Popliteofibular Ligament

For Medical Students

Structure and Location

The popliteofibular ligament runs from the popliteus tendon down to the fibula. It leaves the tendon close to where the tendon joins its muscle, and it attaches to the styloid process of the fibula.

It has two divisions. The posterior division is the larger and attaches to the back of the styloid; the anterior division is smaller and attaches in front of it.

Conventional teaching gives it a length of about 10 mm, which makes it short, thick and obliquely placed rather than a long cord.

It is part of the popliteus complex rather than a structure beside it. The muscle anchors to the tibia, the tendon to the femur, and this ligament to the fibula, so one unit holds three bones.

It is deep and covered by other structures, which is why most descriptions of the lateral side used to leave it out.

Relations

Above it: the musculotendinous junction of popliteus.

In front and above: the lateral collateral ligament, running down to its own attachment on the lateral face of the fibular head.

Behind: the posterolateral capsule and the lateral head of gastrocnemius.

Lateral and behind: the biceps femoris tendon, and behind that the common peroneal nerve. The nerve lies within a short distance of this ligament's fibular attachment, which 2.10.6 covers.

Function

It is a primary restraint to external rotation of the tibia. Of the three primary lateral structures it carries the largest share of that job.

It contributes to varus restraint as a secondary structure.

Because it anchors popliteus to the fibula, it converts the muscle's pull into a restraint on rotation rather than only into movement. 3.10.5 covers its contribution.

Clinical Relevance

Rotational laxity with a competent collateral ligament points here. The dial test is the examination and 4.13 covers it.

It is the structure most often missed on imaging and at operation, because it is short, deep and oblique.

Its fibular attachment is a few centimetres from the common peroneal nerve, so work on it is work beside the nerve.

MRCS Level

Structure and Location

Describe it as the fibular anchor of the popliteus complex. The complex has three attachments and this is the one that converts rotation into tension.

The posterior division is the functional one. Conventional teaching gives it a cross sectional area roughly twice the anterior division's.

The styloid attachment sits on the posteromedial aspect of the process, not the lateral. The collateral ligament takes the lateral face of the head and this ligament takes the medial side of the styloid, so the two do not compete for bone.

It is present in almost every knee when looked for carefully, which is worth saying because older descriptions called it variable.

Relations

It lies in the deep lamina of layer three with the popliteus tendon, deep to the collateral ligament.

The inferior lateral genicular artery crosses the field above it.

The fabellofibular ligament, when present, runs alongside it from the fabella to the styloid and can be mistaken for it. The distinguishing feature is the upper attachment: one goes to popliteus, the other to the fabella or the capsule.

The common peroneal nerve lies posterolateral. Conventional teaching puts it within about 2 cm of the styloid, which makes every fibular fixation a fixation near a nerve.

Blood Supply and Innervation

Supply is from the inferior lateral genicular artery and from branches of the popliteal artery through the posterolateral capsule.

The vascularity is capsular rather than periosteal, which is relevant where repair rather than reconstruction is being considered.

Nerve supply is from the posterior articular branches and from the recurrent articular branch of the common peroneal nerve.

Function

Sectioning studies make it the largest single contributor to external rotation restraint at 30 degrees of flexion, ahead of the popliteus tendon and the collateral ligament. 3.10.5 carries the figures.

Its contribution falls as the knee extends, where the collateral ligament and the capsule take more.

It and the popliteus tendon act as one structure functionally, so an account of either alone overstates what is lost when the other goes.

Clinical Relevance

Suspect it whenever the dial test is positive at 30 degrees. That is the angle at which it carries most of the restraint.

Expect imaging to under-report it. The ligament is short and oblique, so a single plane rarely contains its whole length, and 5.10.4 covers that.

Identify the fibular styloid as the landmark rather than the head. The two attachments on the fibula are on different bone and a few millimetres apart.

Protect the common peroneal nerve during any fibular fixation, because the styloid and the nerve are within about 2 cm.

FRCS Level

Relations

The fibula carries three attachments within a small area: the collateral ligament on the lateral head, this ligament on the posteromedial styloid, and the biceps tendon wrapping around both. A fibular tunnel has to pass between them.

The nerve is the fourth structure in that field and the only one whose injury does not recover reliably. 2.10.6 holds it and 2.10.7 the landmarks.

Its continuity with the popliteus tendon means there is no clean proximal border. An operation that reattaches this ligament has tensioned the tendon too.

Function

Treat external rotation restraint as belonging to this ligament first and the tendon second, which inverts the order most descriptions imply from their relative sizes.

A reconstruction that reproduces the collateral ligament alone leaves rotation unrestrained, so a lateral construct is judged on whether it crosses the fibula as well as the femur. 7.46 carries the technique.

Its short length makes graft tension sensitive to attachment position in a way a long ligament is not. A few millimetres of error is a large proportion of 10 mm.

Clinical Relevance

Assess rotation at 30 degrees specifically when staging a lateral injury, because that is where this structure carries most of the load.

Plan the fibular attachment from the styloid rather than from the head, and accept that the two lateral attachments are on different parts of the bone.

Consider graft length against the native 10 mm. A construct much longer than the ligament it replaces behaves differently through range.

Identify the peroneal nerve before passing anything through the fibula. This is the closest of the lateral structures to it.