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PubMed This is a summary of 56 peer-reviewed journal articles Updated
Orthopedics

Understanding Multiple Osteochondromas (HME)

At a Glance

Multiple Osteochondromas (HME) is a rare genetic condition causing benign bone bumps to form during childhood. These growths typically stop when a child reaches skeletal maturity. While manageable, they require regular monitoring for joint issues and a small risk of future complications.

Receiving a diagnosis of Multiple Osteochondromas (also known as Hereditary Multiple Exostoses or HME) can feel overwhelming, but it is important to take a deep breath. While the name sounds complex, the most important thing to know is that these are primarily benign (non-cancerous) bone bumps [1][2]. They are a manageable part of life for many families, and understanding the road ahead can help replace fear with a clear plan of action.

Three Stabilizing Facts

If you are currently in a “panic spiral,” keep these three facts in mind:

  1. They are mostly benign. The bumps, called osteochondromas, are non-cancerous growths of bone and cartilage [1][3].
  2. They stop growing when the child stops growing. These bumps typically only grow during the years a child is naturally growing. Once a person reaches skeletal maturity (when the growth plates close after puberty), the bumps generally stop increasing in size [4][5].
  3. It is a manageable condition. While the bumps can cause discomfort or require monitoring, many children with this condition lead active, full lives with the help of a coordinated care team [6][7].

What is this Condition?

Multiple Osteochondromas is a rare genetic condition where multiple “exostoses” (bony outgrowths) develop near the growth plates (the areas of active new bone growth) [1][8]. These growths are capped with a layer of cartilage, which is why they are called osteochondromas (osteo meaning bone and chondroma meaning cartilage) [9][2].

You may hear doctors use different names for the same thing:

  • Hereditary Multiple Exostoses (HME): An older term still commonly used by many families and doctors.
  • Multiple Osteochondromas (MO): The more modern medical term preferred by many specialists today because it more accurately describes the nature of the growths [9][1].
  • Multiple Hereditary Exostoses (MHE): Another common variation you may see in medical records.

How Rare Is It?

This condition is considered rare, affecting approximately 1 in 50,000 to 1 in 100,000 people worldwide [1][10]. It is often caused by a change (mutation) in one of two genes, EXT1 or EXT2, which are responsible for how bone and cartilage grow [7][11].

The Journey: Childhood to Adulthood

Understanding the typical course of the disease helps you know what to watch for at different stages of life.

Childhood (The Active Growth Phase)

Most children are diagnosed by age 12, often as young as 3, when parents or doctors notice a hard bump near a joint like the knee, shoulder, or ankle [12][1].

  • Growth: New bumps may appear, and existing ones may grow larger as the child grows [13].
  • Common Issues: Because these bumps grow near joints, they can sometimes cause “mechanical” problems, such as limited range of motion, pain from rubbing against tendons or muscles, or slight changes in how the limbs align (such as “knock-knees”) [8][14][15].
  • Monitoring: Doctors typically monitor these with regular physical exams and occasionally X-rays to ensure the bumps aren’t putting pressure on nerves or blood vessels [1][7].

Adulthood (The Stable Phase)

Once a person reaches skeletal maturity, the active growth phase of the bumps ends [4].

  • Stability: For many adults, the bumps remain stable and do not cause new issues [5].
  • Long-term Care: Most complications in adulthood stem from pre-existing bumps, such as early-onset osteoarthritis (wear and tear in the joints) or chronic pain if a bump is in a high-friction area [7][16].
  • Malignant Transformation: While rare, there is a small risk (estimated between 1% and 10% over a lifetime) that a benign bump could turn into a chondrosarcoma (a type of bone cancer) [10][12]. Because of this, adults are taught to watch for “red flags” like new pain or growth in a bump that had previously been stable [1][5].

Why Surgery Happens

Surgery is not required for every bump. In fact, many are left alone if they aren’t causing problems. A doctor may suggest surgery if a bump:

  • Causes significant pain [17].
  • Severely limits the movement of a joint [1].
  • Presses on a nerve or blood vessel [18].
  • Affects how a limb is growing (such as causing one leg to be shorter than the other) [19].

