title: Clinical Implications of Hip Flexion in the Measurement of Spinal Bone Mineral Density.
abstract: The aim of this study was to investigate if differences in leg positioning affect spinal bone mineral density (BMD) measurements and the detection of low bone mass. Subjects included 1039 Japanese patients, 878 women and 161 men (mean ages: 67 and 71 years, respectively). Spinal BMD (L1-4) was measured using dual-energy X-ray absorptiometry (DXA) with patients lying in 2 different positions: (1) supine on the scanning table with hips flexed and knees flexed over a 90° support pad (the standard position) and (2) simply supine (the supine position). Predictive indices were calculated for spinal DXA acquired with patients in the supine position. A BMD T-score of -2.5 or lower was set as the threshold for low bone mass. For the standard and the supine positions during scanning in women, BMDs were 0.911 and 0.915 g/cm(2), respectively; in men, they were 1.117  and 1.124 g/cm(2), respectively. The estimated systematic bias in BMD between the positions was 0.42% (95% confidence interval: 0.24, 0.59; p = 0.009). Random errors in the densitometry measurements for the standard and supine positions were 0.66% and 0.84%, respectively. There was no significant difference between the errors (p= 0.164). The likelihood ratios of a positive and negative test for the detection of low bone mass following supine DXA were 121.0 and 0.066, respectively, compared with results acquired using the standard position. In conclusion, DXA measurements acquired with patients in the supine position slightly overestimated BMD vs the standard position. However, the clinical equivalency between the positioning methods for DXA is preserved to the extent that low bone mass can be reliably detected in the supine position.
authors.affiliation: Department of Orthopaedic Surgery, Shinshu University School of Medicine, Matsumoto, Japan. Electronic address: sh.ikegami@gmail.com.
authors.forename: Shota
authors.initials: S
authors.lastname: Ikegami
authors.affiliation: Center for Osteoporosis and Spinal Disorders, Kamimura Orthopaedic Clinic, Matsumoto, Japan.
authors.forename: Mikio
authors.initials: M
authors.lastname: Kamimura
authors.affiliation: Department of Orthopaedic Surgery, Shinshu University School of Medicine, Matsumoto, Japan.
authors.forename: Shigeharu
authors.initials: S
authors.lastname: Uchiyama
authors.affiliation: Department of Orthopaedic Surgery, Shinshu University School of Medicine, Matsumoto, Japan.
authors.forename: Yukio
authors.initials: Y
authors.lastname: Nakamura
authors.affiliation: Department of Orthopaedic Surgery, North Alps Medical center Azumi Hospital, Nagano, Japan.
authors.forename: Keijiro
authors.initials: K
authors.lastname: Mukaiyama
authors.affiliation: Department of Orthopaedic Surgery, Shinshu University School of Medicine, Matsumoto, Japan.
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Kato
mesh_terms: D015502:Absorptiometry, Photon / Q000379:methods*; D000368:Aged; D015519:Bone Density; D005260:Female; D006621:Hip Joint; D006801:Humans; D007564:Japan; D016013:Likelihood Functions; D008159:Lumbar Vertebrae / Q000000981:diagnostic imaging*; D008297:Male; D010024:Osteoporosis / Q000000981:diagnostic imaging*; D056888:Patient Positioning / Q000379:methods*; D012680:Sensitivity and Specificity; D013131:Spine / Q000000981:diagnostic imaging; D016683:Supine Position
keywords: Bone mineral density; dual-energy X-ray absorptiometry; lumbar spine; osteoporosis; supine position