STRUCTURAL ANALYSIS OF HIP BONE MINERAL IMAGE DATA

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Reduction of skeletal structural strength is a prime cause of osteoporotic hip fractures among the elderly. While bone mineral analysis is widely used in assessment of fracture propensity in susceptible populations, conventional analyses do not adequately discriminate those at risk. We have developed an alternative technique based on a single plane bending stress analysis of the femoral neck, in a one legged stance. The work differs from previous efforts along these lines in that it uses data acquired by widely available, conventional bone mineral scanner systems. Moreover, the necessary structural properties of the femoral neck are computed directly from digital bone mineral image data, with an uncomplicated user interactive program. In addition to structural geometry, strength indices incorporating differences in loading and age changes in material strength, are also computed. Preliminary work indicates that structural geometry may be reliably obtained by the method and strength estimates for cadaver femora correlate better with experimentally measured strength than does conventional bone mineral density. This investigation will be designed to determine the intrinsic physical and biomechanical limitations of the method, and to compare its sensitivity and selectively to conventional bone mineral analysis, in both patients and cadaver specimens. Physical limitations will be examined with a computer model of the scanner system, incorporating system geometry, sampling considerations, source emission spectra and tissue attenuation properties. Secondly, a thorough investigation of patient positioning error on geometric measurements will be conducted with a realistic hip phantom. Thirdly, the validity of the single plane bending stress analysis will be evaluated by comparison with finite element analyses using hip image data. Results of these efforts will be used for refinement of the methodology for clinical implementation. Application to patient populations will begin with an examination of the contralateral hip of acute osteoporotic hip fracture subjects. In a larger scale effort, hip bone mineral data from several unrelated, on- going studies dealing with osteoporosis will be supplied for hip strength analysis. These studies include: subjects from the Baltimore Longitudinal Sample on Aging, subjects from two different studies of postmenopausal women under different treatment regimens, and para- and quadriplegic subjects studied serially post trauma, or with long standing paralysis.