Osteochondral lesion

What it means

Every joint surface is capped with a thin layer of smooth, slippery cartilage that lets bones glide against each other, sitting on top of the solid bone beneath it. An osteochondral lesion is an injury that involves both layers together — the cartilage cap and the bone just underneath it (the subchondral bone) — rather than just one or the other. These lesions most often occur in the ankle (at the talus) and the knee, typically at spots where the joint takes a direct impact.

Why it appears on a CT or MRI report

MRI is the preferred way to assess these injuries because it shows both the cartilage and the underlying bone in detail, including swelling (bone marrow oedema), cysts, and whether a fragment has become partly or fully detached. CT is useful for mapping the exact size and depth of the bone involvement, especially when surgery is being planned. Reports typically describe the location, size, and stage of the lesion, and note whether the overlying cartilage is intact, has a crack, or is missing altogether, and whether any fragment remains stable or has become a loose body within the joint.

What it usually means

Osteochondral lesions most commonly follow a specific injury — an ankle sprain, a twisting fall, or a sports collision — where the joint surfaces are compressed or sheared against each other. They range from a mild bruise of the bone with intact cartilage, which often heals with rest, to a fragment of bone and cartilage that has partly separated or broken free and is floating within the joint, which is more likely to cause ongoing pain, clicking, or catching. Smaller, stable lesions in younger patients often heal well with conservative treatment. Larger lesions, unstable fragments, or ones that fail to improve with rest are more likely to need surgical treatment, such as microfracture or cartilage repair techniques, to prevent long-term joint damage.

When to follow up

Any osteochondral lesion found on imaging is worth discussing with an orthopaedic doctor, since treatment depends heavily on size, location, stability, and your activity level. Persistent joint pain, swelling, a sensation of catching or locking, or a feeling that the joint is giving way are reasons to seek a clinical assessment promptly, as these can indicate an unstable fragment. Most people are advised to modify activity and use protective bracing while a treatment plan is worked out, since continuing to load an unstable lesion can make it worse.

A plain-language way to picture it

Picture the joint surface as a smooth ceramic tile glued firmly onto a concrete slab. A hard knock can crack the tile, bruise the concrete underneath, or in a worse case, chip out a small piece of tile with a bit of concrete still attached, leaving it loose and rattling around. An osteochondral lesion is that combined damage to both the tile and the slab beneath it — and whether it needs fixing depends on how loose that chipped piece has become.