抄録
We quantify structural strength of primate scapula (baboon, chimpanzee, and spider monkey) under different loading conditions using finite element (FE) analysis, in order to biomechanically evaluate the relationship between scapular form and locomotor habits. Three-dimensional FE models of their scapulae are generated using consecutive cross-sectional images retrieved from CT. Material property of the bone is assumed to be isotropic, uniform, and constant for all three. The coordinate system of each bone is locally defined by using morphological landmarks, so that equivalent loading conditions can be set for all. In order to approximate actual loading of the bones, the models are fixed at their vertebral boarder and forces are applied at the glenoid and acromion regions. Stress and strain distributions in the bones are then calculated while changing the direction of the force.
The results show that the chimpanzee gross scapular shape is relatively more rigid than that of baboons. In addition, it is selectively more resistive against tensil force to the glenoid in the cranioventral direction, whereas the baboon scapula does not show such directionality in structural strength. This suggests that the chimpanzee scapula may be mechanically adapted to the resultant force applied to it in unimanual suspension. The strength of the acromion is found to be relatively low in the chimpanzee model, but it was selectively rigid against a force in the lateral cranioventral direction, suggesting its mechanical relevance to suspension as well. In contrast, the relatively rigid baboon acromion seems to be adaptive to compressive force acting on it in terrestrial quadrupedal locomotion. The scapula of the spider monkey basically shows similar mechanical tendencies with those of chimpanzee since both are brachiators, but mechanical characteristics of its scapula happened to be unique, inferring that mechanical demands in their suspensory locomotion are essentially different, probably because of the use of the prehensile tail in locomotion in spider monkeys.
