Anterior Cruciate Ligament Force Is Reduced by Anteromedial Reconstructions That Mimic the Role of Deep Medial Collateral Ligament

Abstract

Background:

Combined injuries of the anterior cruciate ligament (ACL) and medial structures, including the superficial and deep medial collateral ligaments (sMCL and dMCL), are common and associated with anteromedial rotatory instability (AMRI). While various medial reconstructions have been developed to address this, their impact on ACL graft loading remains unclear.

Purpose:

To evaluate the effects of different medial reconstructions on ACL load.

Hypothesis:

Adding an anteromedial (AM) reconstruction reduces ACL load more effectively than adding an isolated single-bundle superficial medial collateral ligament (sMCL) reconstruction.

Study Design:

Controlled laboratory study.

Methods:

Eight unpaired knees were tested in a kinematic rig with imposed loads displacing the tibia. This included 5 N·m of external rotation (ER) and internal rotation and a combined 89 N of anterior translation with ER (the AM drawer [AMD] test). Testing was performed in the intact state, after sectioning of the sMCL and deep medial collateral ligament (dMCL) and after 4 different medial reconstructions: (1) modified Lind reconstruction, (2) single-bundle sMCL with AM reconstruction, (3) flat sMCL with flat AM reconstruction, and (4) isolated single-bundle sMCL reconstruction. ACL load was measured by releasing its tibial attachment and securing the ligament to a load cell.

Results:

Sectioning the sMCL and dMCL increased the ACL load during AMD testing at all flexion angles ranging from 18.1% (from 123.34 ± 23.11 N to 145.61 ± 23.66 N; P = .0227) in full extension to 88.0% (from 42.7 ± 20.72 N to 80.21 ± 21.93 N; P < .001) at 90° of flexion and during ER from 0° to 60° of flexion (from intact 19.66 ± 19.9 N to 68.58 ± 38.75 N in ER; P < .001) compared with the intact state. All reconstructions that added an AM reconstruction limb reduced the ACL load during AMD testing across all flexion angles. The isolated single-bundle sMCL reconstruction did not significantly differ from the cutting state at 0° and 60° to 90° (P > .05). During ER in each medial reconstruction, ACL load did not differ significantly from the intact state at any flexion angle, with only the combined single-bundle sMCL and AM reconstruction significantly reducing ACL force at 0° of flexion compared with the MCL-sectioned state (from 118.53 ± 36.06 N to 90.8 ± 18.26 N; 23.4%; P = .0137).

Conclusion:

In this in vitro biomechanical study, medial reconstruction techniques incorporating AM reconstruction in addition to sMCL reconstruction effectively reduced ACL load, restoring the native ACL load profile in knees with combined sMCL/dMCL deficiency. Isolated sMCL reconstruction was insufficient for restoring a normal ACL load.

Clinical Relevance:

An increase in ACL load with AM rotatory instability (AMRI) may be a risk factor for ACL graft failure. AM reconstruction may decrease the likelihood of ACL graft failure in patients with AMRI after combined ACL/MCL injuries.