Tendons

For Medical Students

What It Shows

The knee's tendons include the quadriceps and patellar tendons anteriorly, the hamstrings medially and posteriorly, and the popliteus. 2.4.5 covers the patellar surgical relevance.

They appear dark, like the ligaments, because they are dense organised collagen. 5.5.9 covers the ligaments.

It matters because ultrasound resolves a superficial tendon better, and magnetic resonance imaging shows it alongside everything else in the knee. 5.4.6 covers the patellar tendon on ultrasound.

How It Is Acquired

Assess the extensor tendons on the sagittal images along their length. 5.5.1 covers the standard protocol.

Assess the hamstrings and popliteus on the axial and coronal images, where their courses are crossed. 5.4.8 covers the popliteus tendon on ultrasound.

Use a fluid sensitive sequence for peritendinous change and an intermediate weighting for the substance. 5.2.16 covers fat suppression.

Know that the magic angle effect brightens a normal tendon on short echo time sequences. 5.2.20 covers the magic angle effect.

Check any bright tendon on a long echo time sequence, which is the direct test. 5.2.14 covers T2 imaging.

What Normal Looks Like

Dark tendons of uniform calibre following their expected courses. 5.5.9 covers the ligaments.

A layered quadriceps tendon, whose layers are less separable here than on ultrasound. 5.4.5 covers the quadriceps tendon on ultrasound.

No peritendinous fluid beyond the normal sheath. 5.5.12 covers the bursa.

Some brightness at a curving segment on a short echo time sequence, which is the magic angle effect. 5.2.20 covers the magic angle effect.

MRCS Level

How It Is Acquired

In a viva this is the tissue to name when asked where the magic angle effect causes trouble.

The expected points are the sagittal extensor assessment, the axial and coronal courses, the two weightings, the magic angle effect, and the confirming sequence.

Say that a bright tendon must be checked on a long echo time sequence. 5.2.14 covers T2 imaging.

Say that ultrasound resolves a superficial tendon better. 5.4.6 covers the patellar tendon on ultrasound.

Say that this modality's advantage is context rather than resolution. 5.5.1 covers the standard protocol.

What Normal Looks Like

The reasoning expected is that ordered collagen's signal depends on its angle to the static field, so a tendon curving away from that direction brightens without any tissue change. 5.2.20 covers the magic angle effect.

That effect appears on short echo time sequences and disappears on long ones, which gives a definitive test available within the same study. 5.2.14 covers T2 imaging.

The ultrasound analogue is anisotropy, which arises from different physics and produces the same class of error, and the pairing is worth holding. 5.2.10 covers anisotropy.

This modality's real advantage for tendons is that it images the tendon and the joint together, so an extensor problem and an intra-articular one are distinguished in one study. 5.5.1 covers the standard protocol.

How Good It Is

Magnetic resonance imaging assesses the knee's tendons adequately and in context, and ultrasound assesses the superficial ones better.

Its best contribution is the whole knee context, which separates a tendon problem from an intra-articular one. 5.5.1 covers the standard protocol.

It is limited for fine internal tendon structure and for dynamic assessment, both of which ultrasound gives. 5.4.15 covers dynamic instability.

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

FRCS Level

How Good It Is

At decision level the choice between the two modalities for a tendon is a choice about what else needs looking at.

An isolated superficial tendon question is answered better and faster by ultrasound. 5.4.6 covers the patellar tendon on ultrasound.

A tendon question in a knee with other symptoms belongs here, because one study covers both. 5.5.1 covers the standard protocol.

A popliteus question belongs here, because its intra-articular course is beyond a probe. 5.4.8 covers the popliteus tendon on ultrasound.

A reported tendon abnormality in a functionally normal knee should be checked for the magic angle effect before anything else. 5.2.20 covers the magic angle effect.

Where It Misleads

The commonest error is reporting the magic angle effect as tendinopathy. 5.2.20 covers the magic angle effect.

A superficial tendon question is sent here when ultrasound would answer it better. 5.1.3 covers choosing the correct investigation.

Peritendinous fluid in a normal sheath is reported as pathology. 5.5.12 covers the bursa.

Layer level quadriceps detail is attempted here rather than on ultrasound. 5.4.5 covers the quadriceps tendon on ultrasound.

The confirming long echo time sequence is not reviewed. 5.2.14 covers T2 imaging.

Fellowship Level

Where It Misleads

At fellowship level the tendons are where the two modalities are genuinely complementary and are usually treated as alternatives.

Ultrasound gives resolution and movement, this modality gives context and reach, and the right answer depends on the question rather than on a ranking. 5.4.6 covers the patellar tendon on ultrasound.

Both have a characteristic orientation dependent false positive, the magic angle effect here and anisotropy there, which land on the same tendons from different physics. 5.2.10 covers anisotropy.

Both are also confounded by the appearance occurring in asymptomatic tendons, so the attribution of symptoms is a clinical act in either modality. 5.1.2 covers clinical examination versus imaging.

Ultra short echo time sequences image ordered collagen more directly and change the magic angle problem rather than removing it, and they are not routine. 5.18.4 covers ultra short echo time imaging.

The practical rule is to use ultrasound for an isolated superficial tendon and this modality when anything else in the knee is in question. 5.1.3 covers choosing the correct investigation.