Popliteus Tendon

For Medical Students

What It Shows

The popliteus tendon runs from the lateral femoral condyle, through the joint, to the popliteus muscle behind the tibia. 2.10.2 covers the popliteus tendon anatomy.

Part of its course is intra-articular, which puts that part beyond a probe's reach. 5.2.8 covers reflection.

It matters because the accessible part is the musculotendinous portion and the sheath, and the part that matters to the corner is the part that is not accessible. 2.10.4 covers the posterolateral corner.

How It Is Acquired

Approach posterolaterally with the patient prone or in a lateral decubitus position. 5.4.4 covers the posterior knee.

Find the tendon in its groove on the lateral condyle, which requires the beam to angle under the lateral structures. 2.10.2 covers the popliteus tendon anatomy.

Follow it to the musculotendinous junction and the muscle behind the tibia. 2.10.2 covers the popliteus tendon anatomy.

Assess the sheath for fluid, which is often the only abnormality visible. 5.5.12 covers the bursa.

Accept that the intra-articular portion is not fully assessable and say so. 5.1.6 covers imaging pitfalls.

What Normal Looks Like

A tendon of fibrillar texture within its groove on the lateral condyle. 2.10.2 covers the popliteus tendon anatomy.

A clean musculotendinous junction continuing into the muscle.

A sheath without fluid distension. 5.5.12 covers the bursa.

No colour Doppler signal in the tendon. 5.2.11 covers Doppler imaging.

What Abnormal Looks Like

Fluid distending the popliteus sheath, which is often the first visible change. 5.5.12 covers the bursa.

Thickening or loss of the fibrillar pattern in the accessible portion. 5.5.10 covers the tendons.

An absent tendon in its groove, indicating avulsion or retraction. 5.10.2 covers popliteus injuries.

A fragment at the femoral attachment, indicating a bony avulsion. 5.3.14 covers avulsion injuries.

MRCS Level

How It Is Acquired

In a viva this is the tendon to name when asked which knee tendon ultrasound cannot assess completely.

The expected points are the posterolateral approach, the groove, the musculotendinous junction, the sheath, and the admission of incompleteness.

Say that the intra-articular portion is out of reach. 5.2.8 covers reflection.

Say that sheath fluid is a sensitive but non-specific sign. 5.5.12 covers the bursa.

Say that the corner is assessed on magnetic resonance imaging. 5.10.3 covers posterolateral corner injuries.

What Abnormal Looks Like

The reasoning expected is that an intra-articular tendon is surrounded by bone and joint, so the beam cannot reach it without crossing a cortical surface that reflects nearly everything. 5.2.8 covers reflection.

That makes the sheath, which lies more superficially, the accessible proxy, and a proxy is what sheath fluid is. 5.5.12 covers the bursa.

The popliteus contributes to rotational restraint, so its injury matters functionally more than its accessibility suggests. 3.10.6 covers the posterolateral corner function.

A bony avulsion at the femoral attachment is visible and is the one direct finding ultrasound gets here. 5.3.14 covers avulsion injuries.

How Good It Is

Ultrasound assesses the popliteus least completely of the knee tendons and is useful for its sheath.

Its best contribution is sheath fluid and a femoral bony avulsion, both of which raise a question worth pursuing. 5.3.14 covers avulsion injuries.

It is limited absolutely by the intra-articular course, so a normal study does not exclude a tendon injury. 5.10.2 covers popliteus injuries.

No figures appear for accuracy on this page, under decision 028, and the comparison is the claim: this tendon is assessed less completely than any other knee tendon, which is a comparison rather than a number.

FRCS Level

How Good It Is

At decision level this tendon is a magnetic resonance question and ultrasound contributes only at the margin.

Sheath fluid in a patient with lateral symptoms raises a corner question worth pursuing. 5.10.3 covers posterolateral corner injuries.

A bony avulsion at the femoral attachment is a direct finding with a surgical consequence. 5.3.14 covers avulsion injuries.

A corner injury assessment needs magnetic resonance imaging, because the operative decision rests on structures ultrasound cannot see. 5.10.3 covers posterolateral corner injuries.

A normal ultrasound here should be reported as an incomplete assessment rather than as a normal tendon. 5.20.1 covers structured reporting.

Where It Misleads

The commonest error is reporting the tendon as normal when only part of it was seen. 5.1.6 covers imaging pitfalls.

Sheath fluid is reported as a tendon tear. 5.5.12 covers the bursa.

Anisotropy in the obliquely running tendon is read as pathology. 5.2.10 covers anisotropy.

The approach is not attempted, so the structure is omitted from a lateral examination. 5.4.3 covers the lateral knee.

A normal study is taken to exclude a corner injury. 5.10.3 covers posterolateral corner injuries.

Fellowship Level

Where It Misleads

At fellowship level the popliteus is the structure that shows most clearly why knee ultrasound's limits should be stated in the report.

The tendon's intra-articular course is a physical barrier rather than a technique problem, so no operator skill removes it, and a reader cannot tell from a normal report how much was seen. 5.2.8 covers reflection.

A report that says the tendon was normal and a report that says the accessible portion was normal describe the same examination and license different conclusions. 5.20.1 covers structured reporting.

The popliteus complex is central to posterolateral restraint and is one of the structures whose injury most changes an operation, which makes the gap consequential rather than academic. 3.10.6 covers the posterolateral corner function.

Magnetic resonance imaging shows the whole course and still assesses the corner inconsistently, so the structure is difficult for both modalities rather than only for this one. 5.10.3 covers posterolateral corner injuries.

The practice worth keeping is to report what was accessible and to name what was not, which is the cheapest honesty available in this chapter. 5.20.1 covers structured reporting.