Chondral Defects

For Medical Students

What It Shows

A chondral defect is an area where cartilage is thinned or absent, with the subchondral plate intact beneath it. 5.11.5 covers osteochondral lesions.

It is described by its depth, its area and its location, and by the state of the cartilage around it. 5.11.1 covers normal cartilage.

It matters because a focal defect with healthy surrounding cartilage is a repairable lesion, and diffuse thinning is not. 5.11.8 covers cartilage repair procedures.

How It Is Acquired

Use a cartilage sensitive sequence, since a routine protocol understates the loss. 5.2.18 covers gradient echo imaging.

Assess the depth against the full thickness of the adjacent cartilage. 5.11.1 covers normal cartilage.

Assess the area in two planes, because a defect's extent is easily underestimated from one. 5.5.1 covers the standard protocol.

Assess the surrounding cartilage, which decides whether the lesion is focal. 5.11.3 covers fissuring.

Assess the subchondral plate and marrow, which distinguishes a chondral from an osteochondral lesion. 5.11.7 covers bone marrow lesions.

What Abnormal Looks Like

A focal area of reduced cartilage thickness with fluid signal filling the deficiency. 5.11.1 covers normal cartilage.

A full thickness defect exposing the subchondral plate. 5.5.6 covers the bones.

Shouldered margins where the surrounding cartilage is of normal thickness, which is the repairable pattern. 5.11.8 covers cartilage repair procedures.

Subchondral marrow signal beneath the defect. 5.11.7 covers bone marrow lesions.

MRCS Level

How It Is Acquired

In a viva this is the lesion to describe in four variables rather than to name.

The expected points are the cartilage sequence, the depth, the area in two planes, the surrounding cartilage, and the subchondral plate.

Say that shouldered margins distinguish a repairable lesion. 5.11.8 covers cartilage repair procedures.

Say that the subchondral plate's state separates a chondral from an osteochondral lesion. 5.11.5 covers osteochondral lesions.

Say that a routine protocol understates the depth and the area. 5.5.1 covers the standard protocol.

What Abnormal Looks Like

The reasoning expected is that a repair procedure fills a defect, so it needs walls to fill against, and that is why the surrounding cartilage's thickness determines whether the lesion is treatable rather than its own size. 5.11.8 covers cartilage repair procedures.

A defect in a compartment of diffuse thinning has no walls, which makes it part of a degenerate compartment rather than a focal lesion. 5.3.17 covers joint space narrowing.

Depth matters because a full thickness defect exposes bone and loses the whole load bearing layer, while a partial one retains some. 3.5.2 covers the contact pressures.

Area matters because contact pressure rises around the rim, so a larger defect loads its own margins harder and tends to enlarge. 3.5.1 covers the contact areas.

How Good It Is

Magnetic resonance imaging detects a focal full thickness defect reliably and grades partial thickness loss poorly.

Its best contribution is the full thickness focal lesion with healthy margins, which is the surgical lesion. 5.11.8 covers cartilage repair procedures.

It is limited for depth grading and for area, both of which are routinely underestimated against arthroscopy. 5.21.3 covers the cartilage imaging literature.

No figures appear for accuracy on this page, under decision 028, and no defect size or depth thresholds appear either: the operative thresholds are published quantities and this environment cannot check them.

FRCS Level

How Good It Is

At decision level this page supplies the four variables a cartilage repair decision is made on.

A focal full thickness defect with healthy margins in a young patient with a normally aligned limb is the repair picture, and the imaging supplies three of those four. 5.11.8 covers cartilage repair procedures.

Diffuse thinning across the compartment is a compartment problem, and a repair has nothing to repair into. 5.3.17 covers joint space narrowing.

Malalignment loading the defect has to be addressed or the repair is loaded to failure, which makes the alignment film part of the cartilage assessment. 5.3.7 covers the mechanical axis.

A meniscal deficiency in the same compartment has the same consequence. 5.6.11 covers meniscal extrusion.

Where It Misleads

The commonest error is assessing a defect on a routine protocol and underestimating it. 5.5.1 covers the standard protocol.

The surrounding cartilage is not described, so the lesion's focality is unknown. 5.11.3 covers fissuring.

Area is measured in one plane. 5.5.1 covers the standard protocol.

Alignment and meniscal state are left out of the assessment. 5.3.7 covers the mechanical axis.

A defect is reported without the subchondral plate being assessed. 5.11.5 covers osteochondral lesions.

Fellowship Level

Where It Misleads

At fellowship level the chondral defect is the lesion whose imaging assessment disagrees with arthroscopy most consistently in one direction.

Magnetic resonance imaging underestimates both depth and area against direct inspection, so a lesion judged suitable on imaging can be found otherwise, which makes the imaging a screening step rather than a planning one. 5.21.3 covers the cartilage imaging literature.

The grading systems in use were derived on particular sequences and are applied across protocols, so a grade without its protocol is not comparable with a threshold. 5.20.5 covers reporting cartilage lesions.

The variables that determine a repair's outcome include alignment, meniscal status and the matrix state of the surrounding cartilage, and only the first two are routinely assessed. 5.18.2 covers T2 mapping.

Quantitative area measurement from three dimensional acquisitions is more reproducible than a reported estimate and is not routine, so the number a surgeon plans with is usually an impression. 5.2.18 covers gradient echo imaging.

The defensible position is to report the four variables explicitly and to say that the depth and area are minimum estimates. 5.20.5 covers reporting cartilage lesions.