What Is Exostosis?

Medically Reviewed by Carol DerSarkissian, MD on April 27, 2023
Written by WebMD Editorial Contributors
3 min read

An exostosis is an extra growth of bone that extends outward from an existing bone. Common types of exostoses include bone spurs, which are bony growths also known as osteophytes. An exostosis can occur on any bone, but is often found in the feet, hip region, or ear canal. 

Exostoses develop over time, usually in people with joint damage from arthritis. They are most common in people over 60, but young people can get them, too, especially athletes. Most people with an exostosis don't have symptoms, but it can cause pain in certain situations.

Although exostoses can occur on any bone, they're more common in some parts of the body, particularly in or around the foot or in the hip. Bone spurs are often found:

Under the heel. This type of bone spur can be caused by plantar fasciitis. When your plantar ligament (located in the sole of the foot) pulls on your heel, it can cause a buildup of extra tissue. 

Big toe. The base of the big toe is the most common place to develop arthritis in the foot. When a bone spur develops on the top of the big toe, it can keep you from moving it as much as you need to when you walk. This is called hallux rigidus or stiff big toe.

Back of the heel. Also called a "pump bump," Haglund's deformity refers to a bone spur on the back of the heel. This type of exostosis can occur when pump-style shoes rub against the back of the heel. Though it's called a pump bump, any type of shoe with a rigid back can cause this irritation.

Hip. Osteoarthritis wears away the cartilage in the hip and causes the bones to start rubbing together. This friction leads to the growth of bone spurs.  

Other types of exostoses include:

Osteochondroma. This is a growth of bone and cartilage that happens near the bone's growth plates. It usually affects the long bones in the leg, shoulder, or pelvis. Unlike a lot of bone spurs, this type of exostosis happens in younger people, usually between the ages of 10 and 30.

Hereditary multiple exostosis. This type of exostosis, also called diaphyseal aclasis, occurs in children. Caused by a genetic disorder, it's usually diagnosed around the age of 3 or 4. The gene for hereditary multiple exostosis affects bone growth and causes multiple exostoses to form. The exostoses become bigger as children grow but will stop developing once they reach adulthood.

External auditory exostoses. Also called surfer's ear, this type of exostosis is caused by chronic cold water exposure. It's a buildup of bone growth in the external ear canal. There are usually no symptoms but people with surfer's ear may have hearing loss, ear infections, ear drainage, and earwax impaction. 

There are many different factors that can cause exostosis. These include: 

Many people with exostosis don't have any symptoms. The bone growths themselves don't cause pain, but they can cause problems when they put pressure on nearby nerves, limit your movement, or cause friction by rubbing against other bones or tissues.  

When symptoms do happen, they can include: 

  • Pain near the joint
  • Stiffness
  • Limited movement
  • Bumps, especially in the hands or feet
  • Swelling
  • Weakness
  • Numbness
  • One leg or arm longer than the other

The treatment for exostosis will depend on the cause of the growth and the symptoms. There are some things you can do at home to help, like:  

  • Apply ice to help with swelling.
  • Take nonsteroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen.
  • Use shoe inserts for bone spurs in your feet.
  • Lose weight to put less stress on your joints.
  • Rest.

If home remedies don't help ease your symptoms, your doctor may suggest other treatments, including:  

Some causes of exostosis can't be prevented, but you can reduce your risk factors for most types by doing the following:  

  • Stay at a healthy weight to avoid putting too much stress on your joints.
  • Practice good posture.
  • Use good ergonomics while working.
  • Stretch before exercising.
  • Don't push your body too hard when exercising.
  • Eat a healthy diet.
  • Stay physically fit. 
  • Make sure your shoes are supportive and fit well. 
  • Wear earplugs when your ears will be exposed to cold water.