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°, 60°, and 80° 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° at 40° of flexion, with the increase significant at each flexion angle. The varus orientation also increased significantly by an average of 1.5° at 40° and 80°. The tibia shifted significantly posteriorly at 40° and 60° 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°.

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.