Osteochondritis Dissecans (OCD) of the Knee: Information for Families

What is OCD?

Osteochondritis dissecans (OCD) is a problem with a small area of bone just under the joint surface. The bone in this area becomes weak and does not heal or grow normally.

The smooth cartilage on top usually stays intact at first. If the weak area is not given the chance to heal, it can crack. A piece of bone and cartilage may then loosen or break off inside the knee.

In the knee, OCD most often affects the inner rounded end of the thigh bone (about 3 in 4 cases). It can also affect the outer end of the thigh bone or the back of the kneecap.

OCD is not the same as an osteochondral fracture

An osteochondral fracture happens suddenly, during an injury. For example, when the kneecap dislocates it can knock off a piece of cartilage and bone. The knee usually swells straight away. This often needs an operation soon after the injury.

OCD develops slowly over weeks or months, often without a single injury. This page is about OCD.

Who gets it and why?

OCD is uncommon. It is rare before age 6 and becomes more common in the teenage years. Boys are affected 2 to 4 times more often than girls, though more girls are being diagnosed as more girls play sport.

The exact cause is not known. It is probably a mix of factors:

• Repeated stress. Many small, repeated loads on the knee from sport, rather than one big injury.
• Blood supply. The affected area of bone may have a weaker blood supply.
• Genes. About 1 in 7 children with OCD have a relative who has had it.
• Other factors. Leg alignment, body weight, an unusually shaped meniscus and low vitamin D levels may play a part.

OCD can affect both knees. Up to 3 in 10 children have it in both knees, sometimes without pain in the second knee. Your doctor may suggest an X-ray of the other knee.

Signs to look for

Symptoms are often vague, which can delay diagnosis. Some children have no symptoms, and OCD is found on an X-ray taken for another reason.

Common signs:

• knee pain during or after sport that is hard to pinpoint
• pain that eases with rest and returns with activity
• mild swelling of the knee
• a limp after activity

Signs that a piece may be loose:

• catching, clicking or grinding
• the knee locking or getting stuck
• more swelling

See a doctor if your child has knee pain with sport that lasts more than a few weeks. See a doctor sooner if the knee locks, catches or swells. Hip problems can also cause knee pain in children, so the doctor will usually check the hip too.

How is it diagnosed?

1. Examination. The doctor checks for tender spots, swelling, movement and leg alignment, and examines the hip.
2. X-rays. Several views are taken, including a "tunnel" view with the knee bent. This view shows the back of the thigh bone, where OCD often sits. The other knee may also be X-rayed.
3. MRI scan. This shows the size of the OCD area and the cartilage over it. It helps judge whether the piece is stable or loose, and checks for other damage. It does not use radiation.

MRI is very good at finding OCD, but it cannot always tell for certain whether a piece is loose. Sometimes the only way to be sure is to look inside the knee with a camera (arthroscopy).

In children aged about 6 to 8, the bone at the end of the thigh grows unevenly. This can look like OCD on an X-ray but is normal. A specialist can tell the difference.

Stable or unstable: why it matters

The most important question is whether the affected piece of bone and cartilage is stable or unstable. This, with your child's age and growth, guides treatment.

Children with open growth plates (still growing) heal much better than those who have stopped growing.

Treatment without surgery

For a stable OCD area in a growing child, treatment usually starts without surgery. The aim is to reduce stress on the knee so the bone can heal. Doctors usually try this for at least 3 to 6 months.

There is no single agreed programme. A typical plan has three stages:

1. Protect (about 4 to 6 weeks). Crutches and limited weight on the leg. Sometimes a brace or cast. By the end, the knee should be pain-free.
2. Rebuild (about 6 to 12 weeks). Walking normally again. Physiotherapy to regain movement and build thigh muscle strength. No sport, running or jumping yet.
3. Return (from about 3 to 4 months). If X-rays show healing and there is no pain, running and sport are restarted gradually. An MRI may be repeated to check healing.

The hardest part is often staying out of sport. Stopping the activities that load the knee gives the bone the best chance to heal. Ask the team which activities are safe at each stage.

Your child will have X-rays every 6 to 8 weeks or so to check progress. If the area is not healing after 3 to 6 months, or symptoms get worse, surgery may be suggested.

When is surgery needed?

Surgery is usually offered when:

• a stable OCD area has not healed after 3 to 6 months of treatment without surgery
• the piece is unstable, partly loose or has come off
• the knee catches, locks or swells
• growth has nearly finished, as healing without surgery is less likely

Most operations are done by keyhole surgery (arthroscopy) under a general anaesthetic. The type of operation depends on what the surgeon finds.

Surgeons always try to save the child's own piece of bone and cartilage if they can. Some metal screws need a second operation to remove them. Dissolvable pins avoid this.

Cartilage repair operations are rarely needed in children, and there is less information about how well they work long term.

Recovery and getting back to sport

Your child returns to sport only once the bone has healed on X-ray or MRI and their thigh strength is back to normal. Time alone is not enough.

After drilling (a typical plan)

• Gentle knee bending exercises start straight away.
• Physiotherapy starts from about week 2.
• Crutches for about 6 weeks before full weight on the leg.
• Return to sport after about 4 to 6 months.

After fixation or cartilage repair

Recovery is usually longer. Your surgeon will give you a plan based on the operation. Physiotherapy after any OCD surgery is recommended.

Tips for families

• Keep all X-ray and scan appointments. They show whether the bone is healing.
• Tell the team if pain, swelling or catching come back.
• Build back into sport gradually, with the physiotherapist's guidance.

Outlook

The outlook for children with stable OCD who are still growing is good.

• Without surgery, about half to two thirds of stable OCD areas heal within 6 to 12 months. Results vary a lot between studies.
• After drilling for a stable area that has not healed, most studies report healing in 8 to 10 out of every 10 children.

Healing is less likely when:

• the OCD area is large
• it is in an unusual place, such as the outer thigh bone or the kneecap
• the knee swells, catches or locks
• growth has nearly finished

If a loose piece is not treated, the joint surface can be left uneven. This may raise the risk of arthritis at a younger age, though the exact risk is not known. This is one reason why early diagnosis and follow-up matter.