THE ACETABULAR CUP POSITION: DISLOCATION AFTER TOTAL HIP ARTHROPLASTY

Abstract

Dislocation after total hip arthroplasty (THA) remains a significant clinical problem. The acetabular cup position is one of the main factors in the incidence of dislocation after THA. We reviewed dislocation cases in 247 primary THA

Between 1997 and 2001, 247 patients underwent a primary THA procedure. The original diagnoses in these patients were as follows: osteoarthritis (OA, n = 190), osteonecrosis (ION, n=28), rheumatiod arthritis (RA, n=16), and rapidly destructive coxarthropathy (RDC, n=13). A posterolateral approach was used in all cases. We examined mainly the acetabular cup position (ante-version and inclination angle) using anteroposterior radiographs

Six dislocations (2.4%) occurred : three anterior dislocations and three posterior dislocations. Dislocation rate according to the original diagnoses were as follows, 2 dislocations in OA (1.1%), 2 dislocations in RA(12.5%), 2 dislocations in RDC(15.4%) and no dislocation in ION. All cases were treated with close reduction and no component revision was needed. On X-P measurement of setting the acetabular cup in all cases, the mean ante-version angle was 16.3617;6.8 degrees and inclination angle was 43.3& #61617;7.3 degrees. In comparison with these measurement values, there was no statistical difference between the dislocation groups and no-dislocation groups. The number of the cases within Lewinnek’s safe zone in acetabular cup was 178 (72%). The dislocation rate in these 178 cases was low (1.1%).

Setting the acetabular cup in adequate position is one of the major factors avoiding dislocation after THA. We have been performimg computer - assisted THA since 2003. Computer - assisted surgery enables the acetabular cup position to be precisely planned before surgery and allows superior positioning during surgery.