Rickets

Rickets is a metabolic bone disease of childhood in which growing bone fails to mineralise, at the growth plate (physis) and in osteoid. The hallmark is failure of endochondral ossification: unmineralised cartilage matrix accumulates, and skeletal deformity and growth disturbance follow.

Rickets and osteomalacia. Rickets is the paediatric equivalent of osteomalacia. Osteomalacia affects the osteoid of mature bone in adults; rickets affects cartilage mineralisation in bones that are still growing.

Where it occurs. Rickets is preventable and remains a significant global health problem. Incidence is higher in Northern Europe, Canada and the northern US, where sunlight is limited, and the disease has re-emerged in developed countries as sun exposure has fallen and more infants are breastfed without supplementation. It is endemic in the Middle East and South Asia, where cultural sun avoidance operates despite abundant sunlight.

Who is at risk. The children to look for:

• Exclusively breastfed infants without vitamin D supplementation
• Dark-skinned children in high-latitude countries, whose cutaneous UV-B synthesis is reduced
• Children whose sun exposure is limited by cultural or religious practice (covering clothing) or an indoor lifestyle
• Preterm infants, whose vitamin D requirements are increased
• Infants of mothers with vitamin D deficiency during pregnancy
• Vegan or vegetarian diets without fortified foods
• Chronic kidney disease, which impairs 1-alpha hydroxylation of vitamin D

The vitamin D pathway. UV-B radiation converts 7-dehydrocholesterol in the skin to cholecalciferol (vitamin D3). Hepatic 25-hydroxylase converts D3 to 25-OH vitamin D (calcidiol), the main storage form, and renal 1-alpha hydroxylase converts that to 1,25-OH vitamin D (calcitriol), the active hormone. Calcitriol increases intestinal calcium and phosphate absorption and promotes skeletal mineralisation.

Regulation. Hypocalcaemia triggers PTH release, the secondary hyperparathyroidism of calcium deficiency, and PTH stimulates 1-alpha hydroxylase to increase active vitamin D production. FGF23 inhibits 1-alpha hydroxylase and increases renal phosphate excretion.

At the physis. Endochondral ossification needs adequate calcium, phosphate and vitamin D. When calcium and phosphate availability at the growth plate falls, chondrocytes still proliferate and hypertrophy and cartilage matrix is still produced, but hydroxyapatite cannot be deposited in it. Unmineralised hypertrophic cartilage accumulates and the growth plate widens, to 10-20 times its normal thickness.

The histology. The chondrocytes lose their columnar organisation, hypertrophic chondrocytes persist (failed apoptosis), and the zone of provisional calcification becomes irregular, patchy and incomplete. Vascular invasion and osteoblast and osteoclast activity at the metaphysis are disorganised, producing the metaphyseal widening, cupping and fraying that are the radiographic hallmark.

The skeletal consequences. Soft, unmineralised bone deforms under weight-bearing stress into bowing, genu varum or valgum, and disrupted longitudinal growth causes growth failure and short stature. The skeleton is fragile and fractures pathologically, and frontal bossing, delayed fontanelle closure and the rachitic rosary complete the picture.

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Nutritional (calcipenic) rickets. Vitamin D deficiency reduces intestinal calcium and phosphate absorption. The hypocalcaemia causes secondary hyperparathyroidism, and PTH increases renal phosphate loss and bone resorption, so both calcium and phosphate are low and mineralisation is inadequate.

X-linked hypophosphataemia (phosphopenic rickets). A PHEX mutation raises FGF23. FGF23 wastes phosphate through the kidney by reducing proximal tubular reabsorption, and it inhibits 1-alpha hydroxylase, so active vitamin D is reduced despite a normal 25-OH D. The result is severe isolated hypophosphataemia with a normal calcium.

Vitamin D-dependent rickets. In type I a CYP27B1 mutation leaves 1-alpha hydroxylase deficient, and active vitamin D cannot be produced. In type II a VDR mutation makes the vitamin D receptor defective; the resistance to calcitriol drives 1,25-OH D levels very high.

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The aetiological classification separates rickets from calcium deficiency, rickets from phosphate deficiency, and the vitamin D-dependent forms.

