Posterolateral Approach to Knee (Fibular Head)

The posterolateral corner (PLC) of the knee is a complex anatomic region consisting of static (ligaments) and dynamic (musculotendinous) stabilizers that resist varus and external rotation forces. Understanding PLC anatomy is CRITICAL for successful reconstruction and avoiding common peroneal nerve injury.

Posterolateral Corner Static Stabilizers

1. LATERAL COLLATERAL LIGAMENT (LCL - PRIMARY VARUS RESTRAINT):

Anatomy:

• Origin: Lateral femoral epicondyle (proximal and posterior to popliteus origin)
• Insertion: Fibular head (lateral aspect, just posterior to biceps femoris insertion)
• Length: Mean 69mm (range 60-80mm - LaPrade 2003)
• Function: PRIMARY restraint to varus stress at all knee flexion angles (resists 55-70% of varus load at 0° and 30° - Gollehon 1987)

Biomechanics:

• Isometric through ROM: LCL maintains constant length from 0-90° flexion (isometric ligament - ideal for reconstruction)
• Tightest at 0° extension (maximum varus stability)
• Varus laxity with LCL injury: 5-10mm at 30° flexion (Grade II), greater than 10mm (Grade III)

2. POPLITEUS TENDON (PRIMARY EXTERNAL ROTATION RESTRAINT):

Anatomy:

• Origin: Popliteal sulcus on lateral femoral condyle (anterior and distal to LCL origin)
• Course: Runs POSTERIOR and INFERIOR from femur, passes through popliteal hiatus (opening in lateral joint capsule)
• Insertion: Posterior tibia (popliteal line above soleal line)
• Function: PRIMARY restraint to external rotation of tibia (resists 50-60% of external rotation load at 30° - Shahane 1999)

Clinical Significance:

• Popliteus contracts during knee flexion to "unlock" knee (externally rotates femur on fixed tibia)
• Injury causes increased external rotation (dial test positive - greater than 10° asymmetry at 30° flexion)

3. POPLITEOFIBULAR LIGAMENT (SECONDARY EXTERNAL ROTATION RESTRAINT):

Anatomy:

• Origin: Popliteus musculotendinous junction (proximal aspect of popliteus muscle belly)
• Insertion: Fibular styloid (apex of fibular head)
• Function: Connects popliteus muscle to fibular head, secondary restraint to external rotation and primary restraint to posterior translation of lateral tibial plateau (Shahane 1999)

Biomechanics:

• Popliteofibular ligament tightens in extension (prevents posterior subluxation of lateral tibial plateau)
• Injury contributes to posterolateral rotatory instability (PLRI) - positive dial test at BOTH 30° and 90° flexion

4. ARCUATE LIGAMENT COMPLEX:

Anatomy:

• Y-shaped fibrous structure that reinforces posterior joint capsule
• Originates from fibular styloid, fans out to attach to lateral femoral condyle (superior limb) and posterior joint capsule (medial limb)
• Often absent or attenuated (present in only 80% of knees - Seebacher 1982)

Function:

• Contributes to posterior capsular stability
• Secondary restraint to varus and external rotation

Dynamic Posterolateral Stabilizers

1. BICEPS FEMORIS:

Anatomy:

• Long head: Originates from ischial tuberosity
• Short head: Originates from linea aspera of femur
• Insertion: Fibular head (lateral aspect) - forms conjoined tendon with LCL insertion
• Function: Dynamic varus and external rotation stabilizer (muscle contraction reinforces LCL function)

Clinical Significance:

• Biceps femoris injury often accompanies LCL tears (conjoined insertion - both avulsed together in severe trauma)

2. ILIOTIBIAL BAND (ITB):

Anatomy:

• Extension of tensor fascia lata
• Inserts on Gerdy's tubercle (anterolateral tibial plateau)
• Posterior fibers blend with lateral intermuscular septum and superficial capsule

Function:

• Provides anterolateral stability
• Secondary varus restraint (when knee in extension)

3. LATERAL HEAD OF GASTROCNEMIUS:

Anatomy:

• Origin: Posterior lateral femoral condyle (posterior to LCL femoral attachment)
• Crosses posterior to lateral joint line

