Tibial Tuberosity Osteotomy for Patellofemoral Realignment Alters Tibiofemoral Kinematics

Background: Tibial tuberosity realignment surgery is performed to improve patellofemoral alignment, but it could also alter tibiofemoral kinematics. Hypothesis: After tuberosity realignment in the malaligned knee, the reoriented patellar tendon will pull the tuberosity back toward the preoperative position, thereby altering tibiofemoral kinematics. Study Design: Controlled laboratory study. Methods: Ten knees were tested at 40 degrees, 60 degrees, and 80 degrees of flexion in vitro. The knees were loaded with a quadriceps force of 586 N, with 200 N divided between the medial and lateral hamstrings. The position of the tuberosity was varied to represent lateral malalignment, with the tuberosity 5 mm lateral to the normal position; tuberosity medialization, with the tuberosity 5 mm medial to the normal position; and tuberosity anteromedialization, with the tuberosity 10 mm anterior to the medial position. Tibiofemoral kinematics were measured using magnetic sensors secured to the femur and tibia. A repeated measures analysis of variance with a post hoc Student-Newman-Keuls test was used to identify significant (P<.05) differences in the kinematic data between the tuberosity positions at each flexion angle. Results: Medializing the tibial tuberosity primarily rotated the tibia externally compared with the lateral malalignment condition. The largest average increase in external rotation was 13 degrees at 40 degrees of flexion, with the increase significant at each flexion angle. The varus orientation also increased significantly by an average of 1.5 degrees at 40 degrees and 80 degrees. The tibia shifted significantly posteriorly at 40 degrees and 60 degrees by an average of 4 mm and 2 mm, respectively. Shifting the tuberosity from the medial to the anteromedial position translated the tibia significantly posteriorly by an average of 2 mm at 40 degrees. Conclusion: After tibial tuberosity realignment in the malaligned knee, the altered orientation of the patellar tendon alters tibiofemoral kinematics. Clinical Relevance: The kinematic changes reduce the correction applied to the orientation of the patellar tendon and could alter the pressure applied to tibiofemoral cartilage.