Intraoperative patellar kinematics following resection of the central one-third of the patellar tendon in the ovine stifle joint

Objectives: The bone-patellar tendon-bone complex is routinely harvested for anterior cruciate ligament reconstruction in humans. Patella infera may ensue. However, the contribution from resection of the central one-third of the patellar tendon (PT) to potentially altered patellofemoral kinematics, in addition to those induced by a positional shift of the patella, are yet to be distinguished. Objectives of this study were to characterize changes in intraoperative patellar kinematics and PT length in nine sheep immediately following unilateral resection of the central one-third PT, and again at six, 12 and 24 weeks post-operatively. Methods: Following implantation of bone-screws into the patella and tibia, electromagnetic receivers were anchored to these, and then passively-induced, unloaded patellar kinematics were captured. Patellar kinematics were referenced to the tibial coordinate frame and analysed using non-parametric tests (Wilcoxon Signed Rank Test). Results: Resection alone did cause significant alteration in kinematics at the time of surgery (p <0.05). Postoperatively, a mean increase in PT length of 2.6 mm was detected in the operated stifles, reflected partly as a net 2.8 mm proximal patellar shift (p <0.001). This was accompanied by a mean net six degree medial shift in the patellar tilt pattern (p <0.001). Significant changes to patellar spin in the latter parts of flexion were also observed (p <0.005). Kinematic and length changes did not recover up to 24 weeks postoperatively. Clinical significance: The data obtained in this study suggests that both the patellar height and integrity of the PT are important determinants of patellar kinematics in the ovine stifle joint.