Osteochondroma

What an osteochondroma is

Long bones grow from cartilage growth plates near their ends. An osteochondroma forms when a small piece of growth plate cartilage grows sideways, away from the joint, producing a bony stalk or broad-based bump with a cartilage cap. It grows as the child grows, and usually stops growing when the growth plates close at the end of puberty.

Osteochondromas can be:

• pedunculated: on a narrow stalk
• sessile: broad-based and flatter

Causes

• Solitary osteochondroma: usually no known cause. It may follow radiation therapy in childhood.
• Hereditary multiple exostoses (HME): also called multiple osteochondromas, caused by mutations in the EXT1 or EXT2 genes and inherited in an autosomal dominant pattern, so each child of an affected parent has a 50% chance. People develop many osteochondromas, often with limb deformities and shorter stature.

Symptoms

Many osteochondromas cause no symptoms and are found by chance on x-rays. When symptoms occur:

• a hard, painless lump near a joint
• pain with activity from irritation of overlying muscles or tendons
• a snapping or catching sensation as a tendon slides over the lump
• a bursa (fluid sac) forming over the lump
• numbness, tingling or weakness if a nerve is compressed
• limb swelling or coldness if a blood vessel is compressed
• sudden pain if the stalk fractures

In HME, additional problems include unequal limb length, bowing of the forearm, knee or ankle deformities, reduced joint movement and short stature.

Diagnosis

• X-ray: usually diagnostic, showing a bony outgrowth continuous with the bone marrow of the underlying bone.
• MRI: measures the cartilage cap thickness and shows nerves, vessels and bursae. In adults, a cartilage cap thicker than about 1.5 to 2 cm raises concern for malignant change.
• CT: for complex locations such as the pelvis or spine.
• Genetic testing for suspected HME.
• Biopsy: rarely needed for typical lesions.

Risk of cancer

Malignant transformation into a cartilage cancer (chondrosarcoma) is rare:

• solitary osteochondroma: under 1%
• hereditary multiple exostoses: higher, roughly 1% to 5% over a lifetime

Warning signs are growth after skeletal maturity, new pain in an adult, and a thickening cartilage cap on MRI. People with HME often have periodic monitoring.

Treatment

Observation

Painless osteochondromas that are not causing problems are usually left alone, with periodic x-rays during growth. Most stop growing at skeletal maturity.

Surgical removal

Removal is recommended if the osteochondroma:

• causes pain or limits activity
• presses on a nerve (for example causing foot numbness or ulnar nerve compression at the elbow) or blood vessel
• causes cosmetic concern
• fractures
• shows signs of malignant change

The lump is removed at its base along with the entire cartilage cap and its covering to reduce the chance of regrowth. Recovery often takes a few weeks, with limited activity while the bone heals.

HME management

People with HME may need several surgeries during childhood to remove troublesome lumps and to correct limb deformities, such as guided growth procedures for uneven limbs or forearm correction.

Outlook

The outlook is excellent. Most solitary osteochondromas cause few problems, and surgical removal is usually curative. Recurrence after complete removal is uncommon, though new lumps can appear in HME before skeletal maturity.

Frequently asked questions

What is an osteochondroma?

An osteochondroma is a benign bony bump capped with cartilage that grows from the surface of a bone, usually near the knee, shoulder or hip. It is the most common noncancerous bone tumor and typically appears in children and teenagers.

Is an osteochondroma cancerous?

No, an osteochondroma is benign. Very rarely, the cartilage cap can turn into a type of cancer called chondrosarcoma, mainly in adults. The risk is under 1% for a single osteochondroma and somewhat higher in hereditary multiple exostoses.

Does an osteochondroma need to be removed?

Not usually. Painless osteochondromas that are not pressing on nerves or blood vessels can be monitored. Removal is recommended for pain, nerve or vessel compression, restricted movement, fracture, cosmetic concern or signs of malignant change.

Do osteochondromas stop growing?

Yes. They typically grow during childhood and stop when the growth plates close at the end of puberty. An osteochondroma that grows or becomes painful in adulthood should be evaluated.

What is hereditary multiple exostoses?

It is an inherited condition caused by EXT1 or EXT2 gene mutations that leads to many osteochondromas. It can cause limb deformities, uneven limb lengths and short stature, and carries a slightly higher risk of chondrosarcoma, so regular follow-up is recommended.