An analysis of action of intercostal muscles in human upper rib cage

The actions of the intercostal and paraspinal muscles in stabilizing the human upper rib cage have been analyzed using a geometrically realistic mathematical model of the first six ribs, vertebrae, and associated musculature. The model suggests roles of the deep layers of erector spinae in stabilizing the vertebral column so that it can support the loads placed upon it by the ribs under physiological load. If we assume that the tension exerted by an intercostal muscle is proportional to its local thickness, the model predicts that the observed distribution of intercostal thickness is close to that which minimizes the stresses in ribs when the model is subjected to peak physiological load. The observed shape of the ribs are optimal to withstand the calculated pattern of loading along their length. These calculations raise the hypothesis that the arrangement of intercostal musculature and rib geometry result in an optimally light rib cage, which is capable of withstanding the loads placed upon it. The analysis of the mechanics of the entire model indicates that the geometrical simplifications made in Hamberger's model are not valid when applied to the rib cage.