Anatomy

For Medical Students

Structure and Location

The proximal fibula is the head and neck of a long, thin bone lying lateral and posterior to the tibia. The head is expanded and carries a flat facet on its anteromedial surface for the tibia. From the posterolateral part of the head a small upward projection rises, the styloid process.

Below the head the bone narrows into the neck before continuing as the shaft. The neck is the part that matters clinically, because of what crosses it.

The fibula takes no significant part in the knee joint itself. It does not articulate with the femur and it carries no meniscus.

Relations

Medially: the lateral surface of the proximal tibia, with the superior tibiofibular joint between them.

Laterally and posteriorly: the common peroneal nerve, which crosses the neck of the fibula from behind to the front. It is subcutaneous at that point and lies directly on bone.

Above: the lateral collateral ligament and the biceps femoris tendon converge on the head. 2.3.2 covers the attachments.

Below: the peroneus longus arises from the head and the upper shaft, and its fibres arch over the nerve as it passes forward.

Function

The proximal fibula is an attachment point rather than a load bearing column. It transmits very little axial load compared with the tibia.

Its contribution to the knee is indirect. By anchoring the lateral collateral ligament and the posterolateral structures, it is the distal end of the lateral restraint of the knee.

The superior tibiofibular joint allows small movement as the ankle moves, so the proximal fibula is not rigidly fixed to the tibia.

Clinical Relevance

The head is palpable in everyone and is the landmark for the lateral side of the knee.

The common peroneal nerve lying on the neck is the single most important fact about this bone. Anything done to the proximal fibula puts that nerve at risk, and 2.3.3 covers it.

Because the fibula carries little load, the proximal part can be sacrificed in some operations. The cost is the attachments and the nerve, not the weight bearing.

MRCS Level

Structure and Location

Describe the head, the styloid and the neck. The head carries the tibial facet anteromedially, facing up, forward and medially. The styloid process rises from its posterolateral part and is the attachment of the posterolateral structures. The neck is the constriction immediately below.

The superior tibiofibular joint is a plane synovial joint with its own capsule, reinforced by anterior and posterior tibiofibular ligaments. Its obliquity varies between people, and a more horizontal joint permits more movement than a more oblique one.

Relations

The common peroneal nerve emerges from behind the biceps femoris tendon, crosses the neck under the peroneus longus origin, and divides into the superficial and deep peroneal nerves. It lies of the order of 2 cm distal to the tip of the fibular head at that point.

The superior tibiofibular joint occasionally communicates with the knee through a recess behind the popliteus tendon, which is how a ganglion arising from the joint can reach the nerve.

Anteriorly the anterior compartment arises from the tibia and the interosseous membrane, with the anterior tibial artery passing forward through the membrane above.

Posteriorly the soleus arises in part from the posterior surface of the head and the upper shaft.

Blood Supply and Innervation

The proximal fibula is supplied by the inferior lateral genicular artery above and by the anterior tibial recurrent artery, with branches of the peroneal artery below. The periosteal supply around the head is good, which is relevant where it is used as a vascularised graft elsewhere in the body.

Innervation of the superior tibiofibular joint capsule is from the recurrent branch of the common peroneal nerve and from the nerve to popliteus.

The common peroneal nerve itself is a relation rather than a supply, and it is the structure every description of this bone has to account for.

Function

Axial load through the fibula is a small fraction of that through the tibia, and almost all of it is transmitted distally rather than proximally.

The proximal fibula's real function is to anchor the lateral collateral ligament, the biceps femoris and the popliteofibular ligament. It is the fixed point against which the lateral side of the knee is restrained.

Because the superior tibiofibular joint moves with ankle motion, that fixed point is not entirely fixed, which is part of why posterolateral reconstructions behave differently from medial ones.

Clinical Relevance

Fibular head excision or osteotomy divides the lateral collateral and the posterolateral attachments, so it destabilises the knee laterally unless they are reconstructed.

The nerve's position of a couple of centimetres below the head tip is the practical reason a lateral incision is planned from the head rather than from the joint line.

A ganglion of the superior tibiofibular joint is a recognised cause of common peroneal nerve palsy, and it reaches the nerve because the joint may communicate with the knee.

The fibula is used as a free vascularised graft in reconstructive surgery elsewhere, and the proximal part is usually left to preserve the knee attachments and the nerve.

FRCS Level

Relations

In a posterolateral approach the fibular head is the landmark and the nerve is the constraint. The nerve is identified behind the biceps tendon and followed round the neck, because estimating its position from the skin is less reliable than finding it.

The joint's possible communication with the knee means fluid or air introduced into the knee can appear at the fibular head, and a cyst there can be of knee origin.

Function

Treating the proximal fibula as a fixed point is an approximation. It moves with the ankle, and a reconstruction anchored to it inherits that movement.

That is one argument for tibial based rather than fibular based posterolateral reconstruction, and it is anatomical rather than empirical. Section 7 owns the choice.

Clinical Relevance

Any procedure at the fibular head is a nerve operation as much as a bone operation. Identifying the nerve first is the standard of care rather than a precaution.

In high tibial osteotomy the proximal fibula and the superior tibiofibular joint constrain the correction, and whether the joint is released is part of the plan.

In tumour resection around the proximal fibula the nerve is usually the structure that decides whether limb salvage is possible.

Every published measurement of the nerve's course here is a distance from the fibular head or styloid. One figure appears on this page, registered and unchecked; the rest need a source.