The Posterior Cruciate Ligament (PCL) is one of four major ligaments providing stability to the knee joint, located deep within the knee’s center. This thick band of tissue connects the femur (thigh bone) to the tibia (shin bone). The PCL works with the Anterior Cruciate Ligament (ACL) to form a cross shape, which is why they are called “cruciate” ligaments. Although the PCL is the largest and strongest of the four main knee ligaments, it is still susceptible to injury, causing pain and instability.
The PCL: Anatomy and Primary Function
The PCL originates from the medial femoral condyle and extends diagonally to insert into the posterior section of the tibia, just below the joint line. This positioning places it in the back of the knee, where it serves as the main restraint against the tibia shifting too far backward relative to the femur. The PCL is composed of two distinct bundles that work together to maintain knee stability.
The ligament’s primary role is to prevent the tibia from moving too far backward, providing up to 95% of the total restraining force against this movement. This function is particularly active when the knee is bent, especially around a 90-degree angle. The PCL also acts as a secondary stabilizer, helping to limit internal and external rotation of the knee joint. Due to its strength and location, a significant amount of force is required to cause a PCL tear.
Causes and Signs of a PCL Injury
A PCL injury typically results from a powerful, direct impact to the front of the shinbone while the knee is bent. A classic example is the “dashboard injury” in a car accident, where the bent knee slams against the dashboard, pushing the tibia backward. The ligament can also be damaged when an athlete falls hard onto a highly flexed knee with the foot pointed downward.
The injury can also occur from non-contact mechanisms, such as severe hyperextension or a sudden, forceful twisting motion. PCL injuries frequently involve damage to other knee structures, such as other ligaments or cartilage. The severity is classified into grades: Grade I is a partial tear, and Grade III indicates a complete tear, often combined with other ligament damage.
Immediately following the injury, symptoms include mild to moderate pain and swelling. Unlike an ACL tear, a distinct “pop” is often not felt or heard, which can sometimes lead people to underestimate the severity of the problem. Within a few hours, the knee may become stiff and difficult to move, potentially leading to a noticeable limp or difficulty walking.
Chronic Symptoms
As acute symptoms subside, delayed or chronic signs may emerge, including a feeling of instability or the sensation that the knee is “giving out” during activities. Individuals may also experience pain behind the knee and difficulty walking down stairs. The instability may be more apparent during sporting activities or when trying to kneel.
Diagnosing the Injury and Treatment Options
A physician begins diagnosing a PCL injury by thoroughly examining the knee and comparing it to the uninjured leg, looking for signs of posterior instability. A specific physical test, the Posterior Drawer Test, is performed where the doctor pushes backward on the upper shin to assess how far the tibia shifts. A sign of a PCL tear is a visual “sag” of the tibia, where the shinbone appears to droop backward compared to the femur when the knee is bent.
Imaging tests are then used to confirm the diagnosis and determine the extent of the damage. An X-ray is often ordered first to rule out a bony avulsion, which occurs when the ligament pulls a piece of bone away from its attachment site. The most definitive imaging tool is the Magnetic Resonance Imaging (MRI) scan, which visualizes soft tissues, confirms the grade of the PCL tear, and checks for associated injuries.
The treatment pathway is determined by the injury’s grade, which correlates to the degree of posterior instability. Grade I (partial tear) and Grade II injuries are most often managed non-surgically. This conservative approach begins with the RICE protocol—rest, ice, compression, and elevation—to manage initial pain and swelling.
Non-surgical treatment relies on physical therapy to strengthen the muscles surrounding the knee, particularly the quadriceps, which help stabilize the joint and counteract instability. A brace or crutches may be recommended to limit weight-bearing and protect the healing ligament. The goal is to restore strength and function, often allowing a return to activities without surgery.
Surgical reconstruction is reserved for severe Grade III tears, especially those where the posterior shift exceeds 10 millimeters, or when the PCL injury is combined with damage to other ligaments. The procedure involves replacing the torn PCL with a graft, typically using the patient’s own tendon tissue (autograft) or donor tissue (allograft). This surgery is usually performed arthroscopically, using small incisions and specialized instruments.
Following surgery, a rigorous rehabilitation program spanning six months or more is necessary for a full recovery. While surgical outcomes can be excellent, reconstruction results are sometimes less successful than those for ACL reconstruction, and some degree of residual laxity may remain.