The mean failure load and standard deviation of the normal BMD, osteoporotic and serious osteoporotic group.

<p>“*” stands for the presence of statistical difference between the subgroup B and C; “**” stands for the presence of statistical difference between the subgroup A and C; “***” stands for the statistical intergroup difference of subgroup A among the three BMD groups; “****” stands for the statistical intergroup difference of subgroup B among the three BMD groups; “*****” stands for the statistical intergroup difference of subgroup C among the three BMD groups.