The collateral ligaments are two of the four major ligaments of the knee joint, and, together with the cruciate ligaments, they contribute to the stability of the knee. The medial collateral ligament (MCL) and the lateral collateral ligament (LCL) are found on the sides of the knee, respectively in the inner and outer part, connecting the femur to the tibia. Due to their specific anatomy, they have the paramount function of protecting the knee from varus/valgus stresses (knee that is pushed in or out) and supporting the rotational stability of the joint. Both MCL and LCL injuries typically occur when an external force, that pushes the knee joint inwards or outwards, is applied to the lower limb. Despite being primarily contact injuries, non-contact injuries of these ligaments are also possible, especially during multi-directional sports where high-intensity actions are performed. Due to their high-energy injury mechanisms, associated damages to other surrounding structures are also frequent. Ligament tears are typically classified based on their severity on a 3-grade scale system. Grade I, often referred to as a sprain, is the mildest reportable injury, while grade III, characterised by a full-thickness tear, is the highest level of damage. Patients with MCL or LCL injuries typically report pain located around the ligament area (medial or lateral depending on the injury specifics), swelling, decreased range of motion, and potentially a sense of instability depending on the grade of the tear.
