Posterior cruciate ligament injuries of the knee

1. High-Yield Summary

• Primary Posterior Stabilizer: The posterior cruciate ligament (PCL) is the primary restraint to posterior tibial translation, contributing up to 95% of total posterior restraining force at 90 degrees of knee flexion.
• Dual-Bundle Anatomy: Consists of a robust anterolateral (AL) bundle (larger, taut in flexion) and a posteromedial (PM) bundle (smaller, taut in extension), augmented by variable meniscofemoral ligaments (Humphry and Wrisberg).
• Objective Grading Benchmark: Evaluated primarily via the posterior drawer test at 90 degrees flexion. Normal tibial plateau sits 10 mm anterior to the medial femoral condyle. Grade I: 1 to 5 mm posterior translation (step-off preserved); Grade II: 6 to 10 mm posterior translation (tibia flush with condyles); Grade III: >10 mm posterior translation (tibia subluxates posterior to condyles, indicating combined multiligament or posterolateral corner injury).
• Management Paradigm: Isolated Grade I and II tears heal predictably with nonoperative therapy utilizing dynamic anterior-drawer knee bracing and quadriceps strengthening. Grade III tears, multiligament disruptions, or failed conservative therapy warrant anatomical surgical reconstruction.
• Neurovascular Safety Corridors: The popliteal artery lies within 5 to 10 mm of the tibial insertion footprint at 90 degrees of flexion, demanding mandatory fluoroscopic depth control, posterior capsular visualization, and protective retro-tibial instrumentation during tunnel reaming.

2. Anatomy

The posterior cruciate ligament originates from a broad, semicircular footprint on the anterolateral aspect of the medial femoral condyle within the intercondylar notch and courses posteroinferiorly and laterally to insert into a distinct facet on the central posterior tibia, approximately 10 to 15 mm distal to the joint line. The PCL possesses an average length of 38 mm and a mean midsubstance cross-sectional area of 60 mm², making it substantially thicker and stronger (ultimate tensile strength approximately 2500 to 3000 N) than the anterior cruciate ligament.

Functional Dual-Bundle Architecture

• Anterolateral (AL) Bundle: Represents approximately 65% of the ligament cross-sectional area. It originates from the cephalad, anterior portion of the femoral attachment and inserts on the anterolateral aspect of the tibial PCL facet. The AL bundle tightens in mid-to-deep knee flexion (peak tension at 70° to 90°) and relaxes in extension, resisting high-load posterior displacement during functional athletic maneuvers.
• Posteromedial (PM) Bundle: Represents roughly 35% of the ligament volume. It originates posteroinferiorly on the medial femoral condyle and inserts postero-medially on the tibial facet. The PM bundle becomes taut in terminal extension and deep hyperflexion (>120°), resisting posterior translation at low flexion angles.
• Meniscofemoral Ligaments: Arise from the posterior horn of the lateral meniscus and insert onto the lateral aspect of the medial femoral condyle. The anterior meniscofemoral ligament of Humphry passes anterior to the PCL, whereas the posterior meniscofemoral ligament of Wrisberg passes posterior to the PCL. Present in up to 70% to 80% of individuals, these structures provide significant secondary restraint to posterior translation.

Neurovascular Danger Zones and Surgical Corridors

The central posterior tibial anatomy presents a critical neurovascular danger zone. The popliteal artery and popliteal vein course in close proximity to the posterior knee joint capsule and the PCL tibial insertion. In full knee extension, the popliteal artery is tethered and lies as close as 2 to 3 mm from the posterior cortex. Flexing the knee to 90 degrees allows the popliteal neurovascular bundle to fall posteriorly away from the bone, expanding the clearance to approximately 5 to 10 mm. However, this safety corridor remains narrow. The middle genicular artery branches directly from the popliteal artery at the level of the joint line, penetrating the posterior capsule to supply the cruciate ligaments and synovium.

