Our knowledge of orthopaedics. Your best health.

from the American Academy of Orthopaedic Surgeons

Diseases & Conditions



Staying Healthy


An osteochondroma is a benign (noncancerous) tumor that develops during childhood or adolescence. It is an abnormal growth that forms on the surface of a bone near the growth plate.

Growth plates are areas of developing cartilage tissue near the ends of long bones in children. Bone growth occurs from the growth plate, and when a child is fully grown, the growth plates harden into solid bone.

An osteochondroma is an outgrowth of the growth plate and is made up of both bone and cartilage. If you break down the word from its ancient Greek origins: "osteo" = bone, "chondro" = cartilage, and "oma" = tumor.

As a child grows, an osteochondroma may grow larger, as well. Once a child has reached skeletal maturity, the osteochondroma typically stops growing, too. In most cases of osteochondroma, no treatment is required other than regular monitoring of the tumor to identify any changes or complications.

Osteochondromas can develop as:

  • A single tumor (osteocartilaginous exostosis)
  • Many tumors (multiple osteochondromatosis)

Because symptoms and treatment options may vary depending on which form a patient has, this article discusses them separately.

Solitary Osteochondroma

Solitary osteochondromas are thought to be the most common benign bone tumor, accounting for 35 to 40% of all benign bone tumors. A benign bone tumor is not cancer and does not metastasize (spread) to other parts of the body.

As a child grows, a solitary osteochondroma may develop if bone grows out from the growth plate instead of in line with it. Solitary osteochondromas are commonly found at the end of long bones where they meet to form joints, such as the knee, hip, and shoulder.

This bone outgrowth may have a stalk or stem that sticks out from the normal bone.

  • If the tumor has a stalk, the structure is called pedunculated.
  • If the tumor outgrowth is attached to the bone with a broader base, it is called sessile.

(Left) This X-ray taken of the front of the knee shows a typical pedunculated osteochondroma on the femur. (Right) This X-ray of the shoulder taken from the side shows a sessile osteochondroma on the humerus.


The exact cause of osteochondroma is unknown.

  • It does not result from injury.
  • Both males and females are equally likely to develop it.
  • Osteochondromas are thought to be associated with a gene called EXT 1. However, it is not clear how a defect in this gene may cause the tumors. Researchers are investigating it.

Because the cause of a solitary osteochondroma is unknown, doctors have not been able to find a way to prevent it.


In many cases, solitary osteochondromas do not cause any symptoms, or symptoms may arise long after tumors develop. Osteochondromas are most often diagnosed in patients aged 10 to 30 years.

Symptoms of an osteochondroma include:

  • A painless bump near the joints. The knee and shoulder are most often involved.
  • Pain with activity. An osteochondroma can be located under a tendon (the tough, fibrous tissue that connects muscle to bone). When it is, the tendon may move and snap over the bony tumor, causing pain.
  • Numbness or tingling. An osteochondroma can be located near a nerve, such as behind the knee. If the tumor puts pressure on a nerve, there may be numbness and tingling in the associated limb.
  • Changes in blood flow. A tumor that presses on a blood vessel may cause changes in blood flow from time to time. This can cause loss of pulse or changes in color of the limb. However, changes in blood flow resulting from an osteochondroma are rare.

In some cases, an injury can cause the stalk of a pedunculated osteochondroma to break. This will cause immediate pain and swelling in the area of the tumor.

Doctor Examination

Because many osteochondromas do not cause any discomfort or other symptoms, they are often discovered by accident when an X-ray is done for an unrelated reason, such as a traumatic injury. This is called an incidental finding.

If you or your child do have symptoms that cause you to seek a doctor's care, the appointment will begin with a medical history and a physical examination.

Medical History and Physical Examination

Before a physical examination, the doctor will talk with you about:

  • Your or your child's general health
  • Any symptoms related to the bump

During the physical examination, the doctor will:

  • Look for tenderness over the bone
  • Check your or your child's range of motion in the area of your pain


To diagnose osteochondroma, the doctor will order imaging tests.

X-rays. X-rays provide clear pictures of dense structures like bone and will show the bony growth of an osteochondroma.

Other imaging tests. The doctor may also request computerized tomography (CT) scans or magnetic resonance imaging (MRI) scans to help further define the tumor. These scans can provide more detail than X-rays, especially of soft tissues (including muscles, tendons, nerves, and blood vessels) and the cartilage portion of the tumor. 

An MRI scan may be used to look for cartilage on the surface of the tumor. Although it is rare for an osteochondroma to change into a cancerous tumor, it is possible. In adults, a thick covering of cartilage over the tumor is one sign of such a change. A tumor in an adult patient should be checked for cancer if it is enlarging or has become painful.

Biopsy. While biopsies are needed to diagnose other types of cancer, they usually are not needed to diagnose osteochondromas.


Nonsurgical Treatment

In most cases of solitary osteochondroma, treatment consists of careful observation over time. The doctor may want to take regular X-rays to keep track of any changes in the tumor.

It is often wise to avoid resection — a procedure to remove part or all of a tumor — until the growth plate closes (skeletal maturity) to help reduce the risk that the tumor comes back (local recurrence).

