Lazy-S Incision | Mandatory CPN Protection | Subperiosteal Dissection
Surgical Imaging
The common peroneal nerve must be identified and protected in every case. It crosses the fibular neck 1-2 cm distal to the fibular head. Failure to protect it causes foot drop. Use a vessel loop for gentle retraction. Never place metal retractors directly on the nerve.
A lazy-S incision over the fibular head provides excellent exposure while allowing proximal and distal extension. Longitudinal incisions are acceptable but the S-shape reduces wound tension. The incision is centered over the fibular head and extends 3-4 cm proximally and distally.
The biceps femoris tendon and lateral collateral ligament insert on the fibular head. These must be preserved or carefully reattached if detached. Detachment is often required for full fibular head exposure but reattachment is essential for knee stability.
The anterior tibial artery arises from the popliteal artery and passes forward through the interosseous membrane approximately 2-3 cm distal to the fibular head. Subperiosteal dissection along the fibular neck protects these vessels.
Positioning the knee in 30-40 degrees of flexion relaxes the common peroneal nerve and facilitates its mobilization. Full extension places the nerve under tension and increases injury risk during retraction.
Always document ankle dorsiflexion and great toe extension pre-operatively and immediately post-operatively. This is both medicolegal and clinically essential. Most CPN neuropraxias recover within 3-6 months if the nerve was protected.
At a Glance
The approach to the proximal fibula and common peroneal nerve is a fundamental exposure in orthopaedic trauma and reconstructive surgery. The fibular head serves as the attachment point for the posterolateral corner structures and is the site where the common peroneal nerve is most vulnerable. The approach is performed with the patient supine and the knee flexed to relax the nerve. A lazy-S incision centered over the fibular head allows excellent visualization. The central principle is early identification and protection of the common peroneal nerve before any deep dissection. Subperiosteal elevation along the fibular neck protects the anterior tibial vessels as they traverse the interosseous membrane. This approach is used for CPN decompression, fibular head excision, posterolateral corner reconstruction, proximal tibiofibular joint procedures, and tumour resection.
CPN SAFECPN PROTECTION - Surgical Principles
Hook:CPN is the most important structure - keep it SAFE at every step!
FIBULAPROXIMAL FIBULA APPROACH - Key Steps
Hook:FIBULA approach - always protect the nerve first!
DANGERDANGER STRUCTURES BY LAYER
Hook:Know the DANGER structures at every layer!
Indications and Approach Selection
Primary Indications:
- Common peroneal nerve decompression at the fibular neck (most common)
- Fibular head excision for tumours, nonunion, or arthritis
- Posterolateral corner reconstruction - tunnel placement and graft passage
- Proximal tibiofibular joint arthrotomy, stabilization, or fusion
- Tumour excision involving the proximal fibula
- Revision surgery for failed prior procedures around the fibular head
Why This Approach is Chosen:
The proximal fibula is the site where the common peroneal nerve is most susceptible to compression and injury. Direct exposure allows safe nerve decompression, secure reattachment of posterolateral corner structures, and access to the fibular head for oncologic or reconstructive procedures. The approach provides extensile access proximally along the biceps tendon and distally along the fibular shaft.
Contraindications:
- Active infection over the proposed incision site
- Severe soft tissue compromise requiring delayed surgery
- Medical instability precluding positioning
- Isolated medial or anterior compartment pathology better addressed through other approaches
Alternative Approaches:
- Anterolateral approach to the knee: For intra-articular pathology without CPN involvement
- Posterolateral approach to the tibia: For tibial plateau fractures requiring buttress plating
- Lateral approach to the fibular shaft: For mid-shaft fibula fractures or nonunion
Overview
Approach to the Proximal Fibula and Common Peroneal Nerve provides direct access to the fibular head, fibular neck, and the common peroneal nerve as it winds around the neck. The approach is designed around mandatory early nerve identification and protection.
Key Characteristics:
- Supine position with knee flexed 30-40 degrees
- Lazy-S or longitudinal incision over fibular head
- Early CPN identification before deep dissection
- Subperiosteal dissection protects anterior tibial vessels
- Extensile proximally and distally as needed
Why This Approach Matters:
- CPN injury is a devastating complication causing foot drop
- Proximal fibula procedures require precise nerve localization
- Posterolateral corner reconstruction relies on this exposure
- Tumours of the fibular head demand oncologic margins with nerve preservation
Exam Relevance:
- Classic high-yield approach for Operative Surgery viva
- CPN protection sequence is frequently examined
- Knowledge of danger structures by layer is essential
Anatomy
Bony Anatomy:
The fibular head is a rounded prominence on the posterolateral aspect of the proximal tibia. It articulates with the lateral tibial condyle at the proximal tibiofibular joint. The fibular neck lies immediately distal to the head and is the site where the common peroneal nerve is most vulnerable as it winds around the bone. The anterior tibial artery passes forward through the interosseous membrane approximately 2-3 cm distal to the fibular head.
Muscular and Ligamentous Attachments:
The biceps femoris tendon inserts on the fibular head. The lateral collateral ligament also attaches to the fibular head. The peroneus longus originates from the proximal fibula and lateral tibial condyle. The soleus has a proximal origin from the fibular head and posterior tibia.
Neurovascular Anatomy:
The common peroneal nerve (L4-S2) courses along the posterior border of the biceps femoris, then winds laterally around the fibular neck 1-2 cm distal to the fibular head. It divides into the deep and superficial peroneal nerves within the peroneal compartment. The anterior tibial artery arises from the popliteal artery at the lower border of the popliteus and passes forward above the upper border of the interosseous membrane.
