Patient-specific finite element analyses detect significant mechanical therapeutic effects on osteoporotic vertebrae during a three-year treatment

Analyses of the bone mass alone of osteoporotic vertebrae are not sufficient to predict fracture risks and assess the recovery of bone strength during drug treatment. Instead, finite element analyses (FEAs) is superior, because changes in the vertebral strength are strongly dependent on the inner vertebral stress distribution, which is related to the individual bone shape and bone density distribution in cancellous and cortical region. To investigate how FEAs can detect drug effects, we performed patient-specific FEAs of the first lumbar vertebra of osteoporotic patients at five time points (before therapy, and after 6 and 12 months and 2 and 3 years of therapy) during a 3-year drug treatment with alendronate and vitamin D, in four osteoporotic female patients in this study. The FEAs revealed notable decreases in the compressive principal strains in cancellous bone, but these decreases did not necessarily correspond to increases in the bone densities. In addition, statistical analyses by Friedman's test (nonparametric analysis) showed that evaluation based only on the average compressive principal strains over the 3-year treatment identified drug effects significantly, suggesting that compressive principal strain is an useful indicators for monitoring drug effects. Our data implied that compressive fracture of the vertebrae may be prevented as a result of the drug treatment, in a manner that was optimally detectable by patient-specific FEAs. © 2011 by JSME.