Orthopaedic Surgery - Enchondroma

Basics

An enchondroma is a common benign cartilaginous tumor composed of mature hyaline cartilage within the medullary canal, usually arising in the metaphysis or metadiaphysis of bone.

It most frequently involves the small tubular bones of the hands and feet, particularly the proximal phalanges.

Enchondromas may also occur in the distal femur, proximal humerus, and tibia but are uncommon in the spine, pelvis, and ribs.

They do not arise in bones formed entirely by membranous ossification.

Growth Pattern

A typical enchondroma is a nongrowing or very slowly changing lesion once skeletal maturity is reached.

Cartilage growth usually ceases in adulthood, although progressive mineralization may make the lesion appear radiographically different over time.

Malignant Potential

Small peripheral appendicular lesions are generally benign.

Large cartilaginous tumors arising in the axial skeleton carry a greater concern for malignant behavior and require more careful evaluation.

Epidemiology

Enchondroma is one of the most common benign bone tumors.

It is the most common bone tumor involving the small bones of the hands and feet and represents the most common destructive-appearing lesion encountered in the hand.

Age and Sex

Enchondromas can occur at any age but are recognized more frequently in adults.

In children, many lesions remain radiographically occult because the cartilaginous matrix has not yet mineralized.

Males and females are affected approximately equally.

Etiology

The exact origin is uncertain.

One proposed mechanism is persistence of epiphyseal growth cartilage that fails to remodel normally and remains within the metaphysis.

Another possibility is persistence of part of the original cartilaginous anlage of the developing bone.

Associated Conditions

Enchondroma Protuberans

Enchondroma protuberans is an unusual eccentric variant in which the cartilaginous lesion causes focal cortical bulging or outward extension.

Enchondromatosis

Enchondromatosis describes the presence of multiple enchondromas involving several bones.

The lesions may occur within the medullary cavity or occasionally closer to the cortical surface.

Ollier Disease

Ollier disease is a form of multiple enchondromatosis that characteristically has an asymmetric distribution.

Although multiple bones can be involved, one side of the body is often affected more extensively than the other.

Familial clustering has rarely been described, but a straightforward inherited pattern is not typical.

Maffucci Syndrome

Maffucci syndrome consists of multiple enchondromas associated with soft-tissue vascular lesions, particularly hemangiomas.

The hands and feet are commonly affected.

Diagnosis

General Clinical Features

Most solitary enchondromas are asymptomatic.

They are frequently discovered incidentally when radiographs are obtained for an unrelated problem.

Pain

Enchondromas of the long bones should not ordinarily produce pain.

When a patient with an intramedullary cartilage lesion has pain, another explanation should be sought, including arthritis, tendinopathy, bursitis, fracture, or a more aggressive cartilaginous tumor such as chondrosarcoma.

Pathologic Fracture

In the hand, enchondromas may weaken the involved phalanx sufficiently to cause a pathologic fracture.

Pain in these patients is usually attributable to the fracture rather than to the tumor itself.

Digital Enlargement

If the lesion occupies a substantial portion of a small tubular bone, mild enlargement or expansion of the affected digit may be visible.

Incidental Discovery

Many lesions are identified on routine radiographs or during imaging performed for another condition.

Enchondromas may also demonstrate increased uptake on bone scintigraphy.

Malignant Transformation

Malignant transformation of a solitary enchondroma is uncommon.

When it occurs, it is more often encountered in long bones than in the small bones of the hand.

Enchondromatosis

Clinical Recognition

Multiple enchondromatosis is often recognized by approximately 10 years of age because of palpable masses, limb shortening, asymmetric growth, or angular deformity.

Distribution

Although lesions may occur on both sides of the body, involvement is frequently much greater on one side.

Within a single extremity, the distribution may also be asymmetric.

Growth Disturbance

When lesions involve the region near the physis, affected bones may become shortened, widened, or deformed.

The severity of deformity depends on the number, size, and location of the lesions.

Course After Puberty

The active growth disturbance generally decreases after skeletal maturity because cartilaginous growth slows substantially.

Maffucci Syndrome

Patients with Maffucci syndrome have multiple enchondromas together with soft-tissue vascular malformations.

Phleboliths may be visible within hemangiomas on radiographs.

The hands and feet are especially commonly affected.

Physical Examination

The involved bone should be examined for tenderness, enlargement, deformity, and an associated soft-tissue mass.

Tenderness should raise concern for fracture, another local pain generator, or a more aggressive process.

Imaging

Plain Radiographs

Plain radiographs in at least two planes are the principal imaging studies.

In children with suspected multifocal disease, additional skeletal imaging may be needed to evaluate for other lesions.

