Meniscal Imaging

For Medical Students

What It Shows

The meniscus is built from collagen running around its circumference, which is the arrangement the orientation effect needs. 2.5.1 covers the gross anatomy.

Because the fibres follow the curve, the angle between them and the field is different at the anterior horn, the body and the posterior horn. 2.5.5 covers the MRI anatomy.

It matters because meniscal signal is graded and reported, and part of that signal varies with position for reasons that have nothing to do with the meniscus. 5.6.2 covers meniscal signal grading.

How It Is Acquired

Read the meniscus on more than one plane, because a plane cuts the circumferential fibres at a different angle in each part of the joint. 5.5.8 covers the menisci.

Expect the angle to vary smoothly from front to back rather than at one site. 2.6.1 covers the gross anatomy.

Compare the two menisci in the same knee, since their curvature differs and the field does not. 2.6.5 covers the MRI anatomy.

Test any signal change that could alter management on a long echo time sequence. 5.2.14 covers T2 imaging.

Keep the report to what survives that test. 5.20.2 covers reporting meniscal tears.

What Normal Looks Like

A normal meniscus is uniformly dark on the sequences used to judge its substance. 5.6.1 covers the normal meniscus.

Regions where the fibres approach the critical orientation can carry a faint internal signal that is not a tear. 5.6.2 covers meniscal signal grading.

That signal has no surface and does not reach an articular edge. 5.6.3 covers the horizontal tears.

The meniscal shape, height and position stay normal while it is present. 5.6.11 covers meniscal extrusion.

What Abnormal Looks Like

A tear reaches a surface, and an orientation signal does not. 5.6.4 covers the vertical tears.

A tear has an orientation of its own set by the injury rather than by the scanner. 5.6.5 covers the radial tears.

A displaced fragment is a mechanical finding that no artefact produces. 5.6.6 covers the bucket handle tears.

Degenerate meniscal substance carries signal that persists as the echo time lengthens. 5.6.8 covers the complex tears.

A root injury shows as extrusion, which is a position rather than a signal. 5.6.9 covers the root tears.

MRCS Level

How It Is Acquired

In a viva the expected answer separates internal signal from a tear by whether it reaches a surface.

The expected points are the circumferential fibres, the varying angle, the absence of a surface, the long echo time test, and the mechanical findings.

Say that the two menisci curve differently in the same field. 2.6.1 covers the gross anatomy.

Say that signal grading was built on appearances acquired at uncontrolled angles. 5.6.2 covers meniscal signal grading.

Say that the shape and position of the meniscus are the findings orientation cannot alter. 5.6.11 covers meniscal extrusion.

How Good It Is

The meniscus is where this chapter's claim is weakest and most interesting. The physics applies to circumferential collagen, and how much of the reported meniscal signal it accounts for has not been established here.

Its best contribution is a candidate explanation for part of the over-reporting of meniscal signal, which is a known and costly problem. 5.20.2 covers reporting meniscal tears.

It is limited because degenerate meniscus and orientation both produce internal signal without a surface, so the appearances overlap. 5.6.8 covers the complex tears.

It is limited again because the page states a candidate explanation and no evidence for its size. This environment has no source access, so the chapter will not put a number or a confident claim on it. 5.1.7 covers evidence-based imaging.

No figures appear for accuracy on this page, under decision 028, and no angle, signal grade or meniscal dimension appears either: those are published quantities measured differently between studies and this environment cannot check them.

FRCS Level

How Good It Is

At decision level the question is whether a knee goes to arthroscopy, and meniscal signal without a surface is the commonest reason it should not.

Internal signal with no surface and no mechanical symptom is a reason to treat the patient rather than the scan. 5.6.2 covers meniscal signal grading.

A degenerate meniscus in an arthritic knee changes the operation that is discussed, so the distinction is not academic. 5.20.6 covers reporting OA.

A tear whose plane is set by the injury and reaches a surface is the finding that matters. 5.6.5 covers the radial tears.

Extrusion and root integrity decide more than substance signal does, and neither is orientation dependent. 5.6.9 covers the root tears.

Where It Misleads

The commonest error is grading internal signal as a tear. 5.6.2 covers meniscal signal grading.

The posterior horn is reported as degenerate because it is where the signal tends to appear. 5.5.8 covers the menisci.

One plane is used to call a tear that the other plane does not show. 5.6.4 covers the vertical tears.

An arthroscopy is offered for an appearance without a mechanical symptom. 5.1.4 covers imaging pathways.

The reverse error is also made: a genuine degenerate meniscus is dismissed because the reader has heard that meniscal signal is unreliable. 5.20.8 covers common reporting errors.

Fellowship Level

Where It Misleads

At fellowship level the meniscus is the structure where the chapter's unrealised measurement would be worth most, and where the chapter can promise least.

Meniscal substance quality decides whether a tear is repairable, and no imaging measurement reports it, which is why repairability is assessed through the arthroscope. 5.6.13 covers meniscal repair imaging.

An orientation sensitive measurement of circumferential fibre order would be aimed exactly at that question, and the step from physics to measurement has not been taken in routine practice. 5.19.6 covers the cartilage applications.

A transplanted or repaired meniscus holds fibres at a new orientation, so the post-operative appearance is not comparable with the pre-operative one. 5.6.14 covers meniscal transplantation imaging.

The chapter's rule holds hardest here: the signal that is graded most often is the signal whose driving variable is recorded least. 5.19.1 covers the physics of magic angle imaging.