Explore This Guide

To navigate the specifics of this condition, please explore the sections below:

01

Genetics & Biology: The EXT1 and EXT2 Genes

Learn about the genetics of Multiple Osteochondromas. Understand how EXT1 and EXT2 gene mutations affect bone growth, severity, and family inheritance.

02

Symptoms, Deformities, and Complications

Learn about the symptoms, bone deformities, and complications of Multiple Osteochondromas (HME). Understand nerve pain, leg length changes, and what to expect.

03

Malignant Transformation Risk & Monitoring

Learn about the risk of malignant transformation in multiple osteochondromas. Understand warning signs, cartilage cap monitoring, and when to get an MRI.

04

Treatment Options: Surgery and Pain Management

Explore treatment options for Multiple Osteochondromas. Learn about watch-and-wait approaches, when surgery is necessary, guided growth, and pain management.

05

Building Your Care Team & First Visit Prep

Learn how to build an expert care team for Multiple Osteochondromas (MO/HME). Find out which specialists you need and how to prepare for your first visit.

Common questions in this guide

Will the bone bumps continue to grow in adulthood?
No, these benign bone bumps typically stop growing when a person reaches skeletal maturity. Once the growth plates close after puberty, the existing bumps generally remain stable throughout adulthood.
Is surgery required for all bone bumps in HME?
Surgery is only recommended if a specific bump is causing problems. A doctor may suggest removal if the growth causes significant pain, limits joint movement, presses on nerves, or affects how a limb is growing.
What is the risk of an osteochondroma turning into cancer?
While rare, there is a small lifetime risk of 1% to 10% that a benign bump could turn into a type of bone cancer called chondrosarcoma. Because of this, adults are advised to monitor for red flags like new pain or growth in a previously stable bump.
What causes Hereditary Multiple Exostoses?
This condition is usually caused by a genetic mutation in either the EXT1 or EXT2 gene. These genes are responsible for regulating how bone and cartilage grow during childhood development.

Questions to Ask Your Doctor

Curated prompts to bring to your next appointment.

  1. 1.Which specific gene (EXT1 or EXT2) is involved in my child's case, and how does that affect the likely number of bumps?
  2. 2.What is the current range of motion in the affected joints, and what should we consider our 'baseline'?
  3. 3.How often should we schedule follow-up imaging or physical exams to monitor growth?
  4. 4.What signs (like specific types of pain or changes in appearance) should trigger an immediate call to your office?
  5. 5.Are there certain physical activities or sports we should modify to protect the joints or prevent pain?

Questions For You

Tap a prompt to share your answer — we'll use it plus this page's context to start a tailored conversation.

Related questions

Are HME and Multiple Osteochondromas the Same?

References

References (19)
  1. 1

    Advances in the pathogenesis and possible treatments for multiple hereditary exostoses from the 2016 international MHE conference.

    Phan AQ, Pacifici M, Esko JD

    Connective tissue research 2018; (59(1)):85-98 doi:10.1080/03008207.2017.1394295.

    PMID: 29099240
  2. 2

    Hereditary multiple exostoses: A case report and literature review.

    Ha TH, Ha TMT, Nguyen Van M, et al.

    SAGE open medical case reports 2022; (10()):2050313X221103732 doi:10.1177/2050313X221103732.

    PMID: 35693925
  3. 3

    Venous malformation may be a feature of EXT1-related hereditary multiple exostoses: A report of two unrelated probands.

    Albokhari D, Bailey CR, Hwang F, et al.

    American journal of medical genetics. Part A 2023; (191(6)):1570-1575 doi:10.1002/ajmg.a.63158.

    PMID: 36869625
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    Imaging of benign complications of exostoses of the shoulder, pelvic girdles and appendicular skeleton.

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    Diagnostic and interventional imaging 2017; (98(1)):21-28 doi:10.1016/j.diii.2015.11.021.

