Causes
An ACL injury can occur if you:
- Get hit very hard on the side of your knee, such as during a football tackle
- Overextend your 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 often occurs along with tears to the MCL and the shock-absorbing cartilage in the knee (meniscus).
Most ACL tears occur 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.
Considerations
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. It prevents the knee from bending inward.
- Lateral collateral ligament (LCL) runs along the outside of the knee. It prevents the knee from bending outward.
- 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 backward under the femur.
Women are more likely to have an ACL tear than men.
Definition
An anterior cruciate ligament injury is the over-stretching or tearing of the anterior cruciate ligament (ACL) in the knee. A tear may be partial or complete.
Prevention
Use proper techniques when playing sports or exercising. Some college sports programs teach athletes how to reduce stress placed on the ACL. This involves a series of warm up exercises and jumping drills. There are jumping and landing exercises that have been shown to reduce ACL injuries.
The use of knee braces during vigorous athletic activity (such as football) is controversial. It has been shown to reduce the number of certain knee ligament injuries, but not specifically ACL injuries.
References
Bolgla LA. Gender issues in ACL injury. In: Giangarra CE, Manske RC, eds. Clinical Orthopaedic Rehabilitation: A Team Approach. 4th ed. Philadelphia, PA: Elsevier; 2018:chap 49.
Brotzman SB. Anterior cruciate ligament injuries. In: Giangarra CE, Manske RC, eds. Clinical Orthopaedic Rehabilitation: A Team Approach. 4th ed. Philadelphia, PA: Elsevier; 2018:chap 47.
Cheung EC, McAllister DR, Petrigliano FA. Anterior cruciate ligament injuries. In: Miller MD, Thompson SR, eds. DeLee, Drez, & Miller's Orthopaedic Sports Medicine. 5th ed. Philadelphia, PA: Elsevier; 2020:chap 98.
Gokeler A, Dingenen B, Hewett TE. Rehabilitation and return to sport testing after anterior cruciate ligament reconstruction: where are we in 2022? Arthrosc Sports Med Rehabil. 2022;4(1):e77-e82. PMID: 35141539 pubmed.ncbi.nlm.nih.gov/35141539/.
Kalawadia JV, Guenther D, Irarrázaval S, Fu FH. Anatomy and biomechanics of the anterior cruciate ligament. In: Prodomos CC. The Anterior Cruciate Ligament: Reconstruction and Basic Science. 2nd ed. Philadelphia, PA: Elsevier; 2018:chap 1.
Miller RH, Azar FM. Knee injuries. In: Azar FM, Beaty JH, eds. Campbell's Operative Orthopaedics. 14th ed. Philadelphia, PA: Elsevier; 2021:chap 45.
Symptoms
Early symptoms:
- A "popping" sound at the time of injury
- Obvious knee swelling within 6 hours of injury
- Pain, especially when you try to put weight on the injured leg
- Difficulty in continuing with your sport
- Feeling of instability
Those who have only a mild injury may notice that the knee feels unstable or seems to "give way" when using it.
When to Contact a Medical Professional
Contact your provider right away if you have a serious knee injury.
Get immediate medical attention if the foot is cool and blue after a knee injury. This means that the knee joint may be dislocated, and blood vessels to the foot may be injured. This is a medical emergency.