Morphometric assessment of the proximal portion of the tibia in dogs with and without cranial cruciate ligament rupture.

Based on the clinical observation that dogs with a steep tibial plateau slope had variable tibial morphology, we hypothesized that these dogs could be further characterized using measurements developed by examining computer generated models of specific proximal tibial malformations. A 3D tibial model was created from a normal canine tibia. The model was manipulated to reproduce two specific proximal tibial anomalies representing deformities originating from the tibial plateau or the proximal tibial shaft. Data from these models were used to create specific measurements that would characterize the shape of these anomalies. These measurements included the diaphyseal tibial axis (DTA)/proximal tibial axis (PTA) angle, which defined the orientation of the proximal portion of the shaft in relation to the tibial mid-shaft. These measurements were then made on radiographs of dogs with and without cranial cruciate ligament (CCL) rupture. Models with tibial plateau and proximal shaft deformities had a steep tibial plateau slope (TPS). Models with proximal shaft deformity had a markedly increased DTA/PTA angle. The model with a 10 degree proximal shaft deformity had a DTA/PTA angle of 11.23 degrees. Six dogs (9.0%) had a DTA/PTA angle larger than 11.23 degrees (range, 11.4-13.9 degrees). Dogs in this group had ruptured CCL and a steep TPS. Dogs with CCL rupture had higher TPS (mean, 31.8 +/- 4.1 degrees) and DTA/PTA angle (mean, 6.0 +/- 3.3 degrees) than dogs without CCL rupture (means, 23.6 +/- 3.4 degrees and 4.1 +/- 2.2 degrees, respectively). Dogs with proximal shaft deformity represented a distinct group, which could not be identified using the magnitude of the TPS alone. Characterizing more precisely the shape of the proximal portion of the tibia in dogs contributes to our understanding of the pathogenesis of steep TPS and may facilitate the optimization of the surgical management of dogs with CCL rupture.