The senior one of us performed 438 primary and 181 revision total hip arthroplasties with use of so-called modern prostheses between July 1983 and January 1994. Fifty-three patients, who had had forty-seven primary procedures and twelve revisions, either died or were lost to follow-up less than two years after the operation and were excluded from the study. The results for the remaining 446 patients (391 primary procedures and 169 revisions) were analyzed to determine the influence of patient-related and operative factors and the position of the acetabular component on the rate of dislocation. Dislocation occurred after thirty-two (6 per cent) of the 560 total hip arthroplasties: seventeen (4 per cent) of the 391 primary procedures and fifteen (9 per cent) of the 169 revisions (p = 0.046). There was no relationship between the variables of age, gender, obesity, or preoperative diagnosis and dislocation after either primary or revision arthroplasty. Seven (23 per cent) of the thirty arthroplasties in the patients who had a history of excessive intake of alcoholic beverages (more than 2.1 liters [seventy-two ounces] of beer or more than 0.2 liter [six ounces] of other alcoholic beverages a day) were followed by a dislocation compared with twenty-five (5 per cent) of the 530 arthroplasties in the patients who did not have such a history. This difference was significant for the patients who had had a revision arthroplasty (p = 0.00005), but with the numbers available we could not detect a difference for those who had had a primary arthroplasty (p = 0.264). Radiographic analysis was performed for thirty-two hips that had dislocated and thirty-two that had not (seventeen primary procedures and fifteen revisions in each group), matched exactly according to the type of prosthesis and the operative approach (but not age). We detected no association between either the version or the abduction angle of the acetabular component (within the range of 39 to 56 degrees for the primary prostheses and 38 to 57 degrees for the revision prostheses) and the risk of dislocation. Thirty of the thirty-two hips in each group had an abduction angle of the acetabular component that was in the so-called safe range of 30 to 50 degrees.

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