Lateral Collateral Ligament (LCL) Injuries

LCL Structure:

• Origin: Lateral femoral epicondyle, anterior and distal to popliteus origin
• Insertion: Lateral aspect of fibular head, conjoint with biceps femoris
• Length: Approximately 60mm
• Width: 5-8mm (round, cord-like structure)
• Course: Extra-articular (unlike MCL, not attached to capsule or meniscus)

Key anatomical relationships: The LCL is separated from the joint by the popliteus tendon. The common peroneal nerve passes 10mm posterior to biceps tendon insertion. The lateral inferior genicular artery runs beneath the LCL. Unlike the MCL, the LCL is not attached to the lateral meniscus (the meniscus has popliteomeniscal fascicles instead).

PLC Components (3 layers):

Layer 1 (Superficial):

• Iliotibial band (ITB)
• Biceps femoris tendon

Layer 2 (Middle):

• Lateral retinaculum
• Patellofemoral ligaments

Layer 3 (Deep):

• LCL (fibular collateral ligament)
• Popliteus muscle and tendon
• Popliteofibular ligament
• Arcuate ligament complex
• Fabellofibular ligament (when fabella present)
• Lateral capsule

Critical PLC structures: The triad of LCL + popliteus + popliteofibular ligament represents the core PLC. Injury to all three produces significant posterolateral rotatory instability.

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LCL Function:

• Primary varus stabilizer at all flexion angles
• Maximum constraint at 30° flexion (where cruciates relax)
• Provides 55% of varus restraint at 5° flexion
• Provides 69% of varus restraint at 25° flexion

Secondary stabilizers:

• Cruciates (especially PCL) at 0° extension
• Popliteus complex
• ITB
• Biceps femoris

Varus stress testing biomechanics: At 0° extension, the ACL and PCL are taut and provide secondary varus restraint. At 30° flexion, the cruciates relax and the LCL becomes the isolated primary restraint. Opening at 0° indicates combined LCL plus cruciate injury, while opening only at 30° suggests isolated LCL injury.

LCL Injury Classification

Grading is based on varus stress testing at 30° flexion to isolate the LCL.

Fanelli Classification (Combined PLC Injuries)

Combined injury patterns:

• LCL + PLC: Most common combined pattern (assess with dial test)
• LCL + PCL: Posterolateral knee dislocation variant
• LCL + ACL: Less common, high-energy injury
• Multi-ligament (3+): Knee dislocation spectrum, vascular assessment mandatory

Inspection:

• Lateral ecchymosis (posterolateral suggests PLC)
• Effusion (intra-articular = cruciate involvement)
• Gait assessment (varus thrust in chronic injuries)

Palpation:

• LCL along its course (epicondyle to fibular head)
• Fibular head (avulsion tenderness)
• Lateral joint line
• Peroneal nerve at fibular neck
• Popliteal fossa (popliteus)

Special tests for LCL/PLC injury:

1. Varus stress test (most important) - Test at 0° extension AND 30° flexion. Grade opening as: I (under 5mm), II (5-10mm), III (over 10mm). Note endpoint quality (firm vs soft).

2. Dial test (external rotation) - Test at 30° and 90° flexion, compare ER asymmetry to contralateral side. Over 10° asymmetry at 30° only indicates isolated PLC injury. Over 10° at both 30° and 90° indicates combined PLC plus PCL injury.

3. Posterolateral drawer - At 90° flexion, apply posterior force with external rotation. Positive test indicates PLC injury.

4. Reverse pivot shift - Extend knee from flexion with valgus and external rotation. A reduction clunk indicates PLC laxity and posterolateral rotatory instability.

Peroneal nerve assessment (MANDATORY):

Motor:

• Ankle dorsiflexion (tibialis anterior - deep peroneal)
• Great toe extension (EHL - deep peroneal)
• Ankle eversion (peronei - superficial peroneal)

Sensory:

• First web space (deep peroneal)
• Dorsolateral foot (superficial peroneal)

Vascular:

• Dorsalis pedis pulse
• Posterior tibial pulse
• Cap refill
• Consider ABI if concern for vascular injury

Document clearly: 16% of Grade III LCL injuries have associated peroneal nerve injury. This must be documented BEFORE any intervention. Always assess vascular status with dorsalis pedis and posterior tibial pulses, capillary refill, and consider ABI if concern for vascular injury.

Standard views:

• AP, lateral, skyline views
• Bilateral weight-bearing if chronic
• Stress views if diagnosis uncertain

Findings:

• Arcuate sign: Fibular styloid avulsion (pathognomonic of PLC injury)
• Segond fracture: Lateral tibial avulsion (anterolateral capsule - suggests ACL injury)
• Lateral capsular avulsion
• Fibular head fracture
• Varus alignment (chronic deficiency)

Stress X-rays: Varus stress at 20° flexion with side-to-side comparison. A difference over 4mm is significant. Useful for pre-operative planning and documenting degree of instability.

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Gold standard for soft tissue assessment

LCL findings:

• Increased T2 signal (edema/tear)
• Discontinuity (complete tear)
• Bony avulsion at fibula/epicondyle
• "Wavy" appearance (chronic elongation)

PLC structures to assess:

• Popliteus tendon/muscle
• Popliteofibular ligament
• Arcuate ligament
• Lateral capsule
• Bone bruise pattern (lateral femoral condyle, medial tibial plateau = PLC mechanism)

Associated injuries:

• PCL/ACL status
• Menisci
• Cartilage
• Peroneal nerve (signal change)

MRI sensitivity: 90-95% for complete LCL tears, somewhat lower for partial tears.

