Polar gap after cementless total hip replacement in dogs.

Objective: To determine the incidence and outcomes of total hip replacements with polar gaps in dogs.

Study Design: Retrospective case series.

Animals: One hundred fifty-five client-owned dogs.

Methods: Serial postoperative and follow-up digital orthogonal radiographs of 200 hips in 155 dogs that underwent consecutive index total hip replacement (THR) were examined for the presence of polar gaps. Length and depth of polar gaps were measured and monitored on serial radiographs.

Results: A polar gap was identified in at least 1 zone in 136 (68%) of the ventral-dorsal (VD) radiographs and in 80 (40%) of the lateral radiographs obtained immediately after surgery. Gaps were more common in zones 2 and 5, measuring ≤1 mm in depth in 94 hips on the VD and in 78 hips on the lateral views. No gaps were radiographically visible after 5 weeks postsurgery. No continuous interface radiolucency or lysis was detected, and none of the THR required revision because of loosening.

Conclusion: Polar gaps were identified on the majority of radiographs immediately after THR in our clinical setting and all resolved without complications.

Clinical Significance: Recognition and incidence of postoperative polar gaps after THR may vary among surgeons. Gaps do not warrant clinical intervention.