title: A simple method of computing hip axis length using fan-beam densitometry and anthropometric measurements.
abstract: Hip axis length (HAL), a simple measure obtained from dual X-ray absorptiometry (DXA) scans of the proximal femur, predicts hip fracture, independent of bone mineral density and age. Owing to a magnification error associated with newer fan-beam DXA, automatic calculation of HAL, which is available in pencil-beam DXA, is inaccurate. The purpose of this study was to model HAL, measured from a pencil-beam DXA, as a function of HAL from a fan-beam DXA combined with other anthropometric measures. Proximal femur scans were performed using pencil- and fan-beam DXA in 21 women (ages 24-60). Height, weight, hip circumference, subject thickness, height of the greater trochanter and anterior superior iliac spine from the scanning table, and HAL as measured by a ruler from the scan printouts were recorded. Anthropometric measurements were taken by two researchers; all but the greater trochanter were reproducible (r > or = 0.92). A simple linear model using the manual measurement of HAL from the fan-beam scan, height, weight, body mass index, and hip circumference was able to predict HAL measured using the pencil-beam DXA with a high degree of accuracy (R(2) > or = 0.96). The fan-beam-acquired values of HAL using our model are nonbiased and accurate estimates of the "gold standard" pencil-beam method. This model may provide researchers and clinicians with a simple method of calculating HAL using fan-beam DXA.
authors.affiliation: Division of Geriatrics, UCLA School of Medicine, 10833 Le Conte Avenue, Los Angeles, CA 90095-1687, USA. jyoung@mednet.ucla.edu
authors.forename: J T
authors.initials: JT
authors.lastname: Young
authors.forename: K
authors.initials: K
authors.lastname: Carter
authors.forename: M S
authors.initials: MS
authors.lastname: Marion
authors.forename: G A
authors.initials: GA
authors.lastname: Greendale
mesh_terms: D015502:Absorptiometry, Photon; D000328:Adult; D000886:Anthropometry; D015992:Body Mass Index; D005260:Female; D005269:Femur / Q000000981:diagnostic imaging*; D006615:Hip / Q000033:anatomy & histology*; D006801:Humans; D008875:Middle Aged