What is an Enchondroma of the Femur?
An enchondroma of the femur is a benign, cartilaginous tumor that arises from the medullary (inner) cavity of the femur bone, typically growing up to 3 cm in size and usually causing no pain unless complications develop. 1
Basic Characteristics
Enchondromas are benign cartilage-forming neoplasms that originate from growth plate cartilage which proliferates within the bone's medullary cavity, causing bone expansion. 1, 2 They represent 3-10% of all bone tumors and 12-24% of benign bone tumors. 2
Typical Features:
- Location: While most commonly found in small bones of hands and feet, enchondromas can occur in long bones like the femur (particularly the distal femur metaphysis). 2, 3
- Size: Typically grow to sizes up to 3 cm. 1
- Symptoms: Usually asymptomatic and discovered incidentally; they typically do not cause pain unless pathologic fracture or malignant transformation occurs. 1, 4
- Radiographic appearance: Shows a localized, radiolucent lytic bone defect with punctuate calcifications, usually central or eccentric in the metaphyseal region. 2
Clinical Significance and Risks
Solitary Enchondromas
Most solitary enchondromas in the femur are benign and have an excellent prognosis with very low recurrence rates (<5%). 2 When recurrence occurs, it suggests possible malignancy. 2
Risk of Malignant Transformation
The femur is one of the highest-risk sites for malignant transformation to chondrosarcoma, particularly in patients with multiple enchondromas (enchondromatosis). 1 In enchondromatosis syndromes like Ollier disease, approximately 30% of patients develop chondrosarcoma, with the femur being among the most common transformation sites along with tibia, humerus, pelvis, and scapula. 1
Warning Signs of Malignant Transformation:
- New or increasing pain at the lesion site (though pain can occasionally occur with benign lesions). 1
- Increasing tumor size on serial imaging. 1, 5
- Cartilage cap thickness >2.0-3.0 cm on MRI or CT. 5
Diagnostic Approach
MRI and histopathological examination confirm the diagnosis. 2, 3 Contrast-enhanced MRI is essential to reveal high-grade areas and guide biopsy if malignancy is suspected. 6
A critical pitfall: Differentiation between enchondroma and grade I chondrosarcoma is notoriously difficult even for expert pathologists, with significant interobserver variability. 5 In the femur (a long bone), central cartilaginous lesions should be considered atypical cartilaginous tumors until proven otherwise. 6
Management
Asymptomatic Lesions:
Conservative management with serial radiological follow-ups is appropriate for asymptomatic solitary enchondromas. 2
For patients with new or increasing pain or radiographic evidence of growth, dedicated MRI imaging should be obtained. 5
Symptomatic Lesions:
Operative management is indicated for symptomatic cases, typically involving curettage with autogenous bone graft and prophylactic fixation if needed. 2, 3 Low-grade lesions can be managed by curettage with or without local adjuvant therapy. 6
Multiple Enchondromas (Enchondromatosis):
Patients with enchondromatosis require intensive surveillance given the 30% malignant transformation risk:
- Physical examination every 6-12 months from diagnosis. 1, 5
- Baseline whole-body MRI at diagnosis, with periodic imaging after age 20 years. 1, 5
- Plain radiographs of known lesions every 2-3 years. 1, 5
- Annual dedicated MRI for lesions >5-6 cm or in pelvis/scapula. 1, 5
Additional Complications
Beyond malignant transformation, enchondromas in the femur can cause:
- Pathologic fractures. 1
- Limb deformities and bone shortening. 1
- Leg length discrepancy. 1
- Limitations in joint mobility and gait disturbances. 1
Orthopedic surgeons and oncology providers should be involved in monitoring and treatment, particularly for enchondromatosis patients. 1, 5