SURFACE MOVEMENT ERRORS IN SHANK KINEMATICS AND KNEE KINETICS DURING GAIT

The movement of surface mounted targets (SMT) on a shell at the mid-sh ank and of bone mounted targets attached to the distal shank using a P ercutaneous Skeletal Tracker (PST) were simultaneously measured during free-speed walking of three adult subjects having different body type s. Surface movement errors in shank kinematic estimates were determine d by expressing the segmental motion derived from the SMT relative to the PST-based segment coordinate system (SCS) located at the segment c enter of gravity. The greatest errors were along and around the shank longitudinal axis, with peak magnitudes of 10 mm of translation and 8 degrees of rotation in one subject. Estimates of knee joint center loc ations differed by less than 11 mm in each SCS direction. Differences in estimates of net knee joint forces and moments were most prominent during stance phase, with magnitudes up to 39 N in the shank mediolate ral direction and 9 N.m about the mediolateral axis. The differences i n kinetics were primarily related to the effect of segment position an d orientation on the expression of joint forces and on the magnitude a nd expression of joint moments.