What is the difference between ACL and MCL Tears?

Knee injuries are a common occurrence, especially among athletes and those leading active lifestyles. Two of the most frequently discussed knee injuries are ACL (Anterior Cruciate Ligament) and MCL (Medial Collateral Ligament) tears. These injuries can be painful, disruptive, and can significantly impact an individual's ability to engage in physical activities or even perform everyday tasks.

While ACL and MCL tears both involve the knee and often get lumped together in conversations about knee injuries, they are distinct injuries with unique characteristics, causes, symptoms, and treatments. Understanding the differences between these two types of knee injuries is essential for proper diagnosis, treatment, and rehabilitation.

In this post I will delve into the world of knee injuries and explore the key disparities between ACL and MCL tears. Whether you're a sports enthusiast looking to safeguard yourself from potential injuries or simply curious about the intricacies of the human body, this article aims to shed light on these common knee issues. So, let's start by unravelling the mysteries of ACL and MCL tears and discover why knowing the difference matters when it comes to your knee health.


What is an ACL and an MCL?


The Anterior Cruciate Ligament (ACL)

The ACL is one of the two cruciate ligaments in the human knee joint, playing a crucial role in stabilizing and supporting the knee during various movements and activities. To understand the ACL better, let's break down its anatomy, including its origin, insertion, and its primary function in the knee.

Anatomy of the ACL:

  1. Origin: The ACL originates from the posterior aspect of the femur (thigh bone). Specifically, it attaches to a bony ridge called the intercondylar notch, which is located between the two rounded condyles at the end of the femur.

  2. Insertion: The ACL inserts into the anterior part of the tibia (shin bone), just below the tibial plateau. It attaches to the tibia through a bony prominence known as the tibial spine.

Function of the ACL:

The ACL is a critical component of the knee joint, and its primary function is to provide stability and control during various movements. Here are its main functions:

  1. Stabilization: The ACL plays a pivotal role in preventing excessive forward movement of the tibia in relation to the femur and also restrains excessive rotation of the knee joint. This is particularly important during activities that involve sudden changes in direction, such as pivoting, cutting, and decelerating.

  2. Support for Weight-Bearing: It assists in supporting body weight, especially when the knee is partially bent, as in squatting or descending stairs. Without a functioning ACL, the knee can feel unstable during these activities.

  3. Protecting Other Structures: The ACL helps protect other structures within the knee joint, such as the menisci (cartilage pads that cushion the knee), by minimizing excessive shear and compressive forces.

  4. Coordination: It aids in the coordination of movements, ensuring that the femur and tibia move smoothly and harmoniously during activities like running, jumping, and landing.

It's important to note that the ACL is susceptible to injury, particularly in sports and activities that involve sudden stops, changes in direction, or high-impact forces. An ACL tear is a relatively common knee injury that can have significant consequences, often requiring surgical intervention and rehabilitation to restore function and stability to the knee.

In summary, the Anterior Cruciate Ligament (ACL) is a vital ligament in the knee joint, originating from the femur and inserting into the tibia. Its main functions include stabilizing the knee, supporting weight-bearing activities, protecting other knee structures, and coordinating knee movements. Understanding the role of the ACL is essential in appreciating its significance and the potential consequences of an ACL injury.


The Medial Collateral Ligament (MCL)

The MCL is one of the two crucial, collateral ligaments on the inside of the knee joint, responsible for providing stability and support to the inner side of the knee. To gain a deeper understanding of the MCL, let's explore its anatomy, including its origin, insertion, and its primary function in the knee.

Anatomy of the MCL:

  1. Origin: The MCL originates from the medial femoral condyle, which is a bony prominence on the inner aspect of the femur (thigh bone). It begins at this point and extends downward toward the tibia.

  2. Insertion: The MCL inserts into the proximal (upper) part of the tibia (shin bone). It attaches to the tibia through a bony prominence known as the tibial metaphysis.

Function of the MCL:

The MCL serves several important functions within the knee joint, and its primary role is to provide stability and support to the inner side (medial side) of the knee. Here are its main functions:

  1. Stabilization: The MCL is primarily responsible for resisting excessive widening or opening up of the knee joint on the inner side. It acts as a critical stabilizer during activities that involve forces pushing from the outer side of the knee, such as when the knee is bumped or impacted on the outer side.

