LCL Tear

The lateral collateral ligament (LCL) is the ligament located in the knee joint. Ligaments are thick, strong bands of tissue that connect bone to bone. The LCL runs along the outside of the knee joint, from the outside of the bottom of the thighbone (femur) to the top of the lower-leg bone (fibula). The LCL helps keep the knee joint stable, especially the outside of the joint.
An injury to the LCL could include straining, spraining, and partially or completely tearing any part of that ligament. The LCL is one of the more commonly injured ligaments in the knee (Orthogate, 2006). Because of the location of the LCL, it is common to injure the LCL in conjunction with other ligaments in the knee.

Causes
The main cause of LCL injuries is direct force to the inside of the knee. This puts pressure on the outside of the knee, where the LCL is located, and causes it to stretch or tear.
Symptoms
Symptoms of an LCL injury can be mild or severe, depending on the severity of the sprain or whether or not it is torn. If the ligament is mildly sprained, you may not have any symptoms at all. For a partial tear or complete tear of the ligament, your symptoms may include:
swelling in the knee
stiffness in the joint (potentially locking while moving)
pain or soreness on the outside of the knee
instability in the knee joint, feeling like it is going to give out