What causes a lateral collateral ligament sprain?

A lateral collateral ligament sprain occurs when the ligament on the outer side of the knee tears. This type of sprain is most common in people who play contact sports, such as football.

While knee injuries represent up to 39 percent of all injuries in athletes, lateral ligament injuries are less common. Many lateral collateral ligament (LCL) injuries occur alongside other knee damage.

The LCL connects the thigh bone to the smaller calf bone. It controls the sideways movement of the knee, and, alongside the medial collateral ligament on the inner knee, it contributes to knee stability. An LCL sprain usually occurs when the knee pushes out beyond the usual range of motion. This overstretches and tears the ligament.

The most obvious symptom is pain, which may be mild or severe, on the outer side of the knee. People sometimes hear a snapping or tearing sound when the injury occurs. Other symptoms include: bruising to the skin, general weakness in the knee joint and a feeling that it may give way, numbness in the knee, which may occur due to damage to nerves, stiffness, swelling along the outside of the knee, tenderness around the ligament, especially if with pressure, the sensation that the knee is locking during movement

The severity of symptoms depends on the seriousness of the sprain. Doctors categorize LCL sprains as:

Grade 1: The ligament overstretches but does not tear. It can result in mild pain or swelling. A grade 1 sprain does not usually affect joint stability.

Grade 2: The knee ligament partially tears. Symptoms can include moderate pain, swelling, knee instability, and difficulty using the joint. The skin around the LCL ligament may bruise.

Grade 3: This involves a complete ligament tear. Symptoms include swelling, significant bruising, joint instability, and difficulty putting weight on the leg. A grade 3 sprain increases the risk of injury to other parts of the knee and leg.