MORPHOMETRIC ASSESSMENT OF THE PROXIMAL PORTION OF THE TIBIA IN DOGS WITH AND WITHOUT CRANIAL CRUCIATE LIGAMENT RUPTURE CHRISTIAN S. OSMOND,DENIS J. MARCELLIN-LITTLE,OLA L. A. HARRYSSON,LINDA B. KIDD 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 repre- senting 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 101 proximal shaft deformity had a DTA/PTA angle of 11.231. Six dogs (9.0%) had a DTA/PTA angle larger than 11.231 (range, 11.4–13.91). Dogs in this group had ruptured CCL and a steep TPS. Dogs with CCL rupture had higher TPS (mean, 31.8  4.11) and DTA/ PTA angle (mean, 6.0  3.31) than dogs without CCL rupture (means, 23.6  3.41 and 4.1  2.21, respec- tively). 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. Veterinary Radiology & Ultrasound, Vol. 47, No. 2, 2006, pp 136–141. Key words: biomodeling, canine, cruciate ligament, morphology, tibia. Introduction C RANIAL CRUCIATE LIGAMENT (CCL) rupture is a com- mon orthopedic problem in dogs. 1 CCL rupture oc- curs as a consequence of chronic biochemical or mechanical degenerative processes or, less commonly, af- ter acute trauma. 2,3 CCL injuries have been associated with age, vascular disorders, body condition, and immune-me- diated arthropathies. 4,5 Mechanically, CCL injuries have been associated with a narrow trochlear notch and steep tibial plateau slope (TPS). 6–9 Some reports state that the TPS is steeper in dogs with CCL injuries than in dogs without injuries, while other reports disagree. 10,11 Increased TPS has been hypothesized to lead to CCL injury through an increase in cranial tibial thrust. 12 Even though no causal relationship between a steep TPS and CCL injury has been proven, the correlation of slope and cranial thrust has been confirmed experimentally. 13 To our knowledge, there has been no assessment of the specific morphologic changes present in canine tibiae with a steep TPS. The impetus for this study was the observation that the shape of the proximal portion of the tibia varies in dogs with CCL rupture and a steep TPS (Fig. 1). These differ- ences in shape could result from a number of developmen- tal problems such as having abnormal longitudinal growth of specific aspects of the tibia. We used predictive models to investigate whether specific angular deformities mim- icking growth anomalies of the tibial plateau or the prox- imal tibial shaft would match the shape of the tibia of specific groups of dogs with CCL rupture. One deformity could potentially result from premature closure of the cau- dal aspect of the tibial physis (tibial plateau deformity). Another deformity could result from plastic deformation of the proximal portion of the tibia in relation to its mid- shaft (proximal shaft deformity). In the absence of specific information regarding these deformities, we created com- puter models of canine tibiae with intentional deformities confined to the tibial plateau or involving the entire proximal shaft of the tibia. We made specific measure- ments of anatomic features on these predictive models and Address correspondence and reprint requests to Denis J. Marcellin- Little, at the above address. E-mail: denis_marcellin@ncsu.edu Received June 26, 2005; accepted August 9, 2005. doi: 10.1111/j.1740-8261.2006.00119.x From the Department of Clinical Sciences, College of Veterinary Med- icine and the Department of Industrial Engineering, North Carolina State University, 4700 Hillsborough Street, Raleigh, NC 27606. 136