Evaluation of the effects of cementless total hip replacement on femoral length in skeletally immature dogs.

Objective: To describe percentage length changes in the femur after total hip replacement (THR) performed before skeletal maturity.

Study design: Retrospective study.

Animals: Twenty-four dogs younger than 8.5 months which underwent unilateral THR and had radiographic follow up.

Methods: Preoperative and follow-up radiographs were reviewed. Radiographic measurements included the length of the greater trochanter, femoral diaphysis and distal epiphysis, width of the femur 10 mm distal to the distal aspect of the greater trochanter, width of the femur at 50%, and femoral condylar offset. Percentage changes in length over time were compared among operated and contralateral femurs used as controls. Measurements were collected in triplicate in 10 dogs to evaluate consistency.

Results: All repeated measurements had excellent consistency. The percentage increase in length of the greater trochanter was smaller in operated femurs than controls (mean difference: -11.5%, p = .017), but no differences were observed for the femoral diaphysis and distal epiphysis (-1.0%, p = .595), or the femur overall (-2.3%, p = .232). The percentage increase in femoral cortical width was greater in operated femurs than controls, both 10 mm distal to the greater trochanter (4.6% difference, p = .037) and at 50% length (8.5% difference, p = .030).

Conclusion: In growing dogs, cementless THR decreased trochanteric growth by approximately 10% but did not change diaphyseal growth and femoral growth.

Clinical significance: Cementless THR performed in skeletally immature dogs with severe hip problems did not impact femoral length in a clinically relevant fashion.