Effect of Anterolateral Complex Sectioning and Tenodesis on Patellar Kinematics and Patellofemoral Joint Contact Pressures.

BACKGROUND: Anterolateral complex injuries are becoming more recognized. While these are known to affect tibiofemoral mechanics, it is not known how they affect patellofemoral joint behavior.

PURPOSE: To determine the effect of (1) sectioning the anterolateral complex and (2) performing a MacIntosh tenodesis under various conditions on patellofemoral contact mechanics and kinematics.

STUDY DESIGN: Controlled laboratory study.

METHODS: Eight fresh-frozen cadaveric knees were tested in a customized rig, with the femur fixed and tibia free to move, with optical tracking to record patellar kinematics and with thin pressure sensors to record patellofemoral contact pressures at 0°, 30°, 60°, and 90° of knee flexion. The quadriceps and iliotibial tract were loaded with 205 N throughout testing. Intact and anterolateral complex-sectioned states were tested, followed by 4 randomized tenodeses applying 20- and 80-N graft tension, each with the tibia in its neutral intact alignment or left free to rotate. Statistical analyses were undertaken with repeated measures analysis of variance, Bonferroni post hoc analysis, and paired samples t tests.

RESULTS: Patellar kinematics and contact pressures were not significantly altered after sectioning of the anterolateral complex (all: P > .05). Similarly, they were not significantly different from the intact knee in tenodeses performed when fixed tibial rotation was combined with 20- or 80-N graft tension (all: P > .05). However, grafts tensioned with 20 N and 80 N while the tibia was free hanging resulted in significant increases in lateral patellar tilt ( P < .05), and significantly elevated lateral peak patellofemoral pressures ( P < .05) were observed for 80 N.

CONCLUSION: This work did not find that an anterolateral injury altered patellofemoral mechanics or kinematics, but adding a lateral tenodesis can elevate lateral contact pressures and induce lateral patellar tilting if the tibia is pulled into external rotation by the tenodesis. Although these in vitro changes were small and might not be relevant in a fully loaded knee, controlling the position of the tibia at graft fixation is effective in avoiding overconstraint at time zero in a lateral tenodesis.

CLINICAL RELEVANCE: Small changes in lateral patellar tilt and patellofemoral contact pressures were found at time zero with a MacIntosh tenodesis. These changes were eliminated when the tibia was held in neutral rotation at the time of graft fixation. The risk of overconstraint after a lateral tenodesis therefore seems low and in accordance with recent published reports.