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Objective: To investigate whether preexisting coxofemoral subluxation/luxation predisposes to postoperative total hip replacement (THR) luxation.

Study Design: Case series.

Animals: Dogs (n=100) that had cemented THR (n=109); 23 normal controls.

Methods: A preliminary study was performed to validate our methods of assessing luxation and laxity by comparing dogs with severe hip dysplasia with a control population of normal dogs. For the main study, the records and radiographs of all dogs that had primary THR were reviewed. Measurements taken from preoperative radiographs to quantify hip subluxation/laxity included the Norberg angle, subluxation index, and 2 new measures: acetabular depth ratio (ADR) and dorsal acetabular rim ratio (DARR). Differences between groups that had luxation within 8 weeks and those that did not were investigated.

Results: Postoperative luxation occurred in 13 dogs (12%) within 8 weeks of surgery. Luxation was significantly associated with various measurements (including Norberg angle, ADR, DARR) thought to reflect degree of subluxation/soft tissue tension.

Conclusion: Luxation after canine THR is a multifactorial problem but preexisting subluxation/soft tissue laxity is a significant risk factor for this complication.