Effect of tibial plateau leveling osteotomy on patellofemoral alignment: a study using canine cadavers

Tibial plateau leveling osteotomy (TPLO) has been shown to alter the biomechanics of the femorotibial joint; however, the effect of TPLO on patellofemoral (PF) joint alignment remains unknown. The purpose of this study was to evaluate PF joint kinematics before and after cranial cruciate ligament (CrCL) transection and following TPLO in a cadaveric stifle model with set patellar tendon load, tested in passive range of motion at 90°, 105°, 120°, 135° and 150° of flexion. The PF joint poses were measured on mediolateral projection radiographs using a two-dimensional computer digitization technique. In the subluxated CrCL-deficient stifle, the PF joint had an increase in patellar tilt angle. In the reduced CrCL-deficient stifle treated by TPLO, there was distal and caudal displacement of the patella relative to the femur and a decreased patellar tilt angle. The estimated patellar moment arm following TPLO was not different from the control stifle. On the basis of these results, TPLO alters PF joint kinematics. The changes in PF joint alignment induced by TPLO may be a biomechanical factor predisposing to patellar tendonitis following TPLO.