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Objective - To compare preoperative tibial plateau leveling osteotomy planning using the common tangent method to the current conventional method and evaluate the effect on tibial translation and patellar ligament angle following rotation of the tibial plateau. Study Design – Cadaveric study. Seven paired canine pelvic limbs. Methods- Radiographs of the stifle were taken at 135° of extension prior to and following rotation of the tibial plateau under load (0N and 30N). The tibial plateau of each limb was rotated both according to the common tangent and conventional method. Tibial plateau angle (TPA), tibial translation, and the patellar ligament angles (PLA) were measured radiographically following rotation of the tibial plateau. Results- There was no significant difference between planning methods with regards to the amount of rotation of the tibial plateau or position of the tibia relative to the femur following rotation. There was no significant association between the postoperative tibial plateau angle and position of the tibia relative to the femur between groups. There was no significant difference between the patellar ligament angles following rotation based on the common tangent or conventional method preoperative TPLO planning. Conclusion- Both the conventional and common tangent TPLO planning results in adequate proximal tibial rotation to achieve a PLA of approximately 90°, thereby counteracting the compressive shear forces during ambulation. The TPA for both groups following rotation had no significant impact on the amount of cranial or caudal tibial translation relative to the femur. / Master of Science / Cranial cruciate ligament disease is one of the most common diseases of the stifle in dogs, and causes great discomfort. The tibial plateau leveling osteotomy (TPLO) procedure is designed to change the geometry of the tibia's articular surface, such that the femur no longer slides in a caudal direction during weight bearing. Conventional methods of planning do not consider the curved anatomical surface of the tibial condyles, but rather treat the condyles like a flat surface. The goal of this study was to compare the current conventional planning methods with a new technique, the common tangent method, and to evaluate if the common tangent method improves accuracy and tibial translation after surgery. Results of this study show that there was no statistically significant difference in rotation and tibial position between the two planning groups. However, it was found that the common tangent method consistently required less rotation of the tibial articular surface than the conventional method, but still achieved similar postoperative tibial translation. This implies that there may be overcorrection when performing the TPLO under the current conventional method, which could predispose the patients to strain on the caudal cruciate ligament and patellar ligament leading to discomfort. The common tangent method is a feasible way of planning for a TPLO procedure, and shows potential utility in cases where excessive tibial rotation would otherwise cause increased risk for complications or necessitate a more complex procedure.