Popliteus Injuries

For Medical Students

What It Shows

The popliteus passes from the lateral femoral condyle through the joint to the posterior tibia, with its tendon inside the capsule. 2.10.2 covers the popliteus tendon.

It appears on axial and coronal images running deep to the lateral collateral ligament. 5.5.10 covers the tendons.

It matters because it restrains external rotation as well as acting as a muscle, so its injury has a rotational consequence. 3.10.4 covers the popliteus function.

How It Is Acquired

Assess the tendon at its femoral attachment on coronal and axial images. 2.10.2 covers the popliteus tendon.

Follow it through the hiatus to the musculotendinous junction. 5.5.10 covers the tendons.

Assess the muscle belly for injury, which is a different problem from the tendon. 5.5.2 covers the sports knee protocol.

Assess the popliteomeniscal fascicles, which attach it to the lateral meniscus. 2.6.2 covers the popliteomeniscal fascicles.

Assess the other lateral structures. 5.10.3 covers PLC injuries.

What Normal Looks Like

A continuous tendon from the femoral attachment to the muscle. 2.10.2 covers the popliteus tendon.

A normal femoral attachment with no marrow change. 5.13.1 covers bone marrow oedema.

Intact popliteomeniscal fascicles. 2.6.2 covers the popliteomeniscal fascicles.

A muscle belly of normal signal. 5.5.10 covers the tendons.

What Abnormal Looks Like

Avulsion or discontinuity at the femoral attachment. 2.10.2 covers the popliteus tendon.

Fluid signal along the tendon within the hiatus. 5.5.10 covers the tendons.

Injury at the musculotendinous junction, which heals unlike an avulsion. 5.5.2 covers the sports knee protocol.

Disrupted popliteomeniscal fascicles with a hypermobile lateral meniscus. 5.5.8 covers the menisci.

Injury of the whole corner, with this tendon as one component. 5.10.3 covers PLC injuries.

MRCS Level

How It Is Acquired

In a viva the expected answer gives the tendon a ligament's role.

The expected points are the femoral attachment, the hiatus, the muscle, the fascicles, and the other lateral structures.

Say that the tendon restrains external rotation. 3.10.2 covers the external rotation stability.

Say that the attachment injury is the one that matters for stability. 3.10.4 covers the popliteus function.

Say that fluid in the hiatus is normal in small amounts. 5.5.10 covers the tendons.

What Abnormal Looks Like

The reasoning expected is that the tendon is intracapsular and attaches to the femur inside the joint, so it works as a static restraint there and as a muscle more proximally, and the site of injury decides which function is lost. 3.10.4 covers the popliteus function.

A femoral avulsion removes a rotational restraint and belongs with the corner injury. 3.10.6 covers the posterolateral corner function.

A musculotendinous injury is a muscle strain and recovers on a different timescale. 5.5.10 covers the tendons.

Disrupted fascicles make the lateral meniscus hypermobile, which is a mechanical symptom with no tear to find. 5.5.8 covers the menisci.

How Good It Is

Magnetic resonance imaging shows this tendon well and it is routinely read as though it were only a tendon.

Its best contribution is the femoral attachment and the site of injury along its length. 2.10.2 covers the popliteus tendon.

It is limited because small amounts of fluid in the hiatus are normal, because the fascicles are inconsistently seen, and because the rotational consequence is clinical. 4.13.3 covers the popliteus assessment.

No figures appear for accuracy on this page, under decision 028, and no tendon dimensions or fluid thresholds appear either: those are published quantities measured differently between studies and this environment cannot check them.

FRCS Level

How Good It Is

At decision level a femoral avulsion of this tendon is part of a corner injury and is treated as such. 3.10.6 covers the posterolateral corner function.

A musculotendinous injury alone is managed without an operation. 5.5.10 covers the tendons.

Fascicular disruption with a hypermobile meniscus is an arthroscopic finding more than an imaging one. 5.5.8 covers the menisci.

The cruciates and the rest of the corner decide the operation. 3.10.9 covers the combined PCL and PLC injury.

Chronic injury with rotational laxity needs the examination under anaesthesia. 4.13.5 covers the dial test.

Where It Misleads

The commonest error is reporting the tendon without its attachment site. 2.10.2 covers the popliteus tendon.

Normal hiatal fluid is read as a tear. 5.5.10 covers the tendons.

The tendon is confused with the lateral collateral ligament on coronal images. 2.10.1 covers the LCL.

A muscle strain is reported in the vocabulary of a ligament injury. 5.5.2 covers the sports knee protocol.

Fascicular disruption is omitted, because the fascicles were not assessed. 2.6.2 covers the popliteomeniscal fascicles.

Fellowship Level

Where It Misleads

At fellowship level the tendon arrives reported as tendinopathy in a knee with rotational instability. 3.10.2 covers the external rotation stability.

The report describes the structure and not its role, which is this chapter's recurring failure. 5.20.8 covers common reporting errors.

After a corner reconstruction the tendon's path may have been altered, so the expected appearance is technique specific. 5.10.6 covers the post-operative PLC imaging.

A hypermobile lateral meniscus explains symptoms that every structural report calls normal. 5.5.8 covers the menisci.

Dynamic ultrasound has been used for this and is operator dependent. 5.4.12 covers the PLC structures.

The useful report gives the attachment, the site along the tendon, the muscle, the fascicles and the rest of the corner. 5.20.1 covers structured reporting.