Root Tears

For Medical Students

What It Shows

The root is where the meniscus attaches to the tibia, and a root tear detaches it so the circumferential fibres have nothing to pull against. 2.5.7 covers the root attachments.

The meniscus can then extrude from the joint under load, which is why a root tear behaves like a meniscectomy even though the meniscus is intact. 3.6.9 covers root biomechanics.

It matters because a root tear is a small lesion with a large mechanical consequence, and it is easy to overlook. 5.6.11 covers meniscal extrusion.

How It Is Acquired

Look at the root attachments deliberately, on the coronal images where the root inserts near the centre of the tibia. 5.5.1 covers the standard protocol.

Follow the root on consecutive sagittal images, since the posterior medial root is the commonest site and is small. 2.5.7 covers the root attachments.

Look for the ghost sign, where the root is not visible on a slice it should occupy. 5.6.1 covers the normal meniscus.

Measure extrusion on the coronal image, because extrusion is the consequence and is often more conspicuous than the tear. 5.6.11 covers meniscal extrusion.

Look for subchondral signal change in the same compartment, which accompanies the sudden loss of load distribution. 5.11.7 covers bone marrow lesions.

What Abnormal Looks Like

Fluid signal interrupting the root at its tibial attachment, or a root that cannot be seen where it should be.

Extrusion of the meniscal body beyond the tibial margin on the coronal image, which is the mechanical consequence. 5.6.11 covers meniscal extrusion.

Subchondral marrow signal in the compartment, sometimes with a subchondral insufficiency fracture, in a knee that has suddenly lost its load distribution. 5.13.4 covers insufficiency fractures.

A knee that is otherwise not very degenerate, because a root tear can occur in a compartment with reasonable cartilage. 5.11.1 covers normal cartilage.

MRCS Level

How It Is Acquired

In a viva this is the lesion to name when asked what is easy to miss, and the expected answer links it to extrusion.

The expected points are the deliberate look at the roots, the coronal and sagittal assessment, the ghost sign, extrusion, and the subchondral marrow.

Say that the posterior medial root is the commonest site. 2.5.7 covers the root attachments.

Say that extrusion is the finding to measure. 5.6.11 covers meniscal extrusion.

Say that a root tear behaves mechanically like a meniscectomy. 3.6.9 covers root biomechanics.

What Abnormal Looks Like

The reasoning expected is that the meniscus resists load by developing circumferential tension, and tension needs an anchor at both ends. 3.6.2 covers hoop stress.

Detaching one end converts the meniscus from a load bearing ring into a free structure that is pushed out of the joint. 3.6.11 covers the effects of root tears.

The compartment then loads a smaller area at higher pressure, which is the mechanism of the rapid cartilage loss and the subchondral change. 3.6.5 covers load sharing.

That is why a root tear can produce a sudden clinical deterioration in a knee that was previously tolerable. 5.13.4 covers insufficiency fractures.

How Good It Is

Root tears are detected much better than they used to be, and the improvement came from looking rather than from better sequences.

Its best contribution is detecting a lesion with a specific operative answer in a compartment that may still be worth saving. 5.6.13 covers meniscal repair imaging.

It is missed when the roots are not assessed specifically, and the extrusion is then reported without its cause. 5.20.2 covers reporting meniscal tears.

No figures appear for any accuracy comparison on this page, under decision 028, and the comparison is the claim being made.

FRCS Level

How Good It Is

At decision level a root tear is one of the few meniscal findings with a clear and time sensitive operative answer.

A root tear with preserved cartilage and a correctable alignment is a repair candidate, and the imaging supplies the cartilage and the extrusion. 5.6.13 covers meniscal repair imaging.

The same tear in a worn varus compartment is part of established disease, and the decision is the compartment's. 5.3.16 covers Kellgren-Lawrence grading.

Alignment is central here, because a varus knee loads a medial root repair and an osteotomy is often combined. 5.3.7 covers the mechanical axis.

Subchondral insufficiency fracture with a root tear changes the timetable, because the bone is failing now. 5.13.4 covers insufficiency fractures.

Where It Misleads

The commonest error is not looking at the roots. 5.5.1 covers the standard protocol.

Extrusion is reported as a finding in its own right and the root is not examined. 5.6.11 covers meniscal extrusion.

The oblique course of a normal root is read as a tear. 2.5.7 covers the root attachments.

A root tear in a degenerate compartment is treated as a repairable lesion when the compartment has gone. 4.9.11 covers the examination in the worn knee.

The alignment is not assessed, so a medial root repair is planned into a varus limb. 5.3.7 covers the mechanical axis.

Fellowship Level

Where It Misleads

At fellowship level the root tear is the chapter's clearest example of a lesion whose recognition changed practice, and of the limits that remain.

Detection improved because the roots became part of the search, which is a reporting change rather than a technical one, and it is not uniform between centres. 5.20.1 covers structured reporting.

The distinction between a degenerate root and a torn root is a continuum, and the imaging grades it less reliably than the extrusion it causes. 5.6.11 covers meniscal extrusion.

Repair restores the anchor and does not reliably reverse extrusion, so the mechanical correction is partial and the imaging after repair reflects that. 5.6.13 covers meniscal repair imaging.

Whether repair changes the compartment's long term course is a literature question, and this page states no figure for it. 5.21.1 covers the meniscal imaging literature.

The lesion coexists with alignment and cartilage problems that decide the outcome, so the root tear is the nameable part of a larger mechanical failure. 5.3.7 covers the mechanical axis.