ACL vs MCL Tears: What Is The Difference?
Written By Kobi Nathan, Pharm.D., M.Ed., CDP, BCGP, AGSF
Sleep Disorders
January 24, 2023

ACL and MCL injuries explained

Knee injuries have the potential to be extremely crippling and immobilizing. The most common knee injuries are tears in the ACL (anterior cruciate ligament) and MCL (medial collateral ligament).

Each year in the United States, an estimated 75,000 people will suffer from an MCL injury, while up to 200,000 will experience an ACL injury.

In this article, we’ll take a closer look at ACL and MCL injuries, including what causes them, how to diagnose them, and how to treat and prevent them.

So, whether you’re an athlete, a weekend warrior, an older adult, or just someone who wants to keep their knee healthy, this is the guide you need to understand these two common knee injuries.

Before we explore these two types of knee injuries in detail, we must first have a fundamental understanding of how the knee joint works.

Anatomy of the Knee

The knee joint is supported by both collateral and cruciate ligaments.

The lateral collateral ligament (LCL) and medial collateral ligament (MCL), located on either side of the knee and aid in controlling sideways movement, are examples of collateral ligaments.

Cruciate ligaments, such as the anterior cruciate ligament (ACL) and the posterior cruciate ligament (PCL), are located within the knee joint and help to control forward and backward movement.

Now that we understand the role of each of the four knee ligaments, let’s focus on the topic of our discussion for this article: ACL and MCL injuries.

Understanding the differences between these two types of injuries is important for proper diagnosis and treatment, as well as for preventing future injuries.

What is an ACL injury?

Anatomy of the ACL

The anterior cruciate ligament, or ACL, is a strong band of tissue that connects the thigh bone (femur) to the shin bone (tibia) and helps to stabilize the knee joint.

Unfortunately, ACL injuries are all too common, especially among athletes who play contact sports that involve jumping, cutting, or pivoting.

Causes of ACL injuries

One of the most common causes of a torn ACL is a sudden change in direction, such as when a soccer player makes a quick cut or a basketball player changes direction while dribbling.

A twisting motion, such as when a skier falls and twists their knee, can also cause an anterior cruciate ligament tear.

Additionally, hard impacts to the knee, such as a collision with another player during a sport, can cause an ACL injury.

Symptoms of an ACL tear

Symptoms of an ACL injury can include:

  1. A popping sound
  2. Swelling and knee pain
  3. Difficulty bearing weight
  4. Instability or knee “giving out”
  5. Loss of full range of motion

Diagnosing and treating an ACL injury

Diagnosing an ACL injury typically involves a physical examination and imaging tests, such as an X-ray or an MRI.

Treatment options for an ACL injury vary and depend on the level of injury and the individual.

Older adults, or people who do not lead active lifestyles, may not require surgical intervention if they still have general knee stability.

For these individuals, treatment options can include physical therapy and wearing knee braces to protect their knees from further injuries.

For most others, an ACL tear most certainly involves undergoing an arthroscopy.

Surgery can help restore stability to the knee and prevent further injuries.

In all cases, NSAIDs will likely be prescribed to mitigate inflammation and pain.

Recovery from an ACL injury can be a long process, and it is important to follow a strict rehabilitation program to regain strength and stability in the knee.

Physical therapy is an important part of recovery, and it can take between 4 and 6 months to fully heal and begin participating in sports and other normal physical activity.

Takeaway: An ACL injury is a sprain or tear of the anterior cruciate ligament, which connects the thighbone (femur) to the shinbone (tibia) and helps to stabilize the knee joint. It is usually caused by a hard impact to the knee or from a sharp, twisting movement. Symptoms include pain and swelling, difficulty bearing weight, and a feeling of instability. Most ACL injuries require surgery with supportive treatment.

What is an MCL injury?

Anatomy of the MCL

The medial collateral ligament, or MCL, is a ligament that runs along the inner side of the knee and connects the thigh bone to the shin bone.

Its primary function is to keep the knee stable and in place, especially when the knee is hit from the outside.

Causes of MCL injuries

MCL injuries are often caused by a direct impact to the outside of the knee that pushes the knee inward, such as a collision with another player during a sport or even a car accident.

