gms | German Medical Science

Objectives: Both the superficial medial collateral ligament (sMCL) and deep MCL (dMCL) contribute to the restraint of anteromedial rotatory instability (AMRI). Previous studies have not investigated how MCL reconstructions control AMRI. The purpose was to establish the optimal medial reconstruction for restoring normal knee kinematics in a sMCL and dMCL deficient knee. It was hypothesized that AMRI would be better controlled with the addition of an anatomically shaped (flat) sMCL reconstruction and with the addition of an anteromedial (AM) reconstruction replicating the function of the dMCL.

Methods: A six degree-of-freedom robotic system equipped with a force-torque sensor was used to test 8 unpaired knees in the intact, sMCL / dMCL-sectioned, and reconstructed states. Four different reconstructions were assessed. The sMCL was reconstructed with either a single-bundle (SB) or a flattened hamstring graft aimed at better replicating the appearance of the native ligament. These reconstructions were tested w/o an additional anteromedial (AM) reconstruction. Simulated laxity tests were performed at 0°, 30°, 60° and 90° of flexion: 10Nm valgus rotation, 5 Nm internal and external rotation (ER) and an AM drawer test (combined 134 N anterior tibial drawer in 5 Nm ER). The primary outcome measures of this force-controlled setup were anterior tibial translation (ATT, mm) and tibial rotation (°).

Results and conclusion: Sectioning the sMCL/dMCL increased valgus rotation, ER and ATT with the simulated AM draw test at all flexion angles. SB sMCL reconstruction was unable to restore ATT, valgus rotation and ER at 30°, 60° and 90° of flexion being significantly different to the intact state (P at least < 0.05). Flat MCL reconstruction restored valgus rotation at all flexion angles being non-significantly different to the intact state (P > 0.05). ER was restored at all angles except at 90° but ATT laxity in response to the AM drawer persisted. Addition of an AM reconstruction improved control of ATT being insignificantly different (P > 0.05) to the intact state at all flexion angles. Combined Flat MCL and AM reconstruction restored knee kinematics closest to the intact state. In a cadaveric model AMRI resulting from an injured sMCL and dMCL complex could not be restored by an isolated SB sMCL reconstruction. A flat MCL reconstruction or an additional anteromedial procedure, however, could better restore medial knee stability. In patients presenting with a combined valgus- and anteromedial rotatory instability a flat sMCL and an additional anteromedial reconstruction may be superior to an isolated SB sMCL reconstruction.