Serial Radiographs

Comparison with previous studies or serial radiographs obtained approximately every 3–6 months can help determine whether the lesion is stable.

A typical enchondroma does not enlarge significantly after skeletal maturity.

Typical Radiographic Appearance

The classic lesion is a well-defined central lytic abnormality within the metaphysis or metadiaphysis.

Mild endosteal scalloping may occur.

Intralesional mineralization is variable.

Cartilage Matrix Mineralization

Typical chondroid mineralization patterns are described as rings and arcs, stippled, punctate, or popcorn-like calcifications.

These reflect enchondral mineralization within the cartilaginous matrix.

Small Tubular Bones

In the phalanges and other small tubular bones, the lesion may occupy most or all of the shaft.

The cortex generally remains intact but may appear mildly expanded or thinned.

Pediatric Appearance

In children, enchondromas may remain almost completely radiolucent because the cartilage has not mineralized.

They may therefore resemble a unicameral bone cyst.

Changes With Age

As patients mature, the initially radiolucent cartilage commonly undergoes increasing enchondral ossification and calcification.

This produces the classic ring-and-stipple appearance seen more often in adults.

Dense Mineralization

Occasionally, mineralization becomes so extensive that the lesion resembles a bone infarct.

Periosteal Reaction

A typical uncomplicated enchondroma does not produce a periosteal reaction.

The development of aggressive periosteal change should raise concern for another diagnosis.

Imaging in Enchondromatosis

Radiographs demonstrate multiple radiolucent cartilaginous lesions, usually centered in the metaphyses.

Calcification may appear irregular and longitudinal or streak-like as the lesions extend from the region of the physis.

Cortical Expansion

Affected bones may expand internally because the enchondromas interfere with normal metaphyseal remodeling.

As a result, the bone may fail to develop its normal tubular contour and can develop clubbed or broadened ends.

Distribution Within Bone

Lesions may be intracortical, subcortical, metaphyseal, or occasionally epiphyseal.

The epiphysis and diaphysis are usually relatively spared, although severe disease may involve nearly the entire bone.

MRI

Signal Characteristics

On MRI, an enchondroma typically appears as a well-circumscribed, lobulated lesion with low signal intensity on T1-weighted images and high signal intensity on T2-weighted images.

Surrounding Tissues

A benign enchondroma should not usually produce significant periosteal reaction or extensive surrounding edema.

Such findings warrant closer assessment for fracture or an aggressive lesion.

Bone Scintigraphy

Enchondromas may demonstrate increased radionuclide uptake and therefore appear “hot” on a bone scan.

This does not by itself imply malignant transformation.

Interpretation of Increased Uptake

Although enchondromas generally do not enlarge, they undergo ongoing remodeling.

Increased tracer uptake can therefore be present in a benign lesion.

A change in uptake compared with previous studies may be more significant than a single positive scan.

Pathological Findings

Microscopic Appearance

Typical enchondromas contain small nests or lobules of cartilage separated by normal marrow.

The chondrocytes are generally bland, without significant atypia.

Calcification

Foci of calcification and enchondral ossification are commonly present.

A thin rim or layer of lamellar bone may also be seen.

Cellular Features

At low magnification, the lesions are usually hypocellular with a blue-gray chondroid matrix and inconspicuous nuclei.

At higher magnification, nuclei are small, uniform, and darkly staining.

Binucleated cells are uncommon in typical long-bone lesions.

Bone Permeation

True permeation of pre-existing trabecular bone is not characteristic of enchondroma.

Infiltrative permeation of marrow and trabeculae raises concern for chondrosarcoma.

Ki-67

Enchondromas generally demonstrate very low proliferative activity, and Ki-67 staining is typically negative or minimal.

Hand Lesions

Enchondromas of the hand may look somewhat more cellular and atypical microscopically than comparable lesions in long bones while still behaving benignly.

They may demonstrate mild myxoid change, increased cellularity, and occasional binucleated cells.

These findings should therefore be interpreted in the context of the lesion’s location and imaging appearance.

Differential Diagnosis

Bone Infarct

A heavily mineralized enchondroma may resemble a bone infarct.

The distribution and pattern of mineralization can help differentiate the two.

Chondrosarcoma

The most important differential diagnosis is low-grade chondrosarcoma, particularly in an adult with a painful or enlarging long-bone lesion.

Enchondroma Versus Low-Grade Chondrosarcoma

Distinguishing a benign enchondroma from an active cartilaginous lesion or low-grade chondrosarcoma can be difficult.

Histologic overlap is substantial, so biopsy alone may not provide a definitive answer.

