Nutritional Rickets
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Direct answer
Nutritional rickets is a failure of bone mineralisation in growing children, caused by deficiency of vitamin D, calcium or both. It produces widened, cupped metaphyses and bowed limbs, classically at the knees and wrists. The biochemical pattern is low 25-hydroxyvitamin D, low or normal calcium, low phosphate, raised alkaline phosphatase and secondary hyperparathyroidism.
What you must remember
- Commonest cause: vitamin D deficiency from poor diet and limited sunlight exposure; isolated calcium deficiency is less common.
- Skin and lifestyle: melanin and indoor living reduce cutaneous vitamin D synthesis, which raises the risk in Indian children.
- Radiographic hallmark: widened, cupped and frayed metaphyses with loss of the zone of provisional calcification.
- Biochemistry: low 25-hydroxyvitamin D, low or normal calcium, low phosphate, raised alkaline phosphatase and raised parathyroid hormone.
- Deformity pattern: genu varum in early walkers and genu valgum in older children, with rachitic rosary and craniotabes in infancy.
- Healing signal: the zone of provisional calcification reappears and alkaline phosphatase falls, although radiographic healing lags behind the biochemistry.
- Treatment: vitamin D on a high-dose schedule, with oral calcium, dietary correction and supervised sunlight exposure.
- Residual deformity: persistent limb bowing may need later osteotomy once the child has stopped growing rapidly.
Staging the disease from florid rickets to healing
A 20-month-old girl who has been walking since nine months, with a predominantly breastfed diet and little sun exposure, has bowed legs and widened wrists. The phases of the disease are read from both the radiograph and the blood.
| Phase | Radiographic feature | Biochemical pattern | Clinical sign |
|---|---|---|---|
| Early | Blurred, widened physis with loss of provisional calcification in the metaphysis | Low 25-hydroxyvitamin D; calcium low or normal; phosphate may be borderline | Delayed walking, irritability and mild limb discomfort |
| Florid | Cupping, fraying and splaying of the metaphysis with widened physes | Low phosphate, raised alkaline phosphatase and raised parathyroid hormone | Bowed legs, rachitic rosary, widened wrists and craniotabes |
| Healing | Return of a dense provisional calcification line and a more regular physis | Alkaline phosphatase falls as phosphate and calcium normalise | Progression of the deformity stops and bone remodels |
Radiographic healing lags behind the biochemistry, so films are repeated only after several weeks of treatment. Serum alkaline phosphatase is a practical marker of response in clinical practice. Remodelling of established bowing is slow, and surgery is considered only if the deformity persists after growth is nearly complete.
Where the exam tries to catch you
Examiners test whether you can separate a vitamin D problem from a calcium problem, and recognise rickets from its look-alikes.
- Trap: choosing calcium alone for a child with vitamin D deficiency. Correct: vitamin D is the essential treatment, with calcium added to support mineralisation where dietary intake is poor.
- Trap: assuming raised alkaline phosphatase proves rickets. Correct: it is a non-specific marker of bone turnover, so the diagnosis rests on radiographs, low vitamin D and the characteristic pattern.
- Trap: dismissing bowing as normal because the child walked early. Correct: a varus that persists beyond about 18 months, with wrist widening, indicates rickets and needs biochemical testing.
Frequently asked questions
Which biochemical pattern distinguishes nutritional rickets?
Nutritional rickets shows low 25-hydroxyvitamin D, low or normal calcium, low phosphate, raised alkaline phosphatase and raised parathyroid hormone. The raised parathyroid hormone is secondary, driven by low vitamin D and low calcium.
What is the first-line treatment for nutritional rickets in children?
Vitamin D is the principal treatment, given on a high-dose schedule, with oral calcium to support mineralisation and dietary correction. Doses should follow current paediatric protocols rather than fixed values from memory.
Why does nutritional rickets remain common in Indian children?
Skin pigmentation, indoor living, limited dietary intake and inadequate supplementation all lower vitamin D status. Sunlight is effective only with adequate skin exposure, so children with limited outdoor time are at higher risk.
Which radiographic features mark healing in nutritional rickets?
Healing is marked by the return of the zone of provisional calcification as a dense line at the metaphysis, along with a more regular physis. Alkaline phosphatase falls as treatment takes effect, and the radiograph follows more slowly than the blood tests.