Paediatrics chapters
Rickets
Rickets is defective mineralisation of growing bone, usually from vitamin D deficiency. This chapter covers its types, the skull, chest and limb signs, the blood and X-ray findings, look-alikes, and treatment and prevention.
- Rickets is failure of mineralisation of growing bone and the growth plate; osteomalacia is the same defect in mature bone. Most cases are nutritional vitamin D deficiency, peaking at 6 months to 2 years.
- Classic signs: craniotabes, frontal bossing, delayed fontanelle closure and teething, rachitic rosary, Harrison sulcus, wide wrists, bow legs; bloods show high ALP (most striking), low phosphate, low or normal calcium, high PTH, low 25-OH vitamin D; the wrist X-ray shows cupping, fraying and splaying.
- Treat with vitamin D (stoss 300,000-600,000 IU, or daily 2,000-5,000 IU for 4-6 weeks) plus calcium, then 400 IU daily; a white line of calcification appears within about 2-3 weeks.
On this page
Overview
Rickets is a metabolic bone disease of childhood in which osteoid and growth-plate cartilage fail to mineralise, so bones become soft and the ends of long bones widen. In mature bone (after the growth plates close) the same defect is called osteomalacia.
Rickets is still common in Pakistan despite plenty of sunshine, because of indoor living, covering, pollution, maternal vitamin D deficiency and diets high in cereal and low in dairy.
Vitamin D metabolism
| Step | Where | Product |
|---|---|---|
| UVB light on 7-dehydrocholesterol | Skin | Cholecalciferol (D3) |
| Diet: D3 (oily fish, egg yolk, fortified foods) and D2 (ergocalciferol) (plants, fortified foods) | Gut | Absorbed with fat |
| 25-hydroxylation | Liver | 25-OH-D (calcidiol): main circulating form; best measure of status |
| 1-alpha-hydroxylation (stimulated by PTH and low phosphate) | Kidney | 1,25-(OH)2-D (calcitriol): active hormone |
Actions of calcitriol: raises gut absorption of calcium and phosphate, mobilises calcium from bone, and increases renal reabsorption. The overall effect keeps plasma calcium and phosphate high enough for bone mineralisation.
- Sunlight through window glass lacks UVB.
- Akbar: an infant needs about 30 minutes a week of whole-body (or 2 hours a week of head-only) sun to keep vitamin D adequate; skin synthesis can supply about 80% of the need.
Definition and classification
| Group | Types |
|---|---|
| Calcipenic (low calcium supply or vitamin D action) | Nutritional vitamin D deficiency (commonest); congenital (maternal deficiency); secondary: malabsorption (coeliac disease, cystic fibrosis, cholestasis), liver disease (biliary atresia), anticonvulsants (phenytoin, phenobarbitone), chronic kidney disease; vitamin D-dependent rickets type 1 (1-alpha-hydroxylase defect) and type 2 (receptor resistance); dietary calcium deficiency; rickets of prematurity |
| Phosphopenic (renal phosphate loss) | X-linked hypophosphataemic rickets (commonest non-nutritional form), autosomal dominant and recessive forms, hereditary hypophosphataemic rickets with hypercalciuria; Fanconi syndrome and proximal RTA |
| Other | Distal RTA (acidosis dissolves bone), renal osteodystrophy, hypophosphatasia (a mimic with low ALP) |
Aetiology and pathogenesis
Risk factors for nutritional rickets:
- Exclusively breastfed babies of vitamin D-deficient mothers without vitamin D drops.
- Dark skin, staying indoors, covered clothing, air pollution, winter.
- Prematurity (low stores, rapid growth).
- Diets high in phytate and fibre (cereals, chapati) that bind calcium, and low in dairy.
- Prolonged unfortified milk feeds with little solid food.
Pathogenesis:
- Low vitamin D → poor gut calcium absorption → low plasma calcium.
- Secondary hyperparathyroidism → bone resorption keeps calcium near normal, but PTH causes phosphate loss in urine → low phosphate.
- Low calcium-phosphate product → osteoid and growth-plate cartilage stay unmineralised.
- Cartilage cells keep multiplying, so the growth plate thickens and widens (wide wrists, rosary), and the metaphysis becomes cup-shaped and frayed.
- Soft bone bends under weight and muscle pull (bow legs, Harrison sulcus) and the skull flattens (craniotabes).
- ALP rises because osteoblasts are overactive but ineffective.
Nutritional rickets is a disease of 6 months to 2 years. Rickets that presents after 2 years or does not respond to vitamin D should raise suspicion of renal, hypophosphataemic or vitamin D-dependent rickets.
