A method of residual limb stiffness distribution measurement

A method of recording a residual limb indentation stiffness map was developed for possible use as an aid in calculating prosthetic socket rectifications. The method was tested to determine the level of repeatability attainable. A hand-held, pencil-like device was used, with an air-driven piston that indented the tissue 10 times per second. The indentor tip contained an electromagnetic digitizer element that sensed position and orientation 120 times per second. The examiner moved the device 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 indentation maps typically contained approximately 4,000 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 on whom 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 ranged from 7 to 15%, and averaged 0.67 mm in absolute terms. 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.