Function:

• Dynamic posterior capsular restraint
• May be injured in severe PLC trauma (posterolateral capsule avulsion)

Neurovascular Anatomy

COMMON PERONEAL NERVE (PRIMARY HAZARD):

Course:

• Branches from sciatic nerve at apex of popliteal fossa (varies: high division in 10-15% of patients - sciatic bifurcates proximal to popliteal fossa)
• Descends along medial border of biceps femoris in distal thigh
• Passes LATERALLY across popliteal fossa toward fibular neck
• Crosses fibular neck 2cm distal to fibular head apex (Flandry 1991)
• DIRECTLY ADHERENT to fibular neck periosteum (no intervening soft tissue - highest injury risk zone)

Branches:

• Articular branch to knee joint (proximal to fibular neck)
• Lateral sural cutaneous nerve (proximal leg sensation)
• Superficial peroneal nerve (ankle eversion + dorsolateral foot sensation) - separates at fibular neck
• Deep peroneal nerve (ankle/toe dorsiflexion + first web space sensation) - separates at fibular neck

Injury Manifestations:

• Foot drop (ankle/toe dorsiflexion weakness - tibialis anterior, EHL, EDL, peroneus tertius)
• Weak ankle eversion (superficial peroneal nerve - peroneus longus/brevis)
• Steppage gait (high stepping to clear foot)
• Sensory loss: Dorsum of foot and lateral leg

Protection Strategy:

• Identify nerve FIRST before any dissection around fibular head
• Palpate nerve as cord-like structure 2cm distal to fibular head (crosses fibular neck)
• Use blunt dissection ONLY around nerve (sharp dissection risks transection)
• Retract nerve ANTERIORLY during fibular head exposure (protects from retractors and drilling)

POPLITEAL VESSELS:

• Lie MEDIAL to posterolateral approach (15-20mm medial to fibular head)
• Usually NOT at risk with standard posterolateral dissection (stay lateral to neurovascular bundle)
• May be injured in severe trauma (knee dislocation, tibial plateau fracture with PLC involvement)

Patient Positioning

Setup:

• Supine position on operating table
• Bump or sandbag under ipsilateral hip (elevates posterolateral knee - improves access)
• Leg holder or post at medial thigh (allows knee flexion and varus stress for PLC exposure)
• Alternative: Lateral decubitus position with affected leg up (better for isolated PLC surgery, but difficult for combined ACL/PLC reconstruction)
• Tourniquet on proximal thigh (250-280mmHg for 90-120 minutes) - optional (many surgeons avoid tourniquet to allow nerve stimulator use if needed)

Incision and Superficial Dissection

Skin Incision:

• Longitudinal incision from distal femur to proximal fibular shaft
• Course: Centered over fibular head, extends posteriorly (NOT directly lateral - avoids common peroneal nerve)
• Proximal extent: 8-10cm proximal to fibular head (allows LCL femoral attachment exposure)
• Distal extent: 4-5cm distal to fibular head (exposes fibular neck and peroneal nerve crossing)
• Length: Typically 12-15cm

Landmarks:

• Palpate fibular head (prominent bony landmark on lateral knee)
• Palpate biceps femoris tendon (posterior to fibular head insertion)
• Mark incision posterior to fibular head (stays behind nerve which lies anterior to biceps at neck level)

Superficial Dissection:

1. Incise skin and subcutaneous tissue sharply
2. Identify iliotibial band (ITB) anteriorly (thick fascial layer)
3. Identify biceps femoris tendon posteriorly (palpable cord inserting on fibular head)
4. Develop plane between ITB (anterior) and biceps femoris (posterior)
   • This interval provides access to underlying LCL and lateral joint capsule
   • ITB pulled anteriorly with retractors, biceps pulled posteriorly

Deep Dissection - Common Peroneal Nerve Identification (CRITICAL STEP)

STEP 1: PALPATE COMMON PERONEAL NERVE (Before Deep Dissection):

• Use fingers to palpate cord-like structure crossing fibular neck 2cm distal to fibular head apex
• Roll nerve under fingers (feels like electrical cord - firm, mobile structure)
• If unable to palpate (obese patient, scarring): Use nerve stimulator at low current (0.5-1.0mA) to locate nerve (stimulation causes foot dorsiflexion)

