Courtesy: Dr Sachin Tapasvi, Dr Ashok Shyam, Ortho TV

 

Posterior Cruciate Ligament (PCL) Injuries: Anatomy, Diagnostics, Repair, and Reconstruction

Anatomy and Kinematic Principles

• Femoral Footprint:

  • Very broad insertion extending anteriorly toward the roof of the intercondylar notch.

  • Extends posteriorly along the medial femoral condyle.

  • Insertion is flush with the articular cartilage margin, which is critical for anatomical tunnel placement.

• Fiber Tension Kinematics:

  • No strict anatomical separation into two isolated cords; instead, fibers display a continuum of reciprocal tightening and slackening across flexion and extension.

  • Extension: Posteromedial (PM) fibers tighten and resist hyperextension.

  • Mid-Flexion: Anterolateral (AL) fibers become taut and bear the majority of posterior translation forces.

  • Deep Flexion: Posteromedial fibers tighten once again.

• The “Shallow vs. Deep” Femoral Tunnel Rule:

  • Fiber length change depends heavily on the shallow-to-deep position relative to the articular margin rather than high-to-low positioning.

  • Deep/Proximal in the Notch: Fibers slacken excessively as the knee enters flexion.

  • Shallow/Distal (Flush to Cartilage): Fibers maintain appropriate tension without non-physiological slackening.

• Tibial Footprint and Landmarks:

  • Broad anatomical insertion extending over the posterior tibial facet and blending with the posterior periosteum.

  • Champagne Drop-Off Point: Anatomical transition landmark on the posterior tibia where the cortex slopes downward and fibers of the popliteus are encountered.

• Single-Bundle Tunnel Target:

  • A single-bundle reconstruction aims to replace the anterolateral (AL) bundle.

  • Avoid placing the tunnel in the exact geometric center of the femoral footprint; a central tunnel disrupts the anterior meniscofemoral ligament (Ligament of Humphrey) and misses the functionally critical AL fibers.

Diagnostics: Examination, Stress Radiography, and Grading

• Clinical Examination:

  • The posterior drawer test at 90° of flexion remains the gold standard physical examination tool.

  • Assess loss of the anterior tibial step-off relative to the medial femoral condyle (Grood classification):

    • Grade 1: Tibia remains anterior to the femoral condyles (0–5 mm posterior translation).

    • Grade 2: Anterior tibial plateau sits flush with the femoral condyles (5–10 mm posterior translation).

    • Grade 3: Tibia sags posterior to the femoral condyles (>10 mm posterior translation; usually indicates combined multi-ligament disruption).

• Stress Radiography:

  • Routine non-weight-bearing MRI scans frequently underestimate chronic interstitial laxity.

  • Perform standardized posterior stress radiography (Telos, kneeling view, or hamstring-driven stress views at 90° flexion).

  • Measure posterior displacement of the posterior tibial cortical margin relative to the posterior femoral condyle compared to the uninjured contralateral knee.

  • Intervention Threshold: Side-to-side displacement greater than 8 mm to 10 mm indicates a functionally incompetent PCL requiring surgical consideration. Greater than 12 mm indicates combined PCL and posterolateral/posteromedial corner disruption.

Surgical Indications: Conservative vs. Operative Timelines

• Non-Operative Indications: Isolated Grade 1 and Grade 2 tears (or stable combined tears with low-grade MCL injury) can be managed non-operatively with specialized extension bracing.

• Operative Indications:

  • Grade 3 tears with gross posterior sag.

  • Side-to-side translation $>8\text{ to }10\text{ mm}$ on stress radiographs.

  • PCL-dominant multi-ligament knee injuries (KD injuries).

  • High-grade combined PCL and posterolateral corner (PLC) tears.

• Early vs. Delayed Reconstruction:

  • Early intervention (within 3 weeks to 3 months) in multi-ligament knee injuries significantly reduces subsequent meniscus tears, chondral shear damage, and lateral compartment arthrosis.

  • Chronic delayed reconstructions carry a higher burden of secondary degenerative wear and irreversible cartilage damage.