Calcipenic rickets. Calcium deficiency, from:

• Nutritional vitamin D deficiency, the most common cause
• Dietary calcium deficiency, with a predominantly plant-based diet in developing countries
• Malabsorption of the fat-soluble vitamin: coeliac disease, cystic fibrosis, inflammatory bowel disease, biliary atresia
• Anticonvulsants: phenytoin and phenobarbital induce hepatic vitamin D catabolism

Phosphopenic rickets. Phosphate deficiency, from:

• X-linked hypophosphataemia (PHEX), X-linked dominant and the most common hereditary form
• Autosomal dominant hypophosphataemic rickets (FGF23), with elevated FGF23
• Autosomal recessive hypophosphataemia (DMP1, ENPP1)
• Hereditary hypophosphataemic rickets with hypercalciuria (SLC34A3)
• Tumour-induced osteomalacia (FGF23-secreting tumours)
• Fanconi syndrome (renal tubular phosphate wasting)

Vitamin D-dependent rickets. Type I is 1-alpha hydroxylase deficiency (CYP27B1 mutation) and type II a vitamin D receptor defect (VDR mutation). Both are autosomal recessive.

The features change with age.

Infants (0-12 months). The skeletal signs are craniotabes (soft skull bones with a ping-pong ball sensation), frontal bossing, delayed fontanelle closure, the rachitic rosary (costochondral junction swelling, palpable as beading along the sternum) and Harrison's groove, an indentation along the diaphragm attachment. The infant is hypotonic, a floppy baby, with delayed sitting, crawling and standing, and severe deficiency adds hypocalcaemic seizures, carpopedal spasm, and laryngospasm with stridor. Failure to thrive and growth retardation follow; early diagnosis is critical to prevent permanent skeletal deformity.

Toddlers (1-3 years). The skeletal signs are most visible at this age, which is the peak age for orthopaedic presentation. Genu varum is the most common deformity; the wrists and ankles are visibly and palpably widened, the rosary is prominent, and walking is delayed by leg bowing and muscle weakness, with a waddling gait. Short stature, delayed tooth eruption and dental enamel defects accompany it. Greenstick fractures occur with minimal trauma, and metaphyseal fractures may mimic non-accidental injury.

Older children (over 3 years). Genu valgum is more common than varum at this age. A windswept deformity (varus on one side, valgus on the other), coxa vara, and spinal deformity (scoliosis, kyphosis) also appear, with proximal muscle weakness, bone pain especially in the lower limbs, and easy fatigability. Stature is short relative to genetic potential, and puberty is delayed if the disease is severe. Late-onset rickets is often due to a hereditary form (X-linked hypophosphataemia) or to chronic kidney disease.

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The pattern of calcium, phosphate and the two vitamin D metabolites separates the types; the alkaline phosphatase is raised in all four.

Further tests.

• FGF23, elevated in X-linked hypophosphataemia and tumour-induced osteomalacia
• Genetic testing: PHEX (X-linked hypophosphataemia), CYP27B1 (vitamin D-dependent type I), VDR (type II)
• Renal tubular function (urinary phosphate, amino acids, glucose) for Fanconi syndrome
• Parental vitamin D levels, to assess familial risk

• The Thacher rickets severity score (grading severity). A validated 10-point radiographic score based on the wrist (distal radius and ulna) and the knee (distal femur and proximal tibia). Each site is graded for the degree of metaphyseal fraying, cupping/concavity and the proportion of the growth plate affected (the wrist contributing up to 4 points and each knee physis up to 3), summing to 0 (normal) to 10 (most severe). It lets you objectively grade a child at baseline and track change - it fell from about 1.9 to under 1 on burosumab in the trials.
• The RGI-C (Radiographic Global Impression of Change - grading healing). A paired-comparison tool in which a blinded radiologist scores the change between baseline and follow-up films (roughly -3 markedly worse to +3 completely healed, 0 = no change). It was the primary endpoint of the burosumab phase 3 trial (+1.9 burosumab vs +0.8 conventional) and captures healing that the severity score alone can miss.
• What "healing" looks like on these scores. Recovery is scored as the return of the sharp zone of provisional calcification (the earliest sign), then narrowing of the widened physis, filling-in of the cupped and frayed metaphysis, and a dense metaphyseal healing line - the same radiographic sequence the topic lists under healing, now quantified.
• Why it matters. Objective scoring underpins the evidence base (drug trials), helps decide how long to treat before considering surgery, and gives a defensible viva answer to "how do you know the rickets is healing?" beyond "the X-ray looks better."

Bowing in a small child has several causes, and the age, the biochemistry and the appearance of the growth plates separate them. Hypophosphatasia, an alkaline phosphatase deficiency, also widens the growth plates; its low ALP is diagnostic.

Medical treatment comes first and is the primary treatment for nutritional rickets. The regimen depends on the type.

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Never operate on active rickets. Optimise medically and wait 12-18 months for spontaneous deformity correction; surgery is only for the residual deformity after healing.