Clinical features and skeletal deformities
Early, non-specific: irritability, sweating of the head during sleep, hypotonia, delayed motor milestones, failure to thrive, frequent chest infections, iron deficiency anaemia.
| Region | Signs |
|---|---|
| Skull | Craniotabes (ping-pong ball feel over the occiput or parietal bones; earliest sign, often gone by 1 year); frontal and parietal bossing; caput quadratum (square head); large head; large anterior fontanelle with delayed closure |
| Teeth | Delayed eruption, enamel defects, caries |
| Chest | Rachitic rosary (knobby costochondral junctions); Harrison sulcus (groove along the diaphragm attachment); pigeon chest |
| Spine and pelvis | Kyphosis, scoliosis, lordosis; contracted pelvis (later obstructed labour in girls) |
| Limbs | Widened wrists and ankles; bow legs (genu varum) once walking; knock knees (genu valgum); greenstick fractures |
| Muscles and general | Hypotonia, pot belly, ligament laxity, short stature, waddling gait |
| Hypocalcaemia | Tetany, carpopedal spasm, laryngospasm, seizures (especially in young infants) |
Head to toe: "Craniotabes, Bossing, Rosary, Harrison, Wrists, Bowing."
Investigations
Biochemistry
| Test | Nutritional rickets |
|---|---|
| Serum calcium | Low or normal (normal about 9-11 mg/dL) |
| Serum phosphate | Low |
| Alkaline phosphatase | Raised: the most striking change |
| PTH | Raised |
| 25-OH vitamin D | Low (below about 20 ng/mL supports deficiency) |
| 1,25-(OH)2-D | Variable (may even be high) |
| Urea, creatinine, bicarbonate | Normal (check to exclude renal and RTA causes) |
Telling the types apart
| Type | Calcium | Phosphate | ALP | PTH | 25-OH-D | 1,25-(OH)2-D | Clue |
|---|---|---|---|---|---|---|---|
| Nutritional | Low/N | Low | High | High | Low | Variable | Response to vitamin D |
| VDDR type 1 | Low | Low | High | High | Normal | Low | 1-alpha-hydroxylase defect; early tetany and fits; autosomal recessive |
| VDDR type 2 | Low | Low | High | High | Normal | Very high | Receptor resistance; alopecia |
| X-linked hypophosphataemic | Normal | Very low | High | Normal | Normal | Low or inappropriately normal | Renal phosphate wasting; bow legs at walking age; affected mother; no rosary, tetany or myopathy |
| Renal osteodystrophy | Low | High | High | Very high | Normal | Low | Raised creatinine |
| Hypophosphatasia | N/high | N | Low | N | N | N | ALP enzyme defect |
Low ALP in a child with rickets-like bones suggests hypophosphatasia, not rickets. High phosphate points to renal rickets.
Radiology
Best site: the wrist (distal radius and ulna) in infants; the knee is also useful.
| Active rickets | Healing rickets |
|---|---|
| Cupping (concave metaphysis) | A dense white line of provisional calcification at the metaphysis, seen within about 2-3 weeks of treatment |
| Fraying (irregular, brush-like margin) | Gradual mineralisation of the osteoid |
| Splaying (widened metaphysis) | Deformities correct over months to a year or two |
| Wide gap between epiphysis and metaphysis (thick growth plate) | |
| Low bone density, coarse trabeculae, thin cortex; bowing; greenstick fractures |
The X-ray and biochemistry often become abnormal before clinical signs. The earliest sign of healing on X-ray is the line of provisional calcification.
Differential diagnosis of bone deformities and growth disturbances
| Condition | Distinguishing features |
|---|---|
| Physiological bow legs | Under about 2 years, symmetrical, normal bloods and X-ray; corrects with growth (followed by physiological knock knee at 3-4 years) |
| Blount disease (tibia vara) | Progressive, often one-sided bowing in heavy early walkers; beaked medial tibial metaphysis |
| Scurvy (vitamin C deficiency) | Painful legs, pseudoparalysis ("frog position"), swollen bleeding gums, subperiosteal haemorrhage; X-ray: ground-glass bone, pencil-thin cortex, white line of Fraenkel, Wimberger ring around the epiphysis; sharp scorbutic rosary |
| Osteogenesis imperfecta | Multiple fractures with little trauma, blue sclerae, deafness, normal ALP and calcium |
| Achondroplasia and other skeletal dysplasias | Disproportionate short stature, normal biochemistry, typical X-ray |
| Congenital syphilis | Periostitis, metaphysitis, other stigmata, positive serology |
| Hypothyroidism | Short stature, large fontanelle, delayed bone age, low T4 and high TSH |
| Hydrocephalus (big head, large fontanelle) | Rapid head growth, sunset eyes, raised pressure signs |
| Hypophosphatasia | Low ALP |
| Feature | Rickets | Scurvy |
|---|---|---|
| Deficiency | Vitamin D (or calcium, phosphate) | Vitamin C |
| Pain | Little | Marked tenderness, pseudoparalysis |
| Gums | Normal | Swollen, bleeding |
| Rosary | Rounded, knobby | Sharp, angular |
| X-ray | Cupping, fraying, wide growth plate | Ground-glass bone, Fraenkel line, Wimberger ring |
Management
Nutritional vitamin D deficiency rickets
- Vitamin D, either:
- Stoss therapy: 300,000-600,000 IU orally or IM, as 2-4 doses over 1 day; or
- Daily high dose: 2,000-5,000 IU a day for 4-6 weeks.
