Anterior cruciate ligament (ACL) injury of the knee is a common knee injury, especially among athletes involved in high-impact sports. It is a tear or sprain of the anterior cruciate ligament, which is one of the major ligaments that connects the thigh bone (femur) to the shinbone (tibia) in the knee joint. ACL injuries can vary in severity, from a partial tear to a complete rupture, and can result in significant pain, instability, and impaired function of the knee joint.
Symptoms
- A loud popping sound or sensation at the time of injury
- Swelling of the knee within a few hours of the injury
- Pain and tenderness in the knee joint
- Limited range of motion of the knee joint
- Instability or a feeling of the knee “giving way” during activity
- Difficulty bearing weight on the affected leg
- Pain while walking or running
- Feeling of instability in the knee joint
- Muscle weakness in the thigh or calf
- Joint stiffness and difficulty bending or straightening the knee
Causes
ACL injuries are typically caused by sudden movements or forces that stress the knee joint beyond its normal range of motion. Common causes of ACL injuries include:
- Rapidly stopping or changing direction while running
- Landing from a jump incorrectly
- Direct impact to the knee, such as during a collision or tackle
- Twisting the knee while the foot is planted on the ground
Risk factors
- Participation in high-impact sports, such as basketball, football, and soccer
- Female sex (women are more likely to experience ACL injuries than men)
- Previous knee injuries or surgeries
- Abnormal knee joint anatomy or alignment
- Weakness or imbalances in the leg muscles
Associated conditions
ACL injuries can be associated with other injuries to the knee joint, such as tears to other ligaments or menisci (cartilage pads in the knee joint). They may also lead to long-term complications, such as increased risk of knee osteoarthritis.
Diagnosis
Diagnosis of an ACL injury typically involves a physical exam of the knee joint, including tests to assess stability, range of motion, and muscle strength. Imaging tests such as X-rays, magnetic resonance imaging (MRI), or ultrasound may also be ordered to confirm the diagnosis and evaluate the severity of the injury.
Differential diagnosis
Differential diagnosis of an ACL injury may include other knee injuries such as meniscus tears, collateral ligament injuries, or fractures of the knee joint.
Treatment options
Treatment options for an ACL injury depend on the severity of the injury and the individual’s goals and activity level. Conservative treatment options may include rest, ice, compression, and elevation of the affected leg, as well as physical therapy to help restore range of motion and muscle strength. More severe injuries may require surgical intervention, such as ACL reconstruction surgery, to repair or replace the damaged ligament.
Typical recovery timeframes
Recovery timeframes for an ACL injury vary depending on the severity of the injury and the chosen treatment approach. Conservative treatment options may take several weeks to months to fully recover, while surgical interventions may require several months of rehabilitation and physical therapy to restore full function of the knee joint.
Prognosis
With appropriate treatment and rehabilitation, most individuals with an ACL injury can achieve good outcomes and return to their previous level of activity. However, long-term complications such as osteoarthritis may occur in some cases.