Short term in vivo precision of proximal femoral finite element modeling

As more therapies are introduced to treat osteoporosis, precise in vivo met hods are needed to monitor response to therapy and to estimate the gains in bone strength that result from treatment. A method for evaluating the stre ngth of the proximal femur was developed and its short term reproducibility , or precision, was determined in vivo. Ten volunteer subjects aged 51-62 y ears (mean 55.6 years), eight women and two men, were examined using a quan titative computed tomography (QCT) protocol. They were positioned, scanned, repositioned and re-scanned. The QCT images were registered in three-dimen sional space, and finite element (FE) models were generated and processed t o simulate a stance phase load configuration. Stiffness was computed from e ach FE model, and strength was computed using a regression equation between FE stiffness and fracture load for a small set (n = 6) of experimental spe cimens. The coefficients of variation (COV) and repeatability (COR=2.23* ro ot 2*COV) were determined. The COV for the FE fracture load computed was 1. 85%, and the detectable limit (coefficient of repeatability) for serial mea surements was 5.85%. That is, if a change of 5.85% or more in computed FE f racture load is observed, it will be too large to be consistent with measur ement variation, but instead can be interpreted as a real change in the str ength of the bone. The detectable limit of this method makes it suitable fo r serial research studies on changes in femoral bone strength in vivo. (C) 2000 Biomedical Engineering Society.