Define Osteochondroma. Describe its clinical features and management.
Definition
Osteochondroma (exostosis) is the commonest benign bone tumour. It is a cartilage-capped bony outgrowth on the external surface of a bone, arising from the metaphysis of a long bone (typically around the knee or proximal humerus) and pointing away from the adjacent joint. Its medullary cavity is continuous with that of the parent bone.
Clinical Features
Usually a painless, hard, fixed swelling noticed in a child or adolescent, which stops growing at skeletal maturity. Symptoms arise from mechanical effects: pressure on tendons, nerves or vessels, an overlying bursitis, or a cosmetic lump. Multiple lesions occur in the hereditary condition multiple hereditary exostoses (diaphyseal aclasis).
DANGER / REMEMBER
A previously stable osteochondroma that starts to grow or become painful after skeletal maturity, or whose cartilage cap thickens (> ~1.5–2 cm on MRI), raises concern for malignant transformation to chondrosarcoma — uncommon in solitary lesions but higher in multiple hereditary exostoses.
Management
Asymptomatic lesions are simply observed. Excision is indicated for pain, mechanical symptoms (nerve/vessel/tendon impingement), cosmetic concern, or suspicion of malignant change; the whole cartilage cap and its perichondrium are removed to prevent recurrence.
CLINICAL PEARL
Osteochondroma grows away from the joint and has a cortex and medulla continuous with the parent bone — a useful diagnostic feature. Growth after maturity is the warning sign of transformation.
Pathology
Histologically the lesion is a bony stalk capped by hyaline cartilage that behaves like an aberrant growth plate; it enlarges by endochondral ossification during skeletal growth and normally ceases growing at maturity. In multiple hereditary exostoses, an autosomal-dominant disorder (ext gene mutations), numerous lesions cause bony deformity, limb-length discrepancy and a higher lifetime risk of malignant transformation than a solitary lesion, and often warrant surveillance into adult life.
CLINICAL PEARL
Continuity of the cortex and medulla with the parent bone on imaging confirms an osteochondroma and distinguishes it from a surface lesion such as a periosteal chondroma or, worryingly, a surface osteosarcoma.
Commonest benign bone tumour.
KEY POINT
Key points TO remember
- Commonest benign bone tumour; cartilage-capped metaphyseal outgrowth pointing away from the joint.
- Medulla continuous with parent bone; usually painless; stops growing at maturity.
- Multiple lesions = hereditary multiple exostoses (higher malignant risk).
- Observe if asymptomatic; excise for symptoms or suspected chondrosarcoma (growth after maturity).
EXAM TIP
Sources: Maheshwari's Essential Orthopaedics; Apley & Solomon's System of Orthopaedics and Trauma; AO Principles of Fracture Management.
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