ACL Tears

What Are ACL Tears?

The prevalence of ACL tears among high-profile athletes makes this one of the most recognized sports injuries. The anterior cruciate ligament, or ACL, is one of the two main stabilizing ligaments in the center of the knee. It works with the posterior cruciate ligament, or PCL, as well as the two main ligaments on the sides of the knee — the medial collateral ligament, or MCL, and the lateral collateral ligament, or LCL. Specifically, the ACL works to keep the tibia from sliding forward from under the femur or rotating out from under the femur.

What Causes ACL Tears?

Many people associate an ACL tear with a contact sport such as football due to the high incidence in such sports, especially involving star players like Tom Brady. Certainly having another player hit the athlete on the knee, causing it to buckle and tear the ACL, is a common mechanism for this injury. Less commonly known is that ACL tears may occur more often in noncontact situations. The two classic causes do not involve a direct blow to the knee — landing from a jump with the knee fully extended or hyperextended and planting the foot to change directions. Both are common actions that occur in non-contact sports such as soccer and lacrosse, as well as sports that involve jumping, such as basketball, volleyball, and cheerleading.

Diagnosis of ACL Tears

Many athletes who injure an ACL describe feeling or hearing a loud pop in the knee. A complete tear of the ligament usually causes the knee to become very swollen, often within minutes. Bearing weight on the injured leg is often very difficult. Return to the game or practice is usually not possible due to the pain immediately after the injury. 

In most cases, the knee injury is severe enough for athletes to seek medical attention. In organized sports, athletic trainers, or sports medicine physicians often are present to diagnose the injury on the field or sideline. A trainer or physician often can examine the knee before significant swelling has developed and the athlete starts to guard and protect the knee from abnormal movements. In this scenario, the diagnosis of a torn ACL can be made simply by physical examination of the knee. The tibia can be shifted out from under the femur or the knee can be made to buckle in certain positions.

After a few hours, diagnosis of an ACL injury becomes more difficult. Once the knee is significantly swollen and the athlete resists examination of the knee due to pain, physical examination alone is less effective, even in the emergency room or an orthopaedic surgery clinic. A sports medicine surgeon takes a thorough history to determine the mechanism of injury. The surgeon attempts to perform a physical exam to assess the integrity of the ligament. X-rays are often taken to look for fractures or secondary signs of injury to the ACL. Often an MRI is requested in order to most accurately diagnose the injury in a timely manner. Sometimes athletes wait a few weeks to ice the knee and work on motion, at which time physical examination by the surgeon might allow easier assessment.

Treatment of ACL Tear Decisions

A complete tear of the ACL typically does not heal, but that does not mean every patient with this injury needs surgery. The initial pain, stiffness, or swelling, that usually occurs often improves with ice, compression and elevation, and rehabilitation to restore strength and motion. But instability of the knee typically does not improve, and athletes who perform cutting and pivoting sports or jumping sports often cannot return to sports because their knees buckle trying to compete. These athletes almost always need surgery to return to sports. Older athletes, especially those who are active but don’t participate in these types of sports, might be able to return without surgical treatment. Custom braces made to prevent the knee from giving way can be helpful in this population. The effectiveness of these braces in a high-level athlete who plays a sport for this injury has been questioned.


Surgical treatment of a torn ACL involves making a new ligament rather than trying to sew it back together, which is usually not successful. The ACL can be reconstructed in several ways, all involving grafts or tissue from the patient or from a cadaver. The most popular grafts from the patient include using the middle of the patellar tendon or using the hamstring tendons. Each graft option has its own risks and benefits, and a thorough discussion between the patient and surgeon is critical to determine the best choice. 

Typically an outpatient procedure, ACL reconstruction is performed arthroscopically except for removal of the graft tissue. An MUSC Health surgeon looks throughout the knee to evaluate for injury to other structures, such as the meniscus and articular cartilage and usually treats any identified injuries during the same procedure. 

The patient often awakens from the surgery with a brace as well as a device to allow cold water to flow around the knee. How much weight the patient can put on the leg depends on the status of other structures in the knee, especially the meniscus, as well as the preference of the surgeon.


Other than the quality of the surgery, no other intervention is more crucial to a successful outcome than physical therapy. Working with a physical therapist who specializes in sports injuries can greatly improve success in returning to sports. The rehabilitation process starts almost immediately. Athletes begin therapy two or three days per week initially to work on regaining range of motion. As weight bearing and motion improve, the patient works aggressively to regain muscle strength. As the knee strengthens, the therapist often implements sport-specific functional training to condition the knee for a return to sports. A test to determine the muscle strength at various speeds often helps determine if the knee and surrounding muscles are strong enough to resist forces encountered in sports. The rehabilitation process is lengthy and difficult, but it is crucial to the athlete returning to the same or higher level of sports.

Return to Sports

Success rates of returning to the sports that athletes played before ACL tears are very high, usually noted above 90 percent. The average time it takes to be cleared for sports participation is about six months, but this time can be shorter or longer depending on return of motion and strength and being able to perform the sport-specific functional duties on the reconstructed knee.