Definition
Rickets
- paediatric disorder characterised by deformity and growth retardation
- secondary to defective mineralisation of the growth plate
Osteomalacia
- adult disorder
- defective mineralisation of osteoid
Physiology
Generation of Vit D
Vitamin D3 ingested and absorbed
- activated by sunlight
- need 10 - 15 minutes 3 x per week
25 hydroxylated in liver
1 alpha-hydroxylase in kidney
- active 1,25 vit D3
- calcitriol
- this is under PTH control
Action Vit D
Intestine
- increases Ca and PO4 absorption
Kidney
- decreases Ca and PO4 excretion
Bone
- increases Ca and PO4 release
Pathology
Physis
- hypertrophic zone widens
- provisional zone never forms
- no mineralisation of osteoid
Clinical
Osteopenia
Bowing
- usually develops during periods of rapid growth
- not seen in newborn
- see in toddlers
Fractures
- recurrent clavicle fractures
- stress fractures
Teeth
- delayed formation
- increased dental caries
Kyphoscoliosis
Short stature
- adults < 5 foot
Xray
Tibial and femoral bowing
Pathognomonic signs
- widened physeal plate
- cupping of the metaphysis
Blood Results
Ca2+ low
Phosphorus low
Alk Phos high
Vit D low
Electrolytes
Causes
1. Vitamin D deficiency
Causes
- inadequate sun exposure
- low dietary intake
More common in dark skinned children
- exclusively breastfed
- live in northern cities with low sunlight
- vegetarian diet
Treatment
- daily vitamin D
- 30 minutes daily sunshine
2. Congenital disease
A. Vitamin D dependent rickets Type 1
- defect in 1 alpha hydroxylase
- converts 25 (OH) to 1,25 (OH)
- 1,25 biologically active
B. Vitamin D independent rickets Type 2
- mutations in the vitamin D receptor
- more than 10 types
C. Familial X linked hypophosphataemic rickets
- AD, most common form
- vitamin D resistant rickets
- impaired tubular resorption phosphate
- treatment phosphate + calcitriol
3. Vitamin D metabolism abnormalities
Causes
- renal failure
- phenytoin