Stress-strain curve analysis showing tissue level biomechanical performance.

Values are means ± SE of raw data; N, no of mice; PY, post-yield; MPa, megapascals.*Data analyzed using ANCOVA with a covariate of body mass.tData transformed to satisfy assumptions of normality and variance.rNon-transformable data was ranked.agenotype effect,bsex effect,cdiet effect,dgt*sex effect,egt*diet effect,fsex*diet effect,ggt*sex*diet effect.Yield strain: PKU mice fed GMP and casein had the highest strain at their yield point and PKU mice fed AA had the lowest. There was no difference between WT mice fed the three diets and PKU mice fed AA. Additionally, there was no difference between WT mice fed GMP and AA with PKU mice fed casein.PY strain: Males had a greater strain after yielding than females. WT mice had a greater strain after yielding than PKU mice.Total strain: PKU mice fed AA had a significant reduction in total strain and there was no difference across all other groups.Modulus: The three way interaction demonstrated that females tended to have bones with a higher intrinsic stiffness than males; WT females fed GMP and PKU females fed AA had a higher modulus than WT and PKU males fed GMP as well as PKU males fed casein. Additionally, WT females fed casein or AA had a higher modulus than PKU males fed casein. Among females, PKU mice fed casein had a significant reduction in intrinsic stiffness, moreover WT females fed all three diets and PKU females fed AA had a higher modulus than PKU females fed GMP. Among males, PKU mice fed casein had a significant reduction in modulus compared to male mice fed AA and there was no difference across the other five groups.Yield stress: Wild type mice tolerated more stress before yielding compared to PKU mice. Female mice tolerated more stress before yielding compared to male mice. Mice fed AA and GMP tolerated more stress before yielding compared to mice fed casein.Max stress: Female groups fed GMP and AA had a higher max stress before fracture compared to male groups and female mice fed casein had a higher max stress than males fed casein. Among females, groups fed GMP had the highest max stress, followed by AA and then casein. Among males, groups fed AA had a higher max stress than males fed casein, but males fed GMP were not different from the other two. PKU mice fed casein had a significant reduction in max stress compared to WT and PKU mice fed GMP and AA as well as WT mice fed casein.Toughness: WT mice had tougher bones than PKU mice, as measured by area under the stress strain curve.Failure stress: PKU mice fed AA had a higher stress at fracture compared to WT mice fed AA and PKU mice fed casein. WT mice fed casein and PKU mice fed GMP also had a higher stress at fracture compared to PKU mice fed casein.