soft tissue stiffness.


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