Rickets and Osteomalacia

• Rickets


  Disorder in children that interferes with the deposition of bone in the growth plates

  
• Osteomalacia


  Marked softening of the bone caused by severe vitamin D deficiency

  
• Both rickets and osteomalacia are manifestations of vitamin D deficiency or its abnormal metabolism

  
• The fundamental defect is an impairment of mineralization and a resultant accumulation of unmineralized bone matrix

  
• The normal reference range for circulating 25-(OH)-D is 20 to 100 ng/mL; concentrations of less than 20 ng/mL constitute vitamin D deficiency

  
• Rickets

  • Age: 6 months-2 years
• Risk factors for rickets

  • Diets deficient in calcium and vitamin D
  • Limited exposure to sunlight (northern latitudes)
  • Children born to mothers who have frequent pregnancies
  • Renal disorders causing decreased synthesis of 1,25-dihydroxyvitamin D and phosphate depletion
  • Malabsorption disorders such as celiac disease
  • Exclusive breast feeding
  • Dark skin

  
• Biochemical changes in rickets

  • Lowered levels of active metabolites of vitamin D (25-hydroxy vitamin D and 1, 25-dihydroxy vitamin D)
  • Plasma calcium levels are normal or slightly low
  • Plasma phosphate levels are lowered
  • Plasma alkaline phosphatase is usually raised due to osteoblastic activity

  
• Pathogenesis of rickets

  1. Decrease bone mineralization

  2. Defective endochondral and intramembranous bone growth (ossification)

  3. Overgrowth of epiphyseal cartilage due to inadequate provisional calcification and failure of the cartilage cells to mature and disintegrate

  4. Persistence of distorted, irregular masses of cartilage, which project into the marrow cavity

  5. Deposition of osteoid matrix on inadequately mineralized cartilaginous remnants

  6. Disruption of the orderly replacement of cartilage by osteoid matrix, with enlargement and lateral expansion of the osteochondral junction

  7. Abnormal overgrowth of capillaries and fibroblasts in the disorganized zone resulting from microfractures and stresses on the inadequately mineralized, weak, poorly formed bone

  8. Deformation of the skeleton due to the loss of structural rigidity of the developing bones

  
• Clinical features of rickets

  • Craniotabes: Softened occipital bones may become flattened, and the parietal bones can be buckled inward by pressure; with the release of the pressure, elastic recoil snaps the bones back into their original positions
  • The skull looks square and box-like with frontal bossing due to excess unmineralized osteoid
  • Harrison's sulcus appears due to in drawing of soft ribs on inspiration
  • Rachitic rosary is a deformity of chest due to results from overgrowth of cartilage or osteoid tissue at the costochondral junction
  • Pigeon-chest deformity is the anterior protrusion of sternum due to action of respiratory muscles
  • Bowlegs occur in ambulatory (young) children due to weak bones of lower legs
  • Knocked knees: may occur due to enlarged ends of the femur, tibia and fibula in older children
  • Widening of wrist: Due to lower epiphyses of radius may be enlarged
  • Lumbar lordosis is due to involvement of the spine and pelvis

  
• Complications of rickets

  • Failure to grow
  • Bone fracture
  • Bone deformities
  • Dental defect
  • Seizure (rare)

  
• Osteomalacia


  • Age: Adult

  
• Risk factors for osteomalacia

  • Vitamin D dietary deficiency
  • Decrease sunlight exposure
  • Surgery: Remove part of the stomach such as sleeve gastrectomy
  • Kidney or liver disease: Decrease the body's ability to form active vitamin D
  • Celiac disease
  • Drugs

  
• Biochemical changes in osteomalacia

  • Normal or low serum calcium levels
  • Plasma phosphate levels lowered
  • Raised serum alkaline phosphatase due to increased osteoblastic activity

  
• Clinical features of osteomalacia

  • Muscular weakness
  • Vague bony pains
  • Fractures following trivial trauma
  • Incomplete or greenstick fractures

  
• Histology of osteomalacia

  • The newly formed osteoid matrix laid down by osteoblasts is inadequately mineralized
  • The unmineralized osteoid appears as a thickened layer of matrix arranged about and around the more basophilic, normally mineralized trabeculae

  
• Complication of osteomalacia is bone fracture especially vertebral and femoral neck