Cartilage Injury

Why cartilage is different from every other tissue

Articular cartilage — the glassy white lining on the ends of the bones — has no blood vessels and no nerves. It survives on nutrients diffusing in from joint fluid as you move. That arrangement makes it extraordinarily slippery and durable, and it comes with one enormous drawback: without a blood supply, it has almost no capacity to repair itself.

Cut your skin and it heals in a fortnight. Break a bone and it knits back to full strength. Punch a hole in cartilage and, left alone, it is still a hole years later. Everything in cartilage surgery is an attempt to work around that fact.

Why it is worth treating early

The edges of a cartilage defect carry abnormally high stress, in the same way the edge of a pothole crumbles faster than the road around it. Over years, a defect left untreated tends to enlarge, and the opposing surface it rubs against begins to suffer too. A contained defect in a young knee is a much better problem to have than a large one in the same knee ten years later.

That said, not every defect found on a scan needs treating. Small, stable, symptom-free defects are common and often best watched. The decision rests on your symptoms, your age, the size and depth of the defect, and whether anything else — instability, malalignment, a missing meniscus — is causing it.

The restoration options

Debridement and stabilisation

Trimming an unstable flap back to a stable edge so it stops catching. It does not fill the defect, but it can settle mechanical symptoms with a very quick recovery.

Microfracture

Small perforations are made in the bone at the base of the defect, allowing marrow cells to enter and form repair tissue. Straightforward and effective for small defects, though the tissue formed is fibrocartilage rather than the original hyaline cartilage, and it is less durable under high load.

Osteochondral transfer

A plug of bone and its overlying cartilage is taken from a low-load part of the joint, or from a donor, and press-fitted into the defect. This transplants genuine hyaline cartilage, which is its main attraction, and suits well-contained defects.

Cell-based resurfacing

Cartilage cells or a scaffold are used to regenerate a surface over the defect, usually in two stages. Reserved for larger defects in younger patients and requires a committed, prolonged rehabilitation.

Recovery is slow, and that is not negotiable

Cartilage repair tissue is soft for months before it matures. Most cartilage procedures involve six weeks of protected weight-bearing, continuous gentle movement to nourish the healing surface, and a return to impact activity somewhere between six and twelve months. It is a longer road than a meniscus trim or a ligament reconstruction, and knowing that at the outset matters.

The pay-off, in the right patient, is a joint surface that keeps working for decades rather than a knee heading towards replacement in its fifties.

How it is diagnosed

• Examination to localise the pain and to check for instability and malalignment, both of which change the plan entirely.
• X-rays, including standing alignment views where relevant.
• MRI with cartilage-sensitive sequences, which shows the size, depth and position of the defect and the state of the bone underneath it.
• Arthroscopy, which remains the most accurate assessment — the defect can be seen, probed and measured directly, and treated in the same sitting.