  2. Protection: It helps protect the inner structures of the knee, including the medial meniscus, from excessive stress or injury during movements and impacts.

  3. Supporting Ligament: The MCL works in conjunction with other ligaments, such as the Anterior Cruciate Ligament (ACL) and the Posterior Cruciate Ligament (PCL), to maintain overall knee stability. These ligaments complement each other to ensure the knee functions effectively during various activities.

  4. Contributing to Flexibility: While the MCL's primary role is to prevent excessive widening of the knee joint, it also allows for some degree of flexibility and movement in the knee, particularly during bending and straightening of the leg.

Injuries to the MCL, commonly referred to as MCL sprains or tears, can occur due to direct blows to the outer side of the knee or from twisting motions that place stress on the ligament. MCL injuries are often categorized into different grades, depending on the severity of the tear. Mild MCL injuries may heal with conservative treatment like rest and physical therapy, while severe tears may require surgical intervention.

In summary, the Medial Collateral Ligament (MCL) is a crucial ligament in the knee joint, originating from the femur and inserting into the tibia. Its primary functions include stabilizing the inner side of the knee, protecting inner knee structures, working in concert with other ligaments to maintain knee stability, and allowing for controlled flexibility in the knee. Understanding the role of the MCL is essential for appreciating its importance and addressing an MCL injury effectively.


Knee ligament injuries

Knee ligament injuries are a prevalent orthopedic surgeon's concern, affecting individuals across various age groups and activity levels. These injuries involve damage to the ligaments that stabilize the knee joint, most commonly the Anterior Cruciate Ligament (ACL) and Medial Collateral Ligament (MCL). ACL injuries often occur during activities that involve sudden stops, pivoting, or high-impact movements, such as sports like soccer, basketball, and skiing. MCL injuries, on the other hand, often result from direct blows to the outer knee or twisting motions. Signs and symptoms of knee ligament injuries typically include pain, swelling, instability, and limited range of motion. In some cases, a "popping" sound or sensation may be experienced at the time of injury. Treatment options vary depending on the severity of the injury and may include rest, physical therapy, bracing, or surgical reconstruction for more severe cases. An early and accurate diagnosis and appropriate management are crucial to facilitate recovery and minimize long-term complications in individuals dealing with knee ligament injuries.


Partial Tear vs Complete Tear

Partial tears and complete tears of the Anterior Cruciate Ligament (ACL) and Medial Collateral Ligament (MCL) represent two distinct levels of severity in knee ligament injuries. A partial tear implies that the ligament has sustained damage but remains partially intact, while a complete tear signifies a full rupture of the ligament. In the case of the ACL, a partial tear might cause symptoms like instability, pain, and reduced function, but it may still provide some degree of knee stability. Conversely, a complete tear often results in significant instability, rendering the knee less capable of bearing weight and leading to episodes of giving way. For the MCL, a partial tear usually allows for some preservation of stability and can often heal effectively with conservative treatments. In contrast, a complete MCL tear may require more extensive treatment, potentially including bracing, physical therapy, or even surgery, depending on the severity of the injury. The key distinction lies in the extent of damage, which significantly influences the choice of treatment and the expected outcome for individuals recovering from ACL and MCL ligament injuries.

An acute diagnosis MCL and ACL injuries typically involves a comprehensive physical examination by a medical healthcare provider, often an orthopaedic specialist or physical therapist. The two injuries do share some similar symptoms however it is often quite simple to differentiate between the two by looking at some key differences, especially in terms of the mechanism of injury. The process begins with a thorough medical history review and a discussion of the circumstances surrounding the injury. Physical examinations, including specialized tests such as the Lachman test and anterior drawer test for the ACL, and valgus stress test for the MCL, are performed to assess the integrity of these ligaments. In some cases, imaging studies like MRI scans may be ordered to provide a more detailed view of the ligaments and surrounding structures. These scans can help confirm the diagnosis and assess the severity of the injury. Overall, the combination of clinical evaluation, patient history, and imaging studies allows healthcare providers to accurately diagnose MCL and ACL injuries, enabling them to develop appropriate treatment plans tailored to the individual's specific condition and needs.