Acute Repair Techniques

• Femoral-Sided Avulsions:

  • Infrequent presentation; typically seen in multi-ligament knee dislocations (such as KD-3M patterns where the PCL peels off the medial femoral condyle).

  • Tends to reduce near terminal extension and displace/slacken in flexion.

  • Managed with controlling traction sutures or rigid screw fixation if a sizable osteochondral fragment is attached.

• Tibial-Sided Bony Avulsions:

  • Thin, comminuted bony fragments are amenable to arthroscopic suture pull-out techniques.

  • Large, intact bony avulsion fragments are best managed via open/mini-open reduction and rigid internal screw fixation through a posteromedial (Burks and Schaffer) approach.

Reconstruction Strategies: Single vs. Double Bundle

• Biomechanical Profile: Double-bundle reconstruction restores both translational and rotational kinematics more closely across the entire arc of motion in laboratory simulations.

• Clinical Realities: Clinical comparison trials show no statistically significant outcome differences between single- and double-bundle techniques; the average difference in objective side-to-side laxity is only 1 mm to 2 mm.

• Clinical Decision-Making Algorithm:

  • Single-Bundle Reconstruction Indications:

    • Multi-ligament knee dislocations (reduces operative time, reduces graft burden, and minimizes femoral tunnel convergence).

    • Combined PCL + MCL reconstructions.

    • Cases with significant salvageable native PCL remnants.

  • Double-Bundle Reconstruction Indications:

    • High-grade combined Grade 3 PCL + PLC injuries where rotational and multi-axis restraint requires recreation of both bundles.

Technical Considerations: The “Killer Turn” & Graft Tensioning

• The Killer Turn:

  • Represents the acute, sharp angle that a transtibial PCL graft must navigate as it exits the posterior tibial tunnel and heads anteriorly into the intercondylar notch.

  • High localized shear stress predisposes to graft attenuation, fraying, and long-term stretching.

  • Surgical Mitigations:

    • Starting the tibial tunnel more laterally on the anterior cortex softens the turn.

    • Setting tibial guide angulation to roughly 30° to 45° relative to the tibial plateau; lowering the drill guide angle too far flattens the turn but enters softer metaphyseal bone, compromising distal fixation purchase.

• Graft Tensioning Sequence:

  • Isolated Single-Bundle PCL: Tension and fix at 70° to 90° of flexion with an anterior drawer force applied to restore the native anterior tibial step-off.

  • Double-Bundle PCL: Tension the AL bundle at 90° of flexion; tension the PM bundle near full extension (0° to 15°).

  • Combined ACL + PCL + PLC Reconstruction Tensioning Hierarchy:

    1. First: Tension and fix the PCL to re-establish the central pivot and correct posterior sag.

    2. Second: Tension and fix the ACL.

    3. Third: Tension and fix the peripheral structures (PLC / MCL).

• Graft Material Considerations:

  • Bone-patellar tendon-bone (BTB) or bone-Achilles allografts provide rigid bone-to-bone healing in the tibial tunnel.

  • Soft-tissue grafts (quadrupled hamstring or quadriceps tendon) carry a higher risk of cyclic elongation over time and benefit from robust fixation or internal bracing augmentation.

Rehabilitation & Bracing Protocol

• Immobilization and Sag Prevention: Standard hinged knee braces fail to prevent posterior gravitational sag of the tibia.

• Posterior Tibial Support (PTS) Bracing:

  • Mandatory application of a dedicated PCL / PTS brace with an anteriorly directed force pad behind the proximal calf.

  • Maintain continuous PTS support for the first 4 weeks to protect the healing construct.

  • Dynamic PCL bracing (e.g., dynamic force application across flexion) is continued for a minimum of 13 weeks up to 4 to 5 months.

• Strict Muscle Activation Rules:

  • Active hamstring contractions are strictly prohibited for at least 4 to 6 weeks. Hamstring firing exerts a direct posterior shear force on the proximal tibia, causing acute elongation or failure of the healing graft.

  • Focus early rehabilitation on passive range of motion with anterior tibial support and active quadriceps activation (straight leg raises, quadriceps sets) to provide dynamic anterior stabilization