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Introduction
  • A defect in mineralization of osteoid matrix caused by inadequate calcium and phosphate
    • prior to closure of physis known as rickets
    • after physeal closure called osteomalacia
  • Pathophysiology
    • 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 and bowing
    • Vitamin D and PTH  play an important role in calcium homeostasis 
  • 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
  • Types include 
    • familial hypophosphatemic (vitamin D-resistant) (see below)
    • vitamin D-deficient (Nutritional)
    • vitamin D-dependent (type I & type II)
    • renal osteodystrophy 
    • hypophosphatasia 
Imaging
  • Radiographs 
    • recommended views
      • AP and lateral of affected bone
    • findings
      • physeal widening
      • metaphyseal cupping
      • Looser's zones (pseudofracture on the compression side of bone)
      • decreased bone density
      • prominence of rib heads at the osteochondral junction (rachitic rosary)
      • bowing (often genu varum
Studies
  • Laboratory studies
 
  •  Histology 
    • zone of proliferation is disordered and elongated in growthplate
    • widened osteoid seams
    • swiss cheese trabeculae
    • poorly defined zone of provisional calcification
Familial Hypophosphatemic Rickets (Vitamin D resistant Rickets)
  • Also known as
    • Vitamin D resistant Rickets
    • X-linked hypophosphatemic
  • Most common form of heritable rickets 
    • caused by inability of renal tubules to absorb phosphate
    • GFR is normal
    • impaired vitamin D3 response
  • Genetics
    • X-linked dominant 
  • Presentation
    • tibial bowing as result of widened proximal tibia physis 
  • Labs     
    • low serum phosphorous
    • elevated alkaline phosphatase 
    • serum calcium is usually normal or low normal
  • Treatment
    • medical treatment
      • Calcitriol
        • indications
          •  is standard therapy
      • phosphate replacement
        • indications
          • controversial and counter-intuitive
          • physiology would suggest that phosphate replacement would be beneficial and treatment of 1-3 grams phosphate daily was recommended
          • recent research evaluated the addition of phosphate to the standard vitamin D therapy and found no additional benefit with phosphate therapy
    • surgical treatment
      • corrective surgery
        • indications
          • to correct tibial bowing in severe deformity
Vitamin D-Deficiency Rickets (Nutritional)
  • Nutritional rickets is associated with decreased dietary intake of Vitamin D
    • rare now that Vitamin D is added to milk
    • still seen in 
      • 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
  • Physiology
    • 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
  • Clinical findings 
    • rachitic rosary (enlargement of costochondral junction)
    • bowing of knees
    • codfish vertebrae 
    • retarded bone growth (widened osteoid seams, physeal cupping) 
    • muscle hypotonia
    • dental disease
    • pathologic fractures
    • waddling gate
  • Laboratory values 
    • low to normal serum calcium
    • low serum phosphate
    • elevated alkaline phosphatase
    • elevated parathyroid hormone
    • low vitamin D
  • Treatment
    • Vitamin D (5000 IU daily)
      • indications
        • resolves most deformities
Hereditary Vitamin D-Dependent Rickets (Type I and II)
  • Rare disorder 
  • Clinical features similar to Vitamin D-Deficient Rickets but more severe 
  • Clinical characteristics
    • Type I
      • joint pain/deformity, hypotonia, muscle weakness, growth failure, and hypocalcemic seizures or fractures in early infancy
    • Type II
      • bone pain, muscle weakness, hypotonia, hypocalcemic convulsions, growth retardation, severe dental caries or teeth hypoplasia
  • Pathophysiology     
    • Type I 
      • caused by defect in renal 25-(OH)-vitamin D1 alpha-hydroxylase 
        • prevents conversion of inactive form of vitamin D to active form
      • responsible gene 12q14
    • Type II 
      • caused by a defect in intracellular receptor for 1,25-(OH)2-vitamin D
  • Genetics
    • type II                         
      • autosomal recessive
  • Laboratory values
    • type II is distinguished from type I by markedly elevated levels of 1,25-(OH)2-Vitamin D
  • Treatment
    • physiologic doses (1-2 micrograms/day) of 1,25-(OH)2-Vit D
      • indications
        • type I 
    • daily high dose Vitamin D + elemental calcium
      • indications
        • type II
 

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