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What Is an ACL Injury? 

The anterior cruciate ligament (ACL) is a small piece of tissue with a big job. It helps hold the knee together, keeps the bones in place and provides stability in rotational and side-to-side movement. 

The ACL can be found in the center of the knee, connecting the femur (thigh bone) and the tibia (shin bone). Other ligaments in the area include the: 

  • Posterior cruciate ligament (PCL) 
  • Lateral collateral ligament (LCL) 
  • Medial collateral ligament (MCL) 

Connective tissues of the knee

ACL injuries can happen on their own, or in concert with other ligament injuries.  

Causes and Risk Factors 

ACL sprains (ligament tears or ruptures) are some of the most common and pervasive knee injuries, and they often require reconstructive surgery. Athletes are especially prone to ACL injuries, but nearly anyone can sustain one. 

Contrary to popular belief, most (about 70 percent) ACL injuries happen from non-contact events, rather than direct blows to the knees. Causes of ACL tears can include: 

  • Rapid pivoting or changing direction 
  • Sudden stopping 
  • Direct trauma to the knee 
  • Landing incorrectly from a jump


ACL injuries often happen in soccer and any other sport that involves rapid changes of direction

Some research suggests that female athletes are two to eight times more likely to experience an ACL tear as compared with male athletes. Researchers believe that differences in anatomy and ligament strength may contribute to the higher risk of ACL injuries for women. 


Symptoms of an ACL tear can include: 

  • A popping sound 
  • Pain 
  • Swelling 
  • Knee instability 
  • Difficulty or inability walking 

ACL sprains are classified in grades based on severity. 

  • Grade 1 sprains are mild. The ligament may be stretched but it is intact. 
  • Grade 2 sprains are moderate. The ligament usually has a partial tear. 
  • Grade 3 sprains are severe. The ligament has either detached from the femur or tibia, or has torn in half. 

Most ACL sprains are either grade 1 or grade 3. The ligament is usually intact or torn through; partial tears are rare. 


ACL injuries can be difficult to diagnose due to the nature of the symptoms. Many other knee injuries create similar symptoms. 

Doctors will start with a physical examination and a medical history. During the medical history, they will want to hear about any recent injuries the patient may have had, and the circumstances around those injuries. A physical exam will test for symptoms of an ACL tear and the knee’s range of motion. 

If the history and exam are inconclusive, imaging studies may be ordered. An X-ray will not show soft tissue such as ligaments, but it can be helpful in ruling out other sources of knee pain such as a fracture. Magnetic resonance imaging (MRI) and computed tomography (CT) scans can show damage to a ligament. 


Treatment for an ACL injury will depend upon the knee’s stability and the patient’s activity level and desire to return to sports. Grade 1 sprains can be treated conservatively, but ACL ruptures will require an ACL reconstruction

Conservative, nonoperative treatment can include: 

  • RICE: Rest, ice, compression and elevation 

  • physical therapy or strength and conditioning program 

  • Bracing and crutches to limit weight bearing and movement of the joint 

ACL ruptures require reconstructive surgery

Grade 3 ACL ruptures typically require reconstructive surgery. When an ACL injury requires surgery, surgeons usually replace the ACL with new connective tissue, either from the patient’s own body (an autograft) or from a donor (an allograft). This tissue replacement acts as a scaffold over which the body builds a new connection between the femur and tibia. 

An ACL reconstruction is usually performed arthroscopically, with small incisions, small tools and a flexible camera attached to a video monitor. Physical therapy will be required after surgery. Most people will recover in four to six months; however, athletes in sports that require rapid stopping or changing direction, such as basketball, may need 9 to 12 months to return to play. 

If you suspect you have experienced, or have been diagnosed with, an ACL tear, request an appointment with one of our sports medicine specialists today. 

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