Hip implant sinking after total hip replacement in 145 dogs

Abstract

OBJECTIVE: To describe postoperative subsidence observed after total hip replacement (THR) with the BFX standard stem. STUDY DESIGN: Retrospective case series. SAMPLE POPULATION: A total of 177 THR procedures in 145 dogs. METHODS: Clinical and radiographic follow-up data were collected between 12 weeks and six months postoperatively. A proportion correction was used to calculate subsidence between immediate postoperative and follow-up radiographs. Canal flare index, coronal canal fill, sagittal canal fill, coronal stem orientation and sagittal stem orientation were measured. RESULTS: There were 24/177 (13.6%) intra- and postoperative complications. Of these, 11/177 (6.2%) were stem complications. Eight stem complications were intraoperative femoral fissures; one fissure progressed to postoperative femoral fracture. Subsidence was associated with stem complications (p = .005) and was not associated with non-stem complications (p = .76) or prosthetic luxation (p = .07). There were seven stems with more than 5.0 mm of subsidence; of these only 1/7 had a stem complication. There were 26 stems with more than 3.0 mm of subsidence; of these only 3/26 had a stem complication. There was no association between any femoral or stem measurements and subsidence. CONCLUSION: Subsidence of the BFX standard stem was associated with stem complications, which were mostly intraoperative femoral fissures. Thresholds of 3.0 and 5.0 mm were poorly predictive of complications, and substantial subsidence was often clinically inconsequential. CLINICAL SIGNIFICANCE: Cutoffs for excessive subsidence may have limited clinical utility. The significance of postoperative subsidence should be interpreted in the context of other clinical findings.