Dislocation after total hip arthroplasty. Treatment with an above-knee hip spica cast.

A study was undertaken of 32 dislocations occurring during a nine-year period in 25 of 1280 postoperative total hip arthroplasty patients. Dislocations occurred in 0.6% of 1030 primary procedures, 1.6% of 165 conversions of hemiarthroplasties to total arthroplasties, and 20% of 85 revisions of previous total hip arthroplasties. Average time to dislocation was 31 days after primary procedures and 106 days after revisions. Acetabular cup malposition and poor patient cooperation appeared to be the causes of dislocation after primary procedures. Trochanteric absence or compromise was a factor in dislocation after revision. Treatment consisted of 13 closed reduction and 19 open reductions. An above-knee hip spica cast was employed for six weeks following closed or open reduction in 16 patients. These 16 patients have been followed up for an average of 32 months (28-45 months). Only one redislocation has occurred.