Does Your Child Have Lumps on Their Bones? What You Need to Know About HMO

Have you noticed small bumps forming near your child's arms or legs around their bones? Your child might feel mild pain, or they might not feel any pain at all. Please do not panic, because not every single lump is a dangerous health problem. Today, we will explore a rare medical condition that causes these exact signs so you can stay fully informed.

This condition is called Hereditary Multiple Osteochondromas, which doctors often shorten to HMO. Understanding this condition will help you support your child and work closely with your doctor.

What Is Hereditary Multiple Osteochondromas?

Simply put, HMO is a genetic medical condition. This means it happens because of a small change or mutation in our genes, which serve as the basic blueprint for how our bodies grow. Because of this change, certain bones develop non-cancerous, harmless growths known in medical terms as osteochondromas. These growths are not cancer, so you do not need to worry about them spreading.

Are There Other Names For HMO?

Yes, you might run into a few different names when researching this condition online or talking with specialists. Doctors sometimes use these alternative terms:

• Hereditary Multiple Osteochondromas (HMO): This is the most common modern name.
• Multiple Hereditary Exostoses: This name was used often in past medical literature.
• Diaphyseal Aclasis: A more traditional clinical term.

No matter which name you see, they all describe the exact same medical condition. Do not let these different names confuse you during your research.

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What Is an Osteochondroma?

As mentioned earlier, an osteochondroma is a non-cancerous, harmless bone lump. Think of it this way: instead of growing normally, certain cells in your bones grow in a slightly unusual way to form these extra lumps.

These lumps usually form on the flat surface of a bone or near the ends where children grow. These areas are called growth plates, which contain flexible tissue known as cartilage. A small cap of cartilage covers the top of each lump. The most important thing to remember is that these lumps are not cancer, and they never spread through your body. That brings great relief to many parents.

Who Gets HMO and How Common Is It?

Doctors usually diagnose HMO during early childhood or as children enter their teenage years during adolescence. Boys and girls can get this condition in equal numbers.

However, HMO is not a very common condition. Statistics show that roughly one in every 50,000 people develops this condition. Because it is so rare, it is completely normal if you have never heard about it before today.

What Causes HMO? Is There a Genetic Link?

Yes, HMO is primarily a genetic condition linked directly to our genes. Around 90% of people with HMO develop it because of changes or mutations in the EXT1 or EXT2 genes. These specific genes give instructions to our DNA on how to build important proteins in our bodies. Unfortunately, doctors have not yet found the exact genetic cause for the remaining 10% of cases.

In most cases, parents pass these genetic changes down to their children. If a mother or a father carries this gene change, their child might inherit it. However, some children with HMO have parents who do not carry the gene change. This means the condition can sometimes appear as a brand new mutation in a family with no prior history.

What Are the Symptoms of HMO?

HMO causes painful or painless lumps to form on one or multiple bones. These lumps are the osteochondromas. You might also notice several other common physical signs:

• Unusual bone growth, including changes in the lower arm bones that might make an arm look slightly curved.
• Frequent bone fractures and injuries near growth plates.
• Differences in arm or leg length, known as limb length discrepancy, where one leg or arm is shorter than the other.
• Stiffness in joints that makes movement difficult.
• Pinched nerves caused by bone lumps pressing against nearby nerve pathways.
• Early joint wear and tear, known as premature osteoarthritis, during young adulthood.
• Pain and stiffness in ankles or knees that makes walking uncomfortable.
• Short-term and long-term pain that can sometimes feel intense.
• A generally short stature compared to peers.

Children feel more pain when these bone lumps grow near blood vessels or nerves. Sometimes, these lumps cause no pain at all and only appear as visible bumps under the skin.

Important: If you spot these lumps on your child's body or if your child often complains of bone pain, please schedule an appointment with a doctor right away.

Is HMO Contagious?

No, HMO is not a contagious disease. You cannot catch it from someone else through casual contact or touch, just like you would catch a cold. It is entirely a genetic condition.

However, if you have HMO, you have roughly a 50% chance of passing the gene mutation to your child during each pregnancy.

How Do Doctors Diagnose HMO?

If you or your doctor notice a lump near a bone or spot other HMO signs like curved limbs and pain, the medical team will begin a thorough evaluation:

1. They will take a detailed family medical history to see if close relatives have experienced similar symptoms.

2. They will perform a complete physical exam to check the size and location of any lumps and test your joint movement.

What Medical Tests Are Used?

After the physical exam, doctors usually order imaging tests to take a closer look inside the bones.

• Doctors often start with a simple X-ray test to clearly view the osteochondroma lumps.
• To gather more details or check if nerves are affected, doctors may also order: .
• A CT scan.
• An MRI scan.

Doctors use the information from these tests to confirm whether your child has HMO.

How Is HMO Treated? What Are the Options?

Treatment for HMO is never a one-size-fits-all approach. It depends entirely on your symptoms, the number of lumps, their locations, and how much they impact daily life. Doctors recommend several different management strategies:

• Observation of the tumor or watchful waiting: If the lumps cause no major problems or pain, doctors may suggest waiting and watching to see if they change or grow over time.
• Pain management: Doctors can recommend safe medicines like paracetamol or ibuprofen to control pain. Stronger pain relief options may be prescribed when necessary.
• Physical therapy: Physical therapists teach exercises to keep joints flexible and strengthen muscles, which helps reduce discomfort.
• Surgery:.
• Surgical removal of one or more lumps: Doctors perform surgery to remove a lump if it causes severe pain, presses on a nerve, blocks joint movement, or raises any concerns.
• Surgeries to lengthen limbs or correct alignment: Specialized surgeries help correct curved limbs or uneven arm and leg lengths caused by HMO.

Can Treatment Cause Complications?

