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What Is an ACL Injury?

The anterior cruciate ligament (ACL) is one of the two major ligaments inside the knee joint. The ACL, along with the posterior cruciate ligament (PCL), connects the thighbone (femur) and the shinbone (tibia). The ACL is in the middle of the knee joint and helps control the movement of these two bones, providing stability to the knee and preventing the shinbone from moving out of place.

An injury to your ACL can range from a mild sprain to a grade 3 tear. Injuring your ACL makes it initially difficult to stand on your own weight and walk and down the road can cause your knee to buckle with day to day activities as well as athletics. ACL injuries also put your knee at risk for wear and tear arthritis of the knee.

What are ACL injury symptoms?

Because the ACL is so vital to the mobility of your body, it is often easy to tell when you’ve injured it. Common torn ACL symptoms include:

  • Feeling or hearing a popping or snapping in the knee
  • Severe pain, instability, and swelling in your knee
  • An inability to move bend and move your knee either fully or partially
  • Being incapable of standing up and holding your weight

What are the grades of an ACL injury?

ACL injuries are categorized based on the severity of the injury as seen on an MRI scan. They do not necessarily correlate with how the knee feels or functions.

A grade 1 ACL sprain is when the ligament is overstretched and mildly damaged. 

Grade 2 tears have moderate damage to the ligament with partial tearing. A grade 2 tear commonly results in joint instability in the knee, making it difficult to walk. Depending on the severity of the tear, surgery may be required to repair the ligament.

A grade 3 tear occurs when the ligament is completely torn and appears separated on MRI. Athletes who injure their ACL usually incur a grade 3 tear and most often require surgery to reconstruct the fibers in the ligament. If you have a grade 3 tear, you may experience immediate swelling, stiffness, pain, and instability in your knee. 

Whether you require surgery to fix your ACL or not, you will need to follow a rehabilitation program to heal from your injury.

  • Resting gives the structures in your knee time to heal and regain the strength for weight-bearing
  • Icing and elevating your knee multiple times a day reduces inflammation and swelling
  • Pain and anti-inflammatory medications can help to reduce swelling and pain. Your doctor may recommend steroid injections for injury sites with intense pain
  • Regular physical therapy can strengthen the muscles in your knee and recover a full range of motion
  • Occasionally sports braces are used, which can provide compression and extra stability during physical activity

Your doctor is more likely to recommend surgery to repair the damaged ligament if you’re an athlete who relies on your strength and agility to perform. They are also likely to recommend surgery if you struggle to return to regular physical activity or have damaged more structures in your knee than just the ACL.

Surgery is usually required for a completely torn ACL because the ligament lacks its own blood supply and therefore does not usually heal by itself. An ACL procedure involves replacing the damaged ligament entirely with a tissue graft. The type of graft that can be used varies and depends on your sport, your activity level, your age and other factors that the surgeon will discuss with you. In very rare instances the ACL can be stitched back together rather than replaced.

Mass General Brigham Sports Medicine physicians work on the most cutting-edge sports medicine research, technology, and treatment. We specialize in various nonsurgical and surgical treatment options for the full spectrum of knee conditions.

Preventing ACL injuries

Training and exercise are the keys to preventing an ACL injury. If you're an athlete committed to playing sports, you might consult a trainer or physical therapist for advice on reducing your injury risk. Educating yourself is the best way to avoid a tear or sprain.

Learn how the Mass General Brigham Center for Sports Performance and Research (CSPaR) can help you to avoid ACL injuries.

You can also focus on improving your technique and strengthening your core and lower body. The type of program you choose to follow will likely depend on your sport and how physically active you intend to be. 

Recovering from ACL injuries

Even the mildest ACL injuries can have challenging recoveries. The worse your injury, the longer your recovery time will be and the higher your risk of developing other issues, such as knee arthritis. 

ACL surgery recovery time is different for everyone and can often take a year or more. Nothing is more critical to recovering from an ACL injury than physical therapy. A good rehabilitation program will focus on regaining motion in your knee and strengthening the muscles around the new ligament. 

If you are looking for a partner to help you recover from and prevent future ACL injuries, our team can help. We have a multidisciplinary team of sports medicine doctors who can develop a customized treatment plan tailored to your unique needs and goals. Request an appointment or call us at 617-726-0500 to learn more. You can also schedule a virtual visit with a Mass General Brigham sports medicine specialist.

Grade 3 ACL tears are the most common types of ACL injuries. This is because the ACL doesn't have much support to protect it from sudden or high-impact moves.

You can tear your ACL by jumping and landing awkwardly, stopping suddenly, or twisting your leg too hard. You can also rip your ACL if another person or object strikes your knee.

Your recovery time will depend on several factors, including the severity of your injury and the type of treatment you need. Many people recover from an ACL injury in six to nine weeks.

People typically report the pain from an ACL injury as moderate to severe. It largely depends on how bad the damage to the ligament is. ACL injuries usually cause a lot of swelling, which can cause the knee to throb and ache. You can hurt yourself more and aggravate the injury by attempting to walk on it without crutches or support.

MCL Injuries and ACL injuries can be hard to tell apart because symptoms are similar for both, with significant swelling and pain in the knee. One main difference is that pain and swelling may be felt more on the inside facing side of the knee with an MCL injury. ACL and MCL injuries, however, often occur together and you may have both. Consult with a doctor for a proper diagnosis. 

Your ability to walk on a torn ACL depends on the severity of the injury and your pain threshold. The ligament keeps the knee in place. Walking on a torn ACL can cause further damage to the joint and worsen your injury.

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