Orthopaedic Surgery - Osteochondroma

Basics

An osteochondroma is a benign cartilage-capped bony projection arising from the surface of a bone.

A solitary osteochondroma is generally considered a benign developmental abnormality related to the growth plate rather than a true neoplasm.

Osteochondromas may occur as:

A solitary lesion

or as part of

Multiple hereditary exostoses (MHE), also called hereditary multiple osteochondromas.

MHE is an inherited genetic disorder characterized by the development of multiple osteochondromas.

Epidemiology

Osteochondroma is one of the most common benign bone tumors or tumor-like lesions encountered in orthopaedic practice.

It usually develops during:

Childhood or adolescence

and typically stops enlarging after skeletal maturity.

Risk Factors

There are no clearly established risk factors for developing a solitary osteochondroma.

Multiple Hereditary Exostoses

MHE follows an:

Autosomal-dominant inheritance pattern.

An affected parent therefore has approximately a:

50% chance of transmitting the pathogenic variant to each child.

Pathophysiology

Osteochondromas are believed to arise from growth-plate cartilage cells that become displaced beneath the periosteum.

Instead of contributing to normal longitudinal growth, these cells grow outward from the metaphysis.

The lesion therefore consists of:

Cortical bone

Medullary bone

and

A cartilage cap.

Continuity With the Parent Bone

A defining feature of an osteochondroma is continuity of:

The cortex

and

The medullary canal

with the underlying parent bone.

This feature is particularly important in distinguishing osteochondroma from other surface bone lesions.

Cartilage Cap

The surface of the lesion is covered by a cartilage cap.

In adults, the cartilage cap is usually thin, often only:

A few millimeters.

In skeletally immature children, the cap can normally be substantially thicker and may reach approximately:

2–2.5 cm during growth.

After skeletal maturity, a thick or enlarging cartilage cap raises concern for malignant transformation.

Etiology

Solitary Osteochondroma

There is no single known cause for an isolated osteochondroma.

It is thought to result from:

Abnormal displacement or development of growth-plate cartilage.

Multiple Hereditary Exostoses

MHE is caused most commonly by pathogenic variants involving the:

EXT1

or

EXT2

tumor-suppressor genes.

Older literature described an additional EXT3 locus, but most genetically confirmed cases are related to EXT1 or EXT2.

These genes are involved in:

Heparan sulfate synthesis and regulation of normal growth-plate development.

Associated Conditions

A solitary osteochondroma generally has no specific systemic associations.

Multiple lesions should raise suspicion for:

Multiple hereditary exostoses.

Diagnosis

Diagnosis is usually based on:

History

Physical examination

and

Characteristic radiographic findings.

Signs and Symptoms

Many osteochondromas are discovered incidentally.

The most common presentation is a:

Firm, painless mass near a joint or metaphysis.

Pain may develop if the lesion causes:

Mechanical irritation

Bursal inflammation

Tendon irritation

Fracture

Nerve compression

Vascular compression

or, rarely,

Malignant transformation.

Physical Examination

The typical finding is a:

Hard, fixed, immobile mass arising from bone.

The examiner should assess:

Size

Tenderness

Skin changes

Joint motion

Neurologic function

Distal vascular status

Mechanical Symptoms

A lesion near a tendon or joint may cause:

Snapping

Restricted range of motion

Local irritation

Pain with activity

Neurovascular Examination

Osteochondromas occasionally compress adjacent:

Peripheral nerves

or

Blood vessels.

Symptoms may include:

Numbness

Weakness

Vascular insufficiency

Pulsatile mass

or other local neurovascular abnormalities.

Imaging

Plain Radiographs

Radiographs are usually diagnostic.

Characteristic findings include:

A bony protuberance arising from the metaphysis

Continuity of the lesion cortex with the parent cortex

Continuity of the medullary canal with the parent bone

Metaphyseal widening or deformity in some cases

The lesion may be:

Sessile

or

Pedunculated.

Pedunculated Osteochondroma

A pedunculated lesion often projects away from the nearby:

Growth plate or joint.

CT

CT is not required for every lesion.

It can be useful when the osteochondroma is located in a complex anatomic region or when the relationship to surrounding structures is uncertain.

CT demonstrates:

Cortical continuity

Medullary continuity

Relationship to adjacent bone and soft tissues

MRI

MRI is also not routinely necessary for a straightforward asymptomatic lesion.

