Attachments

For Medical Students

Structure and Location

Four structures of consequence attach to the proximal fibula.

The lateral collateral ligament, descending from the lateral femoral epicondyle to the lateral aspect of the head.

The biceps femoris tendon, descending from behind to the head, with its own expansions.

The popliteofibular ligament, running from the popliteus tendon to the styloid process.

The peroneus longus, arising from the head and the upper lateral shaft.

Relations

The lateral collateral ligament and the biceps femoris converge on the head from different directions and their fibres blend there. The common peroneal nerve emerges from behind the biceps tendon immediately before crossing the neck, so the tendon is the landmark used to find the nerve.

The popliteofibular ligament lies deep to both, running up and medially to join the popliteus tendon inside the capsule.

The peroneus longus origin arches over the nerve, and the nerve passes between the muscle and the bone.

Function

Together these structures make the fibula the distal anchor of the lateral side of the knee.

The lateral collateral ligament resists varus. The popliteofibular ligament and the popliteus resist external rotation of the tibia. The biceps femoris flexes the knee and contributes to external rotation.

Because they converge on one small bone, an injury or an operation at the head affects varus and rotational restraint at the same time.

Clinical Relevance

An avulsion of the fibular styloid, sometimes called the arcuate sign, indicates injury to the posterolateral structures. The pathology belongs to Section 6; the attachment that avulses is here.

Finding the common peroneal nerve by following the biceps tendon is the practical consequence of the arrangement above.

MRCS Level

Structure and Location

Place each attachment precisely. The lateral collateral ligament inserts on the lateral aspect of the head, in a depression, with its insertion deep to the biceps expansion. The biceps femoris tendon inserts on the head posterolaterally, splitting around the collateral so that part of it passes superficial to the ligament and part attaches behind it. The popliteofibular ligament attaches to the styloid process, which is why an avulsion of the styloid implies that ligament.

The arcuate ligament, where present, arches over the popliteus from the styloid to the posterior capsule. Its presence is variable, which is one reason posterolateral corner descriptions differ between texts.

The anterior and posterior tibiofibular ligaments of the superior joint attach around the facet rather than to these structures.

Relations

Layered from superficial to deep on the lateral side: the iliotibial band most superficially, though it goes to the tibia rather than the fibula; then the biceps femoris with its expansions; then the lateral collateral ligament; then the popliteus and the popliteofibular ligament inside the capsule.

The common peroneal nerve lies behind the biceps tendon above the head and on the neck below it, so the tendon and the nerve are in a fixed relationship that holds in a scarred field as well as a clean one.

The inferior lateral genicular artery runs forward just above the head, deep to the lateral collateral ligament.

Blood Supply and Innervation

The attachments are supplied from the inferior lateral genicular artery and from branches of the peroneal and anterior tibial recurrent arteries. Being extracapsular, they retain a soft tissue blood supply after injury, which is why collateral injuries heal and cruciate injuries do not.

The popliteofibular ligament and the popliteus are intracapsular and share the popliteal and inferior genicular supply.

Innervation is from the common peroneal nerve and its recurrent branch, and from the nerve to popliteus from the tibial nerve.

Function

The lateral collateral ligament is the primary restraint to varus in the first part of flexion and becomes less effective as the knee bends.

The popliteofibular ligament, the popliteus tendon and the arcuate complex together restrain external rotation of the tibia, and they do most of that work in extension and early flexion.

Biceps femoris adds a dynamic contribution to both, which is why the posterolateral corner is described as having static and dynamic components.

Clinical Relevance

Posterolateral corner reconstruction reproduces two or three of these structures rather than all of them, and the fibular attachments are where the distal fixation goes.

The fixed relationship between the biceps tendon and the nerve is the reliable way to find the nerve in a revision or a swollen knee.

A styloid avulsion is an indirect sign of posterolateral injury and should prompt assessment of rotational stability rather than treatment of the fragment alone.

Harvesting or dividing the biceps tendon for reconstruction changes the dynamic restraint as well as providing graft, and that trade is anatomical.

FRCS Level

Relations

The posterolateral corner is a small region with many named structures and a contested nomenclature. The fibular attachments are the part everyone agrees on, which is why reconstructions are described from them.

The arcuate complex's variability means an operative finding that differs from the textbook is more likely to be normal variation than injury, and distinguishing the two is a judgement made at the time.

Function

Restoring varus restraint and restoring rotational restraint are separate goals with separate anatomy, and a single fibular based graft rarely does both well.

That is the argument for two tailed or anatomical reconstructions over single limb ones, and it follows from the fact that the collateral and the popliteofibular ligament run in different directions from nearly the same point.

Clinical Relevance

Fibular fixation in posterolateral reconstruction passes through or around a bone with the common peroneal nerve on its neck. The nerve is identified first in every described technique.

In combined cruciate and posterolateral injury the sequence of reconstruction matters, because tensioning one changes the position in which the other is tensioned.

Where the posterolateral structures cannot be reconstructed anatomically, the alternatives trade restraint for durability. Section 7 owns the comparison.

The published anatomy of this corner is quantitative and the figures differ between authors. None appears on this page, because a contested measurement written from memory is the worst of both.