Diagnosis requires careful correlation of clinical symptoms, serial imaging, lesion location, cortical behavior, and pathology.

Features Favoring Enchondroma

Features supporting enchondroma include absence of pain attributable to the lesion, radiographic stability, relatively uniform matrix mineralization, minimal endosteal erosion, low cellularity, and bland uniform chondrocytes.

Features Suggesting Chondrosarcoma

Concerning findings include persistent lesion-related pain, progressive enlargement, lucent nonmineralized regions, marked endosteal scalloping, cortical thickening or destruction, loss of previously present mineralization, periosteal reaction, increased cellularity, atypia, and permeation of trabecular bone.

Endosteal Scalloping

Deep endosteal erosion involving more than approximately 50% of cortical thickness is more concerning for an aggressive cartilaginous lesion than for a latent enchondroma.

Treatment

General Principles

Most asymptomatic enchondromas do not require surgery.

The principal goals are to confirm radiographic stability and ensure that pain, if present, is not being incorrectly attributed to the lesion.

Evaluation of Pain

Because a typical enchondroma should not cause pain in a long bone, common regional causes should be considered.

For example, pain around a proximal humeral enchondroma may actually arise from rotator cuff disease or glenohumeral arthritis.

Pain near a proximal femoral lesion may result from trochanteric bursitis, hip arthritis, or abductor pathology, while pain near a distal femoral lesion may arise from patellofemoral disease, knee arthritis, or iliotibial-band symptoms.

Activity

Routine activity restriction is generally unnecessary for an uncomplicated enchondroma of a long bone.

Management should instead be based on fracture risk and symptoms.

Hand and Foot Enchondromas

Lesions in the small bones of the hands and feet may weaken the cortex and predispose to fracture.

For this reason, symptomatic or structurally significant lesions are more often treated surgically.

Pathologic Fracture

When a pathologic fracture occurs through a hand enchondroma, the fracture is often allowed to heal first.

Curettage and grafting can then be performed after union if the lesion remains clinically significant.

Surgery

Long-Bone Lesions

Surgery is usually unnecessary for a stable, asymptomatic enchondroma of a long bone.

Observation with serial imaging is generally sufficient.

Curettage

Symptomatic hand lesions are commonly treated by intralesional curettage.

The cartilaginous tissue is removed through a cortical window.

Bone Grafting

Following curettage, the defect may be filled with bone graft or another suitable bone substitute, particularly when substantial structural weakness remains.

Surgical Approach in the Phalanx

A small cortical window can be created along the lateral aspect of the involved phalanx.

The lesion is then thoroughly curetted, and the residual cavity may be grafted.

Enchondromatosis Treatment

Angular Deformity

Surgery may be required when multiple enchondromas cause significant angular deformity.

Corrective osteotomy can be performed, including through involved bone when appropriate.

Limb-Length Discrepancy

Clinically significant limb-length inequality may be managed with epiphysiodesis or limb-lengthening procedures, depending on patient age and the magnitude of discrepancy.

Hand Disease

Large hand lesions that interfere with function or substantially weaken the bone may require curettage and grafting.

Follow-Up

Patients with solitary long-bone enchondromas are commonly followed with serial radiographs at approximately 3–6-month intervals initially, often for 1–2 years.

If the lesion remains stable, surveillance can usually become less frequent.

Return Precautions

Patients should return for reassessment if the involved extremity develops new persistent pain, swelling, or other changes, because these may indicate fracture or more aggressive biological behavior.

Referral

Patients with a cartilage lesion and unexplained musculoskeletal pain should be considered for referral to an orthopaedic oncologist, particularly when radiographic findings are atypical or there is concern for chondrosarcoma.

Complications

Malignant Transformation

The principal oncologic complication is transformation to chondrosarcoma, although this is uncommon in solitary enchondromas.

New pain and documented lesion growth are particularly concerning.

Ollier Disease

Patients with enchondromatosis have a substantially greater risk of malignant transformation than patients with solitary enchondroma.

Historical series have reported development of chondrosarcoma in approximately 30% of patients with Ollier disease, commonly during the third or fourth decades of life.

Maffucci Syndrome

The risk of malignancy is particularly high in Maffucci syndrome.

Affected patients are predisposed not only to chondrosarcoma but also to other malignancies involving organs such as the brain and pancreas.

Patient Monitoring

Monitoring should focus on clinical symptoms and serial radiographic behavior.

Important warning features include new lesion-related pain, enlargement, increasing cortical erosion, cortical destruction, new periosteal reaction, loss of mineralization, or development of a soft-tissue mass.

Patients with Ollier disease or Maffucci syndrome require more prolonged surveillance because of their substantially higher risk of malignant transformation.