Posterior Cruciate Ligament Injuries

PCL injuries account for 3-40% of knee ligament injuries. Motor vehicle collisions are the most common cause; in sport the injury comes from football, soccer and skiing. Males are affected more often than females. Associated injuries are common, present in 60% or more.

Mechanism. The classic is the dashboard injury: the proximal tibia strikes the dashboard with the knee flexed, and the force drives the tibia posteriorly. After a dashboard injury, always check the vascular status. The other mechanisms:

• Fall on the flexed knee - a direct blow
• Hyperflexion - forced flexion
• Hyperextension - may also tear the PCL
• Sports contact - a direct blow to the tibia

Attachments. The PCL arises from the lateral aspect of the medial femoral condyle, within the notch, and inserts into the posterior intercondylar area of the tibia, in a depression below the plateau. It is 32-38mm long, and its cross-sectional area is greater than the ACL's.

Two bundles. The anterolateral (AL) bundle is the larger and is tight in flexion; the posteromedial (PM) bundle is smaller and tight in extension. The AL bundle is the primary restraint throughout the flexion range, and under load it fails first, followed by the PM bundle.

Blood supply. The middle genicular artery supplies the ligament. Its blood supply is better than the ACL's, which gives the PCL some healing capacity.

Function. The PCL is the primary restraint to posterior tibial translation, providing 95% of that restraint near full flexion. It is a secondary restraint to external rotation, and to varus and valgus in extension. Lose it and the tibia translates further posteriorly, and the kinematics of the knee become abnormal. The meniscofemoral ligaments, Humphrey (anterior) and Wrisberg (posterior), provide some backup to the PCL.

The posterolateral corner. The PLC is commonly injured with the PCL because the mechanism is similar: a varus and external rotation force injures both.

Grading. The injury is graded on the posterior drawer by the residual step-off: where the tibial plateau comes to rest relative to the femoral condyles.

Chronicity. Injuries are classified by the time since injury:

• Acute (within 3 weeks) - hemarthrosis, limited range of motion, an identifiable mechanism
• Subacute (3 weeks to 3 months) - the swelling has settled and the knee is easier to examine
• Chronic (over 3 months) - adaptive changes, possibly OA

Pattern. Combined injuries have worse outcomes if missed, so classify every injury by what else is torn:

• Isolated PCL - a single ligament
• PCL with PLC - the most common combination
• PCL with ACL - a floating knee equivalent
• Multiligament - a knee dislocation pattern, in which vascular assessment is critical

History. PCL injuries are often missed at first presentation. The pain is in the back of the knee and may be mild, the swelling is often less than after an ACL injury, and the instability shows going downstairs and on deceleration. Look for a subtle posterior sag; MRI confirms the diagnosis.

The step-off. With the knee flexed to 90 degrees, the anterior margin of the medial tibial plateau normally sits about 10mm in front of the femoral condyle. When the PCL is torn the tibia drops backwards under gravity and the step-off is lost; a posterior drawer force then displaces the tibia further back.

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Posterior sag sign. With the patient supine and the hip and knee at 90 degrees, observe the profile of the tibial tuberosity. A sagged tibia means a PCL injury.

Posterior drawer. The key test. With the patient supine and the knee at 90 degrees, first make sure the tibia has not already sagged, so that the test starts from a reduced position, then push the tibia posteriorly. Grade by the position of the tibial plateau relative to the femoral condyles, and compare with the other knee.

Quadriceps active test. From the 90/90 position the patient contracts the quadriceps. The test is positive when the tibia translates forward, reducing the posterior sag.

The rest of the examination. Perform the dial test at 30 and 90 degrees for the PLC, set out in the next section, and test varus and valgus to check the collaterals.

The false anterior drawer. The cardinal trap is to mistake a posterior sag for a positive anterior drawer, which is why the drawer starts from a reduced tibia and the two sides are always compared. The mimics separate as follows.

The dial test separates an isolated PLC injury from a combined PCL and PLC injury.

Technique. With the patient prone (preferred) or supine, flex the knee to 30 degrees, then to 90 degrees, and externally rotate both feet. Measure the thigh-foot angle and compare the two sides.

Threshold. An increase of more than about 10 to 15 degrees of external rotation over the normal side is positive. The side-to-side difference is the key, not the absolute angle.

Why 30 versus 90 degrees. At 30 degrees the posterolateral corner is the dominant restraint to external rotation, so an isolated PLC injury increases external rotation at 30 degrees only and the rotation normalises at 90. At 90 degrees the PCL becomes the principal restraint to external rotation, so if the increased rotation persists at 90 degrees the PCL must also be torn. A dial test positive at both angles therefore signals a combined injury, and shifts management toward reconstructing both the PCL and the PLC.

