Osteochondroma

Understanding Osteochondroma

Osteochondroma, also known as osteocartilaginous exostosis, is the most common benign bone tumor, accounting for approximately 35-40% of all benign bone tumors. This growth consists of a bony projection on the external surface of a bone, covered by a cap of cartilage. Despite being classified as a tumor, osteochondromas are actually developmental abnormalities rather than true neoplasms, arising from aberrant growth of the growth plate cartilage.

These benign growths typically develop during childhood and adolescence when the skeleton is still growing, and they usually stop growing once skeletal maturity is reached. Osteochondromas can occur as solitary lesions or as part of a hereditary condition called hereditary multiple exostoses (HME), also known as multiple osteochondromas. While most osteochondromas are asymptomatic and discovered incidentally, some can cause symptoms due to their size or location, requiring medical attention and potentially surgical intervention.

Common Symptoms

Many osteochondromas remain asymptomatic throughout life and are discovered incidentally during imaging for other conditions. However, when symptoms do occur, they typically relate to the size and location of the growth.

Primary Symptoms

• Painless hard lump: Most commonly noticed near joints, particularly around the knee
• Pain or discomfort: Usually due to pressure on nearby structures
• Decreased range of motion: When the growth interferes with joint movement
• Muscle or tendon irritation: From friction against the bony projection
• Numbness or tingling: If the growth compresses nearby nerves
• Vascular symptoms: Rare cases of blood vessel compression

Causes and Risk Factors

The exact cause of osteochondroma development isn't fully understood, but it's believed to result from the separation of a fragment of growth plate cartilage that subsequently grows in an abnormal direction. This process creates the characteristic bony projection with its cartilage cap.

Development Mechanisms

• Growth plate abnormality: Aberrant lateral growth of physeal cartilage
• Genetic factors: Mutations in EXT1 and EXT2 genes in hereditary cases
• Developmental anomaly: Not a true neoplasm but a hamartoma
• Hormonal influence: Growth typically parallels skeletal development

Risk Factors

• Age: Most develop during childhood and adolescence
• Gender: Slightly more common in males (1.5:1 ratio)
• Family history: Hereditary multiple exostoses is autosomal dominant
• Previous radiation: Rarely, radiation therapy can induce osteochondroma formation
• Trauma: Some theories suggest trauma may play a role, though this is debated

Types and Locations

Osteochondromas can be classified based on their number and distribution, with important implications for management and prognosis.

Classification

• Solitary osteochondroma: Single lesion, most common form (85-90% of cases)
• Multiple osteochondromas: Two or more lesions, often hereditary
• Sessile type: Broad-based attachment to the bone
• Pedunculated type: Narrow stalk attachment, more common

Common Locations

• Distal femur: Around the knee, most frequent site (30-40%)
• Proximal tibia: Also around the knee area (15-20%)
• Proximal humerus: Upper arm near shoulder (10-20%)
• Pelvis: Can be challenging to detect and treat
• Scapula: Shoulder blade, may cause mechanical symptoms
• Ribs: Less common but can occur
• Spine: Rare but potentially serious location

Diagnosis

Diagnosing osteochondroma typically involves a combination of clinical examination and imaging studies. The characteristic appearance often makes diagnosis straightforward, but careful evaluation is necessary to rule out other conditions and assess for potential complications.

Clinical Evaluation

• Medical history: Age of onset, growth pattern, symptoms, family history
• Physical examination: Palpation of the mass, assessment of nearby structures
• Range of motion testing: Checking for mechanical limitations
• Neurovascular assessment: Evaluating for nerve or vessel compression
• Growth documentation: Measuring and photographing for monitoring

Imaging Studies

• X-rays: First-line imaging showing characteristic bony projection
• CT scan: Better visualization of bone detail and complex locations
• MRI: Evaluates cartilage cap thickness and soft tissue involvement
• Bone scan: May be used to detect multiple lesions
• Ultrasound: Can measure cartilage cap thickness

Key Diagnostic Features

• Continuity of cortex and medullary cavity with parent bone
• Growth away from the nearest joint
• Cartilage cap thickness less than 2 cm in adults
• Cessation of growth with skeletal maturity

Treatment Options

Treatment of osteochondroma depends on various factors including symptoms, location, size, and potential for complications. Many osteochondromas require no treatment beyond observation.