Indications. Surgery is considered for:

• Residual deformity after medical optimisation (12-18 months of treatment)
• Mechanical axis deviation greater than 10-15 degrees
• Functional impairment: gait disturbance or pain
• Progressive deformity despite treatment, especially in XLH

Contraindications. Surgery is avoided with:

• Active rickets, the biochemistry not yet normal
• Age under 2-3 years, when spontaneous correction is possible
• Mild deformity (less than 10 degrees) with good function
• Poor compliance with medical treatment

Before surgery. Confirm normal biochemistry (25-OH vitamin D greater than 75 nmol/L, normal calcium, phosphate and ALP), radiographic healing with the zone of provisional calcification restored, and no active rickets clinically or radiographically.

While the physes are open. Guided growth (hemiepiphysiodesis) is preferred in the growing child because it is minimally invasive and corrects gradually. A medial or lateral tension-band plate (eight-plate) is used, or staples, which are now less common. Correction takes 12-24 months, is reversible if it overshoots, and needs compliant follow-up every 3-6 months. Severe deformity, greater than 20-30 degrees, is corrected by proximal tibial or distal femoral osteotomy, acutely or gradually in an external fixator.

After skeletal maturity. Corrective osteotomy is the definitive treatment: single-level (proximal tibia or distal femur) for a unifocal deformity, double-level for a multi-apical one. Dome, wedge, or opening or closing wedge osteotomies are fixed internally with plate and screws or with an external fixator.

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Guided growth. For a growing child with open physes and genu varum or valgum that remains greater than 10-15 degrees after medical optimisation. The eight-plate technique:

1. Supine on a radiolucent table
2. Fluoroscopy to confirm the level of the physis
3. Small incision over the target physis: lateral for varus, medial for valgus
4. Plate straddling the physis with two screws, one epiphyseal and one metaphyseal
5. Position confirmed fluoroscopically

Rate and follow-up. Expect correction of 1-2 degrees per month, with standing alignment radiographs every 3-6 months. Bilateral and multi-level plating (femur and tibia) may be needed.

Osteotomy planning. For severe deformity or closed physes, at the proximal tibia or distal femur. Find the CORA (centre of rotation of angulation) and plan the correction angle and level. An opening wedge needs bone graft and is more technically demanding; a closing wedge is simpler but shortens the limb; a dome osteotomy allows gradual correction in an external fixator.

Operating on rachitic bone. Bone quality may be compromised by osteopenia, so larger implants give better fixation. Healing is delayed, so the non-weight-bearing period is longer, and the risk of malunion and nonunion is higher in active disease; biochemical optimisation is ensured before and after surgery.

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Skeletal complications. Pathological fractures are metaphyseal and follow minimal trauma, as greenstick or Salter-Harris II injuries. Deformity progresses (genu varum or valgum, coxa vara, scoliosis, kyphosis), and the risk of slipped capital femoral epiphysis is increased in untreated or undertreated rickets. Craniosynostosis is a rare complication, and a severe rachitic rosary can deform the chest wall enough to compromise breathing.

Systemic complications. Muscle weakness takes the form of a proximal myopathy with a waddling gait, and diffuse bone pain makes walking difficult. Severe chronic hypocalcaemia can cause developmental delay and, rarely, a dilated cardiomyopathy. Vitamin D plays a role in immune regulation, and infection risk is increased.

Vitamin D toxicity. Overcorrection causes hypercalcaemia (nausea, vomiting, polyuria, constipation, altered mental status) and hypercalciuria with nephrocalcinosis and renal stones. The risks are excessive supplementation, greater than 10,000 IU daily for prolonged periods, and calcitriol treatment of vitamin D-dependent rickets type I. Monitor serum calcium and the urinary calcium/creatinine ratio; reduce or stop vitamin D, hydrate, and add loop diuretics if severe.

Recurrent deformity. This is the most common complication when surgery is performed on active rickets. Recurrence and deformity progression are high when surgery is performed on biochemically uncontrolled rickets, and recurrence is substantially lower once metabolic control and radiographic healing are established. Prevention is confirming biochemical normalisation, radiographic healing and an adequate duration of treatment before operating; if deformity recurs, repeat the medical optimisation and consider revision only after full healing.

Delayed union and nonunion. The risk factors are active rickets, inadequate medical optimisation and poor compliance with vitamin D. Optimise vitamin D and calcium, consider bone stimulation, and revise a persistent nonunion.

Over- and undercorrection after guided growth. The correction rate with hemiepiphysiodesis is unpredictable, especially in metabolic bone disease. Close follow-up every 3-6 months with standing alignment radiographs, and prompt implant removal, prevent it. A mild error is observed, asymmetry is treated with contralateral surgery, and a severe error with osteotomy.

Hardware complications. Plates and screws can fracture in osteopenic bone, eight-plates migrate in soft bone, and surgical site infection carries the standard orthopaedic risk.

