Patellar Tendon

For Medical Students

What It Shows

The patellar tendon runs from the patellar apex to the tibial tuberosity, close to the skin along its whole length. 2.4.1 covers the patellar anatomy.

That makes it the single best imaged structure in the knee by ultrasound. 5.2.7 covers the frequency selection.

It matters because tendinopathy here is common in athletes, and the imaging appearance occurs in asymptomatic tendons too. 5.1.6 covers imaging pitfalls.

How It Is Acquired

Scan in long axis from the patellar apex to the tuberosity with the knee slightly flexed. 5.4.1 covers the anterior knee.

Scan in short axis as well, because the deep posterior portion is where change begins. 5.2.8 covers reflection.

Keep the beam perpendicular throughout, since the tendon curves at the patellar apex. 5.2.10 covers anisotropy.

Apply colour Doppler, because vascularity distinguishes an active process from a quiescent one. 5.2.11 covers Doppler imaging.

Compare with the other side, since the appearance is best judged comparatively. 5.4.1 covers the anterior knee.

What Normal Looks Like

A uniform bright fibrillar band of even thickness from apex to tuberosity. 5.5.10 covers the tendons.

A thin hypoechoic zone at the deep patellar insertion, which is a normal appearance. 5.2.10 covers anisotropy.

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

Symmetry with the contralateral tendon.

What Abnormal Looks Like

Focal thickening with loss of the fibrillar pattern, usually at the deep posterior proximal portion. 5.5.10 covers the tendons.

Hypoechoic change within the thickened area.

Colour Doppler signal within the tendon, indicating an active process. 5.2.11 covers Doppler imaging.

An anechoic cleft, indicating a tear rather than tendinopathy. 5.4.5 covers the quadriceps tendon.

MRCS Level

How It Is Acquired

In a viva this is the tendon to name when asked where ultrasound is the first line investigation.

The expected points are the two planes, the deep posterior portion, the perpendicular beam, the Doppler, and the comparison.

Say that the appearance is found in asymptomatic tendons. 5.1.6 covers imaging pitfalls.

Say that Doppler separates active from quiescent change. 5.2.11 covers Doppler imaging.

Say that the symptoms rather than the image establish the diagnosis. 5.1.2 covers clinical examination versus imaging.

What Abnormal Looks Like

The reasoning expected is that tendinopathy is a disorganisation of collagen with increased ground substance and water, so the fibrillar pattern is lost and the tendon swells. 5.5.10 covers the tendons.

The deep posterior proximal portion is where the tendon is compressed against the patellar apex in flexion, which is why change starts there. 3.12.3 covers the contact pressures.

Neovascularisation accompanies the active phase, which is what Doppler detects and why its presence changes the interpretation rather than the diagnosis. 5.2.11 covers Doppler imaging.

Because the appearance exists in asymptomatic tendons, the image establishes the tendon's state and the patient establishes whether it matters. 5.1.2 covers clinical examination versus imaging.

How Good It Is

Ultrasound describes this tendon's structure better than any other modality and cannot attribute symptoms to it.

Its best contribution is the structural description plus the activity assessment, in one quick examination. 5.2.11 covers Doppler imaging.

It is limited by the appearance occurring without symptoms, so a positive finding does not establish a cause. 5.1.6 covers imaging pitfalls.

No figures appear for accuracy on this page, under decision 028, and no tendon thickness values or Doppler grades appear either: those are published equipment dependent quantities and this environment cannot check them.

FRCS Level

How Good It Is

At decision level the ultrasound contributes to the loading conversation rather than to an operative one.

A thickened vascular tendon in a symptomatic athlete supports an active tendinopathy, which affects the rehabilitation timeline. 5.4.20 covers tendon procedures.

A thickened avascular tendon suggests chronic structural change, which is a different conversation with the same patient. 5.4.20 covers tendon procedures.

A discrete tear within a tendinopathic tendon is a separate finding with separate consequences. 5.4.5 covers the quadriceps tendon.

Whether to intervene is a Section 6 decision, and the imaging supplies the structural state rather than the indication. 5.1.3 covers choosing the correct investigation.

Where It Misleads

The commonest error is attributing anterior knee pain to an incidental appearance. 5.1.6 covers imaging pitfalls.

Anisotropy at the curved patellar apex is read as tendinopathy. 5.2.10 covers anisotropy.

Probe pressure abolishes the Doppler signal and the tendon is called quiescent. 5.2.11 covers Doppler imaging.

A normal deep insertional hypoechoic zone is reported as a lesion. 5.5.10 covers the tendons.

A thickness is quoted against a threshold from different equipment. 5.20.8 covers common reporting errors.

Fellowship Level

Where It Misleads

At fellowship level the patellar tendon is the clearest example in knee imaging of a finding whose prevalence in asymptomatic people undermines its diagnostic use.

The appearance is found in a substantial proportion of asymptomatic athletic tendons, so its presence shifts the probability of a diagnosis very little. 5.1.6 covers imaging pitfalls.

It is also found in athletes who later become symptomatic, which has made it a candidate screening finding without the predictive performance being established. 5.1.7 covers evidence based imaging.

Doppler vascularity and symptoms correlate inconsistently across studies, partly because the acquisition is not standardised between them. 5.2.11 covers Doppler imaging.

Elastography measures tissue stiffness, which is closer to the mechanical question than echogenicity is, and it is not in routine knee practice. 5.18.1 covers quantitative magnetic resonance imaging.

The disciplined report says what the tendon looks like, says whether it is vascular, and says that neither establishes the diagnosis. 5.20.1 covers structured reporting.