It is useful for evaluating:

Cartilage-cap thickness

Soft-tissue structures

Neurovascular relationships

Bursal formation

Possible malignant transformation

MRI clearly demonstrates continuity of the lesion with the medullary cavity.

Cartilage-Cap Assessment

In a skeletally mature patient, concern increases when the cartilage cap becomes:

Unusually thick

or

Progressively enlarged.

Pain or growth after skeletal maturity also warrants further evaluation.

Differential Diagnosis

Important alternative diagnoses include:

Parosteal osteosarcoma

Heterotopic ossification

Other surface bone lesions may occasionally resemble an osteochondroma.

Parosteal Osteosarcoma

Parosteal osteosarcoma is a low-grade malignant surface tumor.

Unlike an osteochondroma, it generally does not demonstrate the classic:

Continuous cortex and medullary cavity with the underlying bone.

Heterotopic Ossification

Heterotopic ossification develops within soft tissue rather than arising directly from the growth plate or medullary cavity.

Mature lesions may become heavily ossified but do not show the typical architecture of an osteochondroma.

Treatment

General Principles

Most asymptomatic osteochondromas require only:

Observation.

Surgery is unnecessary when the lesion is:

Painless

Stable

Not interfering with function

and

Not suspicious for malignant change.

Activity

Patients with uncomplicated osteochondromas generally may participate in:

Normal activities without restriction.

Restrictions may be needed temporarily if symptoms develop or after surgical excision.

Physical Therapy

Physical therapy usually has no specific role in the treatment of an isolated osteochondroma.

It may occasionally be useful if secondary stiffness or weakness develops after surgery.

Surgery

Simple excision is considered when the osteochondroma is symptomatic.

Indications for Excision

Possible indications include:

Persistent pain

Mechanical irritation

Restricted joint motion

Nerve compression

Vascular compression

Recurrent bursal irritation

Cosmetic or functional deformity

Suspicion for malignant transformation

Surgical Technique

The lesion is excised at its base with removal of the:

Cartilage cap

and

Perichondrial tissue

while preserving as much normal parent bone as possible.

Complete removal of the cartilage-producing tissue minimizes recurrence.

Postoperative Activity

Because excision may temporarily weaken the underlying bone, weight bearing and athletic activity should follow the surgeon’s postoperative instructions.

Contact or high-impact sports may be restricted for approximately:

Several weeks to 3 months, depending on the size and location of the resection.

Follow-Up

Prognosis

The prognosis is excellent.

After complete excision, recurrence is:

Uncommon.

Recurrence is more likely if cartilage-cap tissue remains or if the lesion is excised before skeletal maturity.

Malignant Transformation

Very rarely, an osteochondroma can undergo malignant transformation into a:

Secondary peripheral chondrosarcoma.

The risk is low in solitary osteochondroma and higher in patients with MHE.

Warning Signs for Malignant Transformation

Concerning findings include:

New pain

Rapid enlargement

Continued growth after skeletal maturity

Increasing cartilage-cap thickness

Destruction of surrounding bone

These findings warrant further imaging and specialist evaluation.

Neurovascular Complications

Rarely, the lesion can injure or compress:

A peripheral nerve

or

An artery.

Possible vascular complications include:

Pseudoaneurysm

Thrombosis

or

Distal ischemic symptoms.

Fracture

Fracture may occur through a pedunculated osteochondroma or through the underlying bone after excision.

Postoperative activity restrictions help reduce this risk.

Patient Monitoring

Patients with asymptomatic solitary osteochondromas can usually be followed clinically.

Routine radiographs every 2–3 years were historically recommended in some protocols, although imaging frequency should be individualized.

More frequent assessment is appropriate if the lesion demonstrates:

Pain

Growth

Neurologic symptoms

Vascular symptoms

or

Other concerning changes.

Multiple Hereditary Exostoses

Patients with MHE require broader surveillance because multiple lesions can cause:

Limb deformity

Limb-length discrepancy

Joint restriction

Neurovascular compression

and a higher risk of:

Secondary chondrosarcoma.

Key Principle

Osteochondroma is a benign cartilage-capped bony outgrowth characterized by continuity of its cortex and medullary cavity with the parent bone.

Most solitary lesions require only observation.

Surgical excision is reserved for lesions causing:

Pain, mechanical problems, neurovascular compression, deformity, or concern for malignant transformation.