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The posterior cruciate ligament (PCL) is one of the 4 major ligaments of the knee, along with the anterior cruciate ligament, and the medial and lateral collateral ligaments (ACL, MCL and LCL). The function of a ligament is to hold bones in a joint together and restrict movement in a particular direction.
The PCL is the strongest knee ligament and sits deep inside the knee joint, attaching the tibia to the fibula. It is angled down and back from femur to tibia with a mean angle of 123º in adults, a smaller angle can indicate and ACL injury or abnormality (Zhang et al, 2015). This position and angle allows for the effective function of the PCL to restrict backward (posterior) movement of the tibia relative to the femur.
There are common symptoms related to a torn or injured PCL. Severity of injury will determine what symptoms are experienced and the severity of symptom. Common with all ligament injuries are symptoms such as pain, swelling, bruising, stiffness and loss of range of movement of the joint, and instability of the joint. With a weight-bearing joint like the knee, it is common for there to be pain with weight-bearing activities such as standing or walking, and worse with any impact such as running or jumping.
A sprained or grade 1 tear PCL symptoms will include pain, slight swelling and if there is bruising it will be slight. Grade 1 is the classification given when there is minimal damage to the ligament, so it will be no laxity, so it is unlikely for the joint to feel unstable. Any instability is more likely linked to muscle inhibition, which is common with any knee pain and injury.
A grade 2 or 3 torn PCL will have symptoms, including significant swelling or effusion, that can make the joint feel stiff and can limit the range of flexion and extension. Pain will be higher with a high grade tear relative to a complete rupture. Bruising can take several days to appear. Laxity of the ligament can cause instability of the knee and buckling, or the feeling of giving way.
In most ligament injuries, there is a specific trauma or injury that is the mechanism of injury. A ligament must be overstretched under force, or repeatedly overstretched with lower force, for it to be injured. The most common causes of PCL injury is through road traffic incidence and sports injury. The mechanism of injury for a PCL is high force trauma, as it is a very strong ligament. An impact that forces the tibia backwards relative to the femur, that can be impact of the shin on a dashboard, or landing on a flexed knee (Schulz et al, 2003). Hyperextension or knee dislocation of the knee are also a common causes of PCL injury.
A clinical examination by an experienced doctor or physical therapist will cover the history of your knee injury and symptoms and the patterns and onset of your pain. There are special tests, or orthopaedic tests, that can be used to differentiate the structure that is injured. Classification of PCL injuries will be based on clinical examination and diagnostic imaging from MRI. A PCL MRI will show inflammation and the injury to the ligament.
The posterior draw test, posterior Lachman tests and posterior sag sign are orthopaedic tests, used to assess the PCL injury, indicated by pain and/or laxity. They can sometimes be referred to as PCL R tests, as they are used to assess for a PCL rupture. The test will not be accurate if swelling is present in the knee, such as in the acute phase after injury.
Minimal damage to the ligament with no loss of ligament function. The knee remains stable.
Partial tear of the PCL with a partial loss of function. The knee will feel unstable.
Complete tear of the PCL with complete loss of function. The knee will be unstable and buckle with stress. These will usually be other ligaments damaged concurrently to these PCL injuries.
This is not medical advice. We recommend a consultation with a medical professional such as James McCormack. He offers Online Physiotherapy Appointments for £45.