Anterior cruciate ligament (ACL) injuries

Anterior cruciate ligament (ACL) injuries are injuries to a ligament that connects the upper leg bone (femur) with the lower leg bone (tibia). An ACL injury may result in the knee occasionally buckling or giving out.

An ACL injury can be a partial or complete tear of the ligament, a separation of the ligament from the upper or lower leg bone (avulsion), or a separation of the ligament and part of the bone from the rest of the bone (avulsion fracture). Other parts of the knee can be injured at the same time, including the pads that cushion the knee joints (menisci), another knee ligament, or the tissue that covers the ends of bones (cartilage).

An ACL injury occurs when the knee is straightened beyond its normal limits (hyperextended), twisted, or bent side to side. This may happen when changing direction rapidly, which commonly occurs in sports that require stop-and-go movements. An ACL injury may also occur after contact in a sport or in an accident.

Symptoms of a sudden ACL injury may include feeling or hearing a pop in the knee at the time of injury, pain, swelling, and a feeling that the knee may buckle or give out.

An ACL injury may develop into chronic (long-lasting and recurrent) ACL deficiency (also called insufficiency), resulting in greater knee looseness and sliding of the bones. This abnormal sliding can lead to premature osteoarthritis.

Treatment for ACL injuries depends on the severity of the knee injury and a person's activity level. Treatment includes physical rehabilitation or surgery plus rehabilitation.