PCL Strain: What Is a Posterior Cruciate Ligament Injury and How Do You Know You Have One?
A posterior cruciate ligament strain is a stretch or tear of the strong ligament at the back of your knee. It usually happens when a force pushes the shin bone backwards. Examples are hitting the dashboard in a car accident or landing hard on a bent knee. Symptoms include deep knee pain, swelling and a feeling that the knee gives way.
Key points
- The PCL is the strongest ligament in the knee. Even so, a direct blow or a fall can stretch or tear it.
- Many PCL strains are missed. The knee can feel stable enough to walk on, even when the ligament is damaged.
- Scans done lying down can miss how a PCL injury changes your standing alignment and how your whole leg takes your weight.
- An EOS standing scan captures the alignment of your full leg under load. This gives your specialist a clearer picture for planning next steps.
The posterior cruciate ligament (PCL) sits behind the anterior cruciate ligament (ACL), deep inside the knee joint. Its job is to stop the shin bone from sliding too far backwards compared with the thigh bone. It is thicker and stronger than the ACL, so PCL injuries are less common. But they are also missed more often.
Do you have persistent knee pain, a knee that feels unstable during activity, or a knee that just does not feel right after a knock? If so, a PCL strain may be worth looking into.
What does a PCL tear feel like?
A PCL tear often feels less dramatic than an ACL tear. You may not hear a "pop". Instead, you notice a deep ache at the back of the knee and swelling that builds up over hours. You may also have a vague sense of looseness when walking downhill or on stairs.
Urgent warning. If your knee is badly swollen, you cannot put any weight on it, or you have numbness or tingling in your lower leg, get medical help straight away. Contact your doctor or go to your nearest emergency department.
What causes a posterior cruciate ligament strain?
A PCL strain is usually caused by a direct blow to the front of the shin while the knee is bent. This forces the shin bone backwards and stretches or tears the ligament.
What are the grades of a PCL sprain?
PCL injuries are graded by how much the ligament is damaged and how far the shin bone can shift backwards. Knowing the grade helps guide the best next steps.
- Grade I (mild). The ligament is stretched but not torn. The knee still feels stable. Recovery is typically managed with rest and physiotherapy.
- Grade II (partial tear). Some of the ligament fibres are torn. The knee feels looser than normal, and you may notice it giving way under load.
- Grade III (complete tear). The ligament is fully ruptured. The knee is clearly unstable. Surgical reconstruction may be discussed if other ligaments are also damaged or the knee stays unreliable.
How does a standing scan help after a PCL injury?
A standing, weight-bearing scan shows how your leg alignment really behaves under your body weight. A scan done lying down cannot do this.
When you lie down for a standard X-ray or MRI, gravity is taken away. Your muscles relax. The knee joint settles into a position that may look more normal than it really is. When you stand up and walk, the forces change completely. A damaged PCL lets the shin bone sag backwards. That shift can change the alignment of your whole leg, from the hip down to the ankle.
Your body works as a connected chain. If your PCL is lax, the thigh bone may rotate or your hip may tilt to compensate. This can cause discomfort far from the knee itself. A whole-body standing image, like the one made by an EOS scanner, captures these compensations in a single low-dose exposure, using about 90% less radiation than a standard X-ray, around ten times less.
This full picture helps your surgeon or physiotherapist understand more than the ligament damage. It shows how the injury has changed the way your body moves and carries weight overall. It is especially useful if you have already had an MRI and your knee still does not feel right.
When MRI is the better tool. EOS shows bones, joints and alignment under load. For soft-tissue detail of the ligament itself, cartilage, meniscus or nerve involvement, MRI is usually the better choice. The two work well together.
Wondering if your knee alignment is part of the problem? A short video call from home can help you decide if travelling to London for an EOS scan is the right next step.
Book a free video consultationHow is a PCL injury managed without surgery?
Many PCL injuries, especially grade I and grade II strains, are managed without surgery. Treatment is guided by the grade of injury, how stable the knee is overall and your activity goals. Common approaches include rest, a knee brace and a structured physiotherapy programme to strengthen the muscles around the knee, mainly the quadriceps.
Grade III tears, or injuries where other ligaments are also damaged, may need surgical reconstruction. Your orthopaedic specialist will make that decision based on a clinical examination and imaging.
Understanding your leg alignment before and during recovery can be valuable. If the knee is compensating in a way that puts extra stress on the hip or ankle, targeted rehabilitation can address those patterns early.
Before you start treatment, or change the one you are on, it is worth getting a detailed diagnosis. Knowing whether the cause sits in the pelvis, the legs or the spine changes what will actually help.
Learn more about how standing imaging supports knee assessment and alignment.
Frequently asked questions about PCL strains
Grade I and some grade II tears can heal with rest, a knee brace and physiotherapy. The ligament may stretch slightly but regain enough stability for daily activity. Complete tears rarely heal fully without treatment, though not everyone needs surgery.
Recovery depends on the grade. A mild strain may settle in a few weeks with guided rehabilitation. A partial or complete tear can take several months. Your specialist will set a timeline based on your own injury and progress.
A dashboard knee injury happens when the front of the shin hits the car dashboard in a collision. The knee is bent, and the impact drives the shin bone backwards, stretching or tearing the PCL. It is one of the most common ways this injury happens.
Not necessarily. PCL tears are often less disabling at first, because the knee may still feel stable enough to walk on. However, untreated PCL laxity can lead to long-term problems, including cartilage wear and pain around the kneecap. Each injury needs a proper assessment.
No. ScanAlign is a private, self-pay clinic. You can book directly yourself. You are welcome to bring results from any clinician already involved in your care.
An EOS scan uses about 90% less radiation than a standard X-ray, around ten times less. It captures full-length, weight-bearing images in a single low-dose exposure.
EOS shows bones and joint alignment, not the soft-tissue ligament itself. What it does show is how a PCL injury changes the position of the shin bone compared with the thigh bone when you are standing. It also shows any compensating changes up and down the leg. For imaging the ligament directly, MRI is usually the better tool.
The price for patients travelling from abroad is confirmed during the free video consultation. You can also read the ScanAlign FAQs and cost page.
When the PCL is lax, the shin bone can sag backwards. This changes how your leg carries weight. Your hip may compensate by tilting or rotating to keep you balanced. Over time, this can cause discomfort in the hip, even though the original injury is in the knee. A full-leg standing scan can show these compensating patterns.
You stand in the EOS scanner for a short, comfortable image. No preparation is needed. The scan itself takes only seconds. You receive detailed alignment images and a report that you can share with your treating clinician. Full details are on the FAQs page.
See how your knee really carries your weight
A short, free video consultation from home can help you decide if a standing EOS scan in London is the right next step for your PCL injury.
Book a free video consultationSources
- Schulz MS, Russe K, Weiler A, Eichhorn HJ, Strobel MJ. Epidemiology of posterior cruciate ligament injuries. Archives of Orthopaedic and Trauma Surgery. 2003;123(4):186-191.
- NHS. Knee ligament injuries. nhs.uk. Available at: https://www.nhs.uk/conditions/knee-ligament-surgery/
- Illés T, Somoskeöy S. The EOS imaging system and its uses in daily orthopaedic practice. International Orthopaedics. 2012;36(7):1405-1411.
Written by Abbas Dhami (Specialist Diagnostic Radiographer)
This page is general information and not a diagnosis.
ScanAlign is the trading name of CoreMed Solutions Ltd and operates under The Harley Street Hospital's CQC licence.