The knee joint is located where the end of the thigh bone (femur) meets the top of the shin bone (tibia).
Four main ligaments connect these two bones:
* Medial collateral ligament (MCL) runs along the inside of the knee and prevents the knee from bending out.
- Lateral collateral ligament (LCL) runs along the outside of the knee and prevents the knee from bending in.
- Anterior cruciate ligament (ACL) is in the middle of the knee. It prevents the shin bone from sliding out in front of the thigh bone.
- Posterior cruciate ligament (PCL) works with the ACL. It prevents the shin bone from sliding backwards under the femur.
Women are more likely to have an ACL tear than men.
An ACL injury can occur if you:
- Get hit very hard on the side of your knee, such as during a football tackle
- Overextend the knee joint
- Quickly stop moving and change direction while running, landing from a jump, or turning
Basketball, football, soccer, and skiing are common sports linked to ACL tears.
ACL injuries often occur with other injuries. For example, an ACL tear commonly occurs along with tears to the MCL and the shock-absorbing cartilage in the knee (lateral meniscus).
Most ACL tears are seen in the middle of the ligament, or the ligament is pulled off the thigh bone. These injuries form a gap between the torn edges, and do not heal on their own.