Rickets

Rickets in dog (Image sourced from Bristol Biomed Image Archive with permission)

• Essentially the same disease as osteomalacia
• Caused by Vitamin D and phosphorus deficiency
• In young animals
• Failure of:
  • Mineralisation of osteoid at sites of membranous growth
  • Cartilage vascularisation and mineralisation at sites of endochondral ossification
• Osteoid and catilage build up at those sites

• Histologically:
  • Lines of hypertrophic cartilage cells are lenghtened and disorganised
  • Ossification at metaphysis is poor
  • Persisting osteoid and cartilage -> shaft modelling failure
  • Thuckened physes due to normal chondrocyte proliferation but defective removal
• Ends of bones enlarge -> club-like thickening of metaphysis + compression of epiphysis
  • Most affected:
    • Proximal humerus
    • Distal radius
    • Ulna
    • Ribs
      • Enlargement of costochondral junction - called 'rachitic rosary'

• Weight bearing leads to:
  • Thickening of the physis and
  • Flaring of the excess matrix at the metaphysis
• Histological lesions heal whn diet corected
• Minor deformities correct but major deformities remain
• Occurs after weaning because:
  • In utero and in milk - adeqaute nutrients obtained at expense of dam
• In Foals
  • Rare - long nursing period and relatively slow rate of growth
• In Calves and lambs
  • When diet deficeint of phosphorus and poor exposure to sunlight
• In Puppies, Kittens and Piglets
  • Rapid growth, weaned early -> fulminating rickets if poor exposure to sunlight and lack of vitamin D in diet