Movement loci of selected points on the femoral head for individual total hip arthroplasty patients using three-dimensional computer simulation

Wear of ultra-high-molecular-weight polyethylene (UHMWPE) and the subsequen t adverse tissue reaction to the wear particles has been cited as the predo minant problem affecting total joint arthroplasties. Wear of the UHMWPE ace tabular cup in total hip arthroplasties (THAs) is influenced by the sliding distance and direction of individual points on the femoral head, which has as yet been ascertained only for normal subjects. This study seeks to dete rmine the trajectory of specified points on the femoral head for individual THA patients and the distances traversed by these points. A computer progr am was designed to use gait data from THA patients to simulate the motion o f these points. Gait analysis was performed on 19 THA patients at a period of 5 years after operation. The orientation of the acetabular cup was ascer tained from radiographs to determine the position of the points on the head most involved in the wear process. The loci of the points differed widely in size, shape, and direction between subjects. The largest average distanc e traversed was 140% greater than the smallest average distance traversed. Shorter longitudinal paths would tend to cause less wear than larger, wider paths, which cross a greater number of adjacent paths.