STEP 2: EXPOSE COMMON PERONEAL NERVE:

• Follow posterior border of biceps femoris distally (nerve lies ANTERIOR to biceps at this level)
• Dissect along biceps with blunt technique (finger dissection or Kittner dissector)
• Identify nerve at fibular neck crossing - DIRECTLY ADHERENT to fibular neck periosteum
• Use blunt dissection ONLY to free nerve from fibular neck (sharp dissection risks transection)
• Encircle nerve with vessel loop or rubber drain for protection

STEP 3: RETRACT NERVE ANTERIORLY:

• Gently retract nerve ANTERIORLY away from surgical field using vessel loop
• Minimize retraction time (nerve sensitive to ischemia from prolonged traction)
• Release retraction periodically during case (every 20-30 minutes)

Posterolateral Corner Exposure

After Nerve Protected:

1. Expose Fibular Head:

• Biceps femoris insertion on fibular head (lateral aspect) identified and protected
• LCL insertion on fibular head (posterior to biceps) identified
• Subperiosteal elevation of soft tissues from fibular head if drilling needed (eg biceps/LCL avulsion repair)

2. Identify LCL:

• Proximal: Palpate lateral femoral epicondyle (LCL femoral attachment)
• Distal: Follow LCL to fibular head insertion (posterior to biceps insertion)
• LCL runs in ANTERIOR-TO-POSTERIOR direction (from femoral epicondyle to fibular head)
• Assess LCL integrity (palpate for midsubstance tear, femoral avulsion, fibular avulsion)

3. Expose Popliteus Tendon:

• Locate popliteal hiatus (opening in lateral joint capsule posterior to LCL)
• Popliteus tendon emerges from hiatus, courses to popliteal sulcus on lateral femoral condyle
• Use blunt dissection to expose popliteus (avoid sharp dissection - risks capsule violation and fluid extravasation)

4. Identify Popliteofibular Ligament:

• Originates from popliteus musculotendinous junction (proximal muscle belly)
• Inserts on fibular styloid (apex of fibular head)
• Often attenuated or difficult to identify in acute injuries (merged with hematoma)
• May need to define anatomy by identifying fibular styloid insertion then tracing proximally to popliteus

PLC Reconstruction Techniques

ANATOMIC PLC RECONSTRUCTION (LaPrade Technique - GOLD STANDARD):

Indications:

• Grade III PLC injury (complete tear with varus laxity greater than 10mm at 30° flexion)
• Chronic PLC insufficiency (varus thrust gait, dial test positive greater than 10° asymmetry)
• Combined with ACL or PCL reconstruction (60-80% of PLC injuries are multiligament - Fanelli 2005)

Graft Options:

• Allograft (most common): Achilles tendon (bone block for fibular head), tibialis anterior, semitendinosus
• Autograft: Hamstring (if not needed for ACL), quadriceps tendon

Technique (LaPrade Anatomic Reconstruction):

LCL Reconstruction:

1. Femoral tunnel: Drill 7mm tunnel at anatomic LCL origin on lateral femoral epicondyle (proximal and posterior to popliteus origin)
2. Fibular tunnel: Drill 7mm tunnel through fibular head (lateral to anterior - exits anterior fibular neck, AVOIDING peroneal nerve 2cm distal)
3. Graft passage: Pass graft (eg semitendinosus allograft) through femoral tunnel (femur to fibula), fix femoral side with interference screw or suspensory button
4. Tensioning: Tension graft with knee at 30° flexion, neutral rotation, slight varus stress (restores isometric LCL length)
5. Fibular fixation: Fix with interference screw or suture anchor on fibular head

Popliteofibular Ligament Reconstruction:

1. Popliteus tunnel: Drill 7mm tunnel at anatomic popliteus origin in popliteal sulcus (anterior and distal to LCL femoral origin)
2. Fibular styloid fixation: Attach graft (separate limb or shared with LCL graft) to fibular styloid using suture anchor or bone tunnel
3. Graft passage: Pass graft through popliteus tunnel (posterior to LCL graft - recreates popliteus course)
4. Tensioning: Tension with knee 60-70° flexion, neutral rotation (popliteus/popliteofibular tightest in flexion)