MRI. MRI is the gold standard for diagnosing a PCL injury, with a sensitivity of 99%+ and a very high specificity. Findings include increased signal, discontinuity and thickening; look for a bucket-handle appearance (a horizontal tear pattern) and assess both bundles.

Associated injuries. Always evaluate the PLC, the menisci, the cartilage and the other ligaments. MRI is essential for surgical planning and for identifying all the pathology.

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Radiographs. Plain films show a tibial insertion avulsion fracture. Weight-bearing views assess alignment and arthrosis.

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CT. CT gives detailed characterisation of an avulsion fracture for surgical planning.

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Stress radiography. A Telos device applies a standardised posterior force at 90 degrees and measures the translation; gravity kneeling views compare posterior translation bilaterally, and with standing views. Either gives an objective, numerical side-to-side measurement that is far more reproducible than the manual drawer.

What the number does. It quantifies the instability and grades the injury objectively, flags a likely combined injury when the difference is large, and gives a baseline for monitoring treatment, including graft laxity over time after reconstruction.

The decision. Grade the injury, decide whether it is isolated or combined, and check the PLC with the dial test. Isolated grade I-II injuries are treated conservatively. Combined injuries, with the PLC or ACL or with persistent instability, go to surgery that reconstructs all injured structures, and early: in a combined injury, early surgery prevents PLC contracture.

The isolated grade III knee. Consider surgery in an active patient with significant laxity; a low-demand patient may trial conservative treatment.

Nonoperative treatment. It suits isolated grade I-II injuries, the low-demand patient with grade III, and the patient who prefers it after counselling. The programme:

• Brace in extension initially
• Quadriceps strengthening, which prevents posterior sag
• No hamstring exercises, which increase the posterior force on the tibia
• Progressive return to activity

Absolute indications

• Combined PCL/PLC injury
• Multiligament injury
• Tibial avulsion fracture (fix the fragment)

Relative indications

• Isolated grade III in an active patient
• Failed conservative treatment
• Symptomatic chronic instability

Graft choice. Achilles allograft is the most common graft. BTB autograft offers stronger fixation, and hamstring autograft less morbidity.

Tunnels. The femoral tunnel is placed at the native PCL footprint and the tibial tunnel posteriorly. Double-bundle reconstruction may better restore rotation but is technically demanding, and all-inside techniques minimise dissection.

Combined PCL and PLC. An acute combined injury is reconstructed in a single stage; a chronic one may need staging, with the PLC first because of contracture. The order of surgery is to address the PCL first, then reconstruct the PLC, then tension in the appropriate position. Missing or undertreating the PLC leads to PCL graft failure.

Tibial avulsion. When the bone fragment is good, it is fixed, open or arthroscopically, rather than the ligament being reconstructed. The technique is a posterior approach with screw or suture anchor fixation. Fixation is anatomic and has healing potential, and the outcomes are usually excellent, with bony healing.

Protect the graft. Hamstring activation increases posterior tibial translation, so it is avoided early and the quadriceps are emphasised. The programme progresses more slowly than ACL rehabilitation.

Isolated injuries. Treated conservatively, many do well with rehabilitation, though some develop chronic laxity and OA over time. Reconstruction gives good outcomes in motivated patients, and return to sport is possible.

Combined injuries. Outcomes depend on addressing all the injured structures.

The long term. Chronic PCL deficiency may be well tolerated, but it risks patellofemoral and medial compartment OA. Patellofemoral OA is a common long-term sequela, and medial compartment OA is also increased with chronic laxity. The altered kinematics increase joint loading, and early intervention in combined injuries may prevent this.

Global Epidemiology

PCL injuries account for roughly 3-40% of acute knee ligament injuries depending on the population studied, with the higher proportions reported in trauma centres and the lower proportions in general sports clinics. Two distinct injury populations dominate worldwide: high-energy road-traffic trauma (the classic dashboard mechanism, and the predominant cause of displaced bony tibial avulsions in regions with high motorcycle/two-wheeler use such as parts of South and East Asia) and sporting contact injuries (football/soccer, rugby, skiing). Up to 60% of PCL injuries occur as part of a combined or multiligament injury pattern.

Side-by-Side Guidance

The substantive agreement across societies is greater than the disagreement: isolated grade I-II injuries are rehabilitated, while combined patterns and displaced bony avulsions are operated. Differences are largely emphasis (graft choice, single vs double bundle, timing) rather than principle.

Registry and Outcome Notes

• Unlike arthroplasty, PCL surgery is not captured by dedicated implant registries (NJR/AJRR/AOANJRR track joint replacement, not ligament reconstruction). Outcome evidence therefore comes from prospective cohorts and meta-analyses rather than national registries.
• The Danish and Norwegian knee-ligament reconstruction registries (which began with the ACL) increasingly capture PCL and multiligament procedures, and are emerging as the best population-level data source for revision and re-operation rates.

High- vs Limited-Resource Practice Variation