ACL vs PCL Tear: Cruciate Ligament Injuries Explained

When it comes to sports injuries, few ailments strike fear into the hearts of athletes and sports enthusiasts quite like cruciate ligament tears of the knee. These delicate yet vital structures within the knee joint, known as the anterior cruciate ligament (ACL) and the posterior cruciate ligament (PCL), play an indispensable role in maintaining joint stability and enabling smooth, pain-free movement. When these ligaments sustain damage, it can have a profound impact on an individual's mobility and quality of life.

Whether you're an athlete looking to safeguard your knee health or someone who simply wants to understand these common injuries better, this article is your comprehensive guide to ACL and PCL tears. We'll explore what these ligaments are, how they function, and most importantly, how injuries to them can occur. By the end of this journey, you'll not only grasp the differences between ACL and PCL tears but also gain valuable insights into prevention, treatment, and recovery. So, let's delve into the world of cruciate ligaments and equip ourselves with the knowledge needed to navigate these injuries successfully.

To better understand the difference between the two different knee ligament injuries, it helps to understand the roles of each of the two major ligaments of the joint:


Anterior Cruciate Ligament (ACL)

The anterior cruciate ligament (ACL) is a critical structure within the knee joint, playing a pivotal role in its stability and function. To understand the anatomy and purpose of the ACL, it's essential to have a basic grasp of the knee's structure.

The knee joint is a hinge joint that connects the thigh bone (femur) to the shinbone (tibia). It also involves the kneecap (patella), which is embedded in the tendon of the quadriceps muscle group. The ACL and its counterpart, the posterior cruciate ligament (PCL), are two ligaments that cross each other within the knee joint. They are collectively referred to as the "cruciate ligaments" due to their crossed configuration.


Here's a breakdown of the anatomy and purpose of the ACL:

  1. Location and Structure: The ACL is located deep within the knee joint and runs diagonally from the back of the femur to the front of the tibia. It consists of tough, fibrous tissue that can withstand significant tension.

  2. Stabilisation: The primary purpose of the ACL is to provide stability to the knee joint. It prevents excessive forward movement of the tibia in relation to the femur and helps control rotational movements. This stability is crucial for various activities, including walking, running, jumping, and pivoting.

  3. Limiting Hyperextension: The ACL also limits hyperextension of the knee, which is when the knee joint straightens beyond its normal range of motion. This limitation is essential to protect the knee from injury during activities that involve sudden stops or changes in direction.

  4. Coordination with Other Ligaments: The ACL works in conjunction with other ligaments and structures in the knee, such as the medial collateral ligament (MCL) and lateral collateral ligament (LCL), to maintain overall joint stability and prevent excessive side-to-side or front-to-back movement.

  5. Injury Risk: Unfortunately, the ACL is susceptible to injury, particularly during sports or activities that involve rapid changes in direction, jumping, or direct impact to the knee. ACL injuries are common and can range from partial tears to complete ruptures. When the ACL is injured, it can result in instability, pain, and difficulty with knee movement.

In summary, the anterior cruciate ligament (ACL) is a vital component of the knee joint, contributing to its stability and functioning as a key player in controlling movements and preventing excessive joint displacement. Understanding the anatomy and purpose of the ACL is crucial for athletes and individuals alike, as it can help in injury prevention and guide rehabilitation efforts in the event of an ACL tear.


Posterior Cruciate Ligament (PCL)

The posterior cruciate ligament (PCL) is the other cruciate ligament in the knee joint. The PCL is a strong, thick band of connective tissue that plays a crucial role in knee joint stability and function. To understand its anatomy and purpose, let's delve into its structure and function:

Anatomy of the PCL:

  1. Location: The PCL is situated deep within the knee joint, crossing diagonally from the back of the femur (thigh bone) to the front of the tibia (shin bone). It forms a crossing pattern with the ACL, which is why they are referred to as "cruciate" ligaments, as they cross each other within the joint.

  2. Structure: Like the ACL, the PCL is composed of strong, fibrous tissue that can withstand significant tensile forces. It is thicker and stronger than the ACL, making it less susceptible to injury.

Purpose of the PCL:

  1. Stabilisation: The primary function of the PCL is to provide stability to the knee joint. It prevents excessive backward movement of the tibia in relation to the femur. This is especially important during activities that involve running, jumping, and pivoting, as it helps maintain the alignment of the knee joint.