​Knee ligament injury recovery

Recovery from ACL (Anterior Cruciate Ligament) and MCL (Medial Collateral Ligament) injuries can vary depending on the severity of the injury, individual factors, and the chosen treatment approach. These two types of knee injuries are common in sports and can often occur together. Here's an overview of the recovery process for both ACL and MCL injuries:


ACL Injury Recovery:

1. Initial Assessment and Diagnosis:

  • The first step is to assess the extent of the ACL injury, often through a physical examination, MRI, or other imaging tests.

2. Treatment Options:

  • Non-surgical Treatment: For partial ACL tears or individuals who are not very active, conservative treatment options may be considered. This includes rest, physical therapy, and the use of a brace.
  • Surgical Treatment: Complete ACL tears often require surgical reconstruction, where a graft (usually from the patient's hamstring or patellar tendon) is used to replace the torn ACL.

3. Recovery Time:

  • Non-surgical recovery may take around 6-12 weeks of rehabilitation.
  • Post-surgical recovery typically involves several phases:
    • Immediate post-surgery recovery: Rest and initial rehabilitation exercises (2-4 weeks).
    • Intensive rehabilitation and strengthening: 3-6 months.
    • Return to sports-specific activities: 6-9 months, or longer for some athletes.

4. Return to Play Considerations:

  • Return to sports should be gradual and supervised by a sports medicine professional.
  • Athletes should achieve full range of motion, strength, and stability in the knee before considering a return.
  • Functional tests (e.g., agility drills) may be used to assess readiness.
  • Psychological readiness and confidence are also crucial factors.

MCL Injury Recovery:

1. Initial Assessment and Diagnosis:

  • Similar to ACL injuries, an MCL injury is diagnosed through physical examination and sometimes imaging tests.

2. Treatment Options:

  • Grade I and II MCL sprains: Often managed non-surgically with rest, bracing, and physical therapy.
  • Grade III MCL tears: Surgical treatment may be considered, although it's less common than with ACL injuries.

3. Recovery Time:

  • Grade I MCL sprains may take 2-4 weeks to heal.
  • Grade II MCL sprains may take 4-6 weeks.
  • Grade III MCL tears, whether treated surgically or non-surgically, may require 8-12 weeks or more.

4. Return to Play Considerations:

  • Gradual progression in activity is essential to ensure the ligament heals and regains strength.
  • Return to sports may be allowed when there is no pain, swelling, and full range of motion.
  • Athletes should regain functional stability before returning to high-impact sports.

In both ACL and MCL injuries, rehabilitation plays a vital role in recovery. Physical therapy is typically recommended to restore strength, stability, and range of motion. Athletes should work closely with sports medicine professionals and adhere to their recommendations for a safe and successful return to play.

It's essential to note that individual recovery times can vary widely, and the guidance of a healthcare provider with expertise in sports medicine is critical in managing these injuries and ensuring a safe return to sports activities.


In conclusion, understanding the difference between ACL and MCL tears is pivotal in sports medicine and orthopaedics. These two common knee injuries, while they share some similarities, vary significantly in their treatment approaches, recovery times, and implications for an individual's athletic pursuits. While ACL injuries often require surgical reconstruction and extensive rehabilitation, MCL injuries may be managed conservatively in many cases. Regardless of the injury type, a thorough diagnosis and personalized treatment plan are essential for a successful recovery. By grasping these distinctions, athletes, coaches, and healthcare professionals can make informed decisions and work collaboratively to optimize the healing process, ensuring a safe return to an active and fulfilling lifestyle.

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Arun Gray sports therapist strength and conditioning coach skegness

The author

Arun Gray is a sports therapist and strength & conditioning coach with over 15 years experience in the industry. He also has a personal history with chronic shoulder and back pain along with a range of other sporting injuries.

Arun writes about common injuries and aims to help people understand and manage their pain to prevent having to rely on national healthcare.

Read more about Arun