Bone cysts are fluid-filled holes that form in bones. They mainly affect children and teenagers. They're not usually serious, but they sometimes need to be treated with surgery.

Bone cysts aren't always treated

A bone cyst may not need treatment if it's small and not causing any problems.

They often get better on their own, especially in children and teenagers.

You may have regular X-rays for a few years to check your bone is healing and the cyst isn't getting bigger.

Treatments for bone cysts

A bone cyst might need to be treated if it's:

• large or getting bigger – this could make the bone weaker and more likely to break (fracture) if you injure it
• causing problems like pain, swelling or a lump

The main treatments are:

• draining the fluid with a needle and injecting medicine into the bone to help it heal – this may need to be done several times over a few months
• cutting or scraping out the cyst – the hole may be filled with small pieces of bone taken from another part of your body or from someone who donated bone after they died

Treatment is done under general anaesthetic. You won't usually need to stay in hospital overnight.

Recovering after treatment

It normally takes at least a few months for the bone to heal.

You may need to avoid activities or sports that could damage the bone until it has healed.

You'll have regular X-rays for a few years to check it's getting better.

Causes of bone cysts

The exact cause of bone cysts is unknown. They're not cancer and don't spread to other parts of the body.

The main types of cyst are thought to have different causes:

• unicameral bone cysts – fluid-filled holes that may form if fluid doesn't drain properly from a bone as it's growing
• aneurysmal bone cysts – blood-filled holes that may be caused by a problem with the blood vessels in a bone (possibly due to an injury or a non-cancerous growth)