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]

SAQ 2 (10 marks) — A low Z-score with no fracture, and the safeguarding question

Stem: A four-year-old is referred after three forearm fractures over eighteen months from falls at play, and a DXA lumbar spine Z-score of minus 2.4. Her biochemistry is normal, including a normal alkaline phosphatase. The parents are anxious about osteoporosis and about being blamed. Discuss how you establish or refute the diagnosis, the differential, and the role of the safeguarding assessment. [1] [2]

Model answer

Diagnosis — apply the framework carefully (3 marks). A Z-score of minus 2.4 is low bone mass for age, but the diagnosis of osteoporosis requires a clinically significant fragility fracture as well. The fracture-count criteria are two long-bone fractures before age ten, so the three forearm fractures meet the fracture-history bar if the mechanisms are genuinely low-trauma. The task is to scrutinise each fracture's mechanism: forearm fractures from falls at play in an active four-year-old are often high-impact rather than fragility fractures, so the diagnosis turns on the mechanism, not the number. I would not label this osteoporosis until the mechanisms are confirmed low-trauma and the mimics are excluded. [1] [2]

Differential and the biochemistry (3 marks). The normal alkaline phosphatase excludes hypophosphatasia, the cause that must never be treated with a bisphosphonate. Normal calcium, phosphate, and vitamin D exclude nutritional rickets and metabolic bone disease. The remaining question is whether the low density reflects osteogenesis imperfecta, which presents with recurrent fractures, blue or grey sclerae, dentinogenesis imperfecta, joint hypermobility, and a family history; I examine for these and send type one collagen gene analysis if the phenotype fits. Idiopathic juvenile osteoporosis is rarer and presents later, in the prepubertal years, as a diagnosis of exclusion. [1] [6]

The safeguarding assessment (2 marks). Unexplained or repeated fractures in a young child must always hold non-accidental injury alongside a bone disease, and the two are not mutually exclusive. I take a careful mechanism history for each fracture, examine for bruises and other injuries, review the timing and the presentation, and, where the pattern or the history is inconsistent, involve the child-protection team and request a skeletal survey. A genuine bone disease never closes the safeguarding enquiry on its own. [1] [6]

Plan and communication (2 marks). If the mechanisms are high-impact and the mimics are excluded, the diagnosis is low bone mass for age without osteoporosis, and the management is the foundation — calcium, vitamin D, weight-bearing, and activity guidance — without a bisphosphonate. If a fragility mechanism is confirmed and osteogenesis imperfecta is excluded, the child may warrant a metabolic bone review. Throughout, I address the parents' anxiety directly, explain that a low density alone is not a disease, and reassure them that the safeguarding assessment is standard and not an accusation. [2] [6]