The knee joint is surrounded by a joint capsule with ligaments strapping the inside and outside of the joint (collateral ligaments) as well as crossing within the joint (cruciate ligaments). These ligaments provide stability and strength to the knee joint.
The medial collateral ligament of the knee is on the inner side of the joint and can be stretched or torn when valgus stress (forcing the knee to move inward) is applied suddenly. Ligament sprains are commonly graded on a 1-3 scale, with grade 1 meaning a small sprain with minimal evidence of fiber discontinuity on advanced imaging to grade 3 which implies complete tear with no intact fibers.
This ligament is usually injured traumatically with a sudden valgus stress such as getting clipped or hit from the side, especially when the foot is planted. The MCL can be torn together with other important stabilizing structures in the knee.
Symptoms include pain on the inside aspect of the knee, swelling, a feeling of laxity or instability.
The MCL will usually heal on its own even if completely torn. If the MCL is chronically lax or dysfunctional after an injury, regenerative type injections such as platelet-rich plasma (PRP) or prolotherapy may be of benefit.