Rickets — Orthopaedic Sequelae

Rickets is a disorder of impaired mineralisation of the growing skeleton, affecting the physis and osteoid in children. In adults, the equivalent condition is osteomalacia (affecting unmineralised osteoid in formed bone). Rickets produces characteristic radiographic signs, skeletal deformity, and growth disturbance. The orthopaedic sequelae — including long bone deformity, stress fractures, and pathological fractures — require both medical optimisation and surgical correction.

• Nutritional rickets (Vitamin D deficiency): most common worldwide; inadequate sunlight exposure, poor dietary intake, malabsorption, exclusive breastfeeding without supplementation
• X-linked hypophosphataemic rickets (XLH): most common hereditary form; X-linked dominant; PHEX gene mutation → elevated FGF23 → phosphate wasting in renal tubules; normal calcium and PTH; low phosphate; low-normal 25-OHD; normal or low 1,25-OHD
• Vitamin D-dependent rickets (VDDR): Type I (1α-hydroxylase deficiency); Type II (vitamin D receptor resistance)
• Oncogenic osteomalacia: FGF23-secreting mesenchymal tumour — phosphaturia and osteomalacia; resolves on tumour resection
• Renal osteodystrophy: chronic kidney disease impairs 1,25-OHD synthesis; secondary hyperparathyroidism; complex metabolic bone disease
• Hypophosphataemic forms generally more resistant to treatment and more prone to recurrent deformity after correction

• Normal mineralisation requires: adequate calcium, phosphate, alkaline phosphatase, and vitamin D (1,25-dihydroxycholecalciferol)
• In rickets: failure of provisional calcification at the zone of hypertrophy in the physis — widened, irregular, frayed physis on radiograph
• Physis widens and softens — weight-bearing causes deformity through the structurally weak physis; classic bowing deformity results
• Osteoid accumulates unmineralised — bone is soft and deformable; cortices thin; pseudofractures (Looser zones) develop in adults
• Secondary hyperparathyroidism: low calcium stimulates PTH → phosphate wasting → worsens mineralisation deficit; subperiosteal resorption on radial aspect of middle phalanges (classic sign)
• Alkaline phosphatase: markedly elevated in active rickets — useful screening and monitoring marker

• Looser zones (Milkman fractures) are pathognomonic of osteomalacia in adults — bilateral, symmetrical, perpendicular to cortex; medial femoral neck is classic site; distinguish from stress fractures (which are transverse and often unilateral)
• Subperiosteal erosion on radial aspect of middle phalanges of hand = secondary hyperparathyroidism — classic sign of renal osteodystrophy

• XLH distinguishing feature: normal calcium, normal PTH, low phosphate — unlike nutritional rickets where calcium is also low and PTH elevated
• ALP: elevated in ALL active rickets — best single marker of disease activity; normalises with effective treatment
• FGF23: elevated in XLH and oncogenic osteomalacia — measured in specialist centres; guides targeted therapy

• Genu varum: most common lower limb deformity in nutritional and XLH rickets; predominantly tibial; weight-bearing through weak physis causes progressive bowing
• Genu valgum: more common in late-treated or hypophosphataemic rickets; predominantly distal femoral
• Coxa vara: neck-shaft angle <120°; femoral neck bowing; Trendelenburg gait; develops from physeal weakness at proximal femur — Hilgenreiner epiphyseal angle (HEA) >60° indicates risk of progression and need for valgus osteotomy
• Scoliosis: uncommon but reported; from asymmetric vertebral growth and muscle weakness
• Pathological fractures: Looser zones can complete as true fractures with minor trauma in adults; femoral neck, pubic rami most common; treat underlying metabolic disease first
• Dental abnormalities: enamel hypoplasia, dental abscesses — particularly in XLH; mandibular tori (bony outgrowths) in XLH
• Short stature: universal in untreated rickets — physeal growth arrest from mineralisation failure