Popliteus Tendon Reconstruction (If Needed):

• Drill tunnel from popliteal sulcus to posterior tibia (popliteal line insertion)
• Pass graft through tunnel, fix on posterior tibia with interference screw
• Rarely performed in isolation (usually combined with LCL + popliteofibular reconstruction)

Post-Operative Protocol:

• Hinged knee brace locked in extension for 2 weeks
• Partial weight-bearing (toe-touch) for 6 weeks
• ROM: 0-90° for first 6 weeks (NO deep flexion - protects popliteus reconstruction)
• Full ROM at 6-8 weeks, strengthening at 8-12 weeks
• Return to sport: 9-12 months (ACL timeline if combined)

Indications for Posterolateral Approach

PLC RECONSTRUCTION (PRIMARY INDICATION):

Grade III PLC Injury (Operative Indication):

• Varus laxity: Greater than 10mm opening at 30° knee flexion vs contralateral (Grade III)
• Dial test: Greater than 10° external rotation asymmetry at 30° and/or 90° flexion
• External rotation recurvatum test: Positive (tibia externally rotates and hyperextends vs contralateral)
• Mechanism: Hyperextension + varus force, dashboard injury (knee hitting dashboard in MVA), sports trauma

Combined Ligament Injuries (60-80% of PLC Injuries):

• ACL + PLC (35%): Varus hyperextension injury
• PCL + PLC (25%): Dashboard injury (posterior force + varus)
• ACL + PCL + PLC (15%): Knee dislocation
• Reconstruction timing: SIMULTANEOUS reconstruction (NOT staged - 10% vs 32% failure - Levy 2010)

Grade I-II PLC Injuries (Non-Operative):

• Varus laxity less than 5mm (Grade I) or 5-10mm (Grade II) at 30° flexion
• Dial test less than 10° asymmetry
• Management: Hinged knee brace (blocks varus), physiotherapy for quad/hamstring strengthening (dynamic stabilizers)
• Outcomes: 80-85% successful with non-operative management (Indelicato 1990)

FIBULAR HEAD FRACTURES:

Avulsion Fractures (LCL/Biceps Insertion):

• Large fragment with LCL/biceps attachment displaced greater than 5mm - ORIF via posterolateral approach
• Fixation: Lag screws, plate, or suture anchors depending on fragment size
• Outcomes: 90-95% union with anatomic reduction and stable fixation

Comminuted Fibular Head Fractures:

• Usually part of Schatzker IV tibial plateau fracture (lateral plateau split + fibular head)
• Posterolateral approach for fibular head fixation, separate approach for tibial plateau (anterolateral or lateral)

COMMON PERONEAL NERVE EXPLORATION:

Indications:

• Iatrogenic nerve injury during knee surgery (immediate post-op foot drop with pre-op intact function)
• Traumatic nerve injury with knee dislocation or fibular neck fracture (foot drop at presentation)
• Delayed nerve palsy without recovery by 4-6 months (EMG shows no reinnervation)

Exploration Findings:

• Nerve contusion/neurapraxia (nerve in continuity - most common): Neurolysis (free from scar)
• Nerve laceration/neurotmesis (complete transection): Primary repair (if less than 1cm gap) or nerve graft (sural nerve autograft if greater than 1cm gap)

Outcomes:

• Neurolysis (contusion): 80% functional recovery
• Primary repair: 60% functional recovery
• Nerve graft: 40% functional recovery

Outcomes by Procedure

Anatomic PLC Reconstruction (LaPrade Technique):

• Clinical: Lysholm 88, IKDC 78% normal/nearly normal (LaPrade 2014)
• Objective stability: Varus laxity 12mm → 2mm, dial test asymmetry 15° → 3°
• Graft failure: 12% (revision required)
• Return to sport: 72% return to pre-injury level
• Complications: 5% transient peroneal nerve palsy (all recovered by 6 months)

Combined ACL + PLC Reconstruction:

