Osteoporosis

• Characterised by increased bone porosity due to reduced bone mass
• Makes bone more susceptible to fracture
• May be localised to a specific bone such as in disuse osteoporosis of a limb or may involve the entire skeleton as a manifestation of metabolic bone disease
• Generalised osteoporosis can be primary;
  • Postmenopausal
  • Senile
• Or secondary;
  • Endocrine disorders
    • Hypo-parathyrodism
    • Hyper-parathyroidism
    • Diabetes
    • Addison disease
  • Drugs;
    • Anticoagulants
    • Chemotherapy
    • Corticosteroids
    • Alcohol
  • Neoplasia
  • Gastrointestinal
    • Malnutrition
    • Malabsorption
    • Hepatic insufficiency

 

Pathogenesis

 

• Age related changes
  • Osteoblasts from elderly patients have reduced replicative and biosynthetic function
  • Proteins bound to the ECM such as growth factors which stimulate osteoblastic activity lose their biological potency overtime
  • This underlies senile osteoporosis which is categorised as a low turnover variant
• Reduced physical activity increases the rate of bone loss because mechanical forces are important stimuli for bone remodelling. This also contributes to osteoporosis
• Genetic factors. The type of vitamin D receptor inherited accounts for 75% of the peak mass achieved. Calcium deficiency, increased PTH levels and reduced Vit D may also play a role in senile osteoporosis
• Nutritional state – particularly relevant to adolescent girls
• Hormonal influences – post-menopausal osteoporosis is a hormone dependant acceleration of bone loss that occurs during the decade after menopause. Oestrogen deficiency plays a major role. The effects of oestrogen on bone mass are mediated by cytokines. Decreased oestrogen levels result in increased production of IL-1, IL-6 and TNF by monocytes. These cytokines timulate osteoclast activity
• Glucocorticoids decrease bone mass by increasing bone reabsorption and reducing bone formation. Glucocorticoids should be administered along with bisphosphonates

 

Morphology

 

• Entire skeleton is affected in post-menopausal and senile osteoarthritis, but some areas are more severely involved than others
• In postmenopausal disease, vertebrae are often affected causing stress fractures and eventual collapse
• In both cases patients may have localised disease due to immobilisation
• Cortex and trabeculae are thinned and the haversian systems are widened

 

Clinical course

 

• Vertebral fractures of the thoracic and lumbar vertebrae can occur
• This can result in significant loss of height and deformity such a lumbar lordosis and kyphoscoliosis
• Osteoporosis cant be detected by x-ray until 30-40% of bone mass is lost
• Measurement of calcium, phosphorous and alkaline phosphatase isn’t diagnositic
• Prevention and treatment of senile osteoporosis include;
  • Exercise
  • Appropriate calcium and Vit D intake
  • HRT
  • Bisphosphonates
  • Recombinant PTH