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After guided growth. The child bears weight as tolerated immediately, with no cast or immobilisation. Review is at 6 weeks and then every 3-6 months, with a standing alignment film at each visit.

Implant removal. Remove the eight-plates when the mechanical axis has normalised, under a brief anaesthetic. Delay risks overcorrection, and rebound deformity is watched for afterwards, especially in XLH.

After osteotomy. Protected weight-bearing lasts 6-12 weeks, longer than typical because of the metabolic bone disease, in a cast or brace, and weight-bearing progresses as serial radiographs show callus. Delayed healing is expected, so monitor closely for nonunion and consider bone stimulation if healing is slow.

Medical treatment continues. Vitamin D and calcium continue indefinitely, with biochemistry monitored during healing, to prevent recurrence. Long-term surveillance means annual biochemistry, growth monitoring and a watch for recurrence, especially in XLH, with repeat surgery if deformity recurs.

Nutritional rickets. The prognosis is excellent if treatment is early and complete. Full recovery is expected with adequate treatment, mild deformities correct spontaneously, and surgery is rarely needed with proper medical management. Full height potential is achievable, preserved if treatment starts before age 2, and catch-up growth is variable, better when treated early.

X-linked hypophosphataemia. Hereditary forms require lifelong management. XLH often requires multiple surgeries despite good medical control, and residual short stature is common, with an average height loss of 2-3 SD. Burosumab is showing improved outcomes over conventional therapy.

Surgery. Guided growth achieves correction in more than 90%, osteotomy unites in 85-95% (lower than in normal bone), and recurrence after proper optimisation is less than 10%. In hypophosphataemic rickets, guided growth restores a neutral mechanical axis in around 70% of limbs (Horn 2017).

Untreated or undertreated rickets. The sequelae are lasting:

• Permanent short stature, the growth potential lost if treatment comes after puberty
• Residual deformity (bow legs, knock knees, coxa vara) requiring adult reconstruction
• Early osteoarthritis of the knee (tibiofemoral) and hip from malalignment and abnormal loading
• Chronic mechanical pain from the deformity
• Gait abnormality: waddling or limping

Teeth. Dental problems include delayed tooth eruption, enamel hypoplasia and an increased caries risk, and enamel defects from the critical period of deficiency persist despite treatment.

Related pages: Osteomalacia is the same defect of mineralisation after the physes have closed - the distinction is skeletal maturity, not biochemistry, which is why an adult with these labs has no rachitic metaphyses to look for; Vitamin D Deficiency for the commonest cause and its supplementation thresholds; XLH and Oncogenic Osteomalacia for the FGF23-driven phosphopenic disease that the burosumab trials carded above were built around, and for its acquired tumour-induced mimic; Hypophosphatasia for the rachitic radiograph with a LOW alkaline phosphatase, which is the one biochemical pattern that inverts the usual rule; Renal Osteodystrophy for renal rickets and why it does not respond to native vitamin D; Blount Disease for the principal non-metabolic cause of the bowed toddler, and the differential this page's imaging section exists to settle; Guided Growth for Angular Deformity for the technique in the Horn series; and Calcium Homeostasis and Metabolic Bone Disease for the PTH-vitamin D-phosphate axis underlying every biochemical pattern in the table above.

Infants show craniotabes, toddlers develop genu varum, and older children develop genu valgum or a windswept deformity - and the reason the pattern changes with age is the key to recognising it.

• Rickets amplifies the age-appropriate physiological alignment. Normal tibiofemoral alignment evolves: infants are physiologically varus, passing through neutral at around 18-24 months, reaching peak physiological valgus at about 3-4 years, then settling to the adult angle by roughly 7 years. Because rickets softens the metaphysis and physis so the bone deforms under load, it exaggerates whatever alignment prevails at the age of peak disease activity - hence genu varum in the walking toddler (deforming during the physiological-varus phase) and genu valgum in the older child (deforming during the physiological-valgus phase).
• Windswept deformity (varus in one limb, valgus in the other) reflects asymmetric loading and growth on top of the same soft-bone mechanism.
• The worst change is at the fastest-growing, most-loaded physes. The florid metaphyseal fraying and cupping cluster around the knee (distal femur, proximal tibia) and the wrist (distal radius) - the physes contributing most to longitudinal growth - which is exactly why these are the best radiographs for diagnosis and scoring.
• Practical consequence. The direction of the deformity does not change the medical treatment, but it shapes the surgical plan (which side to tether in guided growth - lateral for varus, medial for valgus) and is a reminder that a young child's mild symmetric bowing may still be physiological, so the biochemistry and the metaphyseal appearance, not the bowing alone, make the diagnosis.