  2. Control of Anterior Movement: The PCL also plays a key role in controlling anterior (forward) movement of the tibia. Together with the ACL, it helps maintain the proper positioning of the bones in the knee joint, preventing them from sliding too far forward or backward during movements.

  3. Coordination with Other Ligaments: The PCL works in concert with other ligaments and structures in the knee, such as the ACL, collateral ligaments (medial and lateral), and menisci, to provide overall stability to the joint. It helps distribute forces evenly across the knee during weight-bearing activities.

  4. Protection of Other Structures: The PCL acts as a protective structure for other important knee components, such as the articular cartilage and menisci. By limiting excessive movement within the joint, it helps reduce the risk of damage to these critical structures.

Injury Risk:

While the PCL is less commonly injured than the ACL, PCL injuries can still occur, typically as a result of significant trauma, such as a direct blow to the front of the knee or a car accident. A PCL tear can vary in severity, ranging from partial tears to complete ruptures. A PCL injury can lead to pain, swelling, and instability in the knee joint usually reuiring some form of physical therapy to heal sufficiently.

In summary, the posterior cruciate ligament (PCL) is a robust ligament within the knee joint, primarily responsible for stabilising the knee by preventing excessive backward movement of the tibia and controlling anterior movement. Its role is essential for maintaining the integrity and function of the knee, particularly during activities that involve dynamic movements and weight-bearing.


Cruciate Ligaments and Knee Instability

Cruciate ligaments, specifically the anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL), are vital components of the knee joint that play a central role in maintaining stability. When these ligaments are compromised, often due to injury or trauma, it can result in knee instability. This instability can manifest as a feeling of the knee giving way or being unable to support the body's weight during activities. It can significantly impact a person's ability to engage in sports, daily activities, and even simple movements like walking or climbing stairs. Addressing cruciate ligament injuries and the resultant knee instability requires thorough evaluation and often involves rehabilitation, or in more severe cases, surgical intervention, to restore stability and function to the knee joint. Understanding the importance of cruciate ligaments and the consequences of their instability underscores the significance of proper care and management for these essential knee structures.


​How is a PCL or ACL injury diagnosed?

Diagnosing a knee ligament injury typically involves a multifaceted approach that combines both physical examination, including specific physiotherapy special tests, and advanced imaging such as MRIs.


Physiotherapy Special Tests:

  1. Lachman Test (ACL): This test involves the practitioner flexing the patient's knee to 20-30 degrees and then applying an anterior force to assess for increased anterior tibial translation. A positive Lachman test often indicates ACL instability.

  2. Anterior Drawer Test (ACL): Similar to the Lachman test, the anterior drawer test assesses anterior tibial displacement with the knee flexed at 90 degrees. Increased anterior translation can indicate ACL injury.

  3. Posterior Drawer Test (PCL): For PCL evaluation, the posterior drawer test is performed. In this test, the knee is flexed at 90 degrees, and the practitioner assesses for excessive posterior tibial translation, which can suggest PCL injury.

  4. Pivot Shift Test (ACL): The pivot shift test assesses the dynamic instability of the knee during rotational movements. It can help identify subtle ACL injuries by detecting abnormal joint motion when the knee is twisted.

  5. Sag Sign (PCL): The sag sign is a simple test where the practitioner compares the heights of the tibial tubercles while the patient is lying down with knees bent. A noticeable difference may indicate PCL laxity.


While physiotherapy special tests provide valuable clinical information, imaging is often necessary for a definitive diagnosis and to assess the extent of ligament damage.

  1. MRI (Magnetic Resonance Imaging): MRI is the most commonly used imaging modality for diagnosing ACL and PCL injuries. It provides detailed images of the ligaments, allowing healthcare providers to visualise the extent of damage, such as partial tears or complete ruptures, as well as any associated injuries to other knee structures like menisci or cartilage.

The combination of physiotherapy special tests and MRI results allows healthcare professionals to make an accurate diagnosis of PCL or ACL injuries. This information is crucial for developing an appropriate treatment plan, which may involve conservative management with physical therapy, bracing, and lifestyle modifications or surgical intervention, depending on the severity of the injury and the patient's goals and activity level.


