The anatomy of the medial collateral ligament of the knee and its significance in joint stability
The medial collateral ligament (MCL) is the most important stabilizer of the medial side of the knee together with the capsuloligamentous complex. As such, it has a distinctive role in joint stability, as far as its biomechanics are concerned, and major joint stability issues onset when it is injured or deficient. One of the main functions of the medial collateral ligament is mechanical as it passively stabilizes the knee and help in guiding it through its normal range of motion when a tensile load is applied. It exhibits nonlinear anisotropic mechanical behaviour, like all ligaments, and under low loading conditions it is relatively compliant, perhaps due to recruitment of “crimped” collagen fibres as well as to viscoelastic behaviours and interactions of collagen and other matrix materials. Continued ligament-loading results in increasing stiffness until a stage is reached where it exhibits nearly linear stiffness and beyond this it continues to absorb energy until it is disrupted. In addition, the function of the MCL has to do with its viscoelasticity which assists the maintainance of joint congruity and homeostasis. The treatment of grade III medial collateral ligament injuries (with gross valgus instability at 0° of flexion) is still controversial. The most severe injuries (especially with severe valgus alignment, intra-articular medial collateral ligament entrapment, large bony avulsions, or multiple ligament involvement) may require acute operative repair or augmentation. In addition, surgical reconstruction is indicated for isolated symptomatic chronic medial collateral ligament laxity. The optimal surgical treatment remains controversial. More studies with evidence of level I and II are required in order to clarify the pros and cons of any solution.