Popliteomeniscal Fascicles

For Medical Students

Structure and Location

Where the popliteus tendon crosses between the lateral meniscus and the capsule, the meniscus has no capsular attachment. Instead it is held by short bands running from its peripheral border to the tendon and its sheath.

These are the popliteomeniscal fascicles. Two are consistently described, an anteroinferior and a posterosuperior, and a third postero inferior band is described by some authors.

Together they form the walls of the popliteus hiatus, with the tendon running through the middle of it.

Relations

Medially and above: the peripheral border of the lateral meniscus, posterolateral part.

Laterally: the popliteus tendon in its sheath, and beyond that the capsule and the posterolateral corner structures.

The hiatus itself communicates with the joint, so the tendon sheath is continuous with the joint cavity at this point.

Function

The fascicles are the only thing holding the posterolateral meniscus in place. They allow it to move, which the meniscus needs to do, while stopping it from moving too far.

Because they attach to a tendon rather than to bone, the restraint is dynamic. When popliteus contracts, the fascicles pull the posterior horn posteriorly and laterally, which is one of the mechanisms that keeps the meniscus out from under the condyle in flexion.

Clinical Relevance

If the fascicles are torn the posterolateral meniscus becomes hypermobile. It can translate into the joint and catch, producing symptoms of a tear with a meniscus that looks intact.

That is the main reason these small structures are named at all. A normal looking meniscus that moves too much is a fascicle problem.

MRCS Level

Structure and Location

The hiatus is bounded by the fascicles. The anteroinferior fascicle runs from the inferior surface of the meniscus forwards and laterally to the tendon sheath; the posterosuperior fascicle runs from the superior surface backwards and laterally. Where a third is present it lies below and behind.

The fascicles are capsular derivatives rather than ligaments, and their size and number vary. That variability is one reason reported anatomy differs.

The tendon sheath within the hiatus is continuous with the synovial cavity, so a probe placed in the hiatus from inside the joint enters the sheath.

Relations

The popliteus tendon passes through the hiatus from its femoral origin to the muscle. It is intra-articular and extrasynovial along part of that course.

The popliteofibular ligament arises from the tendon distal to the hiatus and runs to the fibular styloid. 2.10.3 owns it.

The posterolateral corner structures lie outside the capsule and do not attach to the meniscus, so the meniscus is tethered to the tendon rather than to the corner.

The inferior lateral genicular artery runs just peripheral to the meniscus and crosses the region.

Blood Supply and Innervation

The fascicles carry the vessels and nerves that reach the posterolateral meniscal periphery, because the capsular tissue that would normally do so is absent.

That makes them the vascular route as well as the mechanical tether, and it is why a fascicle tear has consequences for healing as well as for position.

Mechanoreceptors are present in the fascicles, which supports the idea that they take part in dynamic control rather than acting as passive straps.

Function

Three functions are attributed to them: tethering the meniscus, transmitting popliteus contraction to it, and carrying its blood supply across the hiatus.

The dynamic function matters in flexion. As the knee bends, the lateral femoral condyle translates posteriorly a long way, and the meniscus has to move with it without being trapped. Popliteus pulling through the fascicles is part of how that is achieved.

Loss of the fascicles removes the restraint and the dynamic control together.

Clinical Relevance

Hypermobile lateral meniscus is the clinical entity. It presents as lateral joint line pain and catching with normal or near normal imaging, which is why it is missed.

Diagnosis is arthroscopic. The meniscus can be drawn into the joint with a probe, and the test is mobility rather than appearance.

The lesion is commonest in athletes and in knees with a discoid meniscus, where the attachment is abnormal to begin with.

Repair means reattaching the meniscus to the capsule and the sheath. 7.8 onwards owns the technique; the anatomical point is that there is no bone to fix to in this region.

FRCS Level

Relations

The region has no bony attachment and no capsule, so every repair here is soft tissue to soft tissue. That single fact shapes what is possible.

The popliteus tendon is immediately lateral to any suture placed in the hiatus, and capturing it is a recognised error that produces a tether rather than a repair.

Function

Normal lateral meniscal mobility is large and abnormal mobility is larger. There is no line that does not involve judgement, and the judgement is made against the patient's symptoms rather than against a measurement.

Over tightening the region removes the mobility the meniscus needs, so the aim is restraint rather than fixation.

Clinical Relevance

Consider hypermobile lateral meniscus in the athlete with lateral joint line symptoms, a normal scan and a normal looking meniscus, and test it with a probe before concluding the examination is normal.

In discoid meniscus surgery, assess the peripheral attachment after any central reshaping, because the two problems coexist and reshaping without stabilising leaves the instability.

Avoid capturing the popliteus tendon. The suture should engage capsule and sheath without crossing the tendon.

No measurement of normal or abnormal meniscal translation appears on this page. Published thresholds exist and could not be verified; the register is where a reviewer should add them.

Fellowship Level

Clinical Relevance

Three situations where fascicle anatomy is the whole problem.

The athlete with lateral symptoms and a normal scan. The lesion is invisible on imaging because the meniscus is intact, and the only way to find it is to look for it and probe it. A normal diagnostic arthroscopy that did not test lateral meniscal mobility has not excluded this.

The discoid meniscus with peripheral instability. The Wrisberg type has no posterior capsular attachment at all, so the meniscus is held only by the meniscofemoral ligament and whatever fascicles exist. Saucerisation alone leaves a mobile remnant, and that is the commonest route to a disappointing result.

The posterolateral region after previous surgery. Scar can either stabilise a hypermobile meniscus or tether a normal one, and distinguishing the two at revision is done by probing rather than by inspection.

In all three the structures are the same small bands described above. What changes is whether anyone looked for them.