Osteoporosis Definitions

An international consensus definition of osteoporosis states: "Osteoporosis is a systemic skeletal disease characterised by low bone mass and micro architectural deterioration of bone tissue, with a consequent increase in bone fragility and susceptibility to fracture" (AM J Med 1993; 94:646).

Normal Bone vs. Osteoporotic Bone Histology

Normal Bone vs. Osteoporotic Bone Histology

The most common reasons for osteoporosis in older women are:

  1. the effect of the menopause leading to rapid bone breakdown,
  2. impaired intake and absorption of calcium and vitamin D leading to increased age related bone loss, and
  3. decreased physical activity with increasing age

Bone loss in men is in part due to the causes outlined in b) and c) above.

Secondary Osteoporosis Secondary osteoporosis is a reduced bone mass caused by conditions other than age.

Causes of Secondary Osteoporosis

Endocrine or Metabolic Nutritional Drug Usage Other
Acromegaly Alcoholism Azathioprine Ankylosing spondylitis
Anorexia nervosa Calcium deficiency Cyclosporin Cholestatic liver disease
Diabetes type I & II Chronic liver disease Excess thyroid medication Chronic obstructive pulmonary disease
Hyperadrenalism Gastric and small gut resection Glucocorticosteroids Crohn’s Disease
Hyperprolactinemia Vitamin D deficiency Heparin Hypercalciuria
Hyperparpathyroidism Malabsorption Methotrexate Immobilisation
Hypophosphatasia   Phenobarbital Mastocytosis
Porphyria   Phenytoin carbamazepine Multiple Myeloma
Thyrotoxicosis   Vitamin D toxicity Organ transplant
      Renal tubular acidosis
      Rheumatoid arthritis
      Ulcerative colitis

The World Health Organisation has further defined osteoporosis according to the T-scores from a DEXA assessment for post menopausal women.

Normal bone mass is defined as any BMD that is greater than one standard deviation below the young adult mean.

(T-score > -1)

Reduced bone mass (osteopenia) is defined as any BMD between one and two and a half standard deviations below the young adult mean.

(-1.0 > T-score > -2.5)

Osteoporosis is defined as any BMD less than two and a half standard deviations below the young adult mean.

(T-score < -2.5)

[Refer to Appendix 4 for information on male osteoporosis]