Summary

Robotic system was used to compare knee kinematics between different treatments for concomitant lateral meniscus test in the ACL reconstructed knee. ACL reconstruction alone did not fully restore knee kinematics, while additional meniscus repair achieved intact level of knee kinematics. Furthermore, lateral extraarticular tenodesis also normalized knee kinematics without meniscus repair.

Abstract

Objective

Concomitant lateral meniscus tear in the ACL injured knee could lead to insufficient restoration of rotatory knee laxity after ACL reconstruction. Since lateral meniscus tears are not always reparable, additional augmentation procedure, such as lateral extraarticular tenodesis (LET) could be indicated to salvage the stability after the ACL reconstructed knee. However, it is still unknown how the LET affect knee kinematics postoperatively in the ACL reconstructed knee.
The purpose was to compare knee kinematics and in-situ force of ACL/ACL grafts between four different conditions of ACL and lateral meniscus.

Methods

Eight human cadaveric knees were tested using a 6DOF robotic testing system. The knee was flexed from full extension to 90° while the following loads were applied: (1) anterior loading (i.e. 134N anterior tibial load with 100N compression force), (2) a simulated pivot-shift loading (i.e., 7Nm valgus torque, 7Nm internal tibial torque, and 100N compression force). Knee kinematics and in situ force in the ACL or ACL graft were compared under five conditions: intact knee (INT), ACL dissected knee with a complete radial meniscus tear in the posterior horn (ACLD-LMD), ACL-reconstructed knee with a lateral meniscus tear (ACLR-LMD), ACL-reconstructed knee with a repaired lateral meniscus (ACLR-LMR) and ACL-reconstructed knee with LET and a lateral meniscus tear (ACLR-LET).

Results

Anterior tibial translation (ATT) increased by cutting the ACL and the lateral meniscus between full extension and 60° (<0.01). The ACL reconstruction reduced the increase of ATT (p<0.05 or <0.01), but the ATT was still larger than that of intact knee without meniscus repair or LET (p<0.05 or <0.01). Additional meniscus repair or LET achieved the intact level of ATT (p>0.05). (Fig.1 Left) Abnormal lateral translation and valgus occurred by cutting the ACL and the meniscus at 15° and 30° (p<0.05), and they were restored by ACL reconstruction and additional meniscus repair or LET (p<0.05). The coupled anterior tibial translation (cATT) against simulated pivot-shift loading increased by ACL dissection and a meniscus tear from full extension to 30° (p<0.05 or <0.01). ACL reconstruction restored the increased cATT slightly better with additional meniscal repair or LET. (Fig.1 Right) The in situ force of the ACL and ACL graft under both anterior and simulated pivot-shift loading was not different between five conditions of the ACL and the meniscus (p>0.05).

Conclusion

Either additional meniscus repair or LET in addition to the ACL reconstruction was required to restore normal knee kinematics in the ACL and lateral meniscus torn knee. When encountering unrepairable lateral meniscus tear in ACL injured knee, LET might be considered in addition to ACL reconstruction.