Summary

Clinical evidence shows that non-surgical MCL treatment increases the ACL graft failure rate, so we present studies of anatomy, isometry and restraint provided by the deep and superficial MCL plus POL, showing the importance of the deep MCL in control of AMRI, leading to design and testing in-vitro of two novel medial and anteromedial ligament reconstructions that restore native knee stability

Abstract

Introduction

Failure rates following ACL reconstruction are reduced greatly by adding ALL or LET procedures. The clinical evidence is supported by scientific data of ALRI restraint by peripheral structures rather than the ACL. However, video studies show that most ACL injuries are ‘non-contact’ near knee extension, with valgus and external rotation (ER). Therefore, many ACL injuries are combined with MCL injury, causing AMRI. Nonsurgical MCL treatment in combined injuries greatly increases ACL graft failure rates (Swedish registry). We therefore studied AMRI in the native knee and used the results to design anteromedial (AM) reconstructions.
Previous MCL reconstructions have not reproduced the AM anatomy and there is little evidence of their biomechanical performance. We hypothesized that a more ‘anatomic’ MCL reconstruction would restore native knee stability.

Methods

1. The bone attachment locations of the superficial (sMCL), deep (dMCL) and POL were measured in cadavers by optical trackers and, with wire markers, radiographically.
2. The length-change patterns with knee flexion (isometry) were measured with a set of knee displacing loads (A-P, I-E, V-V) using fine sutures led along the ligament fibres.
3. The restraint of tibiofemoral joint laxity (stability) was measured robotically, by repetitive subluxations and sequential cutting of the ligaments, for each ligament.
4. A novel 3-strand anatomic medial reconstruction (sMCL+dMCL+POL strands) was tested in cadavers for restoration of native stability, and compared versus the LaPrade reconstruction (sMCL+POL) in A-P, I-E, V-V and AMRI (combined anterior translation +ER) loading, with optical tracking. Laxity changes were examined by ANOVA with multiple contrasts and post-testing.
5. An AM reconstruction (sMCL+dMCL) was also tested.

Results

The sMCL attaches to the medial epicondyle and is isometric. It is the primary restraint to valgus and secondary to IR-ER. The dMCL attaches 5-6mm distal/posterior and is oriented anterodistally, close to isometric, but elongated by ER: the primary ligamentous restraint of ER near knee extension. The POL is tight in extension and slackens rapidly, so offers no restraint of V-V or ER in flexion. The combined sMCL, dMCL and POL deficiencies primarily caused increased valgus and ER-IR. The anisometric LaPrade reconstruction controlled valgus in extension but not in flexion, nor ER at any angle. In the 3-strand and AM reconstructions the additional anteromedial dMCL graft restored native ER and the isometric sMCL maintained valgus restraint throughout flexion, and both controlled AMRI. POL deficiency had no significant effect on AMRI. The POL restrained IR near knee extension and this was not completely replicated by the reconstructions.

Discussion

During MCL reconstruction, an anteromedial dMCL band is vital to control AMRI: this may help to unload/protect the ACL graft. The sMCL graft should be placed isometrically at the femoral epicondyle, placing the tunnel posteriorly causes graft slackening due to anisometry with knee flexion. A POL graft is superfluous in knees with AMRI. These novel reconstructions may be simplified for clinical use by reducing numbers of tunnels and fixations.
Many ‘isolated’ ACL injuries have MCL damage. The MCL may stretch-out during healing if treated non-surgically – will MCL reconstruction reduce ACL failure rates?