Normal stress pattern of the pubic symphysis

The pelvic ring is stressed by external forces: by partial body weight, by ligament tension, and by muscles forces stabilizing the hip joints. For the symphysis ossis pubis there exist data concerning the type and magnitude of stresses. In one-leg-standing pressure, shear forces are predominant, and in both-leg-standing tensile forces are acting on the pelvic ring. Rupture of the symphysis is problematic due to the variety of its movements. Most literature descriptions of stress in the symphysis reflect only the frontal plane. Our intention was to make morphological as well as experimental investigations on the symphysis ossis pubis to delineate how it will be stressed in the horizontal plane. Twenty pubic bones taken from embalmed adult human cadavers (12 male, 8 female) were used. Horizontal and frontal slices (3 mm thick) of the symphyseal part of the os pubis were made. X-rays and densitometric analysis were performed. The width of the symphysis cartilage in the dorsal and the ventral regions was measured on 15 whole skeleton specimens coming from adult human cadavers. For experimental study an embalmed pelvic ring which had no abnormality was used. The symphysis pubis was cut completely in the midsagittal plane and then the ring was stressed via the cranial sacrum. Our results demonstrate that the symphysis is stressed by bending in the horizontal plane in one-leg-standing. In both-leg-standing the symphysis is stressed by tensile forces.