When performing open posterior procedures (such as tibial inlay fixation or open avulsion repair), the posteromedial approach uses the internervous plane between the semimembranosus/semitendinosus (supplied by the tibial nerve) and the medial head of the gastrocnemius (also supplied by the tibial nerve, but with separate motor branch entry proximal to the incision). Blunt retraction of the medial gastrocnemius lateralward provides safe protection for the popliteal bundle.

3. Pathogenesis

PCL injuries result from high-energy direct impacts or complex athletic deceleration traumas that apply posterior translation forces to the proximal tibia or drive the joint into extreme non-physiological arcs.

• Dashboard Mechanism: The classic trauma vector occurs during motor vehicle collisions when an unrestrained occupant’s flexed knee impacts the dashboard, driving the proximal tibia posteriorly relative to the femur while the knee is flexed at 90 degrees. This directly stresses and ruptures the taut AL bundle and capsule.
• Hyperflexion Trauma: A frequent athletic injury vector encountered in football, rugby, or wrestling. The athlete falls onto a flexed knee with the foot in fixed plantarflexion. The tibial tuberosity strikes the ground first, forcing the tibia posteriorly under bodyweight while the knee is driven into forced hyperflexion.
• Severe Hyperextension: Forced hyperextension causes initial failure of the anterior cruciate ligament and posterior capsule; persistent hyperextension or concomitant varus/valgus torque then ruptures the PCL.
• High-Energy Knee Dislocation: Multiligament knee injuries (Schenck KD classifications) involve simultaneous disruption of the PCL and ACL with one or both collateral ligament complexes, often with complete posterior capsular tearing. These high-energy disruptions carry up to a 20% to 40% risk of popliteal artery intimal tear or transection.

4. Natural History

PCL disruptions constitute between 3% and 20% of all acute knee ligament injuries. True isolated PCL tears account for approximately 40% of cases, whereas over 60% occur in combination with other ligamentous, meniscal, or chondral injuries. Because the PCL has an extensive vascular envelope supplied by the middle genicular artery and is surrounded by a rich synovial sleeve, isolated partial (Grade I) and isolated complete (Grade II) tears exhibit substantial spontaneous healing potential without surgical intervention.

Conversely, persistent Grade III PCL deficiency or combined PCL and posterolateral corner (PLC) laxity leads to altered knee kinematics. Chronic posterior tibial subluxation shifts the contact centroid, dramatically increasing joint contact pressures within the medial femoral condyle and the patellofemoral joint. Long-term natural history cohorts demonstrate that untreated high-grade posterior instability results in progressive medial compartment and patellofemoral chondral wear, with symptomatic arthrosis developing over 10 to 20 years.

5. Clinical Presentation

Patient History

Patients present following motor vehicle trauma, falls onto a flexed knee, or athletic contact collisions. Unlike acute ACL ruptures, patients with isolated PCL tears frequently do not describe an audible “pop” or immediate catastrophic joint giveaway. Instead, presenting symptoms include diffuse posterior popliteal pain, mild-to-moderate effusion, and difficulty decelerating or descending stairs. In chronic cases, the chief complaint is anterior knee pain (patellofemoral overload) rather than acute instability during rotational cutting.

Physical Examination & Provocative Maneuvers

Examination begins with visual inspection of the anterior tibial profile with the knees flexed to 90 degrees. Provocative maneuvers must be systematically evaluated against the contralateral uninjured knee:

6. Imaging and Diagnostic Studies

A structured diagnostic pathway combines standard plain radiographs, objective stress imaging, and advanced magnetic resonance imaging:

