Anterior Cruciate Ligament (ACL) Tear

What Causes a Torn ACL?

An ACL tear usually happens when the knee is suddenly forced beyond its normal range of motion. Sudden pivots, quick changes in direction, awkward landings, or hyperextension of the knee can injure the anterior cruciate ligament. Over 70% of these injuries occur without contact, but a direct blow to the knee can also cause a torn ACL, particularly if the foot is planted and the knee twists under force.

Symptoms of an ACL Tear

People often hear or feel a “pop” in their knee when the ACL tears, followed by rapid swelling over the next hour or two. Severe pain is common immediately after the injury, especially when trying to stand, pivot, or put weight on the leg. There may be a sense of the knee giving way, as the torn ligament can no longer help stabilize the joint. As swelling progresses, you may notice a loss of range of motion, making it harder to bend or straighten the knee. Many patients are able to put weight on the leg, but often require crutches because they do not trust the knee to support them.

Symptoms of an ACL Tear include:

• A “popping” sensation in the knee
• Severe pain
• Rapid swelling
• Reduced range of motion
• A feeling that the knee will give way while bearing weight

Sports and Activities Commonly Linked to ACL Tears

ACL tears are common in sports that involve sudden stops, jumping, pivoting, cutting, or rapid changes in direction.

Activities commonly associated with ACL injuries include:

• Soccer
• Basketball
• Football
• Lacrosse
• Tennis
• Volleyball
• Downhill skiing
• Gymnastics

ACL tears are common sports injuries that can also occur during falls, awkward landings, or other high-impact physical activity.

Diagnosis of an ACL Tear

A knee specialist will diagnose an ACL tear through a thorough physical exam, a review of your symptoms, and imaging when needed. Your provider will check for swelling, decreased range of motion, knee instability, and signs that the torn ligament is no longer properly stabilizing the joint. They will also evaluate for related injuries, such as meniscus tears or damage to other knee ligaments.

Additional imaging studies may be used to help confirm the diagnosis:

• X-rays may help identify a bony avulsion — a small piece of bone that is pulled away when the injury occurs.
• MRI is often used to confirm an ACL tear diagnosis (Figure 2a), and can help characterize other associated injuries such as cartilage, additional ligament, or meniscus tears.

Non-surgical Treatment for ACL Tears

After an ACL tear diagnosis is confirmed, the physician will discuss treatment options. ACL tears do not typically heal completely on their own because the ligament has a limited blood supply. Some patients can manage symptoms without surgical ACL reconstruction, but ongoing knee instability is common, especially during cutting or pivoting sports. In some cases, a knee brace can provide additional support during certain activities.

Surgical Treatment for ACL Tears

Long-term, continued ACL deficiency and instability can increase the risk of meniscus injury and osteoarthritis. Many patients choose ACL reconstruction to restore knee stability, using another tendon from the knee or an allograft (donor tissue) to build a new ACL . Reconstruction options may include the hamstring, patellar tendon, quadriceps tendon, or an allograft. Surgery is most often performed arthroscopically .

Physical Therapy for ACL Tears

Physical therapy is a key part of ACL tear treatment, helping restore range of motion, strength, gait, and knee function. It may be recommended before or after surgery, or as the primary treatment for some patients.

After ACL reconstruction, physical therapy typically continues for 7-9 months, with a gradual return to all sports and activities as recovery progresses.