How Many Bones Must be Broken?

Lilia Malkin, BSc

A fracture is often the first clinical sign of osteoporosis (OP), the silent disease of skeletal fragility characterized by decreased bone mass and deterioration of bone tissue that results in an increased vulnerability to fractures.

The bone mineral density (BMD) criterion frequently used to define osteoporosis was set in 1994 by the World Health Organization (WHO) as more than 2.5 standard deviations below the "young adult mean." An estimated 1.4 million Canadians suffer from OP. In the population aged 50 and over, approximately one in four women and one in eight men are affected. The incidence of the disease increases with age: 70 percent of women have osteoporosis by the age of 80. Predictably, the fracture risk rises with age, with women at higher risk due to both more extensive bone loss and longer average life span. Osteoporotic fractures make a significant contribution to morbidity and mortality in the geriatric population. For instance, the mortality rates within one year of hip fracture are estimated at between 12 and 37 percent, while the average death rate in octogenarians is 2.6 percent per year.

Unfortunately, OP is often asymptomatic prior to the occurrence of a fragility fracture, a break that occurs in the absence of major trauma to the affected bone. The best predictor of fracture risk is low bone density.