The collateral ligaments are two of the four main ligaments of the knee and together with the cruciate ligaments, contribute to the stability of the joint. The medial collateral ligament (MCL) and lateral collateral ligament (LCL) are located on the sides of the knee, on the inner and outer sides, respectively, connecting the femur to the tibia. Due to their specific anatomy, they have the basic function of protecting the knee from varus/valgus stress (knee being pushed in or out) and supporting the rotational stability of the joint. Both LCM and LCL injuries typically occur when an external force pushing the knee joint inward or outward is applied to the lower limb. Although injuries to these ligaments occur primarily through a contact mechanism, non-contact injuries are also possible, especially during multidirectional sports (e.g., soccer, rugby, basketball, etc.) in which high-intensity actions are performed. In general, because of high-energy injury mechanisms (especially in contact injuries), associated damage to other surrounding structures is also often reported. Medial/lateral collateral ligament injuries are usually classified according to their severity by a 3-grade scale. Grade I, often referred to as distraction, is the mildest injury that can be reported, while grade III, characterized by a full-thickness injury, is the highest level of damage. Patients with an LCM/LCL injury usually report localized pain around the ligament area (medial or lateral depending on the specifics of the injury), swelling, reduced mobility and potentially a feeling of instability depending on the grade of the injury.
