The PCL, or posterior cruciate ligament, is one of four major ligaments that hold your knee together. It sits deep inside the knee joint, connecting your thighbone (femur) to your shinbone (tibia), and its main job is to prevent the shinbone from sliding too far backward. It’s less commonly injured than its better-known counterpart, the ACL, but PCL injuries can still cause significant knee instability and long-term problems if left unmanaged.
Where the PCL Is and What It Does
The PCL runs from the inner surface of the thighbone, near the end that forms the knee joint, down to the back of the shinbone about 1 centimeter below the joint line. It’s one of two ligaments that cross inside the knee (the other being the ACL), forming an “X” pattern that provides stability in multiple directions.
The PCL’s primary role is resisting backward movement of the shinbone relative to the thighbone. Every time you walk downhill, slow down from a run, or lower yourself into a squat, the PCL is under tension, keeping the bones properly aligned. It also acts as a secondary stabilizer against excessive knee rotation, particularly when the knee is bent between 90 and 120 degrees. Beyond that, it helps resist side-to-side forces and outward twisting of the lower leg. In short, the PCL quietly keeps your knee tracking correctly through a wide range of movements.
How PCL Injuries Happen
The most well-known mechanism for a PCL tear is the “dashboard injury.” In a car accident, the front of the shinbone strikes the dashboard with the knee bent, driving the shinbone backward and overstretching or tearing the ligament. The same force can occur in sports when an athlete falls directly onto a bent knee with the foot pointed downward, pushing the shinbone posteriorly.
Contact sports like football and rugby account for many athletic PCL injuries. A direct blow to the front of the knee during a tackle, a hyperextension injury from an awkward landing, or a combination of twisting and impact can all damage the PCL. Unlike ACL tears, which often involve a sudden pivot or deceleration, PCL injuries typically result from a direct force to the front of the knee or a fall onto a flexed knee.
Grading a PCL Tear
PCL injuries are classified into three grades based on how far the shinbone shifts backward when a doctor pushes on it:
- Grade I (partial tear): The shinbone shifts 1 to 5 millimeters backward but still sits in front of the thighbone’s lower end. The ligament is stretched or partially torn.
- Grade II (complete isolated tear): The shinbone shifts 6 to 10 millimeters backward and sits roughly flush with the thighbone. The PCL is fully torn, but the other knee ligaments are intact.
- Grade III (complete tear with additional damage): The shinbone shifts more than 10 millimeters backward and actually drops behind the thighbone. This level of displacement usually means other ligaments or structures in the knee are also injured.
Symptoms and Diagnosis
PCL tears are sometimes called the “silent” knee injury because their symptoms can be subtler than an ACL tear. You might feel vague pain and swelling in the back of the knee, a sense of instability when walking on uneven ground, or difficulty with stairs and slopes. Some people don’t realize anything is seriously wrong until weeks later, when persistent discomfort or a feeling of the knee “giving way” prompts them to seek evaluation.
The most reliable physical exam for detecting a PCL tear is the posterior drawer test: a doctor bends your knee to 90 degrees and pushes the upper shinbone backward to see how far it moves. This test has about 90% sensitivity and 99% specificity for detecting PCL laxity, making it highly accurate overall. For milder Grade I tears, though, the sensitivity drops to about 70%, meaning some partial tears can be missed on physical exam alone. Another simple bedside check is the “sag sign,” where the doctor observes whether your shinbone visibly drops backward when the knee is bent and relaxed.
MRI is typically used to confirm the diagnosis, determine whether the tear is partial or complete, and check for damage to other structures like the meniscus or surrounding ligaments.
Treatment: Surgery vs. Rehabilitation
Most isolated Grade I and Grade II PCL tears are treated without surgery. The ligament has a better blood supply than the ACL, which gives it more healing potential. Non-operative treatment centers on structured physical therapy to strengthen the muscles around the knee, particularly the quadriceps, which can compensate for a weakened PCL by resisting backward tibial movement.
Surgery is typically reserved for three scenarios: the PCL has torn along with other knee ligaments, a piece of bone has broken away where the ligament attaches (an avulsion fracture), or an isolated Grade III tear hasn’t improved with rehabilitation. When surgery is needed, the torn ligament is reconstructed using a graft, either from your own tissue or from a donor.
Recovery Timeline
Recovery follows a phased approach regardless of whether you have surgery, but the timelines differ significantly. With conservative (non-surgical) management, sport-specific exercises can begin around 2 to 3 months, and full return to sports is typically possible at 4 to 6 months.
After surgical reconstruction, the timeline stretches considerably. Rehabilitation progresses through five phases spanning more than six months. Sport-specific training usually begins at 6 to 7 months, and most surgeons recommend waiting a full 9 to 12 months before returning to competitive athletics. The initial weeks focus on protecting the graft and restoring range of motion, then gradually shift toward strengthening, balance training, and sport-specific drills. Non-athletic individuals are generally cleared for normal daily activity around 6 months post-surgery.
Long-Term Effects of a PCL Tear
A PCL tear does raise the risk of knee problems down the road, though the numbers may be lower than many people expect. In a large population-based study, 2.71% of people with PCL tears developed knee osteoarthritis during follow-up, compared to 1.90% of matched individuals without PCL injuries. Meniscus tears were also more common: 1.13% in the PCL injury group versus 0.22% in controls.
Reconstruction appears to lower these risks. Among those who had PCL surgery, the rate of subsequent osteoarthritis was 2.30%, compared to 3.46% in those whose tears were not reconstructed. The rate of eventually needing a knee replacement also dropped, from 1.69% without reconstruction to 0.48% with it. These findings suggest that for more severe tears, surgical repair may offer meaningful long-term joint protection, even if the short-term recovery is more demanding.