[Analysis of stress distribution and site of favorable bending plane in the human humerus].

From human humerus diaphyses 5 cross-sections of well defined sites were taken. The shape of these cross-sections was described by x,y-coordinate data. The size of the cross-section area, the positions of the primary and secondary stress minimum as well as the positions of the primary and secondary stress maximum were analysed. The plane with the lowest average stress over the total area of the sites 1, 2 and 3 shifts about 58 degrees from medial = 0 degrees. The increase of stress in direction to the bending planes with a maximum of average stress is lower than 30%. The humerus diaphysis in the proximal part (sites 1, 2, 3) seems to be relatively well adapted to the movements of abduction, adduction, anteversion, and retroversion. However the plane of best adaption seems to be the sagittal one. The cross-sectional site 4 represents a transitional segment with 2 types of torsion of the plane of best adaption to bending stresses. Type A is characterised by a enormous torsion between the cross-sectional sites 4 and 5, type B between the sites 3 and 4. The plane with the lowest average stress of the cross-sectional site 5 is located by 127 degrees. In this plane the diaphysis seems to be well adapted to bending forces in a more sagittal plane.