Changes in tibial plateau angles after tibial plateau-levelling osteotomy in dogs with cranial cruciate deficiency

AIM: To investigate changes in tibial plateau angles measured immediately after surgery and at follow-up in dogs treated for cranial cruciate ligament deficiency using tibial plateau-levelling osteotomy, and to determine the association of host and external factors with this change. METHODS: Records were analysed from dogs treated using tibial plateau-levelling osteotomy. Data included the dog's age, gender, breed, and bodyweight; the tibial plateau angle and mechanical medial proximal tibial angle measured in medio-lateral and caudo-cranial radiographs, respectively, pre- and post-operatively and at follow-up; interval to follow-up, use of a tibial tuberosity pin, type of plate, diameter of the osteotomy blade, and use of the alignment jig during surgery. RESULTS: Data from 364 stifles were analysed, including 163 from male dogs; 52 had bilateral tibial plateau-levelling osteotomy. Mean weight was 35.9 (SD 9.8) kg and age was 5.4 (SD 2.6) years. Mean interval to follow-up was 47 (SD 5.7) days. Overall, the mean tibial plateau angle was reduced from 26.2° (SD 4.7) pre-operatively to 4.5° (SD 3.5) post-operatively, and increased to 7.2° (SD 4.1) at follow-up (p<0.001). The mean mechanical medial proximal tibial angle was reduced from 4.1° (SD 2.4) pre-operatively to 2.7° (SD 2.2) post-operatively, and increased to 3.1° (SD 2.5) at follow-up (p<0.001). The type of plate used was associated with the change in angles between post-operative and follow-up measurements (p = 0.03), but there was no association with any other variables examined. Post-operatively, the tibial plateau angle was 4–6° for 112/364 (30.8%) stifles, and was 4–14° for 125/364 (34.3%) stifles. Type of plate used was associated with the odds of achieving these recommended angles. CONCLUSION: The angular changes in the proximal tibia after tibial plateau-levelling osteotomy were affected by the type of plate used for osteosynthesis, but no significant host factors were identified. Changes in the mechanical medial proximal tibial angle following surgery were also observed despite the use of an alignment jig during surgery. CLINICAL RELEVANCE: Loss in angular reduction following plateau-levelling osteotomy should be expected when using the plate designs included in this study. Placement of a pin through the tibial tuberosity did not prevent the increase in tibial plateau angle between immediate post-operative and follow-up measurements. The use of the alignment jig did not affect the induction of a varus change in the mechanical medial proximal tibial angle during surgery nor the change between immediate post-operative and follow-up measurement.