ABSTRACT
An algorithm was developed to estimate the strength of the femoral neck from data generated by the dual-energy x-ray absorptiometry (DXA). This algorithm considers shape of the proximal femur as well as cross-sectional moment of inertia (CSMI) in the estimate. Proximal femora (10) from cadavers of white adults and an aluminum step wedge were scanned with the Lunar DPX to validate the calculation of CSMI. After scanning, each femoral neck was sectioned at its narrowest portion for direct measurement of CSMI. Three healthy young women were scanned five times each to evaluate the reproducibility of geometric measurements using DXA. There was a strong linear association between the CSMI measured directly and using DXA in both cadaver bones (r2 = 0.96) and the aluminum step wedge (r2 = 0.99). The coefficient of variation for CSMI from repeated measurements using DXA was less than 3%. This indicates that it is possible to estimate reproducibly the bending rigidity of bone from DXA measurements. The data from 306 normal subjects were analyzed to investigate geometric changes in the femoral neck with age. Although there was no strong correlation between CSMI and age in normal subjects of either sex, safety factor (SF, an index of strength of the femoral neck during walking) and fall index (FI, an index of the strength of the femoral neck during a fall) decrease with age in both sexes. We observed an alteration of the geometric structure of the femoral neck with age that may increase the stress on the femoral neck and decrease SF and FI.
Subject(s)
Bone Density , Femur Neck/anatomy & histology , Absorptiometry, Photon , Adult , Aged , Aged, 80 and over , Aging/pathology , Algorithms , Biomechanical Phenomena , Female , Femur Neck/physiology , Humans , Male , Middle Aged , Reproducibility of Results , Tensile Strength , White PeopleABSTRACT
We compared two approaches for determining soft tissue baseline with dual energy X-ray absorptiometry (DEXA) of the spine. An average baseline for the entire L2-L4 region resulted in overestimation of the L2 density by 2% and underestimation of L4 density by 2% in 122 subjects. The results for the L2-L4 region, and for L3, were comparable with both approaches and the precision error in vivo also was comparable (0.8%).
Subject(s)
Absorptiometry, Photon/methods , Bone Density , Absorptiometry, Photon/statistics & numerical data , Adolescent , Adult , Aged , Aged, 80 and over , Female , Humans , Male , Middle Aged , Reference ValuesABSTRACT
To estimate the prevalence of antibody to human immunodeficiency virus-type 1 (HIV-1) among Wisconsin childbearing women (CBW), a continuous blinded HIV-1 seroprevalence survey is being conducted. This survey uses dried blood specimens obtained from infants as part of the Wisconsin Newborn Screening Program. From February 1989 through March 1990, 79,546 specimens from Wisconsin residents were tested for HIV-1 antibody, 21 (0.026%) were HIV-1 seropositive. Among specimens obtained from Milwaukee County CBW, 15 (0.076%) of 19,781 were HIV-1 seropositive compared to 6 (0.010%) of 59,765 obtained from other Wisconsin counties. After adjusting for maternal residence, Wisconsin minority CBW were six times more likely to be HIV-1 seropositive when compared to white CBW. The survey results underscore the need for strategies to prevent HIV-1 infection that focus on women of childbearing age in Wisconsin.
