gms | German Medical Science

Objectives: Objective was to examine the impact of anteromedial reconstructions (AMR) on the potential risk of medial over-constraining. In anteromedial rotatory knee instability (AMRI), the concept of anteromedial and flat reconstruction of the superficial medial collateral ligament (sMCL) and deep MCL (dMCL)gained attention. Kinematically suchlike anteromedial reconstructions have been proven to be superior to single-bundle (SB) MCL reconstructions,but evidence about the resulting medial compartment pressure is lacking. We hypothesized that an AMR reconstruction tensioned with 60 N does not increase the risk for over-constraining.

Methods: Seven cadaveric knees were tested in a kinematic rig with a fixed femur and semi-constrained tibial rod for the application of loads/torques and 100 N axial pre-loading. Testing was performed at 0°, 30°, 60°, 90° of flexion with and w/o superimposed forces/torques (5 Nm internal/external rotation [IR/ER], 89 N anterior translation [ATT] + 5 Nm ER). A pressure sensor (TekscanTM) was installed underneath the medial meniscus. Mean and peak medial compartment pressure (mMCP/pMCP) were recorded in the intact, sMCLdMCL deficient and four states of AMR (modified Lind technique, flat sMCL/dMCL, triangular anteromedial, SB sMCL). A femoral insertion point in the posterior aspect of the sMCL footprint was chosen in all AMR. Reconstructions were tested randomized with 60 N and 20 N of graft tension. Statistically direct paired t- or Wilcoxon tests were used.

Results and conclusion: A sMCL/dMCL deficient knee resulted in a significant reduction of mMCP in neutral rotation at 0° degree of flexion compared to the native knee (p<0.05, 0° native mMCP 0.7±0.4 MPa, MCL cut 0.6±0.4 MPa). None of the AMR increased the mMCP significantly (p>0.05, 0° modified Lind 0.7±0.9 MPa) compared to the native knee across 0-90° of flexion. ER and the ATT tend to decrease the mMCP (all p>0.05 0° native mMCP with ER: 0.6±0.6 MPa) while IR increased the mMCP in 30°, 60°, 90° (p<0.05, 0°native mMCP with IR: 0.7±0.5 MPa). Peak pressures did not reveal significant differences between native and reconstructed knees (p>0.05). Different graft tensioning resulted in a trend towards lower mMCP and pMCP without reaching significance (p>0.05 SB sMCL 0° 60N of tension: 0.7±0.4 MPa, 20N: 0.4±0.3 MPa).

In AMRI an AMR is necessary to restrain knee instability [1]. Almost isometric graft behaviour can be achieved withfemoral insertion located in the posterior aspect of the femoral sMCL footprint [2]. Biomechanically, there was no critical overconstraining by using different AMRs mimicking the dMCL and sMCL. Low changes measured between native knee joints and AMR in this study seem clinically irrelevant.

Figure 1 [Fig. 1]