Musculoskeletal System >
Osteomalacia & Rickets
“Normal bone tissue but with abnormal or impaired bone mineralisation resulting in soft bones“
- Rickets: during growth in children
- Osteomalacia: After epiphysis fusion (adults)
Risk Factors
- Poor diet
- Lack of sunlight e.g. northern hemispheres, darker skin (Asian, Afro-Caribbean, Middle Eastern origin), homebound elderly populations
- Prematurity
- Exclusive breastfeeding (especially for > 6 months)
- Medication – phenytoin or other anticonvulsants
Epidemiology
- Common in the past but fortified foods in 20th century have reduced its incidence.
- However, there is a small increase in cases of rickets in UK due to vit D deficiency in a significant number of population
- More common in people with darker skin as they require more sunlight for adequate vitamin D
Aetiology
- Vitamin D, calcium deficiency – most common cause
- Lack of sunlight
- Poor dietary intake e.g. low-fat diet, lack of dairy products (vegan diet)
- Malabsorption e.g. coeliac disease, Crohn’s disease
- Drug-induced e.g. anticonvulsants – use liver and kidney hydroxylase enzymes that convert Vit D for its own metabolism
- Inherited genetic defect – e.g. congenital deficiency of 1 alpha-hydroxylase (promotes the conversion of active Vit D)
- Liver disease e.g. cirrhosis
- Liver unable to convert inactive vitamin D to 25 hydroxyvitamin D
- Renal failure – kidneys can’t convert 25 hydroxyvitamin D to calcitriol
Clinical Presentation
- Osteomalacia and rickets:
- Diffuse bone and joint pain
- Muscle tenderness
- Proximal myopathy
- Increased fracture risk with minimal trauma
- Hypocalcaemia
- Muscle cramps, twitching, tingling in hands and feet, seizures
- Rickets:
- Bone pain
- Soft, weakened bone resulting in skeletal deformities
- Bowed legs (genu varum)
- Knock knees
- Thickening of ankles, wrists and knees
- Soft skull bones (craniotabes)
- Delayed closure of fontanelles
- Prominent frontal bone
- Scoliosis (rarely)
- Poor bone growth and development
- Shorter height than average
- Protruding abdomen (severe disease)
Pathophysiology
- Calcitriol (vit D3) = hormonally active form of vit D
- Function:
- Promote dietary calcium absorption to maintain calcium levels
- Increases renal tubular calcium reabsorption
- Increase calcium deposition into bones
- Promote bone mineralisation, strengthening and formation (after normalisation of Calcium levels)
- Function:
- Lack of vitamin D → lack of calcitriol → reduced calcium → impaired bone mineralisation (osteoblasts unable to deposit calcium or phosphate into the inorganic matrix)
Investigations
- Blood tests
- Low 25-hydroxy vitamin D
- Raised alkaline phosphatase
- Low calcium and phosphate
- High PTH
- X-ray
- Adults – translucent bands, pseudofractures (looser zones) often in superior and inferior pubic rami
- Children – Metaphyseal cupping and flaring, bowed legs
Management
- Improve dietary intake of Vit D and calcium
- Oral calcium and vit D supplementation or yearly vit D injections
- Vit D injections mainly necessary if oral intake is not possible or patient has intestinal or liver disease
- Adequate sun exposure
- Treating underlying cause
- Vit D supplementation:
- Pregnant and breastfeeding women
- 10mcg of Vit D daily between Oct-March (when days are shorter)
- Babies from birth to 1 year old (regardless of feeding status)
- 8.5-10mcg daily supplement
- Those on formula do not need Vit D as it is fortified unless they are drinking < 500ml a day of formula
- Children between 1-4 years old
- 10mcg daily
- Pregnant and breastfeeding women
Complications
- Skeletal Deformities