I. What is the Posterior Cruciate Ligament (PCL)?
The posterior cruciate ligament (PCL) is the largest and strongest ligament in the knee joint. Together with the anterior cruciate ligament (ACL), it forms the core cruciate ligament system of the knee joint, crossing in an “X” shape inside the knee. The PCL originates from the lateral surface of the medial femoral condyle, running obliquely posterolaterally, and inserts posterior to the intercondylar eminence of the tibia.
The PCL consists of two bundles of fibers with different functions: the larger anterolateral bundle (accounting for approximately 95% of the ligament volume) and the smaller posteromedial bundle (accounting for approximately 5%). The anterolateral bundle is most taut when the knee is flexed at approximately 70°, while the posteromedial bundle plays a major role near extension. This intricate fiber arrangement allows the PCL to continuously provide stable posterior support at various angles of the knee joint.
The peristaltic ligament (PCL) is the primary structure limiting posterior displacement of the tibia relative to the femur, especially when the knee is flexed beyond 30°, providing approximately 95% of the resistance to posterior tibial displacement. Furthermore, the PCL provides rotational stability when the knee is flexed beyond 90°. In short, the PCL is the “first line of defense” for posterior knee stability.
II. Mechanisms of PCL Injuries
PCL injuries are not the most common type of knee ligament injury—accounting for about 3% of outpatient knee injuries—but can reach as high as 38% in acute traumatic knee hematoma. The PCL is the least likely knee ligament to be injured during exercise; the vast majority of PCL injuries are accompanied by damage to other knee ligaments or structures, and isolated PCL injuries are relatively rare.
The classic mechanism of a PCL injury is that an external force acts directly on the anterior aspect of the tibia, subjecting the tibia to a posterior impact force. The most common scenarios include:
Car accident injuries: also known as “dashboard injuries”—when a passenger’s bent knee strikes the car’s dashboard during sudden braking or a collision, the upper tibia receives a backward force, resulting in a PCL tear.
Sports injuries: athletes fall forward with their knees bent, causing the tibial tuberosity to directly impact the ground. This is common in sports such as American football, rugby, basketball, and skiing. Additionally, sudden deceleration or change of direction while running, with the foot fixed to the ground, can also cause PCL injuries without direct impact.
Hyperextension injuries: when the knee joint is forcibly and passively extended, the PCL may also suffer traction injuries.
III. Injury Grading
PCL injuries are generally classified into three grades based on severity:
Grade I (Mild): The ligament has only microscopic tears; the ligament is stretched but the overall structure remains intact, and knee joint stability is largely unaffected.
Grade II (Moderate): Partial ligament tear; the knee joint exhibits mild to moderate laxity and instability. Under stress testing, the posterior displacement of the tibia is 5–10 mm.
Grade III (Severe): Complete ligament rupture or avulsion of the ligament from its bony insertion, resulting in significant knee instability. The tibia shifts posteriorly by more than 10 mm. Grade III injuries typically require substantial external force and are often accompanied by damage to the ACL, collateral ligaments, or other knee joint structures.
IV. Clinical Manifestations and Diagnosis
The symptoms of PCL injuries are sometimes atypical, which can lead to missed diagnoses. Common manifestations include: mild knee swelling, posterior knee pain (worsened by kneeling), and anterior knee pain during running or deceleration (which may appear one to two weeks after the injury). Many athletes can continue competing even after an injury, only realizing later that their knee is “not right.”
In physical examination, the posterior drawer test is the most sensitive and specific method for diagnosing PCL injuries. The physician flexes the patient’s knee to 90° and pushes the tibia posteriorly; if the tibia shifts significantly posteriorly compared to the contralateral side, it suggests a PCL injury.
In terms of imaging, MRI is the gold standard for diagnosing PCL injuries, clearly showing the location and extent of ligament damage. Stress radiographs can objectively assess the degree of posterior tibial displacement and are of significant value in determining the need for surgery. Plain radiographs are valuable for diagnosing avulsion fractures at the ligament insertion point.
V. Treatment Strategies
The choice of treatment plan for PCL injuries requires comprehensive consideration of factors such as injury grade, presence of other injuries, patient age, and exercise needs.
Conservative treatment is suitable for grade I and II isolated PCL injuries. Due to the rich blood supply to the PCL and its strong self-healing ability, conservative treatment often achieves good results. The core components of conservative treatment include: early bracing and immobilization (usually around 6 weeks), control of swelling and pain, and systematic rehabilitation training. The focus of rehabilitation training is quadriceps strengthening exercises while delaying hamstring activation to avoid posterior tibial pull from hamstring contraction during early training, which could worsen ligament damage. Studies show that with physical therapy-guided exercise and bracing intervention, patient-reported outcomes can significantly improve during long-term follow-up.
Surgical treatment is suitable for patients with grade III complete injuries, multiple ligament injuries, or significant instability after conservative treatment. Currently, the mainstream surgical procedure is arthroscopic PCL reconstruction, which can be divided into single-bundle reconstruction and double-bundle reconstruction based on the number of reconstructed bundles. Studies have shown that anatomical double-bundle reconstruction can better restore the original ligament coverage area and normal knee joint kinematics. For isolated PCL injuries with posterior tibial displacement ≥10mm, surgical reconstruction is a clear indication.
VI. Prognosis and Long-Term Impacts
If PCL injuries are not properly treated, they can lead to long-term adverse consequences. PCL dysfunction alters knee joint kinematics, leading to increased load on the medial compartment and patellofemoral joint, thereby accelerating articular cartilage degeneration. Studies have reported that the incidence of medial femoral condyle cartilage degeneration can reach 77.8% five years after a PCL defect.
However, the treatment of PCL injuries remains one of the most controversial topics in knee surgery. There is still no complete consensus on the indications for surgical versus non-surgical treatment, optimal surgical techniques (single-bundle vs. double-bundle, transtibial tunnel vs. tibial embedding fixation, graft selection, etc.). By 2025, experts from 17 countries had reached 11 consensus statements on PCL injury management, laying the foundation for evidence-based guidelines.
Overall, most isolated PCL injuries can achieve good outcomes with standardized conservative treatment. For younger patients, those with high athletic demands, or those with multiple ligament injuries, surgical reconstruction is an effective means of restoring knee joint stability and function. Regardless of the treatment method, systematic and scientific rehabilitation training is a crucial factor in determining the final outcome.