Question 1

What is the posterolateral corner and why is this injury so serious?

Accepted Answer

The posterolateral corner (PLC) is a complex of three structures on the outer back of the knee (lateral collateral ligament LCL, popliteus tendon, popliteofibular ligament) that prevent the knee from hyperextending and the tibia from rotating outward excessively - PLC injuries are serious because they're nearly always combined with ACL or PCL tears (80-90% cases), and missing the PLC injury causes ACL reconstruction to fail in 30-50% of patients due to persistent rotational instability. PLC ANATOMY: Lateral collateral ligament (LCL - fibrous band from lateral femoral epicondyle to fibular head, primary varus restraint). Popliteus tendon (muscle-tendon unit from popliteal fossa to lateral femur, controls external tibial rotation and prevents hyperextension). Popliteofibular ligament (popliteus muscle to fibular head, augments popliteus and LCL function). Together these structures form PLC (prevent: Varus angulation - knee opening outward. External rotation - tibia spinning outward relative to femur. Hyperextension - knee bending backward excessively). INJURY MECHANISM: High-energy varus force (contact sports collision to inner knee, MVA dashboard drives tibia outward - tears PLC structures). Hyperextension (forceful backward knee bending tears popliteus, posterior capsule - common in wrestling, awkward landings). Knee dislocation (most severe - 70-80% dislocations injure PLC + ACL/PCL + often neurovascular structures). WHY SERIOUS: Rarely isolated (80-90% combined with ACL or PCL tears - multi-ligament injury requires complex reconstruction). Missed PLC injury common (15-25% cases - subtle on exam if ACL tear dominates clinical picture, dial test not performed). Consequences of missed PLC: ACL reconstruction fails 30-50% (persistent rotational instability despite intact ACL graft - knee still gives way pivoting). Chronic varus laxity (progressive lateral compartment cartilage wear - arthritis develops 40-60% within 10 years). Peroneal nerve at risk (nerve courses through PLC - 15-30% PLC injuries have nerve damage causing foot drop, numbness - may be permanent 20-40%).

Question 2

How do doctors diagnose PLC injury and why is the dial test important?

Accepted Answer

Dial test is the gold standard physical exam for PLC injury - patient prone (face down), knees flexed to 30° then 90°, examiner rotates both feet outward comparing external rotation symmetry - asymmetry greater than 10° indicates PLC injury (positive at 30° only = isolated PLC, positive at both 30° and 90° = combined PLC + PCL tear). DIAL TEST TECHNIQUE: Patient positioned prone (lying face-down on exam table). Knees flexed to 30° (or can be done supine at 30° and 90°). Examiner externally rotates both feet simultaneously (rotate feet/ankles outward). Compare degree of external rotation (thigh-foot angle measured - normal 10-20°, injured side rotates 10-15° more). Repeat test at 90° knee flexion. INTERPRETATION: Dial test positive at 30° ONLY (>10° asymmetry at 30°, normal at 90°): Isolated PLC injury (popliteus, popliteofibular ligament torn - PCL intact). Dial test positive at 30° AND 90° (>10° asymmetry at both angles): Combined PLC + PCL injury (PCL torn allows additional posterior translation and rotation - more severe injury). Dial test negative (<5° asymmetry): PLC likely intact (may still have Grade I LCL sprain, but PLC complex functional). SENSITIVITY: 85-95% for detecting PLC injury if performed correctly (many clinicians don't perform dial test - contributes to 15-25% missed PLC injuries). IMAGING: X-rays: Arcuate sign (small avulsion fracture fibular head styloid process - PLC injury marker 80-90% cases, pathognomonic). Segond fracture on lateral side (less common than classic Segond on medial side with ACL tears). MRI: Visualizes LCL (high signal indicating tear), popliteus tendon disruption, popliteofibular ligament injury. Bone bruising pattern (lateral femoral condyle and posterior tibia - consistent with varus and hyperextension mechanism). Associated ACL/PCL/meniscus tears (80-90% PLC injuries have other ligament damage). IMPORTANCE CORRECT DIAGNOSIS: Missing PLC injury catastrophic (ACL reconstruction without addressing PLC fails 30-50% - persistent instability, graft rupture). Dial test simple, quick (takes 30 seconds - should be routine in all acute knee injuries). Early diagnosis allows appropriate treatment (acute combined ACL/PCL + PLC reconstruction vs isolated ACL doomed to failure if PLC missed).

Question 3

If I need PLC reconstruction, what are my chances of getting back to sports and normal activities?

Accepted Answer

Isolated PLC reconstruction outcomes are good (75-85% return to sports and activities with stable knee) but combined ACL/PCL + PLC multi-ligament reconstructions have lower success (60-75% good outcomes, 15-25% residual instability, 30-50% develop arthritis within 10 years) - recovery takes 9-12 months for isolated PLC, 12-18 months for multi-ligament injuries, and high-level pivoting sports may not be achievable in complex cases. ISOLATED PLC RECONSTRUCTION OUTCOMES: Return to sport: 75-85% (most return to pre-injury sport level, some modify to lower-impact activities). Knee stability: 80-90% (dial test normalizes, varus laxity eliminated, functional stability for daily activities). Complications: Peroneal nerve injury 5-10% (surgical risk - foot drop, numbness, may be permanent 30-50% cases). Stiffness 15-25% (lose 10-20° ROM vs uninjured side - extensive lateral dissection causes scarring). Graft failure 5-10% (re-tear or stretch-out - higher if premature return to sport). Timeline: 9-12 months return to pivoting sports. MULTI-LIGAMENT (ACL/PCL + PLC) RECONSTRUCTION OUTCOMES: Return to sport: 60-75% (lower than isolated ligament reconstruction - more severe injury, cartilage damage, neurovascular complications). Many modify activity (return to sport but lower level, avoid high-demand pivoting - recreational vs competitive). Knee stability: 70-85% (residual laxity 15-25% despite reconstruction - may need functional bracing for sports). Complications: Peroneal nerve palsy 10-20% (higher risk in multi-ligament cases - nerve often injured at time of dislocation, worsened by surgical traction). Arthritis 30-50% at 10 years (cartilage damage from initial knee dislocation, altered knee kinematics even with stable reconstruction - may require total knee replacement 15-25 years post-injury). Stiffness 20-40% (lose 20-40° ROM - multiple ligament surgeries, prolonged immobilization). Timeline: 12-18 months return to sport. MAXIMIZING OUTCOMES: Experienced surgeon (PLC reconstruction technically demanding - go to sports medicine specialist or knee ligament expert, improves outcomes 15-25%). Compliance with rehab (prolonged bracing 6 weeks non-negotiable - early varus stress causes graft failure). Address peroneal nerve injury (if foot drop present, may need tendon transfer, AFO brace - nerve recovery unpredictable 40-60% full recovery). Realistic expectations (perfect knee unlikely after multi-ligament injury - focus on stable pain-free knee for daily activities, modify sports as needed). Early arthritis surveillance (X-rays every 2-3 years - if arthritis developing, activity modification, injections, eventual knee replacement when severe).

Medical Disclaimer

Posterolateral Corner Injuries (PLC - Outer Knee Ligaments)

📖What is Posterolateral Corner Injuries (PLC - Outer Knee Ligaments)?

🔬What Causes It?

⚠️Risk Factors

You may be at higher risk if:

🛡️Prevention