Osteochondral Lesions

For Medical Students

What It Shows

An osteochondral lesion involves the cartilage and the subchondral bone together, rather than cartilage alone. 5.11.2 covers chondral defects.

It appears as a cartilage defect continuous with a bony abnormality, often with a separable fragment. 5.3.14 covers avulsion injuries.

It matters because the bony involvement changes the repair, since a procedure that fills cartilage cannot restore bone. 5.11.11 covers osteochondral grafts.

How It Is Acquired

Assess the cartilage and the subchondral bone as one lesion rather than as two findings. 5.11.1 covers normal cartilage.

Assess the depth of bony involvement, which determines whether bone needs replacing. 5.5.6 covers the bones.

Look for a separable fragment and for fluid signal at its base, which indicates instability. 5.11.6 covers OCD.

Assess the donor site when a fragment is found elsewhere in the joint. 5.3.4 covers the tunnel view.

Assess the surrounding cartilage, as for any focal lesion. 5.11.2 covers chondral defects.

What Abnormal Looks Like

A cartilage defect continuous with a subchondral bony lucency or irregularity. 5.11.2 covers chondral defects.

A fragment of bone and cartilage separated from its bed. 5.11.6 covers OCD.

Fluid signal at the fragment's base, which indicates it is unstable. 5.11.6 covers OCD.

A displaced fragment lying free in the joint. 5.14.6 covers synovial chondromatosis.

MRCS Level

How It Is Acquired

In a viva this is the lesion to distinguish from a chondral defect, and the distinction decides the operation.

The expected points are the single lesion, the bony depth, the fragment and its base, the donor site, and the surrounding cartilage.

Say that fluid at the base indicates instability. 5.11.6 covers OCD.

Say that bony involvement means an osteochondral rather than a chondral procedure. 5.11.11 covers osteochondral grafts.

Say that a free fragment has a donor site that must be identified. 5.3.4 covers the tunnel view.

What Abnormal Looks Like

The reasoning expected is that cartilage depends on the subchondral plate for its mechanical support, so a lesion crossing the plate removes both the bearing surface and its foundation. 1.2.2 covers the articular cartilage.

That is why a cartilage only procedure fails here: it would fill a defect whose floor cannot carry the load. 5.11.8 covers cartilage repair procedures.

Fluid tracking behind a fragment means synovial fluid has reached its base, which is incompatible with it being attached, so the sign is mechanical rather than inflammatory. 5.11.6 covers OCD.

A fragment that has displaced leaves a donor bed, and finding the bed is what confirms the fragment's origin and the lesion's size. 5.3.4 covers the tunnel view.

How Good It Is

Magnetic resonance imaging stages an osteochondral lesion well and is the only modality that shows fragment stability.

Its best contribution is the fluid signal at the fragment base, which is a stability assessment nothing else provides. 5.11.6 covers OCD.

It is limited for fine bony detail, where computed tomography is better, and for the depth of bony involvement in a sclerotic bed. 5.2.22 covers the computed tomography acquisition.

No figures appear for accuracy on this page, under decision 028, and no lesion 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 lesion needs a procedure that restores bone as well as cartilage.

A stable lesion with intact overlying cartilage may be managed without surgery, and the stability assessment is the imaging's contribution. 5.11.6 covers OCD.

An unstable fragment needs fixing or removing, which is decided on the fluid at its base and the fragment's quality. 4.17.3 covers osteochondral lesions.

A defect with significant bone loss needs an osteochondral procedure rather than a cartilage one. 5.11.11 covers osteochondral grafts.

A displaced fragment with a locking knee is urgent, which is a mechanical rather than a cartilage decision. 4.17.2 covers mechanical symptoms.

Where It Misleads

The commonest error is reporting the cartilage and the bone as two separate findings. 5.11.2 covers chondral defects.

Fluid at the base is not sought, so stability is unassessed. 5.11.6 covers OCD.

A free fragment is reported without its donor site. 5.3.4 covers the tunnel view.

Bony depth is understated in a sclerotic bed. 5.2.22 covers the computed tomography acquisition.

A cartilage procedure is planned for a lesion with bone loss. 5.11.8 covers cartilage repair procedures.

Fellowship Level

Where It Misleads

At fellowship level the osteochondral lesion is where the imaging's stability assessment carries more weight than its accuracy supports.

Fluid at the fragment base is the accepted instability sign and it also appears where granulation tissue or a healing interface holds water, so the sign is not as specific as its use implies. 5.21.3 covers the cartilage imaging literature.

Fragment stability determines management, and the alternative assessment is arthroscopic probing, which is invasive, so a weakly specific imaging sign carries a decision by default. 4.17.3 covers osteochondral lesions.

Bony depth in a sclerotic bed is understated on magnetic resonance imaging and better shown on computed tomography, so a complete assessment needs two studies and usually gets one. 5.2.22 covers the computed tomography acquisition.

Contrast enhanced imaging has been proposed to assess fragment viability and has not become routine, which leaves viability inferred from morphology. 5.2.21 covers advanced magnetic resonance techniques.

The defensible position is to report the stability sign as a sign rather than a conclusion, and to recommend computed tomography where bone loss will decide the procedure. 5.20.5 covers reporting cartilage lesions.