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Updated: Nov 14 2022


Images D resistent - clinical photo_moved.jpg & dosal kyphosis.jpg disorder chart.jpg vertebrae.jpg
  • Summary
    • Rickets is a metabolic bone disease caused by a defect in mineralization of osteoid matrix caused by inadequate calcium and phosphate that occurs prior to closure of the physes. Patients present with characteristic features such as bowing of long bones, ligamentous laxity, brittle bones and enlargement of costal cartilage.
    • Diagnosis is made based on a thorough evaluation of serum labs, clinical features, and radiographic findings.
    • Treatment involves medical management to resolve the underlying etiology of rickets.
  • Etiology
    • Pathophysiology
      • Vitamin D and PTH play an important role in calcium homeostasis
      • disruption of calcium/phosphate homeostasis
      • poor calcification of cartilage matrix of growing long bones
        • occurs at zone of provisional calcification
      • leads to increased physeal width and cortical thinning/bowing
    • Mechanism
      • rickets is 
        • known as osteomalacia if it occurs after physeal closure
        • can be congenital or acquired
        • treatment is usually non-operative with supplementation
    • Associated conditions
      • orthopaedic manifestations include
        • brittle bones with physeal cupping/widening
        • bowing of long bones
        • ligamentous laxity
        • flattening of skull
        • enlargement of costal cartilage (rachitic rosary)
        • kyphosis (cat back)
  • Classification
    • Vitamin D-resistant (familial hypophosphatemic)
      • most common form of heritable rickets
      • presents at 1-2 years of age
      • caused by inability of renal tubules to absorb phosphate
        • GFR is normal
        • vitamin D3 response is impaired
      • genetics
        • X-linked dominant
          • most common form
          • results from mutation in PHEX gene
          • leads to increased levels of FGF23, which decreases renal phosphate absorption and suppresses renal 25-(OH)-1α-hydroxylase activity
        • autosomal dominant
          • results from mutation in FGF23
          • leads to decreased FGF23 degradation
        • autosomal recessive
          • results from mutation in dentin matrix protein 1 (DMP1) gene
          • leads to impaired osteocyte maturation and bone mineralization, and increased levels of FGF23
    • Vitamin D-deficient (nutritional)
      • results from decreased dietary intake of Vitamin D
        • rare now that Vitamin D is added to milk
      • presents at 6 months - 3 years of age
      • risk factors
        • premature infants
        • black children > 6 months who are still breastfed
        • patients with malabsorption syndromes (celiac sprue) or chronic parenteral nutrition
        • Asian immigrants
        • patients with unusual dietary choices (vegetarian diet)
      • pathophysiology
        • low Vitamin D levels lead to decreased intestinal absorption of calcium
        • low calcium levels leads to a compensatory increase in PTH and bone resorption
        • bone resorption leads to increased alkaline phosphatase levels
    • Vitamin D-dependent (type I & type II)
      • rare disorder
      • leads to clinical features similar to Vitamin D-deficient rickets but more severe
      • clinical characteristics
        • type I
          • hypotonia, muscle weakness, growth failure, hypocalcemic seizures, joint pain/deformity, fractures in early infancy
        • type II
          • hypotonia, muscle weakness, growth failure, hypocalcemic seizures, growth retardation, bone pain, severe dental caries or dental hypoplasia
      • pathophysiology
        • type I
          • results from autosomal recessive mutation in renal 25-(OH)-1α-hydroxylase
          • responsible gene 12q14
          • prevents conversion of inactive form of vitamin D to active form
          • leads to decreased calcitriol
        • type II
          • results from autosomal recessive mutation in intracellular receptor for 1,25-(OH)2-vitamin D
          • leads to increased calcitriol
  • Presentation
    • Symptoms
      • listlessness
      • irritability
      • generalized weakness
    • Physical exam
      • tibial bowing
        • due to widened proximal tibial physes
      • rachitic rosary
        • enlargement of costochondral junction
      • bowing of knees
      • retarded bone growth
      • muscle hypotonia
      • waddling gait
      • dental abnormalities
        • delayed dental eruption
        • defective enamel
      • pathologic fractures
  • Imaging
    • Radiographs
      • recommended views
        • AP and lateral of affected bone
      • findings
        • physeal widening
        • metaphyseal cupping
        • decreased bone density
        • Looser's zones
          • pseudofracture on the compression side of bone
        • rachitic rosary
          • prominence of rib heads at the osteochondral junction
        • lower extremity bowing
          • often genu varum
        • codfish vertebrae
        • cat back
          • dorsal kyphosis
  • Studies
    • Histology
      • disordered and elongated zone of proliferation
      • poorly defined zone of provisional calcification
      • widened osteoid seams
      • "swiss cheese" trabeculae
      • abnormally arranged collagen fibers
        • run perpendicular to haversian canals
  • Tested Differential
    • Renal osteodystrophy
    • Hypophosphatasia
  • Treatment
    • Nonoperative
      • calcitriol
        • indications
          • Vitamin D-resistant (familial hypophosphatemic) rickets
          • type I Vitamin D-dependent rickets
      • phosphate replacement
        • indications
          • Vitamin D-resistant (familial hypophosphatemic) rickets
      • Vitamin D
        • indications
          • Vitamin D-deficient (nutritional) rickets
          • type II Vitamin D-dependent rickets (partial 1,25-(OH)2-vitamin D resistance)
      • Calcium
        • indications
          • type II Vitamin D-dependent rickets (total 1,25-(OH)2-vitamin D resistance)
      • Burosumab
        • human monoclonal antibody to FGF-23
        • approved for the treatment of X-linked hypophosphatemia among children 1 year and older
    • Operative
      • corrective surgery (multilevel osteotomy)
        • indications
          • severe tibial bowing
  • Techniques
    • Calcitriol
      • technique
        • 20-30 μg/kg/day split into 2-3 doses in children
        • 0.5-0.75 μg/day split into 2 doses in adults
    • Phosphate replacement
      • technique
        • 20-40 mg/kg/day split into 3-5 doses in children
        • 750-1000 mg/day split into 3-4 doses in adults
        • Must be given in combination with active vitamin D (i.e. calcitriol) in XLH patients, as this prevents the development of secondary hyperparathyroidism as seen in patients treated with phosphate salts alone
    • Vitamin D
      • technique
        • 5000 IU/day for 6-10 weeks
    • Corrective surgery (multilevel osteotomy)
      • technique
        • variety of fixation devices including K-wires, plates, intramedullary nails, and/or external fixation
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