Absorptiometry, Photon Adult Age Factors Aged Aged, 80 and over Biomechanical Phenomena Body Weight Bone Density--physiology Case-Control Studies Female Femoral Neck Fractures--etiology Hip Fractures--epidemiology Hip Joint--anatomy & histology Hormone Replacement Therapy--methods Humans Male Middle Aged Osteoporosis--complications Prognosis Risk Assessment Sensitivity and Specificity