- Then maintenance 400 IU daily under 1 year, 600 IU daily over 1 year.
- Adequate calcium and phosphate from milk and dairy (calcium supplements if intake is low).
- Sunlight exposure and dietary advice for the whole family; treat the mother if deficient.
- Hypocalcaemic tetany or seizures: give IV 10% calcium gluconate slowly with cardiac monitoring first, then oral calcium and vitamin D.
- Review: repeat bloods (ALP falls) and a wrist X-ray to confirm healing.
Other types
| Type | Treatment |
|---|---|
| Dietary calcium deficiency | Elemental calcium (Akbar: about 700 mg/day at 1-3 years, 1,000 mg at 4-8 years, 1,300 mg at 9-18 years) with vitamin D if also deficient |
| Malabsorption | High doses of vitamin D, or 25-OH-D, which is better absorbed; treat the cause |
| VDDR type 1 | Calcitriol (1,25-D) for life with adequate calcium |
| VDDR type 2 | Very high doses of vitamin D or calcitriol plus calcium; response is poor, especially with alopecia |
| Hypophosphataemic rickets | Oral phosphate in several divided doses plus calcitriol |
| Renal osteodystrophy | Calcitriol (does not need renal activation), phosphate restriction and binders |
| Renal tubular acidosis | Alkali therapy; add phosphate and vitamin D in proximal RTA |
| Anticonvulsant rickets | Extra vitamin D |
- Severe deformities that persist after healing may need orthopaedic osteotomy, usually after metabolic control.
Complications
- Hypocalcaemic tetany, laryngospasm, seizures.
- Recurrent chest infections (bronchitis, bronchopneumonia), atelectasis from a soft, deformed chest.
- Iron deficiency anaemia and infections.
- Fractures; permanent deformities (bow legs, knock knees, kyphoscoliosis).
- Short stature.
- Contracted pelvis in girls → obstructed labour in later life.
- Dental caries and enamel defects.
Prognosis
- With treatment, healing starts within days to 2-3 weeks, and bones regain normal structure over 6 months to a year.
- Most deformities resolve within 1-2 years on maintenance vitamin D; in advanced cases some deformity may remain.
- Genetic forms need lifelong treatment and monitoring.
Prevention
- Sunlight exposure of the skin (not through glass).
- Vitamin D 400 IU (10 micrograms) daily for infants, especially breastfed and preterm babies and those whose mothers have little sun exposure.
- Vitamin D for pregnant and breastfeeding mothers.
- Adequate dietary calcium and phosphate (milk, dairy); timely complementary feeding.
- Extra vitamin D for children on long-term phenytoin or phenobarbitone, with malabsorption, or with liver disease.
- Food fortification.
Expect: rickets versus osteomalacia; vitamin D metabolism (skin, liver 25-hydroxylation, kidney 1-alpha-hydroxylation) and calcidiol as the status marker; peak age 6 months-2 years; craniotabes as the earliest sign; rosary, Harrison sulcus, wide wrists, bow legs and delayed fontanelle closure; ALP as the most striking rise with low phosphate and high PTH; wrist X-ray with cupping, fraying and splaying and the healing line; biochemical patterns of VDDR types 1 and 2 (alopecia), X-linked hypophosphataemia (normal calcium, very low phosphate) and renal rickets (high phosphate); anticonvulsants as a cause; scurvy and hypophosphatasia as differentials; stoss therapy doses and 400 IU maintenance and prevention.
Quick revision
- Rickets = unmineralised growing bone; osteomalacia = mature bone.
- Commonest cause: nutritional vitamin D deficiency, 6 months-2 years.
- Craniotabes earliest; then bossing, rosary, Harrison sulcus, wide wrists, bow legs, delayed teeth and fontanelle.
- Bloods: ALP high (most striking), phosphate low, calcium low/normal, PTH high, 25-OH-D low.
- X-ray wrist: cupping, fraying, splaying; healing shows a white calcification line within 2-3 weeks.
- Normal calcium + very low phosphate = X-linked hypophosphataemic rickets; high phosphate + high creatinine = renal.
- Low ALP = hypophosphatasia; painful legs and bleeding gums = scurvy.
- Treat: stoss 300,000-600,000 IU or 2,000-5,000 IU/day for 4-6 weeks, plus calcium; then 400-600 IU/day.
Written by The House Job from standard references (Basis of Paediatrics by Pervez Akbar; Nelson Essentials of Paediatrics; Park's Preventive and Social Medicine).
FAQ
What is the earliest clinical sign of rickets in an infant?
Craniotabes, a soft ping-pong ball feel when pressing the occipital or parietal bones.
Which blood test changes most in rickets?
Alkaline phosphatase, which rises markedly because osteoblasts are overactive but cannot mineralise bone.
When should a child with rickets be investigated for a non-nutritional cause?
When rickets appears after 2 years, there is a family history, or it does not heal with adequate vitamin D.
What is seen on X-ray when rickets starts to heal?
A dense white line of provisional calcification at the metaphysis, usually within 2-3 weeks of vitamin D treatment.