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What is an Osteochondroma?

All children have growth plates at the end of their long bones. These areas of developing cartilage expand and harden into bone as a child grows. An osteochondroma is a benign (noncancerous) tumor on the surface of a bone near a growth plate. They form in children or adolescents. 

Because the growth plates are growing and changing as the child grows, the osteochondroma also tends to grow and change over time. This means that once a child reaches skeletal maturity, the osteochondroma typically stops growing too. 

Solitary Osteochondroma

Solitary osteochondromas are thought to be the most common benign bone tumor. 35-40% of all benign bone tumors are osteochondromas. As a child grows, a solitary osteochondroma may form when a bone grows out from a growth plate instead of in line with it. These osteochondromas are most commonly found where long bones meet joints – such as the knee, hip or shoulder. 

A solitary osteochondroma may have a stalk or stem that sticks out from the normal bone. When the tumor has a stalk, it is called pedunculated. If the tumor has a broad base attachment to the bone, it is called sessile. 

Causes of Solitary Osteochondroma

The exact cause of these bone tumors is unknown. It is not the result of an injury. Males and females are equally likely to develop them. Because the cause is unknown, doctors have not been able to find a way to prevent them. 

Symptoms of Solitary Osteochondroma

In many cases there are no symptoms or they arise long after the tumor has developed. Osteochondromas are most often diagnosed in patients aged 10 to 30 years. Symptoms may include:

  • A painless bump near a joint – most often the knee or shoulder
  • Pain with activity – if the osteochondroma is located under a tendon, the tendon may move or “snap” over it causing pain. 
  • Numbness or tingling – if the osteochondroma is located near a nerve it may put pressure on that nerve causing nearby numbness and tingling
  • Changes in blood flow: if a bone tumor presses on a blood vessel it can interfere with blood flow causing loss of pulse or color in the limb. This is a rare issue. 

Multiple Osteochondromatosis

When multiple osteochondromas are present they may vary in number, location and type. In severe cases, multiple osteochondromatosis can cause bones to grow abnormally. Patients suffering from multiple osteochondromatosis may have short stature, knock-knees and ankles, and deformities of the forearms. 

Children with severe multiple osteochondromatosis are often identified at a young age. It is more common in males than females. The risk of these benign tumors changing to cancer is greater than solitary osteochondroma.

Additional names for this condition are multiple osteocartilaginous exostosis, multiple hereditary exostosis (MHE), familial osteochondromatosis, multiple hereditary osteochondromatosis, or diaphyseal aclasia.

Causes of Multiple Osteochondromatosis

Approximately 70% of the time, multiple osteochondromatosis is inherited. 

Symptoms of Multiple Osteochondromatosis

Similar to those of solitary osteochondroma, often more severe. 

Diagnosis of Osteochondroma

Your doctor will conduct a physical exam, looking for tenderness over the bone and checking for range of motion in the joint near your area of pain. The doctor will likely order an imaging test to get a clear look at the bone. Those imaging tests may include: an x-ray, MRI, or CT scan. 

If you have any symptoms of an osteochondroma becoming cancerous, you should be evaluated by a doctor who specializes in bone tumors – an orthopedic oncologist. Symptoms of an osteochondroma becoming cancerous are:

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

If cancer is suspected, you will need a thorough evaluation that includes imaging scans of the tumors. A biopsy of the tumor tissue will confirm whether there is any cancer. 

Treatment for Osteochondroma

In most cases, no treatment is necessary for an osteochondroma other than regular monitoring to identify any changes or complications. 

Your doctor may consider surgery if the osteochondroma causes pain, puts pressure on a nerve or blood vessel, or has a large cap of cartilage.