Clinical Importance

For Medical Students

Structure and Location

The clinical importance of the proximal fibula is almost entirely about one relation. The common peroneal nerve crosses the neck of the fibula, where it is subcutaneous and lies directly on bone with nothing between the two.

No other major nerve in the limb is as exposed as this. It can be rolled under a finger in a thin person.

Relations

Above the head the nerve lies behind the biceps femoris tendon. It then crosses the neck laterally, passes deep to the origin of peroneus longus, and divides into the superficial and deep peroneal nerves.

Because the muscle origin arches over it, the nerve passes through a tunnel that is fibrous on one side and bone on the other.

The superior tibiofibular joint lies immediately above and medial, and may communicate with the knee.

Function

The deep peroneal nerve supplies the anterior compartment, which dorsiflexes the ankle and extends the toes. The superficial peroneal nerve supplies the lateral compartment and the skin of the dorsum of the foot.

A lesion at the neck of the fibula therefore produces a foot drop and sensory loss over the dorsum, with the first web space the most reliably affected area.

Clinical Relevance

Examine ankle dorsiflexion and first web space sensation in any knee injury, any knee operation and any plaster or splint around the knee.

Pressure at this point is enough to injure the nerve. A tight bandage, a badly placed support, or a long period lying with the leg externally rotated can all do it.

Management of a nerve injury belongs to Sections 6 and 7. What belongs here is that the anatomy makes the nerve both easy to injure and easy to test.

MRCS Level

Structure and Location

The nerve's course has three parts worth naming. Behind the biceps tendon above the head. On the neck, subcutaneous and on bone. Then through the fibular tunnel under the peroneus longus origin, where it divides.

The tunnel is where a compressive lesion most often sits, because that is the only part of the course where the nerve is enclosed.

Relations

The biceps femoris tendon is the landmark above. The peroneus longus origin is the roof of the tunnel below. The fibular neck is the floor throughout.

The recurrent branch leaves before the division and ascends to the anterolateral capsule of the knee, which is why anterolateral knee pain can be referred in this territory.

A ganglion arising from the superior tibiofibular joint can track along the nerve, and because the joint may communicate with the knee, the cyst can be of knee origin.

Blood Supply and Innervation

The nerve's own supply at this level is from the inferior lateral genicular artery and small branches of the anterior tibial recurrent artery, forming a longitudinal plexus in the epineurium.

That plexus is why a nerve can be mobilised over a short distance without devascularising it and why a long mobilisation is different.

The territories to document are the deep peroneal supply to the anterior compartment and the superficial peroneal supply to the lateral compartment and the dorsal skin.

Function

The nerve has no motor function at the knee. Everything it does is distal, which is why a knee problem presents as an ankle and foot problem.

That separation is diagnostically useful: a foot drop with a normal knee examination still points at the fibular neck, and a knee injury with a normal foot does not exclude a traction injury that will declare itself later.

Clinical Relevance

Document dorsiflexion and first web space sensation before and after any procedure around the lateral knee. A deficit found afterwards without a preoperative record is a problem for everyone.

In knee dislocation the nerve is injured in a substantial minority of cases, and the mechanism is traction rather than compression, which is why the prognosis differs from a compressive palsy.

In high tibial osteotomy and in lateral approaches the nerve is at risk, and 7.49 owns the operative detail.

Positioning a patient with the knee flexed over a support, or in prolonged lithotomy, puts pressure exactly here. It is a theatre and ward problem as much as a surgical one.

FRCS Level

Relations

In a scarred or dislocated knee the reliable landmark is the biceps tendon, not the skin or the fibular head, because the tendon and the nerve keep their relationship when everything else has moved.

Where previous surgery has been done laterally, the nerve may be adherent to the neck, and the plane that normally exists between them may not.

Function

A traction injury and a compression injury at the same point behave differently, and that difference is anatomical: a compressive lesion is localised to the tunnel and a traction lesion damages the nerve over a length.

That is why the recovery of a dislocation related palsy is harder to predict than the recovery of a plaster related one.

Clinical Relevance

Identify and protect the nerve in every posterolateral approach, every proximal fibular procedure and every opening wedge osteotomy that approaches the lateral cortex.

In knee dislocation, a nerve deficit changes the plan: it affects the order of reconstruction, the rehabilitation and the counselling, and it is documented before any reduction attempt where possible.

Decompression, repair and grafting of this nerve are owned by 7.49. The anatomical point that governs all three is that the nerve is fixed proximally behind the biceps and distally in the tunnel, so the mobile segment between them is short.

Published figures for the nerve's distance from bony landmarks vary with knee position. One appears on 2.3.1, registered and unchecked. A reviewer should treat it as a starting point rather than a safe margin.