Three Key Relationships:
- The CPN lies superficial to the lateral head of gastrocnemius and deep to the biceps femoris before reaching the fibular neck
- The anterior tibial vessels pass through the interosseous membrane just distal to the fibular neck
- The peroneal artery runs in the posterior compartment and may be encountered with deep posterior dissection
Internervous Plane
Deep Internervous Plane:
There is no classical internervous plane in the superficial layers of this approach. The common peroneal nerve itself is the structure that must be mobilized and protected. Once the nerve is identified and slung, the deep dissection proceeds subperiosteally along the fibular neck and head.
Superficial Dissection:
The approach passes through skin and subcutaneous tissue directly over the fibular head. The fascia over the peroneal compartment is incised. The CPN is identified as it crosses the fibular neck and is carefully mobilized with a vessel loop.
Deep Dissection:
Subperiosteal elevation along the fibular neck and head exposes the bone while protecting the anterior tibial vessels. If posterolateral corner reconstruction is planned, the biceps tendon and LCL are identified and tagged for later reattachment or used for graft passage.
The approach does not rely on a traditional internervous plane between two muscles supplied by different nerves. Instead, the critical plane is the perineural plane around the common peroneal nerve. Once the nerve is protected, all further dissection is subperiosteal on bone. This minimizes risk to the anterior tibial artery origin and the peroneal artery branches. The biceps femoris tendon may be partially released from the fibular head for exposure but must be securely reattached.
Structures at Risk in Each Layer:
- Structure
- Lateral sural cutaneous nerve
- Protection Strategy
- Identify and preserve if encountered
- Structure
- Common peroneal nerve
- Protection Strategy
- Identify first, vessel loop, gentle retraction only
- Structure
- Biceps femoris tendon and LCL
- Protection Strategy
- Tag and reattach if detached
- Structure
- Peroneal artery branches
- Protection Strategy
- Ligate small branches, preserve major vessels
- Structure
- Anterior tibial artery origin
- Protection Strategy
- Stay strictly subperiosteal on fibular neck
Positioning and Patient Setup
Position: Supine with Knee Flexed
Pre-positioning Checklist:
- Confirm no contraindication to supine positioning
- Apply tourniquet high on thigh if planned
- Pad all pressure points including contralateral leg
- Radiolucent table for fluoroscopy if needed
- C-arm positioned for AP and lateral views of knee
Positioning Details:
- Supine position on radiolucent table
- Knee flexed 30-40 degrees over a bolster (relaxes CPN)
- Hip slightly externally rotated to bring fibular head forward
- Foot supported to allow ankle dorsiflexion testing
- Tourniquet applied high on thigh, inflated after draping
Knee flexion is essential to relax the common peroneal nerve. Full extension places the nerve under tension and increases the risk of stretch injury during retraction. Document the position and the nerve status before incision.
Surgical Technique
Patient Position:
Supine with the knee flexed 30-40 degrees over a bolster. The hip is slightly externally rotated to bring the fibular head into prominence. A tourniquet is applied high on the thigh.
Surface Landmarks:
- Fibular head (most prominent bony landmark laterally)
- Lateral joint line of the knee
- Biceps femoris tendon (palpable proximally)
- Fibular shaft (distal to head)
- Common peroneal nerve (can often be palpated as it crosses the fibular neck)
Incision Planning:
A lazy-S incision is marked centered over the fibular head. The proximal limb curves posteriorly along the biceps tendon. The distal limb extends along the posterior border of the fibular shaft. Total length 6-8 cm for standard exposure, extendable proximally or distally.
Structures at Risk
THE most important structure at risk. Winds around the fibular neck 1-2 cm distal to the fibular head. Injury causes foot drop with loss of ankle dorsiflexion and toe extension. Prevention: early identification, vessel loop protection, knee flexion, no metal retractors, release retractors every 20 minutes.
Arises from the popliteal artery and passes forward through the interosseous membrane 2-3 cm distal to the fibular head. Protected by strict subperiosteal dissection along the fibular neck. If injured, repair or ligate depending on collateral flow.
Inserts on the fibular head. May require partial release for full exposure. Must be securely reattached at closure to maintain knee stability and prevent varus laxity. Use heavy non-absorbable suture through bone tunnels or anchors.
Attaches to the fibular head. Tagged and protected or reattached if released. Essential for varus stability of the knee. Reattachment technique must restore isometric tension.
Run in the posterior compartment. Small branches may be ligated. Major vessel injury requires repair. Usually not encountered with correct subperiosteal plane.
Superficial sensory branch that may be encountered during skin incision. Preserve if possible to avoid numbness over the lateral calf. Usually not functionally significant if divided.
CPN Injury Management:
- If nerve identified as damaged intra-operatively: primary repair if transected, or nerve graft if gap present
- Post-operative foot drop: ankle-foot orthosis, physiotherapy, serial nerve conduction studies
- Most neuropraxias recover within 3-6 months; axonotmesis may take 6-12 months
- Exploration indicated if no recovery by 3 months with positive EMG changes
References
Anatomic variations related to decompression of the common peroneal nerve at the fibular head
The anatomical relationship of the common peroneal nerve to the proximal fibula and its clinical significance when performing fibular-based posterolateral reconstructions
Peroneal Nerve Palsy: Evaluation and Management
Outcomes of treatment of acute grade-III isolated and combined posterolateral knee injuries: a prospective case series and surgical technique
Exam Viva Scenarios
Practise clinical reasoning and management decisions out loud
“A 35-year-old man presents with foot drop after a knee dislocation 3 months ago. Nerve conduction studies show compression at the fibular neck. Describe your surgical approach for decompression.”
“A 22-year-old woman has a biopsy-proven osteochondroma of the fibular head causing CPN irritation. Describe your approach for excision.”
“A 28-year-old athlete has chronic posterolateral rotatory instability after a knee injury. MRI shows PLC injury. Describe the surgical approach for anatomic reconstruction.”