• Plain Radiographs: Standard AP, true lateral, and skyline/Merchant views. Radiographs identify associated fractures, such as a bony PCL tibial avulsion, arcuate complex avulsion (fibular head fracture), or Segond fracture. Chronic cases may reveal medial compartment joint space narrowing, posterior tibial subluxation, and patellofemoral osteophytes.
• Stress Radiography (Telos or Kneeling Views): The definitive objective gold standard for quantifying posterior laxity. Bilateral comparative lateral views are obtained under standardized 15 to 20 daN posterior loads or active kneeling. Side-to-side displacement difference defines severity: Partial tears exhibit <8 mm difference; complete isolated PCL tears display 8 to 12 mm difference; combined PCL and posterolateral corner injuries exhibit >12 mm difference.
• Magnetic Resonance Imaging (MRI): MRI possesses a sensitivity and specificity exceeding 95% for acute PCL injuries. On sagittal T1- and T2-weighted sequences, an acute tear demonstrates disruption of the normal low-signal black band, with diffuse hyperintense signal, thickening, or discontinuous contour. In chronic tears, the ligament may appear fibrously continuous but stretched and redundant, emphasizing why stress radiography is indispensable for functional grading. MRI additionally assesses meniscal root attachments, chondral shearing, and associated collateral ligament complexes.

7. Classification

Classification of PCL injuries is based on the degree of posterior tibial translation elicited on physical examination at 90 degrees of knee flexion, quantified by objective stress radiography, and categorized by chronicity and associated structural damage:

8. Treatment

Nonoperative Management

Nonoperative treatment represents the gold standard for acute isolated Grade I and Grade II PCL injuries. Due to the intrinsic healing capacity of the vascularized synovial sheath, conservative rehabilitation yields high rates of patient satisfaction and predictable return to sport.

• Bracing Protocol: Immobilization in full extension or in a specialized dynamic PCL brace (e.g., dynamic anterior counterforce brace) for 4 to 6 weeks. The dynamic brace applies a continuous anterior translation force to the posterior proximal calf that increases as the knee flexes, neutralizing posterior gravitational sag and unloading the healing ligament fibers.
• Quadriceps Activation: Immediate isometric quadriceps strengthening and straight leg raises in the brace. The quadriceps functions as a primary dynamic agonist to the PCL, pulling the tibia anteriorly.
• Hamstring Restriction: Active, isolated open-chain hamstring exercises are strictly prohibited for at least 6 to 12 weeks. Hamstring contraction generates high posterior shear forces that displace the proximal tibia posteriorly, disrupting the healing fibrous callus.

Operative Management

Surgical intervention is directed at eliminating pathological posterior tibial subluxation, restoring native joint kinematics, and protecting the medial and patellofemoral compartments from degenerative wear.

• Transtibial Reconstruction: The most widely utilized technique. An arthroscopic femoral tunnel is drilled in the anatomical AL footprint. A tibial tunnel is created starting on the anteromedial proximal tibia and exiting at the central PCL facet on the posterior tibia under direct fluoroscopic guidance. While reproducible, graft passage around the acute angle at the posterior tibial aperture (“killer turn”) creates concentrated shear stress that can cause graft attenuation over time.
• Tibial Inlay Technique: Performed through a limited open posteromedial approach with the patient in the lateral decubitus or prone position. A bone block attached to the graft is rigidly secured directly into a prepared trough at the anatomic posterior tibial PCL facet using bicortical lag screws. This technique completely eliminates the killer turn and ensures direct bone-to-bone fixation.
• Single-Bundle vs. Double-Bundle Reconstruction: Single-bundle reconstruction restores the dominant AL bundle, tensioned at 90 degrees of flexion. Double-bundle reconstruction anatomically replaces both the AL and PM bundles using two femoral tunnels and either one or two tibial tunnels. Double-bundle reconstruction restores knee kinematics closer to the uninjured state across full range of motion in biomechanical models, though clinical registries show comparable patient-reported outcomes.
• Graft Selection: Robust grafts with high structural stiffness are mandatory. Options include bone-patellar tendon-bone (BTB) autograft, quadriceps tendon with bone block, doubled hamstring tendons, or thick allografts (Achilles tendon with bone block, patellar tendon, or tibialis anterior). Allografts are favored in multiligament reconstructions to avoid donor site morbidity.
• Bony Avulsion Fixation: Displaced bony avulsions (>2 to 3 mm displacement) should be managed with acute anatomical reduction and rigid internal fixation using 3.5 mm or 4.0 mm cannulated cancellous lag screws with washers, or high-strength suture bridge construct.

