Osteoporosis and fragility fractures in children — formative SAQs

SAQ 1 (10 marks) — The steroid-treated child with a vertebral fracture

Stem: A ten-year-old boy with Duchenne muscular dystrophy has been on daily prednisolone for two years. He presents with three weeks of mid-thoracic back pain and has lost two centimetres of height since his last visit. A lateral thoracolumbar spine shows a wedge compression fracture at T12. The lumbar spine DXA Z-score is minus 1.8. Outline the diagnosis, the explanation for the fracture at this density, and the stepwise management. ^{[5] [1]}

Model answer

Diagnosis (3 marks). This is osteoporosis. The defining move is that a vertebral compression fracture alone satisfies the ISCD definition of osteoporosis regardless of the bone density, so the Z-score of minus 1.8 — which by itself would only be labelled low bone mass for age — becomes osteoporosis the moment the T12 wedge is present. The Z-score, never the T-score, is used in a child. The cause is secondary: glucocorticoid therapy compounded by progressive immobility in Duchenne muscular dystrophy. ^{[1] [5]}

Why the fracture appears at this density (2 marks). The bone density number estimates only one part of bone strength; the other part is bone quality, which the DXA cannot see. Glucocorticoids suppress osteoblast formation and drive osteocyte apoptosis while reducing muscle mass, and the immobility of advancing Duchenne removes the weight-bearing signal through the mechanostat, so the vertebra fails on quality as much as on mineral. The vertebral-fracture risk in steroid-treated children clusters in the first one to three years after glucocorticoids start. ^{[5] [6]}

Management — the foundation (2 marks). Correct calcium and vitamin D, confirm the 25-hydroxyvitamin D is replete, review the glucocorticoid regimen with the neuromuscular team, and maximise safe weight-bearing and a standing program within the limits of the disease. The endocrine and bone surveillance now standard in Duchenne care is engaged. ^{[6] [4]}

Management — the bisphosphonate (3 marks). Start an intravenous bisphosphonate, with zoledronic acid the first-line agent, established by the phase three randomised trial in paediatric glucocorticoid-induced osteoporosis. Ensure the child is calcium and vitamin D replete first to prevent the symptomatic hypocalcaemia of the acute post-infusion dip, premedicate with paracetamol for the flu-like first-dose reaction, and plan the weight-based dosing and interval with the treating service. Monitor with a repeat lateral spine and DXA, track the bone turnover markers down, and reassess at eighteen to twenty-four months for a treatment holiday. ^{[3] [4]}