What Is an ACL Tear? 6 Common Questions About a Common Sports Injury

Content medically reviewed by Dr. Nicholas Lesmeister, orthopedic surgeon

At a pickup basketball game last weekend, one of your teammates felt a sudden pop and pain in their knee. The injury was later diagnosed as an ACL tear, but what does that mean?

ACL injuries are common knee injuries among people in the United States, particularly those who play sports. Each year, approximately 1 in 3,500 people experience an ACL tear, accounting for nearly half of all knee injuries.

Wondering what this injury entails and how it’s treated? Dr. Nicholas Lesmeister, an orthopedic surgeon at Essentia Health, answers a few common questions about ACL tears below.

1. What Is an ACL Tear?

An ACL tear is an injury to the anterior cruciate ligament (ACL) in the knee. This ligament is found inside the knee joint, crossing paths with the posterior cruciate ligament (PCL). Together, these knee ligaments control the front and back motions of your knee.

The ACL connects your thigh bone to your shin bone. When you experience an ACL tear, the ligament stretches excessively or snaps, leading to instability in the knee.An anterior cruciate ligament injury is considered a sprain. These injuries fall into one of three categories, depending on the extent of damage –

• Grade one: The ACL is stretched but remains intact.
• Grade two: The ACL is partially torn, causing the knee to feel unstable.
• Grade three: The ACL is completely torn, leaving the ligament in two pieces.

According to the American Academy of Orthopaedic Surgeons (AAOS), partial tears of the ACL are rare. Most ACL injuries involve complete or nearly complete tears.

2. What Causes an ACL Tear?

An ACL can tear for many reasons. It’s possible to injure the ACL as a result of car accidents or falls, but often, the tears occur during physical activity.

Common causes of ACL tears include –

• Being tackled by or colliding with another athlete during a sporting event
• Changing direction quickly
• Landing awkwardly after jumping
• Slowing down quickly while running
• Stopping suddenly

While ACL injuries can happen as a result of contact with another athlete, they more often occur without contact as an athlete makes normal movements.

Anyone who is athletic is at risk of an ACL tear, but research has shown that female athletes are at a higher risk. Researchers are still studying why this is the case, although it’s thought to be related to hormonal fluctuations, anatomical differences, and variations in body mechanics and strength.

3. What Happens When You Tear Your ACL?

The first sign of an ACL injury is often an audible pop when the ACL tears. Other symptoms of an ACL injury may include –

• Instability in the knee joints
• Loss of range of motion
• Pain
• Swelling
• Tenderness

While it’s possible to walk after an ACL injury, you may experience discomfort while walking and a feeling of instability in your knee. Symptoms of an ACL tear vary in severity depending on the grade of sprain you have and whether you damaged any other parts of the knee.

The AAOS notes that approximately half of all ACL tears are accompanied by injuries to other knee structures, such as the medial collateral ligament (MCL), the lateral collateral ligament (LCL), meniscus, or cartilage. While it’s also possible to tear the PCL, that ligament is stronger and less likely to tear.

4. How Is an ACL Tear Diagnosed?

When you visit a medical provider after experiencing a knee injury, your provider will perform a thorough physical exam, looking carefully at your knee and asking you about your symptoms. They may also manually move your knee or ask you to move it, allowing them to check your range of motion and knee stability.

If your provider suspects you have an ACL tear, they’ll order imaging tests to confirm the injury and its severity. This may include X-rays, a CT scan, or an MRI. MRI scans can be particularly helpful in diagnosing ACL tears since they capture detailed images of soft tissues like ligaments.

If you’re diagnosed with an ACL tear, your provider may refer you to a sports medicine specialist or an orthopedic surgeon for treatment.

5. How Is an ACL Tear Treated?

An ACL tear can be treated in multiple ways—and they don’t all require surgery.

Your orthopedic surgeon or sports medicine specialist may recommend nonsurgical treatment, such as bracing, physical therapy, and over-the-counter medications, to treat a grade one or grade two sprain.

However, if you’re physically active or an athlete, you may benefit from surgery, even with a low-grade sprain. According to the AAOS, nonsurgical treatment for a partially torn ACL may leave the knee feeling unstable.

ACL reconstruction is the surgery used to repair a damaged or torn ACL. Orthopedic surgeons perform it using arthroscopy, which is a minimally invasive procedure that involves a small tube with a camera and a light inserted through a small cut in your knee.

During an ACL reconstruction, the damaged ACL is replaced by a graft made of tendon from your body or from a tissue donor. If necessary, your surgeon can also repair other injuries to the knee during the same surgical procedure.

6. How Long Is ACL Tear Recovery?

Recovery after an ACL repair is a marathon, not a sprint. During the hours and days after surgery, it’s important to carefully follow your provider’s instructions for managing your pain. Before surgery, you may participate in physical therapy, which you’ll pick back up after surgery.

Actively participating in rehabilitation will help you regain your abilities after surgery, including range of motion, balance, the ability to bend your knee, and eventually your ability to walk and then run. You’ll also learn improved body mechanics to help you strengthen the knee and prevent future injury.

Key Takeaways

ACL tears are common knee injuries among people in the United States, often affecting athletes. These injuries vary in severity depending on whether the ACL is stretched or torn.

If you experience an ACL tear, a medical provider can diagnose the injury using a physical exam and imaging scans. Treatment may include nonsurgical therapies such as medication and physical therapy, but ACL reconstruction surgery is recommended in many cases.

This surgical procedure helps to repair the ACL by replacing the ligament with a tendon graft. After surgery, following a structured rehabilitation plan will help get you back on your feet and back to your daily life.