In the Enneking classification of benign musculoskeletal tumours, which of the following is an example of a Stage 1 (latent) lesion?

• A Giant cell tumour of the distal radius breaching the cortex
• B Unicameral bone cyst of the proximal humerus with cortical thinning
• C Osteochondroma of the distal femur ✓
• D Aggressive aneurysmal bone cyst with soft tissue extension

Explanation

Enneking divided benign tumours into Stage 1 latent (remain static or heal spontaneously, e.g., osteochondroma, non-ossifying fibroma), Stage 2 active (progressively grow but remain confined by reactive tissue, e.g., typical unicameral bone cyst) and Stage 3 aggressive (breach barriers and recur after intralesional excision, e.g., giant cell tumour, aggressive ABC). The cyst given with cortical thinning behaves actively, and the last two options are classic Stage 3 lesions.

Reference: Campbell's Operative Orthopaedics, 14th ed.

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