A Pitfall on Postoperative Radiographs in Dogs After Tibial Plateau Leveling Osteotomy

Objective: To identify the cause of an occasional radiolucent line in the tibia on postoperative radiographs after tibial plateau leveling osteotomy (TPLO) in dogs. Study Design: Retrospective case series and ex vivo experiment. Sample Population: Dogs (n = 80; 87 stifles) with cranial cruciate ligament (CCL) rupture that had TPLO; and 4 canine tibia specimens. Methods: Medical records (2007-2010) and radiographs of dogs that had TPLO were reviewed and examined for presence of a radiolucent line on postoperative radiographs. The TPLO procedure was reproduced ex vivo to determine the origin of this line by use of metallic wires to identify bone contours. Results: A curvilinear radiolucent line was visible in 14 (16%) tibias and was 5.4 times more likely to be visible with lateral misalignment of the tibial diaphysis relative to the plateau and 2.6 times more likely visible on caudocranial radiographs with the stifle in outward rotation. Fracture complication rate was higher in dogs with this radiolucent line (P = .02) and with lateral misalignment of the tibial diaphysis relative to the plateau (risk ratio, 3.8). The line could be reproduced ex vivo and caused by superimposition of the craniomedial border of osteotomy with the tibial plateau. Conclusions: The radiolucent line was a spurious fracture line created by the medial margin of the tibial osteotomy and confounding factors such as tibial misalignment may explain the apparently associated higher complication rate.