Movement loci of selected points on the femoral head for individual THR patients using three dimensional computer simulation

This study determines the trajectory and distances traversed of specified points on the femoral head For individual total hip replacement (THR) patients and normal subjects. A computer program utilises gait data obtained from 19 THR patients 5 years post-operation and 9 normal subjects to simulate the motion of these points. The loci of the points differed widely in size, shape and direction between subjects. The average sliding distance of the points differed between normal subjects (22.225 mm, range: 18.52-26.88 mm) and THR patients (18.06 mm, range: 10.08-24.41 mm). The loci traced varied between THR patients from thin, longitudinal paths wide to wider, elliptical paths. The average aspect ratio of the loci varied between THR patients from 0.11 to 0.4. Longitudinal wear paths are associated with unidirectional motion, orientation hardening and higher wear resistance. Shorter, longitudinal paths would tend to cause less wear than larger, wider paths which cross a greater number of adjacent paths.