title: An investigation of the diagnostic value of bilateral femoral neck bone mineral density measurements.
abstract: This paper describes a study to assess the clinical value of bilateral femoral neck bone mineral density (BMD) measurements. Although a range of factors will determine clinical decisions, the classification of the site with the lowest T-score is likely to have significant bearing on the management of a patient. While it is common practice to measure BMD at the lumbar spine and a single neck of femur, knowledge of the BMD of the second femur may also be of diagnostic value. Using dual-energy X-ray absorptiometry, BMD of the lumbar spine and right and left femoral neck was measured in a group of 2372 white, Caucasian women (mean age +/- SD, 56.6 +/- 13.9 years) routinely referred for bone densitometry. Analysis of the measurements showed a significant (p = 0.02) but small difference between the mean BMD of the right (0.840 +/- 0.152 g/cm2) and left (0.837 +/- 0.150 g/cm2) femoral neck. Further investigation of femur scans revealed 79 (3.3%) patients in whom one side was osteoporotic while the other side and spine were normal or osteopenic using the World Health Organization diagnostic criteria in combination with manufacturer's reference data. Patients in whom the femoral neck BMD measurements differed by less than the precision error of the system were then excluded. This left only 51 (2.2%) patients, that is 29 (1.2%) for right femur and spine scan and 22 (0.9%) for left femur and spine scan, in whom knowledge of both femoral neck BMD measurements could have altered the classification of the lowest site assessed to osteoporotic. These data suggest that there is only a small benefit from performing bilateral femoral neck BMD measurements. Since BMD measurements are only one of a range of factors considered as part of a patient's management, it is suggested that the extra time, cost and radiation dose associated with measurement of the second femur may not be justified.
authors.affiliation: Department of Medical Physics and Bioengineering, Southampton University Hospitals NHS Trust, UK. gwp@soton.ac.uk
authors.forename: G W
authors.initials: GW
authors.lastname: Petley
authors.forename: P A
authors.initials: PA
authors.lastname: Taylor
authors.forename: A J
authors.initials: AJ
authors.lastname: Murrills
authors.forename: E
authors.initials: E
authors.lastname: Dennison
authors.forename: G
authors.initials: G
authors.lastname: Pearson
authors.forename: C
authors.initials: C
authors.lastname: Cooper
mesh_terms: D015502:Absorptiometry, Photon / Q000379:methods; D015519:Bone Density / Q000502:physiology*; D005260:Female; D005272:Femur Neck / Q000000981:diagnostic imaging / Q000503:physiopathology*; D006801:Humans; D008875:Middle Aged; D010024:Osteoporosis / Q000000981:diagnostic imaging*; D011237:Predictive Value of Tests; D012680:Sensitivity and Specificity