Vascular assessment (if concern):

• ABI (Ankle-Brachial Index): Under 0.9 abnormal
• CT angiography if suspicion of vascular injury
• Duplex ultrasound

Nerve studies:

• EMG/NCS if peroneal nerve injury suspected
• Timing: 3 weeks post-injury for wallerian degeneration

EUA (Examination Under Anaesthesia): Indicated if pain precludes adequate examination. Often combined with arthroscopy for intra-articular assessment. Document all stability testing findings carefully during EUA.

Acute phase (Week 0-1):

• PRICE protocol (Protection, Rest, Ice, Compression, Elevation)
• Functional hinged brace (optional)
• Weight-bearing as tolerated
• NSAIDs for pain/inflammation

Recovery phase (Week 1-3):

• ROM exercises (aim full ROM by 2 weeks)
• Quadriceps and hamstring strengthening
• Proprioception exercises
• Stationary cycling

Return to sport (Week 3-6):

• Sport-specific drills
• Functional brace for contact sports initially
• Full return when strength 90% and no pain with stress

Expected outcome: Full recovery, 2-4 weeks typical

Acute phase (Week 0-2):

• Hinged knee brace locked 0-90° initially
• Protected weight-bearing with crutches
• Ice, compression, elevation
• Gentle ROM within brace limits

Progressive phase (Week 2-6):

• Increase brace ROM weekly
• Progress to full weight-bearing
• Quadriceps/hamstring strengthening
• Pool exercises when wound healed
• Proprioception training

Functional phase (Week 6-12):

• Wean from brace
• Sport-specific rehabilitation
• Agility and plyometric progression
• Functional testing before return

Expected outcome: Return to sport 6-12 weeks, excellent prognosis

Bracing protocol:

• Hinged brace locked in extension initially
• Progress ROM weekly based on healing
• 6-8 weeks in brace minimum

Rehabilitation:

• Protected weight-bearing 2-4 weeks
• Early ROM to prevent stiffness
• Progressive strengthening
• Assess stability at 6 weeks

If healed (stable at 6 weeks):

• Continue rehabilitation
• Return to sport 3-4 months
• May have mild residual laxity but functional stability

If unstable at 6 weeks:

• Consider delayed reconstruction
• Especially if symptomatic instability
• Combined with any cruciate reconstruction

Key: Close follow-up essential, as some will need surgery

Treatment decisions are based on injury severity, associated structures, and patient demands.

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Surgical Timing Guidelines

Acute Phase (under 3 weeks):

• Best window for primary repair
• Tissue quality allows direct suturing
• Consider augmentation with internal brace

Subacute Phase (3-6 weeks):

• Repair possible if tissue quality adequate
• Increased risk of scarring affecting reduction
• Assessment of tissue viability critical

Chronic Phase (over 6 weeks):

• Primary repair not possible
• Reconstruction with graft required
• May need staged approach if multiple ligaments

Absolute surgical indications:

• Combined LCL + PLC injury (Fanelli B/C)
• Combined LCL + cruciate injury
• Multi-ligament knee injury
• Bony avulsion with displacement (repair/fixation)
• Peroneal nerve injury requiring exploration
• Failed non-operative treatment of isolated Grade III

Relative surgical indications:

• High-demand athlete with isolated Grade III
• Persistent symptomatic instability
• Varus thrust gait in chronic injury

Timing: Acute injuries (under 3 weeks) allow primary repair or augmented repair. Subacute injuries (3-6 weeks) can be repaired if tissue quality is adequate. Chronic injuries (over 6 weeks) require reconstruction as tissue is not repairable.

Acute repair:

• Direct suture repair of torn ligament
• Anchor fixation if bony avulsion
• May augment with internal brace

LCL reconstruction (chronic):

• Graft options: Hamstring autograft, allograft (Achilles, tibialis anterior)
• Technique: Anatomic tunnels at femoral epicondyle and fibular head
• Fixation: Interference screws, suspensory fixation

PLC reconstruction (Larson technique):

• Figure-of-eight graft reconstruction
• Recreates LCL and popliteofibular ligament
• Single graft through fibular tunnel, two femoral tunnels

LaPrade anatomic reconstruction:

• Two separate grafts: LCL and popliteofibular
• Most anatomic reconstruction
• Technically demanding but excellent outcomes

Combined procedures: LCL/PLC can be combined with PCL reconstruction or ACL reconstruction (less common). May stage or perform simultaneously depending on tissue quality and surgeon preference.

Approach:

• Lateral or posterolateral incision
• Identify and protect peroneal nerve FIRST
• Full exposure of fibular head

Graft passage:

• Fibular tunnel: Anterior to posterior
• Protect neurovascular structures
• Graft fixed in 30° flexion, neutral rotation

Tension:

• LCL tensioned at 30° flexion
• PLC structures tensioned at 30° flexion, neutral rotation
• Avoid over-constraint

Common errors to avoid: Non-anatomic tunnel placement, over-tensioning which restricts motion, failure to address all injured structures, and missing concomitant cruciate injury are the most frequent technical errors leading to suboptimal outcomes.