What is Osteoporosis?
The World Health Organization defines osteoporosis as: "A disease characterized by low bone mass and micro architectural deterioration of bone tissue, leading to enhanced bone fragility and a consequent increase in fracture risk." There are many risk factors for osteoporosis (follow the link to see a list of the most important).
Loss of bone is a normal consequence of aging (read about pathophysiology of bone in the Bone Physiology and Primary Prevention section). Osteoporosis occurs because of this loss of bone, but is only important when it results in fragility fractures. Fragility fractures, defined as fractures which occur in the absence of significant trauma, are the best predictors of osteoporosis and future fragility fractures. The diagnosis of osteoporosis should be made based on the presence of a fragility fracture, even without corroboration from Bone Mineral Density (BMD) measurement.
It would be preferable, if we could predict which patients have osteoporosis and increased risk of fragility fracture, prior to the occurrence of a fracture. Fracture risk is impacted by bone quality. Bone quality is affected by bone turnover, architecture, damage accumulation, matrix, mineralization and mineral properties. Bone quality is not directly measurable, so we use BMD as a surrogate for bone quality. However, the majority of fractures occur in patients who have normal BMD by DEXA. Learn about the Limitations of DEXA.
The WHO sponsored the development of the FRAX tool to improve predictions of which patients are at highest risk for fracture, using a combination of risk factors and BMD.
Fracture risk is also impacted significantly by fall risk. Fall risk is impacted by frailty, alcohol use, medication use (particularly benzodiazepines or other sedatives and medications with anticholinergic properties), impaired vision, cognition, and balance. Many of these risk factors can and should be modified (see evidence based strategies for Exercise and Fall Prevention).
Summary
Fragility fractures are a better predictor of future fragility fractures than BMD.
BMD is a relatively poor predictor of future fracture. The FRAX calculator should improve our ability to predict and treat the patients at highest risk for fracture.
Fall risk is a modifiable risk factor for fracture and should be assessed and treated when appropriate.