Symptoms of an MCL injury

Symptoms of an MCL injury can include:

  1. Pain and swelling along the sides of the knee
  2. Difficulty bearing weight
  3. Instability or knee “giving out”
  4. Catching or “locking” of knee

Diagnosing and treating an MCL injury

A physical exam and imaging tests, like an X-ray or MRI, are used to diagnose an MCL tear, just like they are used to diagnose an ACL injury.

Unlike ACL injuries, treatment options for an MCL injury are more straightforward and can include rest, ice, physical therapy, and, in some cases, a brace.

Surgery is rarely required for an MCL injury.

NSAIDs may also be prescribed to control pain and inflammation.

When recovering from an MCL injury, physical therapy is often used to help the knee get stronger and more stable.

In some cases, a knee brace may help support the knee during the recovery process. Your orthopedic specialist will most certainly prescribe crutches.

Recovery time can vary depending on the severity of the injury. Still, most people can return to normal activities within one to three weeks, especially if they have a minor or partial tear (grade 1).

A more severe or complete tear (Grades 2 and 3) will take longer to heal, but they will inevitably get better with rest, wearing knee braces, and physical therapy.

Takeaway: An MCL injury is a sprain or tear of the medial collateral ligament, the ligament that runs along the inner side of the knee. It is usually caused by a direct impact on the outer side of the knee. Symptoms include pain and swelling, difficulty bearing weight, and a feeling of instability. Most MCL injuries don’t need surgery, and the time it takes to heal is usually shorter than for an ACL injury.

Prevention and Rehabilitation

Tips for preventing ACL and MCL injuries

Here are some tips to help prevent these types of ligament injuries:

  1. Strengthen your core and thigh muscles
  2. Incorporate balance exercises into your workout
  3. Wear proper shoes and equipment
  4. Warm up before exercise

Rehabilitation exercises and protocols

Rehabilitation is an important part of recovery from knee injuries, such as ACL and MCL injuries.

A physical therapist will make a rehabilitation plan for you that is based on your injury and your goals for getting better.

Some common exercises that may be included in a rehabilitation program include:

  • Strengthening exercises to help rebuild the muscles around the knee
  • Stretching exercises to help improve flexibility and range of motion in the knee
  • Balance exercises to help improve stability and reduce the risk of future injuries
  • Plyometric exercises to strengthen the power, agility, and coordination of the knee

It’s important to do what your physical therapist tells you to do and stick to your rehabilitation program to get the best results.

Takeaway: Preventing knee injuries is crucial to maintaining overall knee health. Some ways to avoid knee injuries are to strengthen the core and thigh muscles, do balance exercises, wear the right shoes and gear, and warm up before exercise. Rehabilitation is also an important part of recovery from knee injuries, and a physical therapist will design a program specific to your injury and recovery goal. If you stick to the program and do what the physical therapist says, you will get the best possible results.

ACL and MCL injuries in the older adult

As the US population ages, more and more older people are getting hurt while playing sports.

People over 40 are still active and participate in competitive sports.

Many people in this age range choose surgery to fix an ACL injury so they can get back to the sports they used to play.

According to a review by Best and colleagues, people over 40 who aren’t athletes and don’t do much physical work may benefit from activity modification and physical therapy instead of surgery.

ACL reconstruction can improve function and make it easier to return to sports for people who have had non-surgical injuries or athletes who participate in physically demanding sports.

When deciding if a patient is a good candidate for surgery, many things should be considered, such as scheduling, graft choice, and rehabilitation after surgery.

MCL tears are common in people between the ages of 55 and 65, and they are treated the same way as they are in younger people, usually with the RICE method and anti-inflammatory drugs.

For more severe injuries, arthroscopy may be necessary.


Knee injuries like ACL and MCL tears can be very painful and make it hard to play sports or do other things.

Understanding the differences between these two types of injuries is important for proper diagnosis and treatment, as well as for preventing future injuries.

In this article, we’ve taken a closer look at ACL and MCL injuries, including what causes them, how to diagnose them, and how to treat and prevent them.

We’ve also talked about the differences between the two injuries, such as their location and how they happen, their symptoms and how to diagnose them, their treatment options, and how long they take to heal.

It’s important to seek professional help if you’re experiencing knee injury symptoms.

With the proper diagnosis and treatment plan, the injury can have less of an effect on you, and you can return to your normal activities as soon as possible.

Also, if you follow tips for injury prevention and recovery, you can keep your knee healthy and reduce the chance of getting hurt again.

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