Some people who undergo surgery to remove osteochondroma lumps might develop scars. Like any surgical procedure, there is a small risk of infection or temporary nerve irritation. However, surgical teams take every precaution to keep these risks as low as possible.

Can You Prevent HMO?

In truth, there is nothing you can do to prevent HMO because it is a genetic condition.

However, if you know that HMO runs in your family and you plan to have a child, you can explore prenatal genetic testing to see if your baby will inherit the condition. Examples include:

• Chorionic Villus Sampling (CVS).
• Genetic amniocentesis.

These tests check whether an unborn baby carries HMO. If parents use fertility treatments like IVF, preimplantation genetic testing is another option to consider. Discuss these choices with your doctor for expert guidance.

How Do I Know If My Child Is at Risk for HMO?

If you, your partner, or a close family member has HMO, it is very important to inform your pediatrician so they know your child faces a potential genetic risk.

If your family has no history of HMO, the risk of your child developing it is very low. Even so, because a brand new gene mutation can sometimes occur, doctors never rule out the possibility entirely.

What Can I Expect If My Child Has HMO?

Every child with HMO experiences the condition differently. Some children develop only a few osteochondroma lumps. This others develop many.

The good news is that once a child's growth plates close, meaning they finish growing taller and their bones stop lengthening, these lumps generally stop growing too.

However, in rare cases, lumps can recur even after growth plates close.

HMO can also cause other symptoms. Some children and adults experience fatigue, pain, and stiffness that makes moving around or completing daily tasks more challenging.

Not everyone with HMO needs medical treatment, but some people require surgery or physical therapy. Doctors can also suggest medicines to help manage pain effectively.

How Long Does This Condition Last?

HMO is a lifelong condition, meaning it cannot be cured completely. However, most people with benign osteochondromas live a normal life expectancy. The most important step is managing symptoms, taking prescribed treatments, and maintaining a high quality of life. Talk with your doctor regularly about treatment options that help your child stay healthy and happy.

Can Osteochondroma Lumps Turn Into Cancer? This Is What Many Fear Most.

This is a very important question. Yes, very rarely, osteochondroma lumps in people with HMO can turn cancerous, or malignant. This happens in only about 2% to 5% of people with HMO (meaning 2 to 5 out of every 100 people). When this happens, harmless lumps transform into bone cancers called chondrosarcoma or osteosarcoma.

Your doctor will watch closely for warning signs that an osteochondroma might be turning cancerous:

• If your child develops new lumps after puberty, or if an existing lump suddenly starts growing rapidly.
• If a painless osteochondroma suddenly becomes painful or if existing pain worsens greatly.
• If the cartilage cap over a lump becomes thicker than 2 centimeters, which doctors measure using an MRI scan.

Doctors can successfully remove most cancerous lumps with surgery. Depending on the cancer stage and whether it has spread, known as metastasized, your child might not need extra treatments like chemotherapy or radiation therapy. This highlights why regular checkups with your doctor remain so vital.

How Do You Care for a Child With HMO? What Can Parents Do?

If your child has HMO, paying close attention to their symptoms is essential.

• If your child develops new symptoms—especially sudden changes in lump size, increased pain, or numbness—notify your doctor right away.
• Follow all medical instructions carefully, including medicine schedules, exercise routines, and appointment dates.
• Never let your child suffer through pain without support. Talk with your medical team to find effective pain management strategies.
• Look after your child's mental health too, as living with a chronic condition can present emotional challenges. Talk openly with your child and offer constant support.

Whenever you need urgent support or experience an emergency, call 911 (US/Canada) or 999 (UK) or visit your nearest Emergency Department (ER / A&E) right away.

When Should You Seek Medical Advice? What Are the Emergencies?

If your child has a confirmed diagnosis of HMO, seek immediate medical advice in these situations:

• Your child develops new lumps.
• An existing lump grows rapidly in size.
• Pain increases suddenly or severe new pain develops, especially after puberty.
• The skin over a lump becomes red, swollen, and warm to the touch, which signals a possible infection.
• Your child experiences numbness or weakness in an arm or leg.

Never ignore these warning signs. Seeing a doctor quickly helps prevent major complications.

Can Children With HMO Also Have Autism?

Some parents ask about this connection. Medical specialists have reported a few cases where children have both HMO and autism spectrum disorder. However, experts still do not know if there is a direct, clear connection between these two conditions. Researchers are still studying whether the gene mutations that cause HMO (the EXT1 and EXT2 genes) play any role in autism development. At this time, no firm medical conclusion exists.

Final Thoughts: What to Remember Most.

HMO, or Hereditary Multiple Osteochondromas (sometimes called Multiple Hereditary Exostoses), is a genetic condition where harmless bone lumps (osteochondromas) form along children's and teenagers' bones and growth plates.

Although HMO is a lifelong condition that can cause pain and skeletal changes, treatments like surgery, physical therapy, and pain management help relieve symptoms, correct bone shape, and support a healthy life.

The most important thing to remember is that if your child shows these signs, stay calm and schedule an appointment with a qualified doctor right away. Talk openly with your doctor to decide which medical tests and treatment choices suit your child best. Your support and understanding give your child great strength to live a happy life with this condition.

Sources & References:

• Cleveland Clinic. (2024). Hereditary Multiple Exostoses (HMO): Overview & Symptoms.
• Mayo Clinic. (2025). Osteochondroma: Diagnosis and Treatment Guidelines.
• National Health Service (NHS UK). (2024). Multiple Hereditary Exostoses: Patient Guide.
• Centers for Disease Control and Prevention (CDC). (2025). Understanding Genetic Bone Disorders in Children.
• National Institutes of Health (NIH / PubMed Central). (2024). Clinical Review on Hereditary Multiple Osteochondromas and EXT1/EXT2 Mutations.