    PMID: 27316575
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    Osteochondromas: An Updated Review of Epidemiology, Pathogenesis, Clinical Presentation, Radiological Features and Treatment Options.

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    In vivo (Athens, Greece) 2021; (35(2)):681-691 doi:10.21873/invivo.12308.

    PMID: 33622860
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    Multiple Exostoses Syndrome and Basilar Artery Aneurysm: A Case Report.

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    Journal of vascular and interventional neurology 2018; (10(2)):28-32.

    PMID: 30746007
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    Hereditary Multiple Exostoses: Current Insights.

    D'Arienzo A, Andreani L, Sacchetti F, et al.

    Orthopedic research and reviews 2019; (11()):199-211 doi:10.2147/ORR.S183979.

    PMID: 31853203
  8. 8

    Multiple hereditary exostoses and enchondromatosis.

    Jurik AG

    Best practice & research. Clinical rheumatology 2020; (34(3)):101505 doi:10.1016/j.berh.2020.101505.

    PMID: 32253147
  9. 9

    Novel exostosin-2 mutation identified in a Chinese family with hereditary multiple osteochondroma.

    Ruan W, Cao L, Chen Z, et al.

    Oncology letters 2018; (15(4)):4383-4389 doi:10.3892/ol.2018.7838.

    PMID: 29541207
  10. 10

    Hereditary multiple exostoses: an educational review.

    Rueda-de-Eusebio A, Gomez-Pena S, Moreno-Casado MJ, et al.

    Insights into imaging 2025; (16(1)):46 doi:10.1186/s13244-025-01899-6.

    PMID: 39982564
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    Hereditary Multiple Exostoses: New Insights into Pathogenesis, Clinical Complications, and Potential Treatments.

    Pacifici M

    Current osteoporosis reports 2017; (15(3)):142-152 doi:10.1007/s11914-017-0355-2.

    PMID: 28466453
  12. 12

    Identification of a new mutation in an Iranian family with hereditary multiple osteochondromas.

    Akbaroghli S, Balali M, Kamalidehghan B, et al.

    Therapeutics and clinical risk management 2017; (13()):15-19 doi:10.2147/TCRM.S111717.

    PMID: 28053536
  13. 13

    Daughter and mother diagnosed with hereditary multiple exostoses: A case report and a review of the literature.

    Mărginean CO, Meliţ LE, Mărginean MO

    Medicine 2017; (96(1)):e5824 doi:10.1097/MD.0000000000005824.

    PMID: 28072741
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    Management of Lower Extremity Deformity in Children with Hereditary Multiple Exostoses.

    Whalen MJ, van Bosse HJP

    Journal of the Pediatric Orthopaedic Society of North America 2025; (13()):100277 doi:10.1016/j.jposna.2025.100277.

    PMID: 41158744
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    Reconstruction of the Hip in Multiple Hereditary Exostoses.

    Lee DH, Paley D

    Children (Basel, Switzerland) 2021; (8(6)) doi:10.3390/children8060490.

    PMID: 34201373
  16. 16

    Total knee arthroplasty with simultaneous tibial shaft osteotomy in patient with multiple hereditary osteochondromas and multiaxial limb deformity - a case report.

    Grzelecki D, Szneider J, Marczak D, Kowalczewski J

    BMC musculoskeletal disorders 2020; (21(1)):233 doi:10.1186/s12891-020-03245-x.

    PMID: 32284061
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    Management of nerve compression in multiple hereditary exostoses: a report of two cases and review of the literature.

    Payne R, Sieg E, Fox E, et al.

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    C1 C2 spinal cord compression in hereditary multiple exostoses: case report and review of the literature.

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  19. 19

    Rapidly acquired valgus deformity of the knee after osteochondroma resection in multiple hereditary exostoses pediatric patients: A report of two cases.

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    PMID: 34815827

This page provides general information about Multiple Osteochondromas (HME) for educational purposes. Always consult your pediatric orthopedist or genetic specialist for personalized medical advice and treatment.

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