Musculoskeletal Oncology and Metabolic Bone Disease
What this domain tests
Staging, biopsy principles, primary bone tumors, skeletal metastases, and metabolic bone disease including osteoporosis.
Core rules
- Enneking staging uses grade (low/high), compartment (intracompartmental A, extracompartmental B), and metastases (III). Stage I latent lesions are often observed; stage II aggressive lesions need wide resection.
- Biopsy is performed at the definitive treating center, by the surgeon who will resect, through a longitudinal approach that can be excised en bloc, without contaminating other compartments. Unplanned excision before referral worsens outcomes.
- Osteosarcoma typically arises in the metaphysis of the distal femur or proximal tibia in adolescents, with a sunburst pattern and Codman triangle. Treatment is neoadjuvant chemotherapy, wide resection, and reconstruction; response to chemotherapy predicts survival.
- Skeletal metastases: use Mirels score for impending fracture risk. Scores of 9 or more warrant prophylactic fixation; 8 is borderline.
- Osteoporosis: T-score of -2.5 or lower at the hip or spine, or a FRAX 10-year risk of major osteoporotic fracture of 20% or hip fracture of 3%. Long-term bisphosphonates are linked to atypical subtrochanteric fractures.
Worked example
A 60-year-old with breast cancer and hip pain has a 3 cm lytic lesion in the peritrochanteric region with moderate pain. Mirels: site peritrochanteric 3, pain moderate 2, lytic 3, size one-third to two-thirds 2 = 10. Answer: prophylactic cephalomedullary fixation before radiotherapy, since the score exceeds the threshold.
Traps that cost marks
- Biopsying outside the definitive center and contaminating the resection bed.
- Ordering a transverse biopsy that cannot be excised with the tumor.
- Treating a pathologic fracture before staging the primary tumor.