Summary

This Abstract provides insight in the isometry and length changes of theoretical lateral extra-articular reconstructions of the anterolateral aspect of the knee.

Abstract

Background

Combining lateral extra-articular reconstruction (LER) and intra-articular anterior cruciate ligament (ACL) reconstruction has been proposed in an attempt to restore laxity of the knee that has a torn ACL. Historically, LER procedures have not been successful, possibly because of biomechanically unfavorable positioning. A LER that is isometric throughout knee movement would theoretically minimize the risk of undesirable graft behavior. However, the effect of changing LER attachment sites on its length changes during in vivo dynamic knee motion remains unknown.

Purpose

To assess the isometry and length changes of theoretical LER grafts attached to various points on the lateral femoral condylar area and to either Gerdy’s tubercle or the anatomic attachment site of the anterolateral ligament (ALL) to the tibia.
Study Design: Descriptive laboratory study.

Methods

Eighteen healthy knees with no history of lower extremity injury or surgery were studied. The subjects performed a sit-to-stand motion (~90° flexion to full extension) and each knee was studied using magnetic resonance and dual fluoroscopic imaging techniques. The three dimensional wrapping paths of each theoretical LER graft were measured. Grafts showing least length change during the sit-to-stand motion were considered to be most isometric.

Results

The most isometric attachment site on the lateral femoral condyle to either studied tibial attachment site was posterior-distal to the femoral attachment of fibular collateral ligament (FCL). It had a mean length change of approximately 3%. Moving the femoral attachment point anteriorly resulted in increased length of the LER graft with increasing flexion; more posterior attachments resulted in decreased length with increasing flexion. Moving the attachment site in the proximal-distal direction had a less profound effect. Moving the tibial attachment from Gerdy’s tubercle to the tibial attachment site of the ALL affected the overall isometric distribution on the femoral epicondyle. The posterior-proximal area of the lateral femoral condyle was found to show graft length changes in which the LER was tighter in lower flexion angles and slacker in increased flexion.

Conclusion

The most isometric attachment site on the femur for a LER would be posterior-distal to the femoral attachment of the FCL. Different length changes for LER grafts were found for with respect to different femoral attachment sites. Desirable graft fixation locations for treating anterolateral rotatory instability were found in posterior-proximal to the femoral FCL attachment.
Clinical Relevance: The present data could be used both in biomechanical and clinical studies as a guideline for the planning LER surgical procedures.