WEDNESDAY, Sept. 27 (HealthDay News) -- Australian researchers say they've developed a mathematical formula that's 75 percent accurate at predicting which older women are most at risk for fractures -- a frequent cause of disability and death.

Called the Fracture Risk -- or FRISK -- score, the new tool takes into account a variety of risk factors, including bone density, and is meant to help doctors tailor their treatment strategy to help women prevent bone breaks.

"The equation is a simple combination of bone mineral density at the spine and femoral neck [the upper part of the thigh bone, close to the hip joint], the number of previous fractures sustained, body weight and a falls score derived from the number of falls in the previous year," said study author Margaret Joy Henry, a statistician at the University of Melbourne, where the formula was developed.

"Doctors commonly assess bone mineral density at the spine and femoral neck and will have this data available to include in the equation," she said. "The previous number of fractures and falls are self-reported by the patient, and weight is easily measured."

The new scoring method goes beyond what physicians currently use to decide how likely a woman is to suffer a fracture. "Currently doctors use T-scores (which compare a person's bone density to a group of young females with peak bone density) and Z-scores (a comparison to age-matched peers) at separate anatomical sites (generally the spine and hip) to assess a patient's fracture risk," she said. "However, there has not been a method to combine the contribution of the different anatomical sites to an individual's overall fracture risk."

"This study provides an evidence-based equation to aid doctors in assessing their patient's fracture risk," Henry said.

The findings are published in the October issue of Radiology.

For the study, Henry and her colleagues measured bone density in 231 women, with a mean age of 74, who had had a fracture in the previous two years. Then they measured the bone density of 448 women, mean age 72, who had not suffered a break. The researchers then developed the equation based on the measurements in this study group. Then they tested it on a third group of women, 600 in all, median age 74. The researchers followed the women for six years to see how the formula worked.

The results: The formula predicted fractures 75 percent of the time. While previous researchers have found that lighter body weight led to an increased risk of fractures in older women due to the lower body mass that often accompanies light body weight, the Australian researchers found that heavier body weights seemed to increase the force applied to the skeleton during a fall, and therefore increased risk.

On a 0-10 scale, a FRISK score of 5.4 or greater was associated with an expectation of fracture. For every one unit increase in the FRISK score, the odds of having a fracture increased by 1.75, the researchers found.

The new formula is "a move in the right direction, to find a better way to discuss fracture risk," said Dr. Robert Heaney, a scientist at the Osteoporosis Research Center at Creighton University, in Omaha, Neb. "There are efforts worldwide to try to do a better job of predicting" fractures, he said.

An even better method may be in the works, said Dr. Mone Zaidi, director of the Mount Sinai Bone Program at Mount Sinai School of Medicine, in New York City.

"The World Health Organization is developing what will be a more validated test," he said. "The FRISK score is a very simplistic view of the whole thing, by no means complete."

More information

To learn more about osteoporosis, visit the National Osteoporosis Foundation.