What is rickets and how is it different from osteomalacia?
The 2016 Global Consensus on nutritional rickets defines it as a disorder of defective chondrocyte differentiation and mineralisation of the growth plate and defective osteoid mineralisation, caused by vitamin D deficiency and/or low calcium intake in children. Because the growth plate is still open, the defect shows up as widened, irregular metaphyses and bent long bones.
Osteomalacia is abnormal matrix mineralisation in established bone. A child with open growth plates has both rickets and osteomalacia; an adult whose growth plates have fused can only have osteomalacia. The classic late radiological sign of osteomalacia is the Looser zone (pseudofracture).
| Feature | Rickets | Osteomalacia |
|---|---|---|
| Who | Children (open growth plates) | Adults, or children's established bone |
| Site of defect | Growth plate and osteoid | Osteoid of mature bone |
| Typical signs | Wrist widening, rosary, bowing, craniotabes | Bone pain, proximal muscle weakness, fatigue |
| Key X-ray | Cupping, fraying, splaying of metaphysis | Looser zones (late), osteopenia |
What are the types of rickets?
Rickets is traditionally split into calcipenic (calcium-deficient) and phosphopenic (phosphate-wasting) forms. Low phosphate is actually the common final pathway: in calcipenic rickets, secondary hyperparathyroidism makes the kidney waste phosphate, and the growth-plate chondrocytes need phosphate to mature and die in order.
| Type | Defect | Clue |
|---|---|---|
| Nutritional — vitamin D deficiency | Low vitamin D intake / sunlight → low 25(OH)D | Infant, exclusive breastfeeding without supplement, dark skin, covered clothing |
| Nutritional — calcium deficiency | Dietary calcium < 300 mg/day | Older child after weaning; 25(OH)D normal or borderline; common in Africa and South Asia |
| VDDR type 1A | CYP27B1 (1α-hydroxylase) mutation — cannot make 1,25(OH)2D | Low calcitriol despite normal 25(OH)D; autosomal recessive |
| VDDR type 1B | CYP2R1 (25-hydroxylase) mutation | Low 25(OH)D; responds to calcifediol |
| VDDR type 2A (hereditary vitamin D resistance) | Vitamin D receptor (VDR) mutation — end-organ resistance | High calcitriol; alopecia in about two-thirds |
| X-linked hypophosphataemic rickets (XLH) | PHEX mutation → excess FGF23 → renal phosphate wasting | Normal calcium, low phosphate, normal/low calcitriol; the commonest inherited rickets |
Hypophosphataemic rickets differs from the calcipenic forms in two exam-relevant ways: the serum calcium is normal and PTH is usually normal, and it does not respond to ordinary vitamin D. That is why older books called it 'vitamin D-resistant rickets'. Its biochemical signature is a low renal tubular phosphate threshold (reduced TmP/GFR) driven by FGF23.
What are the clinical signs of rickets?
Bone deformities usually appear before 18 months of age, with the peak between 4 and 12 months (Gentile & Chiarelli). The signs follow the bones that are growing fastest at that age — skull in young infants, ribs and wrists in older infants, legs once the child bears weight.
| Sign | What it is | Typical age |
|---|---|---|
| Craniotabes | Softening of the skull bones — the skull dents on pressure and springs back | Early infancy |
| Frontal bossing | Prominent forehead from excess unmineralised osteoid | Infancy |
| Delayed fontanelle closure | Anterior fontanelle normally closed by about 2 years | Infancy–toddler |
| Rachitic rosary | Enlarged costochondral junctions — beading along the front of the chest | Infancy |
| Harrison sulcus | Horizontal groove of the lower chest, where the diaphragm pulls in the soft ribs | Infancy–toddler |
| Wrist (and ankle) widening | Swollen metaphyses at the distal radius and ulna | Older infant |
| Leg deformity | Genu varum (bow legs), genu valgum (knock knees) or windswept deformity | After walking starts |
| Delayed tooth eruption | Teeth erupt late | Infancy |
The Consensus also lists non-skeletal features that make rickets dangerous rather than cosmetic: hypocalcaemic seizures and tetany, hypocalcaemic dilated cardiomyopathy (heart failure, arrhythmia, even cardiac arrest), and failure to thrive with poor linear growth. Muscle weakness and recurrent respiratory infections are also reported.
How do the lab values differ between the types of rickets?
In nutritional rickets the Global Consensus states that 25(OH)D, serum phosphorus, serum calcium and urinary calcium fall, while PTH, ALP and urinary phosphorus are invariably raised. Serum calcium can still be normal because PTH is defending it at the cost of bone and phosphate — so a normal calcium does not exclude rickets.
| Type | Calcium | Phosphate | ALP | PTH | 25(OH)D | 1,25(OH)2D |
|---|---|---|---|---|---|---|
| Vitamin D deficiency | L or N | L or N | H or VH | H | L | Variable |
| Calcium deficiency | L or N | L | H | H (usually) | N or borderline | H (about 1.5–2× normal) |
| VDDR type 1 | L | L or N | VH | H | N | L |
| VDDR type 2 | L | L or N | VH | H | N | H |
| XLH (hypophosphataemic) | N | L | H | N or H | N | L or N (inappropriately) |
- ALP is raised in essentially every form of rickets — the exception is hypophosphatasia (HPP). A child with rickets-like bones whose ALP is not raised = think hypophosphatasia.
