To elucidate compositional changes of the tendon of the peroneus longus muscle with aging, the authors investigated age-related changes of elements in the insertion of tendons of the peroneus longus muscle (peroneus longus tendons) in Thai, Japanese, and monkeys and the relationships among element contents by direct chemical analysis. After ordinary dissections at Chiang Mai University and Nara Medical University were finished, the peroneus longus tendons were resected from the subjects. The peroneus longus tendons were also resected from rhesus and Japanese monkeys bred in Primate Research Institute, Kyoto University. The wraparound regions of the insertion tendons of the peroneus longus muscle in contact with the cuboid bone were used as the peroneus longus tendon. After ashing with nitric acid and perchloric acid, element contents were determined with an inductively coupled plasma-atomic emission spectrometer. It was found that there were no significant correlations between age and the seven elements, such as Ca, P, S, Mg, Zn, Fe, and Na, in the peroneus longus tendons of Thai and Japanese. The Ca content higher than 10 mg/g was contained in seven cases out of 34 peroneus longus tendons of Thai (incidence=20.6%) and in one case out of 22 peroneus longus tendons of Japanese (incidence=4.5%), respectively. All of the peroneus longus tendons with the Ca content higher than 10 mg/g were found in Thai and Japanese men. In the peroneus longus tendons of monkeys, the Ca and P content increased suddenly at 2 years of age and reached to about 40 mg/g at 5 years of age. Thereafter, the Ca and P content did not increase in the peroneus longus tendons of monkeys at old age. Regarding the relationships among element contents, significant direct correlations were found among the contents of Ca, P, Mg, Zn, and Na in Thai and monkeys, whereas significant inverse correlations were found between S and element contents, such as Ca, P, Mg, Zn, and Na, in Thai and monkeys.
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