Exostoses (Osteochondromas) – A Comprehensive Medical Guide

Overview

Exostoses, more commonly called osteochondromas, are benign (non‑cancerous) bone growths that arise from the surface of a bone near the growth plate. They consist of both bone and cartilage and are usually attached to the outer layer of the skeleton. Osteochondromas are the most frequent type of benign bone tumor, accounting for 30–50 % of all benign bone lesions.^{[1] Mayo Clinic}

**Who is affected?**

• Most cases are diagnosed in children or adolescents, typically between ages 5 and 20, when the growth plates are still active.
• There is a slight male predominance (about 1.5 : 1 male‑to‑female ratio).^{[2] CDC}
• Patients with hereditary multiple exostoses (HME, also known as multiple osteochondromas) inherit a genetic mutation and may develop dozens of lesions.

**Prevalence**

• Solitary osteochondromas occur in ~1 % of the general population.^{[3] NIH}
• Hereditary multiple exostoses affect roughly 1 in 50,000–100,000 people worldwide.^{[4] WHO}

Symptoms

Many osteochondromas are discovered incidentally on X‑rays performed for unrelated reasons and cause no symptoms. When symptoms do occur, they reflect the size, location, and any irritation of nearby structures.

Common symptoms

• Visible or palpable lump – a hard, non‑painful bump under the skin, most often near the knees, shoulders, or wrists.
• Localized pain – aching that worsens with activity or when the growth is pressed.
• Restricted range of motion – especially when the exostosis is near a joint.
• Clunking or snapping sensation – the bone protrusion may catch tendons or ligaments during movement.

Location‑specific symptoms

• Knees (distal femur, proximal tibia) – pain with kneeling or squatting; possible “locking” of the joint.
• Shoulder (proximal humerus) – limited overhead reach; tingling if the growth presses on the brachial plexus.
• Forearm (proximal ulna, radius) – forearm pronation/supination restriction; ulnar nerve irritation causing numbness.
• Spine (rare) – spinal canal narrowing, leading to back pain or neurologic deficits.

Red‑flag symptoms that may suggest malignant transformation

• Rapid increase in size after skeletal maturity.
• New onset of night pain that is not relieved by over‑the‑counter analgesics.
• Swelling, redness, or ulceration over the lesion.
• Neurologic changes (weakness, numbness) due to compression of nerves or spinal cord.

Causes and Risk Factors

Osteochondromas develop from an abnormal out‑growth of the growth plate (physis). The exact trigger for sporadic (solitary) lesions is not fully understood, but the following mechanisms are recognized:

Genetic causes

• Hereditary Multiple Exostoses (HME) – autosomal dominant inheritance of mutations in either the EXT1 or EXT2 genes, which encode enzymes necessary for heparan sulfate synthesis. Defective heparan sulfate disrupts normal cartilage organization, leading to multiple exostoses.^{[5] Cleveland Clinic}
• Family history of multiple lesions dramatically increases risk.

Non‑genetic (sporadic) factors

• Random somatic mutations during bone growth.
• Trauma is often reported by patients, but evidence suggests it is more likely to draw attention to a pre‑existing lesion than cause it.

Risk factors

• Male sex (higher incidence).
• Active growth plates (children and adolescents).
• Known family mutation (for HME).
• Prior radiation exposure to bone (rarely implicated).

Diagnosis

Diagnosis is usually straightforward when a characteristic bony protuberance is identified on physical exam and imaging. The work‑up includes:

Clinical evaluation

• History – onset, growth pattern, pain, functional limitation, family history.
• Physical exam – size, consistency, mobility, relationship to joints and neurovascular structures.

Imaging studies

• Plain radiographs (X‑ray) – first‑line. Osteochondroma appears as a bony outgrowth with a continuity of cortical and medullary bone with the parent bone.^{[1] Mayo Clinic}
• Computed tomography (CT) – provides detailed view of cortical continuity, especially useful for lesions near complex anatomy (e.g., pelvis, spine).
• Magnetic resonance imaging (MRI) – assesses cartilage cap thickness (critical for detecting malignant transformation) and relationship to surrounding soft tissues, nerves, and vessels.
• Ultrasound – can measure cartilage cap thickness in superficial lesions, especially in children.

Laboratory tests

Usually not required, but in cases where malignancy is suspected, serum alkaline phosphatase and inflammatory markers may be checked.

