Bone remodeling in hip fracture.

Hip fracture incidence has shown strong upward secular trends in many societies with wide differences in age adjusted incidence between nations. Falls and reduced physical activity have emerged as the strongest risk factors in epidemiological studies, while clinical investigations have pointed to secondary hyperparathyroidism as an important candidate cause of the loss of femoral cortical bone in old age. Until recently there have been few studies performed directly on the region of interest in the proximal femur. Non-invasive methodology using 85Sr has now been developed by our group for measuring bone formation and (with concurrent serial DXA densitometry) resorption in the femoral neck. Bone turnover averaged about 8% annually in controls. A group of younger cases of femoral fracture showed similar indices of total and regional bone formation to a control group; but their resorption was higher. To further investigate this, a femoral neck bone biopsy technique has been developed which can be applied to fracture cases treated by arthroplasty. Preliminary studies have established that the anatomical asymmetry of the neck in cross-section is considerable and imposes restraints on the interpretation of smaller or incomplete femur biopsies. Prospects are quite good that, in the absence of tetracycline pre-labeling, mineralization can be studied by assessment of alkaline phosphatase-positive surfaces in cryostat sections. Moreover, such sections will permit study of other anatomically localized metabolic activities as well as antigen expression and osteocyte viability. Candidate mechanisms for the regional decline in bone quality as well as bone mass in subjects suffering hip fracture can now be investigated more effectively.