A PCL injury is a sprain or tear of the posterior cruciate ligament, a thick band of tissue deep inside your knee that prevents your shinbone from sliding too far backward beneath your thighbone. It’s one of the two cruciate ligaments in the knee (the other being the more well-known ACL), and while PCL tears are less talked about, they account for a significant share of acute knee injuries. Most isolated PCL injuries heal well without surgery, but higher-grade tears and those involving other ligaments can require reconstruction.
What the PCL Does
The posterior cruciate ligament sits inside the knee joint, crossing behind the anterior cruciate ligament to form an “X” shape. Its primary job is resisting posterior tibial translation, which in plain terms means it stops your lower leg bone from shifting backward relative to your upper leg bone. Every time you walk downhill, decelerate from a run, or land from a jump, the PCL is absorbing force and keeping the joint stable. When it tears, the knee loses that backward restraint, and the shinbone can sag posteriorly under load.
How PCL Injuries Happen
The classic mechanism is a direct blow to the front of a bent knee. The most common real-world scenario is a dashboard injury: during a car collision, your knee strikes the dashboard while bent, driving the shinbone backward and overloading the PCL. One study found that 57% of PCL injuries resulted from traffic accidents.
In sports, PCL tears happen during contact or falls. A football player landing on the front of a flexed knee with the foot pointed downward, or a soccer player colliding knee-first with the ground, can tear the ligament through the same backward-force mechanism. Falls onto a bent knee during basketball, rugby, or skiing follow the same pattern.
Grades of PCL Injury
PCL injuries are classified into three grades based on how far the shinbone displaces backward during examination:
- Grade I (partial tear): 1 to 5 mm of backward displacement. The shinbone still sits in front of the thighbone’s lower end. The ligament is stretched or partially torn but still functional.
- Grade II (complete isolated tear): 6 to 10 mm of displacement. The front of the shinbone sits flush with the thighbone. The PCL is fully torn, but no other ligaments are damaged.
- Grade III (complete tear with additional damage): More than 10 mm of displacement. The shinbone drops behind the thighbone, which typically signals that the joint capsule or other ligaments are also injured.
Symptoms to Recognize
PCL injuries don’t always announce themselves as dramatically as ACL tears. There’s usually no loud pop, and many people can still walk afterward. In the acute phase, you’ll notice joint swelling and pain that limits how far you can bend the knee, typically losing 10 to 20 degrees of deep flexion. The knee may feel vaguely unstable or “off” rather than buckling the way an ACL-deficient knee does.
Chronic PCL injuries tell a different story. Over weeks and months, the main complaint shifts to pain along the front and inner side of the knee rather than a sense of instability. You might notice increasing difficulty with slopes, stairs, or activities that load the knee in a bent position. This pain comes from altered joint mechanics forcing extra stress onto the kneecap and the inner compartment of the joint.
How a PCL Tear Is Diagnosed
The posterior drawer test is the most reliable hands-on exam for a PCL tear. With the knee bent to 90 degrees, a clinician pushes the upper shinbone backward and measures how far it travels. In one controlled, blinded study of sports medicine specialists, the posterior drawer test reached 90% sensitivity and 99% specificity, making it the standout among several physical tests.
MRI has become the gold standard for confirming a PCL tear and assessing its severity. One large study of over 200 patients with surgically confirmed diagnoses found MRI accuracy approaching 100%. MRI also reveals whether the meniscus, other ligaments, or cartilage are involved, which directly affects the treatment plan. In subtle or partial tears, stress X-rays taken with the knee bent to 70 to 90 degrees can sometimes detect displacement that physical exams miss.
Non-Surgical Treatment
Most isolated grade I and grade II PCL tears are managed without surgery. The approach centers on immobilization followed by progressive strengthening, and the results are generally good.
In the first two to four weeks, the knee is immobilized to prevent the shinbone from sagging backward while the ligament heals. Some protocols use a specialized PCL brace that pushes the upper shinbone forward. In one study using this type of dynamic brace, the average posterior sag dropped from 7.1 mm at injury to 2.3 mm at 12 months. Patients wore the brace for four months while bearing full weight and moving through a range of motion up to 110 degrees.
Quadriceps strengthening is the cornerstone of rehab. The quadriceps muscle on the front of the thigh actively pulls the shinbone forward, directly counteracting the backward drift that a torn PCL can no longer prevent. Early exercises include quad sets (tightening the thigh muscle while the leg is straight) and straight leg raises. If the quadriceps isn’t firing well on its own, electrical muscle stimulation can help jump-start activation. As strength builds, double-leg exercises like squats and leg presses are added but kept to no more than 70 degrees of knee bend to avoid stressing the healing ligament. Hip strengthening supplements the program by improving overall limb control and reducing load on the knee.
Before progressing to running, you need to demonstrate single-leg strength and stability, have no swelling, and be pain-free during functional activities.
When Surgery Is Needed
Surgery is reserved for specific situations: acute avulsion fractures (where the ligament pulls a chunk of bone off its attachment), grade III tears that don’t respond to rehab, and PCL tears combined with damage to other knee ligaments. Isolated grade I and II tears rarely require reconstruction.
PCL reconstruction replaces the torn ligament with a graft. Surgeons can use tissue from your own body (the patellar tendon, hamstring tendons, or quadriceps tendon) or donor tissue. Achilles tendon from a donor is currently the most commonly used graft for both acute and chronic PCL reconstructions, chosen for its large cross-sectional area and strength. When the PCL has pulled a bone fragment off the tibia, the fragment is reattached directly rather than replacing the ligament entirely.
Long-Term Joint Health
A PCL-deficient knee doesn’t just feel unstable. It changes how forces distribute across the joint over time. Biomechanical studies on cadaver knees show increased strain on both the medial and lateral menisci when the PCL is missing. This altered loading accelerates wear. In a nationwide population study, patients with PCL tears had a higher cumulative incidence of meniscus tears (1.13% vs. 0.22%), osteoarthritis (2.71% vs. 1.90%), and eventual knee replacement (0.91% vs. 0.62%) compared to people without PCL injuries. The differences are statistically significant, though the absolute numbers remain relatively low, especially for isolated injuries managed with good rehabilitation.
This is why consistent quadriceps strengthening matters long after the initial injury heals. A strong thigh muscle compensates for the lost ligament restraint, reduces abnormal joint loading, and helps protect the cartilage and menisci from accelerated breakdown over the years that follow.