Ceramic acetabular cups for total hip replacement - Part 6: Cup design, inclination angle and antetorsion angle have an influence on the range of motion and impingement

The present investigation focuses on total hip replacement using ceramic ac etabular components. The relationship between the position of the cup and t he range of motion (ROM) was investigated. A Limited range of motion may ca use impingement, which is defined as contact between the femoral neck and t he rim of the acetabular cup. Impingement may result in wear, chipping; fra cture or dislocation of the femoral head. Joint movements were simulated in a three-dimensional CAD program. The results obtained underscore the importance of correct positioning and d esign of the cup for achieving a ROM as close to the physiological situatio n as possible. With ceramic cups, the inclination angle should not be more than 45 degrees, and the antetorsion angle between 10 and 15 degrees. If th e cup is too vertical, the risk of dislocation and fracture of the ceramic increases. If, on the other hand, the angle of inclination is too small, fl exion and abduction will be greatly limited. The study shows that acetabular components with non-recessed ceramic insert s should not be used. Slight recession of the insert helps to avoid impinge ment. The ROM is reduced and the risk of impingement appreciably increased when mushroom-shaped femoral heads (XL heads) or ceramic inserts protected by a polyethylene ring are used.