High strains near femoral insertion site of the superficial medial collateral ligament of the Knee can explain the clinical failure pattern.

The three dimensional (3D) deformation of the superficial medial collateral ligament (sMCL) of the knee might play an important role in the understanding of the biomechanics of sMCL lesions. Therefore, the strain and deformation pattern of the sMCL during the range of motion were recorded in five cadaveric knees with digital image correlation. During knee flexion, the sMCL was found to deform in the three planes. In the sagittal plane, a rotation of the proximal part of the sMCL relative to the distal part occurred with the center of this rotation being the proximal tibial insertion site of the sMCL. This deformation generated high strains near the femoral insertion site of the sMCL. These strains were significantly higher than in the other parts and were maximal at 90° with on average +3.7% of strain and can explain why most lesions in clinical practice are seen in this proximal region. The deformation also has important implications for sMCL reconstruction techniques. Only a perfect anatomic restoration of the insertion sites of the sMCL on both the proximal and distal tibial insertion sites will be able to reproduce the isometry of the sMCL and thus provide the adequate stability throughout the range of motion. The fact that knee motion between 15° and 90° caused minimal strain in the sMCL might suggest that early passive range of motion in physical therapy postoperatively should have little risk of stretching a graft out in the case of an anatomical reconstruction.