Posterolateral Approach to Knee (Fibular Head)

What it exposes. The posterolateral approach to the knee gives direct access to the fibular head and the structures of the posterolateral corner (PLC) for repair or reconstruction of the lateral collateral ligament (LCL), the popliteus tendon and the popliteofibular ligament (PFL). The common peroneal nerve is the highest-risk structure: it crosses the fibular neck roughly 2cm distal to the fibular head apex, closely applied to bone. The single most important principle of the approach is to identify and protect the common peroneal nerve before any dissection around the fibular head. Why this approach. It is the workhorse exposure for anatomic PLC reconstruction and the only approach that simultaneously controls the fibular head, the LCL femoral and fibular attachments, the popliteus and the PFL while keeping the common peroneal nerve under direct vision throughout. PLC injuries are rarely isolated - the majority occur with ACL and/or PCL tears in multiligament knee injuries - and modern practice favours anatomic reconstruction of all torn structures performed concurrently with cruciate reconstruction rather than repair plus staged cruciate surgery (Geeslin 2015). Indications. - PLC reconstruction (primary indication): Grade III PLC injury (varus laxity greater than 10mm at 30°, dial test greater than 10° asymmetry), and chronic PLC insufficiency with a varus thrust gait or recurrent giving way.

• Combined ligament injuries (the majority): ACL plus PLC (varus hyperextension), PCL plus PLC (dashboard injury), and ACL plus PCL plus PLC (knee dislocation). Reconstruct all torn structures concurrently with the cruciate(s) - acute repair plus staged cruciate reconstruction fails far more often (about 38%) than concurrent reconstruction of all torn structures (about 9%, Geeslin 2015).
• Fibular head fractures: avulsion of the LCL or biceps insertion displaced greater than 5mm (ORIF), and comminuted fractures as part of a Schatzker IV tibial plateau injury.
• Common peroneal nerve exploration: iatrogenic injury with immediate postoperative foot drop and intact preoperative function, traumatic palsy at presentation, or a delayed palsy with no recovery by 4-6 months on EMG.

Position & landmarks. Supine with a bump or sandbag under the ipsilateral hip to roll the knee into internal rotation and bring the posterolateral corner up; a leg holder or post at the medial thigh allows flexion and varus stress for exposure. Lateral decubitus is an alternative for isolated PLC work but is awkward when combining with ACL or PCL reconstruction. A proximal-thigh tourniquet at 250-280mmHg is optional - many surgeons avoid it so a nerve stimulator can be used if the nerve is hard to find. Palpate the fibular head (prominent lateral landmark) and the biceps femoris tendon (cord inserting on the fibular head, with the nerve along its posteromedial border), and centre the incision over and just posterior to the fibular head.

Work down through the layers posterior to the fibular head, identifying and protecting the common peroneal nerve before any bony work, then expose the PLC structures from superficial to deep.

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Structures at risk, by layer

Common peroneal nerve injury classification and recovery. The common peroneal nerve is the most common complication of this surgery. Mechanisms include drill penetration through the fibular head into the nerve roughly 2cm distal to the apex, direct trauma while freeing it from the fibular neck, excessive retractor traction and thermal injury from electrocautery.

Extensile options. Extend proximally along the femur (8-10cm) to expose the LCL femoral attachment on the lateral epicondyle; extend distally along the fibular shaft to follow the fibular neck and the course of the common peroneal nerve. A straight lateral approach (between the ITB and biceps, anterior to the biceps) is used for Schatzker I-III tibial plateau fractures and is distinct from the posterolateral approach, which is more posterior (posterior to the biceps) for the PLC structures and the fibular head. Closure. Layered closure over the reconstructed PLC; the lateral capsule and ITB-biceps interval are repaired. A haematoma drain is used at the surgeon's discretion. The knee is splinted or braced in extension.

• Anatomic PLC reconstruction (LaPrade) - the principal operation done through this exposure.
• Fibular head fracture ORIF - lag screws, a plate or suture anchors for an avulsion fragment.
• Common peroneal nerve exploration - neurolysis, primary repair or nerve grafting. Anatomic PLC reconstruction (LaPrade technique - gold standard). Reconstruct both the LCL (femoral epicondyle to fibular head) and the popliteofibular ligament (popliteus to fibular styloid), using allograft (Achilles tendon with a bone block, tibialis anterior or semitendinosus) or autograft (hamstring or quadriceps tendon). Allograft is preferred for combined ACL plus PLC so the hamstrings are preserved for an ACL autograft.

Combined ACL or PCL plus PLC: reconstruct concurrently, not staged. For a combined injury, reconstruct all torn structures in a single setting with the cruciate(s). Pooled data show about 9% posterolateral failure when all torn structures are reconstructed concurrently versus about 38% with acute repair of the corner plus staged cruciate reconstruction (Geeslin 2015); the mechanism of failure is that an unaddressed or under-reconstructed PLC leaves varus and rotatory laxity that overloads the cruciate graft (Gollehon 1987). The surgical sequence is PLC first, then ACL: drill and tension the PLC grafts (LCL at 30°, popliteus-PFL at 60-70°), then tension the ACL last, because PLC laxity allows the tibia to subluxate and would over-tension the ACL graft. The exception is severe soft-tissue injury with massive swelling or blisters after a knee dislocation with vascular repair - brace for 1-2 weeks for the swelling to settle, then perform the combined reconstruction (not separate staged procedures). Common peroneal nerve exploration. Findings dictate management: a nerve in continuity (contusion or neurapraxia, the most common) needs neurolysis (about 80% functional recovery); a clean laceration needs primary repair (about 60% recovery); and a gap greater than 1cm needs a sural nerve autograft (about 40% recovery). Fibular head fracture ORIF. Fix a large avulsion fragment (LCL or biceps insertion) displaced greater than 5mm with lag screws, a small plate or suture anchors depending on fragment size. Anatomic reduction and stable fixation give about 90-95% union; peroneal nerve injury is present in about 10-15% at presentation (associated with the fracture) and is iatrogenic in about 2-5% during surgery. Post-operative protocol. Hinged knee brace locked in extension for 2 weeks; partial weight-bearing (toe-touch) for 6 weeks; range of motion 0-90° for the first 6 weeks (no deep flexion, to protect the popliteus reconstruction); full range of motion by 8-12 weeks with strengthening; return to sport at 9-12 months (longer and the ACL timeline determines return when combined).