- 25(OH)D is the test of vitamin D status (body stores); 1,25(OH)2D is the active hormone and is not used to diagnose deficiency — it may be normal or even high in nutritional rickets.
- Vitamin D status thresholds (Global Consensus): sufficient > 50 nmol/L, insufficient 30–50 nmol/L, deficient < 30 nmol/L (divide by 2.5 for ng/mL: 20 and 12 ng/mL).
- Dietary calcium thresholds for children over 12 months: sufficient > 500 mg/day, insufficient 300–500, deficient < 300 mg/day.
What are the X-ray signs of rickets?
Changes are most obvious where growth is fastest: the knee (distal femur, proximal tibia) and the wrist, especially the distal ulna. A single wrist or knee film is usually enough to confirm the diagnosis; the Global Consensus says rickets is diagnosed on history, examination and biochemistry and confirmed by radiographs.
| Sign | What you see |
|---|---|
| Loss of the zone of provisional calcification | The crisp white line at the end of the metaphysis is lost — an early change |
| Widening of the physis | Growth plate looks wider because unmineralised cartilage accumulates |
| Cupping | Concave, cup-shaped metaphyseal end |
| Fraying | Indistinct, brush-like metaphyseal margin |
| Splaying | Metaphyseal end becomes wider than normal |
| Rachitic rosary | Expanded anterior rib ends on chest X-ray |
| Bowing and Looser zones | Bowed long bones once walking; pseudofracture on the compression side |
| Generalised osteopenia | Thin cortices and coarse trabeculae |
Healing: the first radiological response is a dense 'healing line' — the zone of provisional calcification reappearing at the end of the metaphysis. In one Indian study of nutritional rickets this line was present in 83% of children by 3 weeks and in 100% by 6 weeks, and every child had complete radiological resolution by 6 months. A missing healing line by 6 weeks should make you question compliance or the diagnosis.
What are the treatment doses for nutritional rickets?
The Global Consensus recommends vitamin D for a minimum of 12 weeks (90 days), given either daily or as a single large oral dose ('stoss'), plus calcium — 500 mg/day of elemental calcium, from diet or supplements, regardless of age or weight. Calcium is needed because rickets that is partly calcium-driven will not heal with vitamin D alone.
| Age | Daily dose for 90 days | Single (stoss) dose | Maintenance daily dose |
|---|---|---|---|
| < 3 months | 2,000 IU | Not recommended | 400 IU |
| 3–12 months | 2,000 IU | 50,000 IU | 400 IU |
| > 12 months to 12 years | 3,000–6,000 IU | 150,000 IU | 600 IU |
| > 12 years | 6,000 IU | 300,000 IU | 600 IU |
- Stoss therapy is convenient when daily adherence or follow-up is doubtful, but it carries a higher risk of hypercalcaemia (Uday & Högler) — and it is not used under 3 months of age.
- Calcium-deficiency rickets heals with calcium; in Nigerian trials adding vitamin D made ALP fall faster than calcium alone.
- VDDR type 1A is treated with calcitriol or alfacalcidol (physiological doses cure it); VDDR type 1B with calcifediol, which bypasses the 25-hydroxylase defect.
- XLH: conventional treatment is oral phosphate plus calcitriol/alfacalcidol; burosumab, a monoclonal antibody against FGF23, is the newer targeted option. Plain vitamin D does not work.
How is rickets prevented?
The Global Consensus recommends 400 IU (10 μg) of vitamin D daily for all infants from birth to 12 months, and at least 600 IU (15 μg) daily after 12 months, in line with the Institute of Medicine. Children over 12 months should also get adequate dietary calcium (sufficiency > 500 mg/day).
- High-risk groups: infants of vitamin D-deficient mothers, exclusively breastfed infants without supplements, dark skin (especially African and South Asian descent), and living at higher latitudes; children under 3 years are the main target group.
- Pregnancy: supplementing deficient mothers protects the newborn, whose vitamin D stores at birth depend on the mother's status.
- Population level: food fortification is the long-term strategy and supplementation of high-risk groups the short-term one; the life-threatening complications of nutritional rickets are entirely preventable.
How is rickets tested in NEET PG and INI-CET?
- Image questions — a wrist or knee X-ray with cupping and fraying, or a child with bow legs and a rosary; identify rickets.
- Lab-pattern questions — a table of calcium, phosphate, ALP and PTH; decide between nutritional rickets, VDDR and hypophosphataemic rickets.
- Early signs — craniotabes in a young infant; loss of the crisp zone of provisional calcification on X-ray; peak presentation 4–12 months.
- Doses — prevention 400 IU/day in infancy; treatment per the consensus table; stoss doses.
- Alopecia + rickets → VDDR type 2 (receptor defect). Normal calcium + low phosphate + bowing in a family → XLH.
Related pages: practise previous papers at NEET PG Pediatrics PYQs and NEET PG Biochemistry PYQs, and see the most repeated topics.