ACL Injuries in Sport

ACL injuries are a common and often devastating occurrence in the world of sports. These injuries frequently happen during high-impact and contact sports like soccer, basketball, football, and skiing, where sudden changes in direction, pivoting, or landing from a jump can place immense stress on the knee joint. The ACL is a crucial ligament that helps stabilise the knee, preventing excessive forward movement of the tibia (shinbone) in relation to the femur (thighbone) and controlling rotational forces. When an athlete sustains an ACL injury, it can result in immediate pain, swelling, and, most importantly, a loss of stability in the knee. The instability can affect an athlete's performance, leading to decreased agility, difficulty cutting and pivoting, and an increased risk of further injury. ACL injuries often necessitate surgical intervention, followed by extensive rehabilitation to regain strength and mobility. They not only pose physical challenges but can also have a psychological impact on athletes, requiring mental fortitude to overcome. As such, ACL injuries in sports are not just about the physical recovery; they involve a holistic approach to rehabilitation, including mental resilience and a strong support system, to help athletes return to peak performance levels.


​Cruciate Ligament Surgery

Cruciate ligament surgery, whether for the anterior cruciate ligament (ACL) or posterior cruciate ligament (PCL), is a significant medical procedure designed to restore stability and function to the knee joint following ligament injury. The surgery typically involves reconstructing the torn ligament using a graft, often sourced from the patient's own hamstring or patellar tendon or from a donor. The procedure is performed via arthroscopic surgery, which involves making small incisions and using a tiny camera to guide the surgeon. During surgery, damaged ligament remnants are removed, and the new graft is meticulously placed in the same position as the original ligament. This surgical intervention aims to recreate the ligament's function, enabling the knee to withstand various stresses and movements. Post-surgery, a rigorous rehabilitation program is crucial to ensure the graft heals properly and the patient regains strength, stability, and range of motion. While cruciate ligament surgery has a high success rate, it's not without risks, and the recovery process can be demanding. However, for athletes and individuals seeking to regain their pre-injury level of activity and function, it represents a vital step toward a return to an active and pain-free life.


Recovery times of PCL and ACL Injuries

Recovery times for cruciate ligament injuries, such as those involving the anterior cruciate ligament (ACL) or posterior cruciate ligament (PCL), can vary widely depending on several factors. These factors include the severity of the injury, the type of treatment (conservative management or surgery), the individual's overall health, age, and adherence to rehabilitation protocols.

For less severe cases or when opting for non-surgical treatment, recovery can take several weeks to a few months. This involves a structured physical therapy treatment plan, strengthening exercises, and gradually reintroducing weight-bearing activities.

In contrast, surgical reconstruction of the cruciate ligament typically extends the recovery timeline. In the case of ACL reconstruction, recovery can take anywhere from 6 to 12 months or longer to return to pre-injury levels of activity. During the first few weeks, patients may use crutches and wear a knee brace. Physical therapy is crucial, beginning with range-of-motion exercises and gradually progressing to strengthening and functional activities. The type of surgery an injured patient may undergo can vary, often to the preference of the orthopedic surgeon and the type of injury (full vs partial tears and if there is any further damage to the other ligaments of the knee such as the MCL or LCL - the two collateral ligaments either side of the joint). 

Achieving a full recovery and returning to sports or demanding physical activities often requires patience and diligent effort. It's essential to follow the guidance of healthcare professionals and adhere to the prescribed rehabilitation plan to ensure a successful and lasting recovery while minimising the risk of reinjury. While the process can be challenging, many individuals regain not only their knee stability but also their confidence and performance in their chosen activities after undergoing cruciate ligament injury recovery.


PCL (Posterior Cruciate Ligament) and ACL (Anterior Cruciate Ligament) injuries are both common knee ligament injuries, but they differ in several key aspects. The ACL is often injured during abrupt changes in direction or landing from jumps, leading to anterior knee instability. PCL injuries, on the other hand, usually result from direct blows to the front of the knee, causing posterior instability. While both injuries can lead to pain, swelling, and instability, PCL injuries tend to be less common and often exhibit milder symptoms. Treatment approaches also vary, with ACL injuries frequently requiring surgical reconstruction and PCL injuries often managed non-surgically through rehabilitation and physiotherapy. Understanding these differences is crucial for accurate diagnosis and appropriate treatment decisions tailored to each patient's unique circumstances.

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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