• Simultaneous: 10% graft failure, Lysholm 87, IKDC 82% normal (Levy 2010)
• Staged: 32% graft failure (3-fold higher - NOT recommended)

Non-Anatomic PLC Reconstruction (Historical):

• Biceps tenodesis or single-structure reconstruction (LCL only): 30-40% failure rate
• Abandoned in favor of anatomic reconstruction (LCL + popliteofibular - LaPrade technique)

Fibular Head Fracture ORIF:

• Union rate: 90-95% with anatomic reduction and stable fixation
• Nonunion: 5% (usually with inadequate fixation or severe comminution)
• Peroneal nerve injury: 10-15% at presentation (associated with fracture), 2-5% iatrogenic during surgery

Intraoperative Complications

1. COMMON PERONEAL NERVE INJURY (2-10% - MOST COMMON):

Mechanism:

• Direct trauma during nerve dissection from fibular neck (nerve adherent to bone - Flandry 1991)
• Excessive traction with retractors (nerve ischemia from prolonged retraction greater than 30 minutes)
• Drill penetration through fibular head into nerve 2cm distally
• Thermal injury from electrocautery near nerve

Prevention:

• Identify nerve FIRST before any fibular head dissection (palpate as cord 2cm distal to apex)
• Use BLUNT dissection ONLY to free nerve from fibular neck (NO sharp dissection)
• Retract nerve ANTERIORLY with vessel loop (gentle tension, release periodically)
• Avoid drilling distal to fibular head (nerve 2cm away)
• NO electrocautery within 1cm of nerve (use bipolar if hemostasis needed near nerve)

Recognition:

• Intraoperative: If patient under regional anesthesia with incomplete motor block, loss of foot dorsiflexion during case
• Post-operative: Foot drop, weak ankle eversion, sensory loss dorsum of foot

Immediate Management:

• Stop surgery if nerve injury suspected intraoperatively
• Inspect nerve - assess for laceration vs contusion
• If laceration: Primary repair with 8-0 or 9-0 nylon microsurgical sutures (requires microscope or loupe magnification)
• If contusion: Neurolysis (free from hematoma/scar), complete planned reconstruction, document injury
• If thermal injury: Debride devitalized nerve segment, consider nerve grafting if greater than 1cm defect

Post-Operative Management:

• AFO (ankle-foot orthosis) to prevent foot drop and protect from tripping
• Physical therapy for ankle strengthening and gait training
• Serial EMG at 6-8 weeks (signs of reinnervation indicate recovery)
• Nerve exploration if NO recovery by 4-6 months (revision neurolysis vs nerve grafting)
• Tendon transfer if no recovery by 12 months (tibialis posterior to dorsum of foot - restores dorsiflexion)

Outcome:

• Neurapraxia (mild contusion): 90-95% complete recovery by 6-9 months
• Axonotmesis (moderate crush): 60-70% recovery by 12 months
• Neurotmesis (complete transection): Requires repair/graft (40-60% functional recovery)

2. POPLITEAL VESSEL INJURY (Less than 1%):

Mechanism:

• Excessive medial dissection beyond midline of popliteal fossa
• Drill penetration through posterior tibia during popliteus tunnel creation (artery lies on posterior tibia)
• Sharp dissection in posterior capsule (artery adherent to capsule medially)

Prevention:

• Stay LATERAL to biceps-semimembranosus interval (popliteal vessels lie MEDIAL)
• Use fluoroscopy for popliteus tunnel drilling (ensure drill does NOT penetrate posterior cortex)
• Blunt dissection in posterior capsule (avoid sharp dissection medially)

Recognition:

• Pulsatile bleeding from surgical field (arterial injury)
• Expanding hematoma in popliteal fossa
• Loss of pedal pulses (distal ischemia)

Management:

• Immediate pressure on bleeding site (compress with gauze)
• Proximal/distal control with vascular clamps or tourniquets
• URGENT vascular surgery consultation - DO NOT attempt repair unless trained
• Primary repair (if less than 1cm defect) or reverse saphenous vein graft (if greater than 1cm defect)
• Fasciotomy if ischemia time greater than 4-6 hours (compartment syndrome risk)

Outcome:

• Primary repair within 6 hours: 85-90% limb salvage
• Delayed repair (greater than 6 hours): 70-75% limb salvage, 10-15% amputation rate

Postoperative Complications

1. GRAFT FAILURE (12% Anatomic PLC, 32% Staged ACL+PLC):

Risk Factors:

• Non-anatomic reconstruction (single-structure - LCL only)
• Staged reconstruction for combined ACL/PCL + PLC injuries (varus/rotatory laxity overloads ACL/PCL graft)
• Inadequate graft tensioning (over-tightened or under-tightened)
• Early return to pivoting sports (before 9-12 months)
• Non-compliance with rehabilitation protocol (early weight-bearing, excessive ROM)

Diagnosis:

• Recurrent varus laxity: Greater than 10mm at 30° flexion
• Dial test: Greater than 10° asymmetry at 30° and/or 90° flexion
• Functional instability: Varus thrust gait, giving way during pivoting
• MRI: Graft discontinuity, fluid signal within graft (graft rupture or stretching)

Management:

• Revision PLC reconstruction: Remove failed graft, revise tunnels (may need to reposition if non-anatomic), new graft (allograft typically used for revision)
• Address combined instabilities: If ACL/PCL also loose - revise ALL ligaments simultaneously (NOT staged)
• Longer rehabilitation: 12 months minimum before return to sport (revision grafts slower to incorporate)

Outcome:

• Revision anatomic PLC reconstruction: 70-75% good outcomes (lower than primary 85-90%)
• Multiple revisions (greater than 2): 50-60% good outcomes (diminishing returns with each revision)

2. PERSISTENT ROTATORY INSTABILITY (10-15%):

Mechanism:

• Non-anatomic reconstruction (LCL only without popliteofibular ligament - incomplete external rotation restraint)
• Missed combined ligament injuries (ACL/PCL not reconstructed - overloads PLC reconstruction)
• Graft stretching (over time - gradual laxity increase)

Clinical Manifestation:

• Dial test remains positive: 10-15° asymmetry at 30° and/or 90° flexion
• Varus laxity normal: Less than 5mm at 30° flexion (LCL graft intact)
• Functional symptoms: Difficulty with cutting/pivoting, instability sensation

Management:

• If LCL-only reconstruction: Revision with anatomic technique (add popliteofibular ligament reconstruction - LaPrade technique)
• If combined ligament laxity: Address ACL/PCL laxity (reconstruct deficient ligaments)
• If mild instability (5-10° dial test asymmetry): Non-operative management with bracing and activity modification (avoid pivoting sports)

Outcome:

• Revision with anatomic technique: 70% improvement in rotatory stability
• Non-operative management: 60% able to return to low-demand activities (avoiding pivoting sports)

3. STIFFNESS (5-10%):

Mechanism:

• Prolonged immobilization (brace locked in extension greater than 2 weeks)
• Aggressive early ROM (violates healing popliteus/popliteofibular ligament - tightens in flexion)
• Capsular adhesions (arthrofibrosis)
• Concomitant procedures (ACL/PCL reconstruction increases stiffness risk)

Clinical Manifestation:

• Flexion contracture: Unable to achieve full extension (0°) - most common
• Loss of flexion: Less than 120° flexion (normal 130-140°)

Prevention:

• Balanced rehabilitation: Gentle ROM 0-90° for first 6 weeks, gradual progression to full ROM by 8-12 weeks
• Early mobilization: Remove brace at 2 weeks, start passive ROM (avoid locked brace greater than 2 weeks)
• Avoid aggressive stretching in first 6 weeks (protects healing ligaments)

Management:

• Physical therapy (first-line): Progressive ROM exercises, joint mobilization, stretching
• Manipulation under anesthesia (MUA): If flexion less than 90° at 3 months despite therapy
• Arthroscopic lysis of adhesions: If MUA fails or arthrofibrosis confirmed on MRI (thick fibrotic tissue in notch/suprapatellar pouch)

Outcome:

• Physical therapy: 70-80% achieve functional ROM (0-120°) within 6 months
• MUA: 60-70% achieve functional ROM (additional 20-30° flexion gain)
• Lysis of adhesions: 50-60% achieve functional ROM (difficult salvage procedure)