Femoral cortical thickness index in a population of dogs undergoing total hip replacement.

Objective: To establish a femoral cortical thickness index (CTI) for dogs undergoing total hip replacement (THR), determine the reproducibility of the established CTI measurements, and assess the efficacy of CTI as a preoperative variable in the femoral fracture/fissure occurrence in dogs undergoing THR.

Study design: Retrospective study.

Animals: A total of 224 dogs with THR.

Methods: Medical records for dogs undergoing THR were reviewed retrospectively, analyzing only the first side in dogs with bilateral THR. Three measuring points were defined on preoperative mediolateral radiographs: immediately distal to the lesser trochanter, one-quarter-, and midway down the femur. The CTI was calculated from the mean cortical and femoral diaphyseal diameters at the established locations. A total of 10 dogs with varying CTI scores were selected for interobserver comparisons and pre-/ postoperative analyses. The relationship between CTI and perioperative fissure/fracture risk was then evaluated.

Results: Interobserver and pre-/ postoperative measurement comparisons showed near-perfect correlation. Analysis of 224 dogs revealed a significant association between lower CTI and incidence of perioperative fractures (p < .0001). The mean CTI for all dogs was 0.285, while it was statistically lower at 0.246 for dogs that sustained fissures/fractures. No other statistically significant risk factors were identified.

Conclusion: This study quantitatively assessed femoral cortical thickness in dogs undergoing THR. The findings confirmed that lower CTI is a repeatable and accurate predisposing factor for perioperative fissure/fracture risk in canine THR.

Clinical significance: Factoring CTI into the clinical decision making may minimize fracture risk, especially in dogs with other possible risk factors such as abnormal BCS.