Biomechanics of tibial plateau leveling of the canine cruciate-deficient stifle joint: a theoretical model

OBJECTIVE: To evaluate the effect of tibial plateau leveling on the biomechanics of the canine stifle. STUDY DESIGN: Analysis of a 3-dimensional (3-D) anatomically accurate theoretical model of the canine stifle. METHODS: A 3-D, 3-segment mathematical model of the normal canine stifle was modified to simulate the effect of rotation of the tibial plateau during tibial plateau leveling osteotomy (TPLO). The model examined the normal stifle, the stifle with a tibial plateau angle (TPA) of 0 degrees, and the stifle with a TPA of 5 degrees. Analysis of the models at 10 consecutive equally spaced positions during the stance phase yielded data such as ligament forces and joint reaction forces at each position. RESULTS: Rotation of the tibial plateau to a TPA of 0 degrees almost eliminates forces in the cranial cruciate ligament (CCL) throughout the stance phase. Rotation to a TPA of 5 degrees did not, however, substantially decrease the load in the CCL. Both procedures increased the load in the caudal cruciate ligament (CaCL). CONCLUSIONS: Cranial tibial thrust (CTT) is converted into caudal tibial thrust when the TPA is 0 degrees ; however, rotating the plateau to a TPA of 5 degrees does not eliminate the CTT. CLINICAL RELEVANCE: The TPLO procedure performed as currently recommended (rotating the tibial plateau to a TPA of 5 degrees) may not eliminate the CTT, but only reduce it. Both TPLO procedures evaluated here were found to increase the load in the CaCL.