PCL Injuries — Diagnosis & Management

The posterior cruciate ligament (PCL) is the strongest ligament in the knee — approximately 1.3–2× as thick and twice as strong as the ACL — yet it is less frequently injured. It courses from the lateral aspect of the medial femoral condyle in the intercondylar notch to the posterior aspect of the tibial plateau, approximately 1 cm below the articular surface. Its primary function is to resist posterior tibial translation relative to the femur; it also provides secondary restraint to varus, valgus, and external rotation. PCL injuries occur in approximately 3–20% of all knee ligament injuries and are frequently associated with other ligamentous injuries (combined in 85% of cases). Isolated PCL injuries often go unrecognised — their natural history and the indications for surgical reconstruction remain more controversial than for ACL injuries.

• PCL anatomy — two bundles: the anterolateral bundle (ALB) — larger, primary bundle; tight in flexion; the main restraint to posterior tibial translation at 90° flexion; the posteromedial bundle (PMB) — smaller; tight in full extension; contributes to rotational stability; most PCL reconstructions aim to restore the ALB; double-bundle PCL reconstruction (restoring both ALB and PMB) is technically possible but evidence for superiority over single-bundle is limited; the PCL is extrasynovial but intracapsular (unlike the ACL which is intrasynovial); its extrasynovial position gives it a better blood supply and enhanced healing potential compared to the ACL — this is why isolated PCL injuries have a higher rate of satisfactory non-operative healing
• Mechanisms of injury: (1) dashboard injury — the most common; a direct posteriorly directed force applied to the proximal anterior tibia with the knee flexed at 90° (e.g., knee hitting the dashboard in a motor vehicle collision); (2) fall on a flexed knee with the foot in plantarflexion; (3) hyperextension of the knee; (4) combined valgus/varus with rotation (associated multi-ligament injury); vehicular accidents account for ~45% and sports injuries ~40% of PCL tears
• Associated injuries in PCL tears: isolated PCL injury occurs in only ~15% of cases; combined injuries (84.7%) most commonly include ACL (48.2%), posterolateral corner (PLC) structures (popliteus, popliteofibular ligament, lateral collateral ligament), posteromedial corner (PMC), and medial collateral ligament; knee dislocation carries a 25% incidence of nerve injury (common peroneal nerve most vulnerable — assess for foot drop) and 18% incidence of vascular injury (popliteal artery — must exclude with vascular assessment and CT angiography or ABI measurement)

• PCL injury grading (posterior tibial translation vs contralateral): Grade I (partial tear) — 1–5 mm increased posterior translation; tibia remains anterior to femoral condyles on lateral view; Grade II (complete isolated PCL tear) — 6–10 mm increased posterior tibial translation; tibia flush with or just posterior to femoral condyles; Grade III (complete PCL tear with associated ligamentous injury) — >10 mm posterior translation; tibia lies posterior to femoral condyles; Grade III virtually always indicates combined ligamentous injury (PLC, PMC, ACL, or multi-ligament knee injury); the grade determines management — Grade I–II isolated tears are predominantly managed non-operatively; Grade III or combined injuries are more likely to require surgical reconstruction
• Clinical examination — key tests: (1) Posterior drawer test — the most sensitive and specific clinical test for PCL injury (sensitivity ~90%); with the knee at 90° flexion and foot stabilised, the examiner pushes the tibia posteriorly; increased posterior translation relative to the contralateral side indicates PCL injury; a positive posterior drawer test in the presence of a normal-feeling ACL (no anterior laxity on Lachman) suggests isolated PCL injury; (2) Posterior sag sign (Godfrey`s test) — with both hips and knees at 90° flexion in the supine patient, the PCL-deficient tibia sags posteriorly under gravity — the tibial tuberosity drops inferiorly relative to the contralateral side; (3) Quadriceps active test — with the knee at 90°, the patient contracts the quadriceps against resistance; in PCL deficiency the tibia reduces anteriorly from its posteriorly sagged position (the quadriceps pull the tibia anteriorly — this is diagnostic of PCL injury)
• Assessment of posterior tibial sag: before performing the posterior drawer test, the examiner must establish whether the tibia is already posteriorly sagged (if sagged, even a normal anterior drawer could be misinterpreted as a positive ACL test — the `false-positive anterior drawer`); look for the posterior sag sign first; if present, the anterior draw is unreliable for ACL assessment until the sag is corrected

