RELATIONSHIP OF FEMORAL-HEAD AND ACETABULAR SIZE TO THE PREVALENCE OFDISLOCATION

Two clinical studies, one prospective randomized and one retrospective , were performed to evaluate the relationship of femoral head size and acetabular component outer diameter to the prevalence of dislocation of the modular total hip replacement. Between October 1995 and April 1 996, 31 primary total hip arthroplasties in 30 patients were randomize d to a femoral head diameter of 22 mm or 28 mm, for two groups of acet abular components of outer diameters of 56 mm or larger and 54 mn or s maller. Head size (22 mm) and acetabular component outer diameter (gre ater than or equal to 56 mm) were found to increase the risk of disloc ation. From December 1984 to January 1994, 308 primary total hip arthr oplasties were performed through a posterior approach by one surgeon u sing a modular 28 mm femoral head and one type of uncemented acetabula r component. The rate of dislocation for acetabular components with an outer diameter of 62 mm or larger was increased significantly (five o f 36 hips, 14%) compared with those with an outer diameter of 60 mm or smaller (11 of 272 hips, 4%).