Monocortical locking screws in the tibial diaphysis maintain tibial plateau angle and support osteotomy union after tibial plateau leveling osteotomy in dogs

Objective: To evaluate the effect of distal monocortical locking screw fixation on construct stability and bone healing following tibial plateau leveling osteotomy (TPLO) in dogs. We hypothesized that monocortical fixation would result in acceptable maintenance of tibial plateau angle (TPA) of < 5° and satisfactory osteotomy union. Methods: Medical records from a companion animal referral hospital between December 8, 2021, and February 23, 2024, were retrospectively reviewed. Dogs were included if TPLO was performed for cranial cruciate ligament insufficiency using monocortical screws in the distal tibial segment and complete radiographic follow-up was available. Change in TPA between postoperative and follow-up radiographs were recorded. Bone healing was assessed using the modified Radiographic Union Scale for Tibial Fractures. Associations between outcomes and clinical variables were evaluated with linear regression models. Results: A total of 117 dogs met the inclusion criteria. Median change in TPA during healing was 2.15° (95% CI, 1.70° to 2.65°), and no evaluated variables were associated with TPA change. Median modified Radiographic Union Scale for Tibial Fractures score was 10 (range, 4 to 12), consistent with satisfactory radiographic union at a mean follow-up time of 43 days. The overall complication rate was 8.5%, including an infection rate of 2.6%. Conclusions: Use of monocortical distal tibial screws within a titanium alloy conical locking TPLO system was associated with acceptable maintenance of TPA and satisfactory radiographic union scores. Clinical Relevance: Monocortical distal tibial fixation may provide sufficient stability to support osteotomy healing per manufacturer recommendations. Additional studies are needed to evaluate outcomes for different locking systems, patient size categories, screw combination, and longer-term follow-up periods.