Indications & Contraindications

Absolute Indications for Surgery:

• Acute Grade III PCL injuries with gross instability (>10 mm posterior translation on drawer or >12 mm on stress views).
• Combined multiligament injuries (PCL + PLC, PCL + ACL, or knee dislocations).
• Displaced bony PCL avulsion fractures (>2 to 3 mm displacement or articular incongruity).
• Failed nonoperative management with persistent symptomatic instability, functional limitation, or dynamic posterior sag.

Contraindications to Reconstruction:

• Advanced tricompartmental osteoarthritis (Kellgren-Lawrence Grade 3–4).
• Severe uncorrected varus or valgus malalignment (coronal malalignment must be corrected with osteotomy prior to or concurrently with ligament reconstruction).
• Active localized or systemic infection.
• Inability to comply with strict postoperative non-weight-bearing and bracing rehabilitation.

9. Outcome

Modern operative and nonoperative management strategies yield favorable clinical and functional outcomes when adhering to strict treatment algorithms:

• Nonoperative Outcomes: Long-term follow-up studies of isolated Grade I and II tears demonstrate mean subjective IKDC scores of 85 to 90 and high rates of athletic return. Residual radiographic laxity does not strongly correlate with subjective disability in low-to-moderate demand cohorts, provided quadriceps strength is preserved.
• Reconstruction Functional Scores: Both single-bundle and double-bundle PCL reconstructions provide statistically significant and clinically meaningful improvements in Lysholm scores (improving from 40–50 preoperatively to 80–90 postoperatively), subjective IKDC scores, and Tegner activity levels.
• Joint Preservation: Restoring posterior stability unloads the patellofemoral articulation and medial compartment. Successful stabilization decelerates chondral deterioration and reduces the long-term risk of secondary meniscal tears.

10. Complications

Complications associated with PCL management can be divided chronologically into intraoperative, early postoperative, and late structural issues:

11. Pearls and Pitfalls

• The Anterior Step-Off Rule: During graft fixation, the tibia must be actively pulled anteriorly into its normal anatomic relationship (medial tibial plateau 10 mm anterior to the medial femoral condyle) at 90 degrees of flexion before locking the graft. Tensioning the graft while the tibia remains posteriorly subluxated permanently captures the knee in posterior sag and guarantees clinical failure.
• Beware the False-Positive Lachman: A patient with an intact ACL and a ruptured PCL starts with the tibia resting posteriorly subluxated. An inexperienced examiner applying an anterior drawer or Lachman maneuver pulls the subluxated tibia back to neutral and misinterprets this motion as anterior cruciate laxity. Always palpate the resting tibial step-off before performing cruciate testing.
• Always Interrogate the Posterolateral Corner: Isolated PCL reconstruction in the presence of an unrecognized Grade II or III posterolateral corner (PLC) injury leads to catastrophic graft failure. The unconstrained rotatory torque stretches out the PCL graft. If the Dial test demonstrates increased external rotation, the PLC must be repaired or reconstructed concurrently.
• Coronal Alignment Dictates Survivorship: In chronic PCL deficiency accompanied by varus malalignment, the mechanical axis passes through the medial compartment, opening the lateral side and imposing excessive tensile load on the PCL graft. Coronal alignment must be corrected with a valgus high tibial osteotomy (HTO) prior to or simultaneously with ligament reconstruction.
• Fluoroscopic Depth Protection: Never advance a tibial guide pin or cannulated reamer without real-time lateral fluoroscopic imaging. A finger or metallic safety shield placed through a posteromedial portal directly behind the posterior tibial cortex confirms safe tool clearance.

