Predicting fracture risk should include bone geometry, age, height, weight

Many implant manufacturers are educating surgeons, insurers and hospital personnel about newer technology.

Issue: August 2004

IOF icon Although the measurement of bone mineral density is regarded as the gold standard in determining if a patient is at risk for sustaining a fragility fracture, additional factors may prove a better predictor than bone mineral density alone.

Researchers from GE Healthcare in Madison, Wis., and the Osteoporosis Diagnostic and Treatment Center in Richmond, Va., said bone mineral density (BMD) scans are more effective when merged with measurements of bone geometry, patient age, height and weight to form a “Fall Index.”

Kenneth G. Faulkner, PhD, chief scientist with GE Healthcare, and his colleagues obtained dual energy x-ray absorptiometry (DXA) scans of 422 women, including 58 with prior hip fracture, using the Lunar Prodigy system (GE Healthcare). They found that the Fall Index — which mathematically estimates the ability of a femur to withstand a fall — was significantly lower in the 58 women who had sustained a broken hip. BMD measurements were also significantly lower in these women.

“The Fall Index predicts hip fracture better than bone density alone,” said Faulkner, who added that verification studies are needed to confirm the results.

Faulkner said the technique of measuring the Fall Index was first published 10 years ago by Yoshikawa and colleagues in the Journal of Bone and Mineral Research.

Measuring the Fall Index requires bone densitometers that measure not just bone density but also bone geometry, such as cross-sectional area and moment of inertia. Most modern densitometers are equipped with these capabilities, though they have only recently become commercially available on some systems, he said.

In the new study, Faulkner and his colleagues compared patients’ BMD with their cross-sectional moment of inertia (CSMI), cross-sectional area (CSA) at the femoral neck and their Fall Index for assessing hip fracture risk.

The investigators took DXA measurements of the patients’ nonfractured femur. They measured BMD of the femoral neck, as well as CSMI, CSA and Fall Index using the Lunar Hip Strength Analysis program.

There was no significant trend with age for the BMD-adjusted CSA, CSMI and Fall Index values, he reported. When researchers statistically compared the results for fracture cases and controls, the femoral neck BMD was significantly lower in the fracture group compared to controls, as has been reported by other scientists.

However, after adjustment for BMD, neither CSMI nor CSA were significantly different between the groups, but the Fall Index was significantly lower in the fracture group, consistent with a reduced capacity to withstand a fall.

Femur Strength Index

“There is a difference between measuring femoral density and femoral structure,” Faulkner said. “We feel the Fall Index — which we now more accurately call the ‘Femur Strength Index’ — is excellent because it predicts how much force there would be in a fall, how strong the femur is and if it could withstand that force.

“While the bone density measurement alone does a very good job of differentiating fracture control … it wasn’t until we started getting specific with the patients about their weight and their fall forces that we saw [real differences] between the patients.”

For more information:

Faulkner KG, Wacker WK, Barden HS, Burke PK. Fall index predicts hip fracture independent of age and bone density. #OC3. Presented at the International Osteoporosis Foundation World Congress on Osteoporosis. May 14-18, 2004. Rio de Janeiro.