The Relationship between Form and Function of the Human Vertebra in Ordinary Posture and Movement.

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The aim of the present study is to investigate the relationship between form and function of the human vertebra in ordinary posture and movement by using material mechanics and the animal experiment. Vertebrae from the 3rd cervical to the last lumber vertebra of 52 modern Japanese (26 males and 26 females), 6 chimpanzees, 30 macaques (Japanese monkeys). And 6 Japanese serows were used in the present study. Moreover, the effects of an erect bipedal standing exercise on the morphology of vertebral body were investigated in seventeen growing male rats that were divided into two groups (8 controls and 9 exercises). The following results indicate the relationship between ordinary posture and movement of human vertebra. (1) Cross-sectional area (A) and the area moment of inertia of right-left axis (I_x) increased significantly in the lumbar vertebral region. (2) Area moment of inertia of antero-posterior axis (I_y) increased gradually from the 3rd cervical to the last lumbar vertebra, and reached a peak in the last lumbar vertebra. (3) Maximum principal moment of Inertia (I_max) increased remarkably from the 10th thoracic to the last lumbar vertebra. (4) Minimum principal moment of inertia (I_min) increased gradually from the 3rd cervical to the last lumbar vertebra. (5) Polar moment of inertia (I_p) increased remarkably from the 11th thoracic to the last lumbar vertebra. (6) Section index (SI) showed a tendency of shape changes from the circle into oval form in the cervical and lumbar vertebral region. (7) All values significantly increased in the human compared with other animals. Our results showed that lumbar vertebral region of human was considerably tough and strong, and that it could stand especially against the right-left bending force as compared with other animals.