• Nutritional rickets: vitamin D supplementation (high-dose loading then maintenance); calcium supplementation; dietary counselling; sunlight exposure; ALP normalisation confirms response
• XLH: oral phosphate supplementation + calcitriol (active vitamin D) — conventional treatment; multiple daily doses required; risk of nephrocalcinosis with over-treatment
• Burosumab (Crysvita): anti-FGF23 monoclonal antibody — FDA/EMA approved for XLH in children and adults; significantly superior to conventional therapy in normalising phosphate and improving growth, rickets severity, and walking ability; given subcutaneously every 2 weeks
• VDDR Type I: calcitriol (1,25-OHD) replacement — bypasses defective 1α-hydroxylase; excellent response
• Renal osteodystrophy: alfacalcidol or calcitriol; phosphate binders; dialysis or transplantation for end-stage renal disease
• Surgical timing rule: never correct deformity in active rickets — operate only when biochemically controlled (ALP normalised, phosphate maintained); operating in active disease leads to recurrent deformity

• Hemiepiphysiodesis (guided growth): first-line for genu varum/valgum in skeletally immature with >2 years growth remaining and well-controlled disease; tension band plate on the convex side; gradual correction over 12–24 months; reversible
• Osteotomy: for severe deformity, skeletal maturity, or when guided growth insufficient; tibial osteotomy for varum; distal femoral osteotomy for valgum; fix with intramedullary nail or plate
• Coxa vara: valgus intertrochanteric osteotomy when HEA >60° or progressive with symptoms; aim for neck-shaft angle of 140–150° and HEA <40°; fix with blade plate or paediatric hip screw system
• Ilizarov/hexapod frame: for severe or multiplanar deformity requiring gradual correction; allows simultaneous correction of angular, rotational, and length abnormalities; particularly useful in XLH where deformity is often complex and recurrent
• Looser zone fractures in adults: immobilise and optimise medical treatment; surgical fixation (IM nail or plate) for displaced complete fractures or non-union

• Recurrent deformity after osteotomy in XLH: the most frustrating clinical problem — weak bone and ongoing phosphate wasting mean deformity recurs predictably if medical management is suboptimal; ensure burosumab or conventional therapy is optimally dosed and monitored before and after surgery; ALP must be within normal range perioperatively
• Burosumab in XLH: superior to phosphate + calcitriol in all clinical outcomes — start in childhood; reduces rickets severity score, improves growth, and reduces surgical burden compared to historical conventional therapy; do NOT combine with oral phosphate (risk of hyperphosphataemia)
• Enthesopathy in XLH adults: calcification of tendons, ligaments, and joint capsules — Achilles tendon, plantar fascia; progressive and disabling; may require local corticosteroid injection or surgical excision; burosumab may slow progression
• Spinal stenosis in XLH: ligamentum flavum and posterior longitudinal ligament ossification — can produce significant lumbar or cervical stenosis in adults; manage as per standard spinal stenosis; decompression when symptomatic
• Nephrocalcinosis monitoring: urinary calcium:creatinine ratio and renal ultrasound annually in XLH patients on conventional phosphate + calcitriol therapy — nephrocalcinosis risk is real; less with burosumab

• Radiographic signs: physeal widening + cupping + fraying at metaphysis; Looser zones in osteomalacia
• ALP: elevated in all active rickets — best single marker; normalise before surgery
• XLH: normal calcium, normal PTH, low phosphate — key distinguishing biochemistry from nutritional rickets
• Looser zones = pathognomonic of osteomalacia; bilateral symmetrical bands perpendicular to cortex at medial femoral neck
• Never operate in active rickets — deformity recurs; correct disease biochemically first (ALP normal)
• Coxa vara: HEA >60° = progressive; valgus osteotomy indicated; aim for neck-shaft angle 140–150°
• Burosumab: anti-FGF23 antibody; approved for XLH; superior to conventional therapy; do not combine with oral phosphate
• Hemiepiphysiodesis (guided growth): first-line for angular deformity in immature skeleton with >2 years growth; requires biochemical control first
• XLH enthesopathy in adults: tendon calcification; spinal stenosis from ligamentous ossification — a distinct and important long-term complication
• Nutritional rickets: low Ca, low PO4, high ALP, high PTH, low 25-OHD — treat with Vitamin D + calcium supplementation