• Plain radiographs: AP and lateral knee; assess for tibial avulsion fracture at the PCL tibial insertion (a bony PCL avulsion is visible as a small flake of bone at the posterior tibia on the lateral view); Segond fracture (lateral tibial plateau avulsion — indicates ACL tear, not PCL); joint space for associated bone injury; stress radiographs (kneeling view — the patient kneels on the affected knee and a lateral X-ray is taken; gravity causes posterior tibial subluxation in PCL deficiency; posterior tibial translation ≥8 mm compared to contralateral knee = PCL deficiency; the Telos stress device is an alternative standardised method)
• MRI — gold standard: accuracy 96–100% for PCL tears; sagittal T2-weighted images are the primary sequence; the normal PCL appears as a smooth, homogeneous, low-signal curved band; a torn PCL on MRI: (1) high T2 signal within the ligament substance (oedema/haemorrhage — acute injury); (2) apparent thickening — an AP diameter >7 mm on sagittal T2-weighted images is highly suggestive of a ruptured PCL (the torn ligament maintains continuity as a single thickened structure in 62% of acute tears — it does not gap like an ACL); (3) frank discontinuity (complete disruption — less common); (4) bony tibial avulsion — cortical flake at the posterior tibial insertion with retracted ligament; IMPORTANT: chronic PCL tears are easily missed on MRI — the ligament scars in continuity and may appear grossly intact despite functional laxity; quantitative T2 mapping and stress radiographs help in this scenario
• CT: limited role for isolated PCL soft tissue injury; useful for characterising bony avulsion fractures (PCL tibial avulsion — size of bony fragment, degree of displacement, planning for ORIF); CT angiography for suspected vascular injury in knee dislocation
• Vascular assessment in knee dislocation / high-grade PCL injury: ankle-brachial index (ABI) <0.9 = vascular injury requiring CTA; ABI >0.9 with normal pulses = low risk; popliteal artery injury can occur with a soft ABI (intimal tear without occlusion) — serial vascular assessment over 24–48 hours is prudent in high-energy injuries

• Graft choices: bone-patellar tendon-bone (BPTB) — historically preferred for PCL reconstruction due to reliable bone-to-bone healing at the femoral and tibial tunnels; hamstring tendon (4-strand semitendinosus/gracilis) — popular alternative; allograft (Achilles tendon, BPTB allograft) — commonly used for PCL reconstruction particularly in combined multi-ligament injuries where multiple graft sources are needed; the PCL tibial tunnel is the most technically demanding part of the reconstruction due to the proximity of the posterior neurovascular structures — the popliteal artery and tibial nerve lie immediately posterior to the tibial PCL footprint; the `killer turn` — the acute angle the graft must make at the posterior tibial tunnel exit is a recognised cause of graft stress and failure in PCL reconstruction
• Tibial inlay technique: an alternative to the transtibial tunnel technique; a bone block graft is placed directly into a trough at the posterior tibial PCL footprint (avoiding the need for a posterior tibial tunnel) — eliminates the `killer turn`; requires prone positioning with a posterior approach to the knee; less commonly used due to technical complexity but biomechanically addresses the graft angulation problem
• The `kill zone` / posterior capsule risk: when reaming the tibial PCL tunnel, the drill exits through the posterior cortex of the tibia; the popliteal artery is at risk; a PCL drill guide is used to protect the posterior structures; intraoperative fluoroscopy confirms guide pin position; the transseptal portal approach to the tibial tunnel (through the posterior capsule via an arthroscopic transseptal window) was developed to improve visualisation and reduce neurovascular risk
• Post-operative rehabilitation: weight-bearing as tolerated in a brace locked in extension (prevents posterior sag); hamstring activation delayed for 6–8 weeks; quadriceps strengthening commenced early; return to sport typically 9–12 months (slower than ACL reconstruction due to the challenges of PCL graft healing)

• PCL anatomy: lateral aspect of medial femoral condyle → posterior tibial plateau 1 cm below articular surface; ALB (larger, flexion-tight) + PMB (smaller, extension-tight); extrasynovial → better blood supply → superior healing potential vs ACL
• Mechanism: dashboard injury most common (posterior force on flexed knee); fall on flexed knee with plantarflexed foot; hyperextension; 85% combined injuries — ACL (48%), PLC, PMC most common partners
• Grading: I (1–5 mm) — partial, non-op; II (6–10 mm) — complete isolated, non-op; III (>10 mm) — complete + associated ligament injury, likely surgical; tibia posterior to femoral condyles on lateral = Grade III
• Posterior drawer test: most sensitive/specific clinical test (~90% sensitivity); 90° flexion, push tibia posteriorly; assess posterior sag sign FIRST to avoid false-positive anterior drawer
• Posterior sag sign (Godfrey): tibia drops posteriorly at 90° hip/knee flexion under gravity; Quadriceps active test: quad contraction at 90° reduces posteriorly sagged tibia anteriorly = diagnostic of PCL deficiency
• MRI PCL tear: AP diameter >7 mm on sagittal T2 = ruptured PCL; 62% of acute tears maintain continuity (thickened, not gapped); chronic tears scar in continuity — easily missed on standard MRI; stress radiographs confirm; bony avulsion = cortical flake at posterior tibia
• Knee dislocation: 25% nerve injury (common peroneal — foot drop); 18% vascular injury (popliteal artery); ABI <0.9 → CT angiography; serial vascular assessment 24–48 hours
• Non-operative success for Grade I–II: brace in extension; quad strengthening; avoid hamstrings; PCL heals better than ACL due to blood supply; satisfactory outcomes in most isolated low-grade tears
• Bony tibial avulsion: ORIF with screw fixation; superior to reconstruction (native PCL intact); acute surgery preferred
• Surgical pearls: `killer turn` at posterior tibial tunnel = graft stress/failure risk; tibial inlay eliminates this; protect popliteal artery during tibial tunnel drilling; combined PCL + PLC = unstable, always surgical