A 17-year-old boy presents with a 3-month history of knee pain. MRI shows a 9 cm intramedullary lesion of the distal femoral metaphysis with periosteal elevation and a soft tissue mass. Biopsy confirms osteosarcoma. According to the Enneking (MSTS) staging system, this would be classified as Stage IIB if which criterion is met?
- A Extra-compartmental spread (soft tissue extension beyond periosteum) ✓
- B Presence of skip lesions in the same bone
- C Regional lymph node involvement
- D Serum alkaline phosphatase >3× upper limit of normal
Correct answer: A. Extra-compartmental spread (soft tissue extension beyond periosteum)
Explanation
The Enneking (MSTS) staging system classifies bone sarcomas by histological grade (I = low, II = high) and compartmental status (A = intracompartmental, B = extracompartmental), with Stage III indicating distant metastases. Stage IIB means high-grade tumor with extra-compartmental spread — defined as extension beyond the original anatomical compartment (e.g., through periosteum into soft tissue). Skip lesions are a distinct adverse finding but do not define the IIB designation per se; they imply Stage III equivalence by some classifications.
Reference: Maheshwari Essential Orthopaedics, 6th ed.
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Written and medically reviewed by the StethoPrep medical team.