Hip axis length measurement using dual-energy X-ray absorptiometry.

Hip axis length (HAL) has been reported, in the United States, to influence the risk of hip fractures independently from age and proximal femoral bone mineral density. Last-generation dual-energy X-ray absorptiometry units can perform automatic hip axis length measurements. The present study was designed to evaluate the feasibility of this measurement in clinical practice and to establish the range of normal values obtained in French women using single- and fan-beam absorptiometry. Short-term reproducibility determined by performing two measurements with repositioning in 50 women was 1.67%. Long-term reproducibility calculated based on five measurements taken at six-month intervals in 60 women was 1.5%. No statistically significant differences were found between hip axis length on the right and left sides in 50 women. Mean values calculated based on measurements in 190 women aged 54 +/- 12 years (single-beam absorptiometry) and in 50 women aged 80 +/- 5 years (fan-beam absorptiometry) were 10.4 +/- 0.6 cm and 11.5 +/- 0.7 cm, respectively. Hip axis length was correlated with height but not with age or femoral neck bone mineral density. Our data are consistent with studies conducted in the United States. The interpretation of hip axis length measurements requires knowledge of the type of X-ray beam used (single or fan-shaped). Whether hip axis length predicts the hip fracture risk in Europeans remains to be demonstrated.