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 nati ons. Falls and reduced physical activity have emerged as the strongest risk factors in epidemiological studies, while clinical investigation s have pointed to secondary hyperparathyroidism as an important candid ate cause of the loss of femoral cortical bone in old age. Until recen tly there have been few studies performed directly on the region of in terest in the proximal femur. Noninvasive methodology using ''Sr has n ow been developed by our group for measuring bone formation and (with concurrent serial DXA densitometry) resorption in the femoral neck. Bo ne turnover averaged about 8% annually in controls. A group of younger cases of femoral fracture showed similar indices of total and regiona l 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 arthr oplasty. Preliminary studies have established that the anatomical asym metry of the neck in cross-section is considerable and imposes restrai nts on the interpretation of smaller or incomplete femur biopsies. Pro spects are quite good that, in the absence of tetracycline pre-labelin g, 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 w ell as antigen expression and osteocyte viability. Candidate mechanism s for the regional decline in bone quality as well as bone mass in sub jects suffering hip fracture can now be investigated more effectively.