Biopsy

Reserved for lesions with suspicious features (e.g., caps >2 cm in adults, rapid growth). Histology shows a cartilage‑covered bony stalk; malignant change shows atypical chondrocytes and infiltrative growth.

Treatment Options

Most solitary osteochondromas do not need active treatment. Management is individualized based on symptoms, functional impact, and risk of complications.

Observation (Watchful waiting)

• Serial clinical exams and imaging every 12–24 months until skeletal maturity.
• Patient education on self‑monitoring for rapid growth or new pain.

Surgical intervention

Indicated when the lesion causes pain, functional limitation, neurovascular compromise, or shows signs of malignant transformation.

• Excision (en bloc resection) – removal of the bony stalk and cartilage cap. Goal: complete removal of the cartilaginous cap to reduce recurrence risk.
• Intralesional curettage – rarely used; higher recurrence rates.
• Minimally invasive techniques (e.g., endoscopic resection) are being explored for select superficial lesions.

Post‑operative care

• Physical therapy to restore range of motion and strength.
• Weight‑bearing restrictions for 4–6 weeks if the lesion involved a weight‑bearing bone.
• Regular follow‑up X‑ray at 6‑months to confirm complete excision.

Medication & symptom management

• Analgesics – acetaminophen or NSAIDs for mild pain.
• Activity modification – avoiding activities that stress the affected region.
• In HME patients, bisphosphonates have been studied for pain relief, but evidence is limited.

Genetic counseling

For families with HME, referral to a genetics professional is recommended to discuss inheritance patterns, prenatal testing, and family planning.

Living with Exostoses (Osteochondromas)

While many people live normal lives with minimal impact, thoughtful daily management can reduce discomfort and prevent complications.

Activity & Exercise

• Low‑impact activities (swimming, cycling, walking) are generally safe.
• Avoid repetitive overhead motions if lesions are near the shoulder or elbow.
• Strengthening the surrounding musculature can alleviate stress on the bone.

Self‑monitoring

• Measure the size of any palpable lump every 3–6 months.
• Note any new or worsening pain, especially at night.
• Watch for skin changes (redness, ulceration) over the growth.

Protective gear

For athletes or individuals in high‑impact sports, wearing padded sleeves or braces over the lesion can prevent trauma.

Regular medical follow‑up

• Children with solitary lesions: annual orthopedic review until growth plates close.
• HME patients: multidisciplinary clinic (orthopedics, genetics, radiology) every 1–2 years.

Psychosocial aspects

Visible deformities can affect self‑esteem, especially in teenagers. Counseling or support groups (e.g., patient advocacy organizations for HME) can be beneficial.

Prevention

Because most osteochondromas are congenital or arise from genetic mutations, true primary prevention is limited. However, certain measures may reduce secondary complications:

• Early detection through routine pediatric examinations.
• Prompt evaluation of any new bony lump.
• Avoiding unnecessary high‑impact sports that could traumatize a lesion.
• In families with known EXT1/EXT2 mutations, genetic counseling can inform reproductive choices.

Complications

If left untreated when indicated, osteochondromas can lead to several problems:

• Fracture – the stalk may serve as a weak point, especially after trauma.
• Neurovascular compression – can cause numbness, weakness, or ischemia (e.g., radial nerve palsy from a forearm exostosis).
• Joint dysfunction – limited motion or early osteoarthritis from mechanical irritation.
• Malignant transformation – ≈1 % of solitary lesions and up to 5 % of HME lesions may evolve into chondrosarcoma, most often after skeletal maturity.^{[6] NIH}
• Cosmetic deformity – especially when lesions are large or located on visible areas such as the forearm or shin.

When to Seek Emergency Care

References

1. Mayo Clinic. Osteochondroma. https://www.mayoclinic.org.
2. Centers for Disease Control and Prevention. Bone Tumors in Children. https://www.cdc.gov.
3. National Institutes of Health (NIH) – Office of Rare Diseases. Osteochondroma. https://rarediseases.info.nih.gov.
4. World Health Organization. WHO Classification of Tumours of Bone. 2020.
5. Cleveland Clinic. Hereditary Multiple Exostoses (HME). https://my.clevelandclinic.org.
6. National Cancer Institute. Chondrosarcoma Treatment (PDQ®)–Health Professional Version. https://www.cancer.gov.