Posterolateral Tibial Plateau Bone Loss in the Setting of ACL Insufficiency Leads to Altered Kinematics During a Simulated Pivot Shift That Can Be Corrected With Combined ACL Reconstruction and Lateral Extra-articular Tenodesis But Not ACL Reconstruction Alone.

BACKGROUND

Posterolateral tibial plateau impaction fractures commonly occur in the setting of anterior cruciate ligament (ACL) tears and have been reported to affect clinical outcomes after ACL reconstruction (ACLR), but their biomechanical significance is not well understood.

PURPOSE

To evaluate the biomechanical effect of increasing depths of anteroposterior lateral tibial plateau bone loss on knee kinematics in the ACL-deficient knee and to evaluate the effect of ACLR with and without lateral extra-articular tenodesis (LET) on knee kinematics in the setting of posterolateral tibial plateau bone loss.

STUDY DESIGN

Controlled laboratory study.

METHODS

This study used 16 cadaveric knee specimens subjected to simulated pivot-shift, anterior tibial translation (ATT), and internal rotation (IR) testing via a robotic system. ACL-deficient specimens with 5, 10, and 15 mm of posterolateral tibial plateau bone loss were examined in addition to specimens that underwent ACLR with and without LET in the setting of 15-mm bone loss. Statistical analysis was performed using 1-factor, random-intercepts mixed-effects models to compare ATT, IR, and valgus angulation during a simulated pivot-shift test.

RESULTS

During pivot-shift testing, we observed significant increases in ATT, IR, and valgus angulation when comparing between the ACL intact with no bone loss state and all deficient ACL with bone loss states. For the reconstruction with 15-mm bone loss states, ACLR + LET was able to significantly improve ATT and IR, although valgus angulation remained significantly increased compared with the intact state (mean difference, 0.6 ± 4.0 mm, -4.8° ± 5.7°, and 2.0° ± 3.3°, respectively), while significant differences in ATT, IR, and valgus angulation remained when comparing isolated ACLR to the intact state (mean difference, 4.1 ± 2.8 mm, 3.2° ± 2.1°, and 3.4° ± 2.5°, respectively).

CONCLUSION

With increasing amounts of posterolateral tibial plateau bone loss, there were increased values of ATT, IR, and valgus angulation observed with a simulated pivot shift in ACL-deficient knees in a cadaveric model. In the setting of 15-mm posterolateral tibial plateau bone loss, ACLR combined with LET resulted in a significant decrease in both ATT and IR, but these parameters remained significantly elevated with isolated ACLR.

CLINICAL RELEVANCE

In the setting of high-grade posterolateral tibial plateau bone loss, significant laxity remained after ACLR compared with the ACL-intact state, whereas ACLR with LET was able to better restore kinematics to the ACL-intact state. This suggests that the addition of LET to ACLR should be considered in the setting of high-grade posterolateral tibial plateau bone loss.