Tendon Imaging

For Medical Students

What It Shows

A tendon is the clearest case of ordered collagen in the knee, so it shows the orientation effect most strongly. 5.5.10 covers the tendons.

The extensor tendons run close to the field direction in a knee lying in the scanner, and the oblique tendons do not. 2.4.1 covers the anatomy.

It matters because a brightened normal tendon is reported as tendinopathy, and the clinical consequence is an investigation or a procedure for a tendon that is intact. 4.16.1 covers the quadriceps tendon.

How It Is Acquired

Look for the effect wherever a tendon changes direction within the imaged volume. 5.5.2 covers the sports knee protocol.

The popliteus runs obliquely through the lateral knee and is the knee's most reliable site for it. 5.10.2 covers popliteus injuries.

The distal biceps femoris and the hamstring attachments turn as they approach bone. 2.10.5 covers the biceps femoris.

The patellar and quadriceps tendons are usually spared by their orientation and are affected where the knee is flexed in the scanner. 4.16.2 covers the patellar tendon.

Repeat the appearance on a long echo time sequence before reporting it. 5.2.14 covers T2 imaging.

What Normal Looks Like

A normal extensor tendon is uniformly dark on every sequence. 5.5.10 covers the tendons.

A normal popliteus tendon can be bright on a short echo time sequence and dark on a long one, and both appearances are normal. 5.2.15 covers proton density imaging.

The brightness is confined to the segment at the critical orientation and stops where the tendon straightens. 5.2.20 covers the magic angle effect.

The tendon keeps its normal size and outline while it is bright. 5.4.8 covers the popliteus tendon.

What Abnormal Looks Like

Real tendinopathy thickens the tendon as well as brightening it. 4.16.6 covers hamstring tendinopathy.

Real tendinopathy stays bright when the echo time lengthens. 5.2.14 covers T2 imaging.

A tear interrupts the fibres, and orientation never does. 5.5.9 covers the ligaments.

Surrounding oedema or a bursal collection accompanies disease and not geometry. 5.5.12 covers the bursa.

Tenderness over the bright segment moves the question from the scanner to the patient. 4.16.3 covers jumper's knee.

MRCS Level

How It Is Acquired

In a viva this is the page to use when asked how to confirm an unexpected bright tendon.

The expected points are the oblique course, the short echo time, the long echo time test, the preserved tendon size, and the clinical correlation.

Say that the site is predictable from the anatomy rather than random. 2.10.2 covers the popliteus tendon.

Say that the tendon's calibre and outline are the features orientation leaves alone. 5.5.10 covers the tendons.

Say that ultrasound produces an equivalent error by a different mechanism. 5.2.10 covers anisotropy.

How Good It Is

For tendons the effect is the best understood false positive in knee magnetic resonance imaging, and it is still the one most often reported as disease.

Its best feature is that the sites are anatomically predictable, so a reader can expect them rather than discover them. 5.4.8 covers the popliteus tendon.

Its limit as a measurement is the chapter's general one: the tendon's angle was not chosen and was not recorded, so the degree of brightening carries no comparable meaning. 5.20.1 covers structured reporting.

Ultrasound examines tendons dynamically and at a chosen angle, which is the control magnetic resonance imaging lacks here, and it brings its own orientation error instead. 5.2.10 covers anisotropy.

No figures appear for accuracy on this page, under decision 028, and no angle, echo time or tendon thickness appears either: those are published quantities and this environment cannot check them.

FRCS Level

How Good It Is

At decision level this page stops a procedure being offered for a normal tendon.

A reported partial tear of the popliteus in a knee with no lateral tenderness and a normal examination is checked on the long echo time sequence first. 5.10.2 covers popliteus injuries.

A reported hamstring insertional change in an asymptomatic knee is the same pattern at a different site. 4.16.6 covers hamstring tendinopathy.

An intact tendon with normal calibre and a bright segment is a reason for suspicion rather than for action. 5.5.10 covers the tendons.

The examination decides, because the finding the scan cannot produce is tenderness. 4.16.2 covers the patellar tendon.

Where It Misleads

The commonest error is reporting a popliteus tendinopathy that does not exist. 5.10.2 covers popliteus injuries.

A tendon procedure is offered on the strength of one weighting. 5.4.19 covers PRP procedures.

The clinical picture is not used to challenge the report. 5.1.2 covers clinical examination versus imaging.

An asymptomatic patient enters follow up for an artefact. 5.1.4 covers imaging pathways.

The opposite error is made at the same sites: a genuine popliteus injury in a lateral corner injury is dismissed as orientation. 5.10.3 covers PLC injuries.

Fellowship Level

Where It Misleads

At fellowship level the tendon pages of this chapter describe a solved problem that is still being got wrong, and the interesting question is why.

Everything needed to avoid the error is standard, available and cheap, so its persistence locates the problem in reporting practice rather than in physics. 5.20.8 covers common reporting errors.

The structures affected are the ones a lateral corner reconstruction depends on, so the cost of both the false positive and the false negative is operative. 5.10.6 covers post-operative PLC imaging.

A post-operative tendon graft sits at whatever orientation the surgeon gave it, so the effect's site becomes technique specific after an operation. 5.17.1 covers ACL reconstruction.

The unrealised measurement is the same one the chapter opens with: order within a tendon, which is what tendinopathy is, and which brightness at an unrecorded angle cannot quantify. 5.19.2 covers the collagen architecture.