12. Controversy

Several clinical debates remain active regarding optimal PCL reconstruction strategies:

• Single-Bundle versus Double-Bundle Reconstruction: Biomechanical investigations consistently demonstrate that anatomic double-bundle reconstruction restores normal knee kinematics and posterior stability across full flexion more closely than single-bundle techniques. However, large clinical trials and systematic reviews indicate that subjective patient-reported outcome measures (Lysholm, IKDC) and failure rates do not significantly differ between single-bundle and double-bundle cohorts at long-term follow-up. The added complexity, operative time, and cost of double-bundle surgery remain debated.
• Transtibial versus Tibial Inlay Technique: The transtibial approach is less invasive and avoids patient repositioning, but creates the “killer turn” at the posterior tibial aperture that may induce graft fraying and attenuation. The tibial inlay technique eliminates the killer turn and provides direct bone-to-bone fixation, but requires an open posterior exposure with increased operative morbidity. High-level comparative clinical trials have demonstrated comparable long-term functional scores between the two approaches.
• Role of Synthetic Ligament Augmentation: Synthetic devices such as the LARS (Ligament Advanced Reinforcement System) have shown encouraging short-to-midterm results in select international centers, demonstrating rapid rehabilitation without donor site morbidity. Nonetheless, widespread adoption remains limited in North America due to historical concerns regarding particulate wear debris, foreign body synovitis, and unpredictable long-term failure rates observed in earlier generations of artificial ligaments.

13. Evidence-Based Synthesis

Modern clinical decision-making is grounded in high-quality randomized controlled trials and prospective registry analyses, corroborated by seminal biomechanical and anatomical descriptions.

14. References

• Krott NL, Wengle L, Whelan D et al. Single and double bundle posterior cruciate ligament reconstruction yield comparable clinical and functional outcomes: a systematic review and meta-analysis. Knee Surg Sports Traumatol Arthrosc. 2022. doi:10.1007/s00167-022-06907-6 [Level I (Therapeutic): Systematic Review & Meta-Analysis]
• Chahla J, Moatshe G, Cinque ME et al. Single-Bundle and Double-Bundle Posterior Cruciate Ligament Reconstructions: A Systematic Review and Meta-analysis of 441 Patients at a Minimum 2 Years’ Follow-up. Arthroscopy. 2017. doi:10.1016/j.arthro.2017.06.049 [Level I (Therapeutic): Systematic Review & Meta-Analysis]
• Shelbourne KD, Clark M, Gray T. Minimum 10-year follow-up of patients after an acute, isolated posterior cruciate ligament injury treated nonoperatively. Am J Sports Med. 2013. doi:10.1177/0363546513486771 [Level IV (Prognostic): Prospective Longitudinal Cohort Study]
• Spiridonov SI, Slinkard NJ, LaPrade RF. Isolated and combined grade-III posterior cruciate ligament tears treated with double-bundle reconstruction with use of endoscopically placed femoral tunnels and grafts: operative technique and clinical outcomes. J Bone Joint Surg Am. 2011. doi:10.2106/JBJS.J.01638 [Level IV (Therapeutic): Prospective Clinical Cohort Study]
• Grassmayr MJ, Parker DA, Coolican MR et al. Posterior cruciate ligament deficiency: biomechanical and biological consequences and the outcomes of conservative treatment. A systematic review. J Sci Med Sport. 2008. doi:10.1016/j.jsams.2007.07.007 [Level I (Systematic Review): Systematic Review & Evidence Synthesis]

15. Master Class Pro-Tip

The most catastrophic technical pitfall in posterior cruciate ligament reconstruction is fixing the graft while the proximal tibia remains posteriorly subluxated. Before securing either femoral or tibial fixation, the surgeon must manually verify that the anatomic 10 mm anterior tibial step-off is palpably and fluoroscopically restored to neutral under a sustained anterior drawer force at 90 degrees of flexion. Furthermore, never overlook coronal alignment in chronic cases: an uncorrected varus mechanical axis imposes unrelenting tensile stress across the reconstructed graft, virtually guaranteeing stretch-out and premature failure unless corrected with a concurrent or staged valgus-producing high tibial osteotomy.

Master Class Surgical Pearl: Posterior Cruciate Ligament Reconstruction