Hereditary multiple exostosis

What is hereditary multiple exostosis?

Hereditary multiple exostosis (HME), also known as multiple hereditary osteochondromatosis or diaphyseal aclasis, is a genetic condition in which multiple benign bony growths called osteochondromas develop on the surfaces of bones throughout the body. Each growth has an outer layer of cartilage (the cartilage cap) and a bony stalk arising from the underlying bone.

Is it hereditary?

Yes. HME follows an autosomal dominant inheritance pattern — meaning a child of an affected parent has a 50% chance of inheriting the condition. It is caused by mutations in the EXT1 or EXT2 genes. In some cases it occurs without a family history (new mutation). Genetic counselling is available for affected families.

Where do osteochondromas develop?

In HME, osteochondromas typically develop near the growth plates of rapidly growing bones. Common sites include:

• Distal femur (lower thigh bone) and proximal tibia (upper shin bone) around the knee

• Proximal humerus (upper arm bone near the shoulder)

• Forearm bones (radius and ulna) — can cause bowing and wrist deformity

• Shoulder blade (scapula)

• Ribs and pelvis

• Small bones of the hands and feet

The growths tend to enlarge during childhood and adolescence when the child is growing, and usually stop growing when skeletal maturity is reached.

What problems can HME cause?

• Pain from the bumps themselves, particularly when they rub on muscles, tendons, or nerves

• Restricted joint movement, particularly at the knee, ankle, or shoulder

• Forearm length discrepancy and wrist deformity (caused by unequal growth of the radius and ulna)

• Leg length discrepancy

• Angular deformity of the knee or ankle

• Nerve or blood vessel compression (uncommon)

• Cosmetic concern from prominent bumps

Treatment of HME

Conservative management

Not all osteochondromas in HME require surgery. Many are managed with observation and regular review. Surgery is considered when a lesion is causing pain, limiting function, causing deformity, or compressing nearby structures.

Surgical excision of symptomatic osteochondromas

When a specific osteochondroma is causing problems, it can be surgically removed. The principles are the same as for a solitary osteochondroma: the lesion is excised flush with the underlying cortex including the cartilage cap. The specimen is sent for histopathological examination.

Correction of forearm deformity

In HME, unequal growth of the radius and ulna can cause significant forearm bowing and wrist deviation. Surgical options include osteochondroma excision, radial osteotomy, ulnar lengthening, or a combination — depending on the specific deformity.

Correction of angular or length deformity

Guided growth techniques (8-plates) or corrective osteotomies may be required for significant angular deformity of the knee, ankle, or leg length discrepancy.

Anaesthetic and hospital stay

• General anaesthetic for all surgical procedures

• Hospital stay depends on the procedure — many excisions are day case

• More complex deformity corrections may require 1-2 nights

Risks of surgical excision

• Wound infection

• Bleeding or haematoma

• Recurrence — rare after complete excision with the cartilage cap

• Injury to adjacent nerves, blood vessels, or tendons

• Incomplete excision — particularly near major vessels or nerves

• Anaesthetic risks

Long-term management and surveillance

Note: Malignant transformation — what parents need to know 

The risk of malignant change (sarcomatous transformation) in HME is estimated at 5-12% over a lifetime — significantly higher than for a single solitary osteochondroma. Warning signs that require prompt assessment include: a growth that starts to enlarge rapidly after skeletal maturity, new or worsening pain, or a change in the consistency of a lesion. All patients with HME should have lifelong surveillance through a specialist clinic so that any concerning changes are identified and investigated promptly. Regular monitoring does not mean cancer is likely — it means any change will be caught early.

Note: Lifelong surveillance 

HME is a lifelong condition that requires ongoing specialist follow-up. Annual or 2 yearly or 5 yearly review in a specialist clinic is recommended throughout childhood and into adulthood. Parents and patients should know the warning signs of change in any lesion and seek prompt review if concerned. Genetic counselling is available for the family, particularly for family planning. 

Patient support: The Hereditary Multiple Exostoses (HME) Support Group UK provides information and peer support for affected families.

Note:When to seek urgent help A lump that starts growing rapidly after your child has stopped growing New or significantly worsening pain in a known lump Wound infection signs: redness, discharge, temperature above 38.5°C Numbness or weakness in a limb near a known growth

This information is for general guidance only and is not a substitute for a consultation with Mr Wadia. If you are worried about your child, please seek medical advice