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Your Ultimate Guide to ACL and MCL Tears

Updated: Mar 30, 2023


From everyday activities like walking the dog to the rigorous training programs of elite athletes, we ask a lot from our knees. When one of them is injured, it can be a major disruption to daily life. Knee injuries are especially common in athletes, forcing them on the sideline for months or even an entire season. Some of the most common knee injuries a sports medicine doctor sees involve two ligaments: the ACL and MCL. And while these injuries are often lumped together, they are actually quite different. So, where is your ACL/MCL, and what does that actually stand for?

Overview of the knee joint

Anatomy of Knee. Image from

The knee is a complex joint formed where three bones meet: the femur (thigh bone), the tibia (shin bone), and the patella (kneecap). There are 4 major ligaments in the knee that span between the femur and the tibia, including the Anterior Cruciate Ligament (ACL), Posterior Cruciate Ligament (PCL), Medial Collateral Ligament (MCL) and Lateral Collateral Ligament (LCL). These ligaments are made of collagenous tissue and help stabilize the knee joint by preventing excessive and undesired motion.

The most commonly injured knee ligaments are the ACL and MCL. The ACL runs diagonally in front of the knee, connecting the front of your tibia to the back of your femur. This is a major stabilizing ligament and is responsible for controlling the rotation of your knee and preventing the tibia from moving too far forward. The MCL runs along the inside of the knee to connect the top of the tibia to the bottom of the femur and helps prevent the knee from bending inward.

Anatomy of the knee.

What is an ACL tear?

The ACL tears more often than any other knee ligament, accounting for more than 50% of knee injuries in athletes. There are an estimated 200,000 ACL injuries occurring every year in the United States alone. ACL tears tend to occur while playing sports that involve jumping, sudden stops, or changes in direction – movements that are common in sports like basketball, soccer, volleyball, or tennis. The dynamic forces created by these motions tend to stress the ACL and can push the tibia out of position. Unfortunately, for reasons that are still not entirely clear, women are four to eight times more likely to suffer an ACL injury than men who play the same sport.

What is an MCL tear?

The MCL is usually injured from a hit or blow to the outside of the knee, such as when athletes collide with each other (i.e., a football tackle). If the knee is pushed too far inward or suddenly twisted, the MCL can stretch or tear. Athletes in high contact sports have the highest risk of MCL injuries, however they can occur through a variety of sports – for example, as a result of the cutting maneuvers commonly used in basketball and soccer, or even from hyperextending the knee when skiing. Repeated stress to the knee can also cause the ligament to lose its elasticity, eventually leading to injury.

Both ACL and MCL injuries can range from mild to severe:

  1. A Mild Grade I sprain means the ligament has been overstretched, but is still intact. A mild sprain should still be evaluated by a sports medicine doctor, as it can increase your chance of developing repeated or more severe injuries.

  2. A Moderate Grade II Sprain occurs when the ligament is partially torn. This will cause some pain and swelling, making it difficult to move your knee.

  3. A Severe Grade III Sprain means the ligament has completely torn. The knee joint will be very unstable, making it hard or impossible to put weight on your leg.

So, which is worse?

The primary job of most ligaments is to provide stability to the surrounding joint, so either type of injury will impair a person’s knee function and result in discomfort. Generally, an ACL tear is considered worse as it may require surgery and a longer time to fully recover, while MCL tears can usually heal on their own.

Symptoms: It can be difficult for a person to tell the difference between a torn ACL and torn MCL because they can have similar symptoms such as swelling, decreased range of motion, bruising, and significant pain in the knee. It will also be difficult to put weight on the leg with more severe injuries because the knee joint becomes unstable.

A common difference between the two is that a severe ACL tear typically occurs with a much more distinctive popping sound compared to an MCL tear. ACL injury traditionally occurs without any contact, whereas an MCL tear occurs when a force contacts the lateral aspect of the knee forcing it to bend inward. ACL tears occur when the foot is planted and twisting occurs at the knee. There are special maneuvers your sports medicine doctor will perform in the office to assess each individual ligament for damage. Additionally, the location of pain and swelling can provide insight into which ligament is injured. With an ACL injury, you will likely feel pain in the center of your knee. However, an MCL tear will cause is pain and swelling on the medial side of the knee because of the location of the ligament.

If you experience a knee injury, especially one accompanied by a loud popping sound, it is recommended that you splint/stabilize the knee and get evaluated as soon as possible. Ice, as well as elevating the knee will help with swelling until you can see your doctor. It is critical that you are evaluated by a sports medicine doctor to get an accurate diagnosis, as this will help inform your treatment plan. The doctor will complete a medical history and physical examination, and sometimes an X-ray or magnetic resonance imaging (MRI) scan to evaluate for ligament damage and rule out any injury to the bones.

Treatment and recovery: Your sports medicine doctor will help you develop a treatment plan based on the injury location and severity as well as your personal and athletic goals.

ACL Tears: For mild or moderate injuries, treatment can include non-surgical options such as rest, ice, and elevation of the knee. Your sports medicine doctor will also help develop a physical rehabilitation program to assist in the recovery process and reduce the risk of future ACL injuries. Unfortunately, severe injuries, i.e., a complete tear of the ACL, will often require surgery to repair the damaged ligament. This is recommended if multiple ligaments are damaged, if the injury is causing instability in your knee in daily activities, or for athletes wishing to continue in their sport - especially sports that involve jumping, cutting or pivoting. In reconstructive knee surgery, the damaged ACL is replaced with a piece of tendon from elsewhere in the body (or from a donor). Find out more about ACL reconstruction surgery here.

While it can take between 6-12 months to recover from ACL reconstruction, if paired with focused rehabilitation, you can usually restore the stability and function of your knee. Luckily, most people (including athletes) can eventually return to their pre-injury activity level.

MCL Tears: Generally, minor MCL injuries heal on their own with a conservative treatment plan similar to that of minor ACL tears. Your doctor may recommend anti-inflammatory medication to ease the pain and swelling and a compressive sleeve or knee brace to provide support and stability to the knee. Surgery is far less common for MCL tears, however physical therapy to help strengthen the muscles and improve your knee’s range of motion is often recommended. Recovery time may take up to 8 weeks with appropriate rest and rehabilitation.

Prevention and outlook for ACL and MCL tears

Taking preventative measures to lower your risk of ACL or MCL tears can help strengthen your knees long term and reduce the likelihood of a devastating knee injury. While some injuries just can’t be prevented, there are some simple things you can do to minimize your chance risk of knee injury. These include targeted strength training, appropriate warm up and stretching, and focusing on proper technique.

The successful return to play after an ACL or MCL injury is a top priority of your sports medicine physician. However, returning before you have regained full mobility, strength, balance and agility can result in repeated injuries or decreased performance. It is critical to work with a sports medicine doctor after your injury to develop a treatment plan that give you the best chance at a full recovery.


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