Surgical Treatment

The doctor may consider surgery if the osteochondroma:

  • Causes pain
  • Puts pressure on a nerve or blood vessel
  • Has a large cap of cartilage — a sign in adults that the tumor may be changing from noncancerous to cancerous

To completely remove an osteochondroma, the doctor will perform a surgical procedure called excision. In an excision, all of the tumor and an area of surrounding tissue are removed. In the procedure, the tumor will be removed at the level of the normal bone.

How long it takes to return to daily activities will vary depending on the tumor's size and location. If you or your child have any pain or discomfort, you may want to limit some activity for a period of time. The doctor will provide you with specific instructions to guide your or your child's recovery.

Multiple Hereditary Exostosis (MHE)

Multiple hereditary exostosis (MHE) is the most common term used to describe multiple (more than one) osteochondromas. It is also referred to as multiple osteochondromatosis, multiple osteocartilaginous exostosis, familial osteochondromatosis, multiple hereditary osteochondromatosis, or diaphyseal aclasia.

The number and location of the osteochondromas vary. Both pedunculated and sessile tumors may develop. In more severe cases, MHE can cause bones to grow abnormally. For example, many patients have:

  • Short stature
  • Inward bowing of the knees and ankles
  • Deformities of the forearms or hands
Multiple osteochondromas

Tumors in the femur and tibia are apparent in these X-ray of a child's knee.

Due to these more obvious signs, children with severe MHE are often identified early. However, like solitary osteochondroma, mild MHE may not be diagnosed until early adulthood. 

The risk of these benign tumors changing to cancer (malignant transformation) is more common in patients with MHE:

  • There is about a 10% lifetime risk of developing a chondrosarcoma for patients with MHE.
  • In patients with a solitary osteochondroma, the lifetime risk of malignant transformation is less than 1%.


  • About 70% of the time, MHE is inherited in an autosomal dominant fashion (meaning a parent passes it down to all of their biological children). The other 30% of cases occur randomly.
  • MHE is more common in males than females.
  • Like solitary osteochondroma, alterations in genes called EXT genes are thought to be the cause of this disease. Research is being conducted to see whether this is true.


The symptoms of MHE are similar to those of solitary osteochondroma.

  • It causes multiple firm, bony bumps to develop around the knees, ankles, wrists, shoulders, and chest wall.
  • It can cause painless bumps at the sites of tumors.
  • Pain can develop at sites of large osteochondroma if the tumors put pressure on soft tissues, nerves, or blood vessels.

Doctor Examination

Diagnosing MHE includes a medical history and physical examination, as well as imaging tests.

X-rays. Most commonly, X-rays will show a classic appearance in someone with MHE. Doctors will often request a skeletal survey, which uses X-rays to look at all of the bones in your or your child's body. Sometimes, however, the doctor might recommend just getting X-rays of painful sites.

Orthopaedic oncology evaluation. If you or your child have any symptoms of a tumor becoming cancerous, you should be evaluated by a doctor who specializes in the treatment of bone tumors (an orthopaedic oncologist).

Children who have not reached skeletal maturity (their growth plates are still open) typically visit  the orthopaedic oncologist once a year to help ensure that the child’s bones are growing as expected.

Symptoms and signs of a tumor becoming cancerous are:

  • Growth of an osteochondroma after puberty
  • Pain at the site of an osteochondroma
  • A cartilage cap thicker than 2 cm

If cancer is suspected, you or your child will need a thorough evaluation that includes MRI and CT scans of the tumors. The doctor may also order a CT scan of the chest to look for any disease that may have traveled through the bloodstream to your lungs. A biopsy of the tumor tissue will confirm whether there is any cancer.

If an osteochondroma becomes cancerous, it most commonly changes into a cancer called chondrosarcoma.


Nonsurgical Treatment

In most cases, treatment consists of careful observation over time. The doctor may want to take regular X-rays to keep track of any changes in the tumors.

Reasons for surgical removal of tumors include:

  • Abnormal growth around a joint
  • Pain
  • Pressure on nerves or blood vessels
  • A large cap of cartilage on the tumor

Surgical Treatment

If surgical removal of an osteochondroma is needed, the surgeon uses special tools to remove the bony tumor.

Deformities such as inward bowing of the knees or ankles may require surgery to straighten the bone. This surgery is sometimes called guided growth, and it can help straighten bone using plates and screws

It is important to note that malignant transformation, where a noncancerous tumor becomes cancerous, usually does not occur in children. While most patients never develop cancer, if you notice an osteochondroma growing after you or your child are done growing, you should get evaluated by your orthopaedic oncologist.

Last Reviewed

December 2023

Contributed and/or Updated by

Alexandra Kathleen Callan, MD, FAAOSRajiv Rajani, MD

Peer-Reviewed by

Thomas Ward Throckmorton, MD, FAAOSStuart J. Fischer, MD

AAOS does not endorse any treatments, procedures, products, or physicians referenced herein. This information is provided as an educational service and is not intended to serve as medical advice. Anyone seeking specific orthopaedic advice or assistance should consult his or her orthopaedic surgeon, or locate one in your area through the AAOS Find an Orthopaedist program on this website.