Osteochondritis Dissecans (OCD) of the Knee

Patient information for parents and carers — Dr Christopher Spelman, Orthopaedic Surgeon

What is osteochondritis dissecans

Osteochondritis dissecans (OCD) is a condition affecting the joint surface, in which a small area of bone just beneath the cartilage (the subchondral bone) loses its blood supply and weakens. Because the overlying cartilage depends on the bone beneath it for support, the cartilage and its bony base can soften and, in some cases, partially or completely separate to form a fragment – which may stay in place, become loose, or detach entirely into the joint as a loose body. In the knee, OCD most commonly affects the end of the thigh bone (femur), classically the outer part of the inner (medial) femoral condyle.

The exact cause is not fully understood, but repetitive stress or microtrauma to the growing joint, together with vulnerability of the local blood supply, is thought to be central; genetic factors may contribute in some children.

Juvenile versus adult OCD — an important distinction

Whether the growth plates are still open is the single most important factor in OCD of the knee, because it strongly influences healing and treatment:

●      Juvenile OCD (open growth plates) – occurs in children and adolescents whose bones are still growing. These lesions are usually stable and have a good capacity to heal, often without surgery.

●      Adult OCD (closed growth plates) – occurs once growth is complete. These lesions are more likely to be unstable, rarely heal on their own, and have a less favourable prognosis, more often requiring surgery.

Symptoms

Early OCD often causes vague, activity-related aching in the knee, sometimes with a limp and swelling after sport. As a lesion becomes unstable or a fragment loosens, more mechanical symptoms appear – catching, clicking, the knee giving way, or true locking if a fragment has become a loose body. Some lesions are found incidentally on an x-ray taken for another reason.

Diagnosis and assessment of stability

X-rays (including special views such as a tunnel/notch view) usually show the lesion and its location. MRI is then used to assess the most important question – whether the fragment is stable or unstable – by looking for fluid or a high-signal line tracking behind the fragment, cysts, and the state of the overlying cartilage. Determining stability, along with the child’s skeletal maturity and the size and site of the lesion, guides treatment.

Treatment

Treatment is tailored to the stability of the lesion and the child’s remaining growth.

Stable lesions in a growing child

A stable juvenile OCD lesion with intact cartilage is usually given the chance to heal without surgery. This involves a period of activity restriction – avoiding running, jumping and impact sport – sometimes with a brace or a spell on crutches, for around three to six months, with x-rays to monitor healing. This works in roughly half to two-thirds of children.

Lesions that fail to heal, or unstable lesions still attached

If a stable lesion does not heal with non-operative treatment, or the lesion is unstable but still has adequate bone attached, keyhole surgery is used. Drilling (making fine channels into the lesion, either through the joint surface – transarticular – or from behind it – retroarticular) stimulates a healing blood supply. Where a fragment is unstable but reconstructable, it is fixed back in place with small screws or bioabsorbable pins, often with bone grafting behind it.

Detached fragments and established defects

If a fragment has detached and left a defect, the options are to fix the fragment if it still has enough healthy bone, or to remove it and treat the resulting cartilage defect with a restoration technique – such as microfracture for small defects, or transfer of the patient’s own cartilage-and-bone plugs (OAT), cell-based repair (ACI/MACI) or donor osteochondral allograft for larger ones.

Recovery

Non-operative treatment relies on consistent activity restriction while the lesion heals, followed by a graduated return to sport once healing is confirmed. After surgery, recovery depends on the procedure – drilling and fixation are usually followed by a period of protected weight-bearing and a structured rehabilitation programme, with return to sport guided by healing on imaging rather than time alone.

Outcomes and what the evidence shows

The prognosis for juvenile OCD is considerably better than for the adult form. With non-operative treatment, around 50–66% of stable juvenile lesions heal over six to twelve months; larger lesions, and those with swelling or mechanical symptoms at presentation, are less likely to heal and more likely to need surgery. Where surgery is required, drilling of stable but non-healing lesions achieves high radiographic healing rates – reported around 86–91% (transarticular and retroarticular giving broadly similar results) – and fixation of unstable fragments has success rates commonly in the range of 75–100%. Achieving healing while the joint surface remains congruent gives the best chance of protecting the knee from arthritis in the long term.

Complications

The main concerns relate to the joint surface and its long-term health:

●      Failure to heal, or progression of an initially stable lesion to instability.

●      Detachment of a fragment to form a loose body, which can cause locking and damage the joint.

●      A residual cartilage defect where a fragment cannot be saved, and an increased long-term risk of osteoarthritis, particularly with larger lesions and in the adult form.

●      Procedure-specific risks – hardware irritation or the need to remove fixation, incomplete healing after drilling, and the general low risks of knee arthroscopy (infection, blood clots, stiffness).

Summary

Osteochondritis dissecans is a problem of the cartilage and the bone beneath it, and in the knee most often affects the thigh bone. In growing children the lesions are usually stable and often heal with a period of activity restriction, while unstable or non-healing lesions – and most adult lesions – need surgery to stimulate healing, fix the fragment, or restore the joint surface. Early diagnosis and careful assessment of stability give the best chance of a good long-term result. Dr Spelman will stage the lesion and tailor treatment to your child’s knee and stage of growth.