ACL injuries


An ACL injury is a tear or sprain of the anterior cruciate ligament (ACL) — one of the major ligaments in your knee. Ligaments are strong bands of tissue that connect one bone to another. The ACL, one of two ligaments that cross in the middle of the knee connecting the thigh bone (femur) to the shinbone (tibia), help stabilize the joint. ACL injuries most commonly occur during sports that involve sudden stops, changes in direction, and jumping— such as soccer, football, basketball, volleyball, and downhill skiing. Many people hear or feel a “pop” in the knee when an ACL injury occurs. The knee feels unstable and may be too painful to bear weight. Swelling typically occurs within hours of the injury because the joint fills with fluid or blood.  

Treatment may include rest, rehabilitation and activity limitations, or surgery to replace the torn ligament. Prevention programs to correct strength deficits and imbalance, along with improved cutting and landing mechanics, may reduce the risk of ACL injury. Wearing a knee brace doesn’t appear to prevent ACL injury or reduce the risk of recurring injury after surgery.

ACL injuries often happen during sports and fitness activities that can put stress on the knee:

  • Sudden change of direction (cutting)
  • Pivoting with your foot firmly planted
  • Landing awkwardly from a jump
  • Stopping suddenly
  • A direct blow to the knee
  • Feeling or hearing a “pop” in the knee
  • Severe pain and inability to continue activity
  • Rapid swelling
  • Knee tightness and loss of motion
  • A feeling of instability or “giving way” with weight bearing

Seek immediate care if any injury to your knee causes signs or symptoms of an ACL injury. The knee joint is a complex structure and the same injury mechanism can damage the ligaments, joint surface cartilage, meniscus, and bone. It’s important to get a prompt and accurate diagnosis to determine the severity of the injury and get proper treatment.

There are a number of factors that increase your risk of an ACL injury, including:

  • Being female, possibly due to differences in anatomy, muscle strength, and hormonal influences
  • Participating in certain sports, such as soccer, football, basketball, gymnastics, and downhill skiing
  • Poor conditioning

Nonoperative management with focused physical therapy, activity modification, and bracing are considered for patients with isolated ACL injuries who do not plan on returning to cutting, pivoting, and jumping sports. Operative management with ACL reconstruction is recommended for patients with associated injuries, such a repairable meniscus tear and those who desire to participate in high demand sports. ACL reconstruction is an arthroscopically assisted procedure where a tendon graft is accurately placed into the knee to replace the function of the ACL.

People who experience an ACL injury are at higher risk of developing arthritis in the knee. Recurrent giving-way episodes can cause additional damage to the joint surface cartilage, meniscus, bone, and other ligaments. However, arthritis may occur even if you have surgery to reconstruct the ligament. Multiple factors likely influence the risk of arthritis, such as the severity of the original injury, the presence of related injuries in the knee joint, and the level of activity after treatment.

Proper training and exercise can help reduce the risk of ACL injury. A sports medicine physician, physical therapist, athletic trainer, or other specialist in sports medicine can provide assessment, instruction, and feedback that can help you reduce risks.

Programs to reduce ACL injury include:

  • Exercises that strengthen leg muscles, particularly hamstring exercises, to ensure an overall balance in leg muscle strength
  • Exercises to strengthen the core, including the hips, pelvis, and lower abdomen
  • Training and exercise emphasizing proper technique and knee position when jumping and landing from jumps
  • Training to improve technique when performing pivoting and cutting movements

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