Delamination

For Medical Students

What It Shows

Delamination is separation of cartilage from the subchondral plate while the cartilage surface remains continuous. 5.11.1 covers normal cartilage.

It appears as a line of fluid signal at the cartilage to bone interface rather than at the surface. 5.11.3 covers fissuring.

It matters because the surface looks intact, so a probe at arthroscopy can pass over it, and magnetic resonance imaging is the modality that shows it. 4.17.5 covers articular cartilage defects.

How It Is Acquired

Use a cartilage sensitive sequence and look specifically at the deep interface rather than the surface. 5.2.18 covers gradient echo imaging.

Look for fluid signal between cartilage and the subchondral plate. 5.5.6 covers the bones.

Assess the surface separately, since it is characteristically intact. 5.11.2 covers chondral defects.

Assess the subchondral marrow, which is usually abnormal beneath it. 5.11.7 covers bone marrow lesions.

Confirm in a second plane, because a line at an interface is exactly what partial volume averaging produces. 5.2.5 covers magnification.

What Abnormal Looks Like

A linear fluid signal at the cartilage to bone interface with an intact overlying surface. 5.11.1 covers normal cartilage.

A flap of cartilage separated at its base but attached at one edge. 5.11.2 covers chondral defects.

Subchondral marrow signal beneath the separated area. 5.11.7 covers bone marrow lesions.

A surface that appears normal, which is the feature that makes the lesion dangerous. 4.17.5 covers articular cartilage defects.

MRCS Level

How It Is Acquired

In a viva this is the lesion to name when asked what imaging shows that arthroscopy can miss.

The expected points are the deep interface, the fluid line, the intact surface, the subchondral marrow, and the second plane.

Say that the intact surface is why arthroscopy can miss it. 4.17.5 covers articular cartilage defects.

Say that a line at an interface is the classic partial volume artefact. 5.2.5 covers magnification.

Say that the marrow change beneath supports the finding. 5.11.7 covers bone marrow lesions.

What Abnormal Looks Like

The reasoning expected is that cartilage is anchored to bone through its deep calcified zone, so a shear injury can fail that anchorage while leaving the tangential surface layer continuous. 1.2.2 covers the articular cartilage.

That is why the lesion is a shear mechanism rather than an impaction one, and why it accompanies the injuries that load the surface tangentially. 3.5.8 covers the contact mechanics after cruciate injury.

An unanchored layer cannot transmit load to bone, so the compartment is mechanically deficient despite an intact surface. 3.5.2 covers the contact pressures.

The subchondral marrow responds to that altered load, which is why marrow signal beneath an intact surface should prompt a look at the interface. 5.11.7 covers bone marrow lesions.

How Good It Is

Magnetic resonance imaging is the only practical way to detect delamination, and it is detected only when it is looked for.

Its best contribution is that it finds a mechanically significant lesion an intact surface conceals. 4.17.5 covers articular cartilage defects.

It is limited because the finding is a line at an interface, which is also what partial volume averaging produces, so false positives and negatives both occur. 5.2.5 covers magnification.

No figures appear for accuracy on this page, under decision 028, and the comparison is the claim: this lesion is detected better here than by arthroscopic inspection of the surface, which is a comparison rather than a number.

FRCS Level

How Good It Is

At decision level this finding changes an arthroscopic plan before the arthroscopy.

A delaminated area identified pre-operatively tells the surgeon where to probe, which converts a lesion that would be missed into one that is addressed. 4.17.5 covers articular cartilage defects.

A delaminated flap is a different repair problem from a defect, because the layer has to be removed before anything is filled. 5.11.8 covers cartilage repair procedures.

Delamination accompanying a cruciate injury is part of the compartment's prognosis. 5.7.4 covers the acute cruciate injury.

Unexplained subchondral marrow signal with an intact surface should raise it. 5.11.7 covers bone marrow lesions.

Where It Misleads

The commonest error is not looking at the deep interface at all. 5.11.1 covers normal cartilage.

A partial volume line at the interface is reported as delamination. 5.2.5 covers magnification.

An intact surface is taken to mean intact cartilage. 4.17.5 covers articular cartilage defects.

The marrow change is reported without the interface being examined. 5.11.7 covers bone marrow lesions.

A single plane appearance is accepted. 5.5.1 covers the standard protocol.

Fellowship Level

Where It Misleads

At fellowship level delamination is the clearest case in this chapter of imaging outperforming direct inspection, which is rare enough to be worth stating.

The reference standard for cartilage is usually arthroscopy, and for this lesion the reference standard is the weaker test, which makes published accuracy figures for it structurally unreliable. 5.21.3 covers the cartilage imaging literature.

The finding is a line at an interface, and partial volume averaging produces the same appearance, so the same anatomy that makes imaging superior also makes it uncertain. 5.2.5 covers magnification.

Its prevalence is probably underestimated, because it is reported only where it is sought and sought only where it is known about. 5.20.5 covers reporting cartilage lesions.

Three dimensional thin slice acquisition addresses the partial volume problem directly, which makes this one of the findings most likely to be reported more often as protocols change. 5.2.18 covers gradient echo imaging.

The practical recommendation is to look at the deep interface deliberately in any knee with subchondral marrow change and an intact surface. 5.11.7 covers bone marrow lesions.