Conservative Management

• Observation: Regular monitoring for asymptomatic lesions
• Activity modification: Avoiding activities that cause symptoms
• Pain management: NSAIDs for mild discomfort
• Physical therapy: To maintain range of motion and strength
• Protective padding: For lesions prone to trauma

Surgical Treatment

Surgery is considered when specific indications are present:

• Persistent pain: Not responsive to conservative measures
• Mechanical symptoms: Interference with joint motion or tendon function
• Neurovascular compression: Causing significant symptoms
• Cosmetic concerns: Particularly in visible locations
• Suspected malignant transformation: Though rare (less than 1%)
• Growth after skeletal maturity: Concerning for malignancy

Surgical Techniques

• Marginal excision: Complete removal including cartilage cap and perichondrium
• Arthroscopic excision: For certain accessible locations
• Open excision: Traditional approach for larger or complex lesions
• Prophylactic removal: Sometimes considered for high-risk locations

Hereditary Multiple Exostoses

Hereditary Multiple Exostoses (HME), also known as Multiple Osteochondromas, is an autosomal dominant disorder characterized by the development of multiple osteochondromas throughout the skeleton.

Characteristics of HME

• Multiple lesions: Usually more than 2, often dozens
• Bilateral distribution: Typically affects both sides of the body
• Early onset: Usually apparent by age 5-10 years
• Growth disturbances: May cause limb length discrepancies
• Angular deformities: Particularly forearm and ankle
• Short stature: Common due to growth disturbances

Management Considerations

• Regular surveillance for all lesions
• Genetic counseling for affected families
• Higher risk of malignant transformation (1-5%)
• May require multiple surgeries throughout life
• Orthopedic monitoring for deformities
• Psychological support for body image concerns

Complications

While most osteochondromas are benign and remain asymptomatic, various complications can occur, particularly with larger lesions or those in problematic locations.

Mechanical Complications

• Fracture: Of the stalk in pedunculated lesions
• Bursitis: Inflammation of bursa overlying the lesion
• Tendon irritation: Snapping or inflammation
• Joint impingement: Limited range of motion
• Growth disturbances: In children with lesions near growth plates

Neurovascular Complications

• Nerve compression: Causing pain, numbness, or weakness
• Vascular compression: Potentially causing claudication or thrombosis
• Pseudoaneurysm formation: From chronic vessel irritation

Malignant Transformation

Though rare, malignant transformation to chondrosarcoma can occur:

• Risk less than 1% for solitary lesions
• Risk 1-5% for multiple hereditary exostoses
• Usually occurs in adulthood
• Warning signs include pain, growth after maturity, thick cartilage cap

Follow-up and Monitoring

Appropriate follow-up depends on the individual case but generally involves regular monitoring to ensure the lesion remains stable and to detect any complications early.

Surveillance Protocol

• Asymptomatic solitary lesions: Annual clinical evaluation until skeletal maturity
• Multiple lesions: More frequent monitoring, every 6-12 months
• Post-surgical: Follow-up to ensure complete excision and healing
• Adult patients: Periodic evaluation if symptoms develop

Imaging Follow-up

• Baseline imaging for comparison
• Repeat imaging if symptoms change
• MRI if concerned about cartilage cap thickness
• Annual imaging for high-risk lesions

Living with Osteochondroma

Most people with osteochondroma lead normal, active lives. Understanding the condition and knowing when to seek medical attention ensures optimal outcomes.

Activity and Lifestyle

• Sports participation: Usually unrestricted unless symptomatic
• Contact sports: May need protection for prominent lesions
• Regular exercise: Important for overall bone health
• Occupational considerations: Rarely limiting

When to Contact Your Doctor

• New or increasing pain in the lesion
• Noticeable growth of the mass
• Development of new symptoms
• Concerns about appearance or function
• Planning for pregnancy (genetic counseling if hereditary)

Prognosis

The prognosis for osteochondroma is excellent. Most lesions stop growing at skeletal maturity and cause no long-term problems. Even when surgery is required, outcomes are typically very good with low recurrence rates (less than 2%) when properly excised. For those with hereditary multiple exostoses, regular monitoring and appropriate intervention when needed allow for normal life expectancy and good quality of life.