A Barycentremetric study of the sagittal shape of spine and pelvis: the conditions required for an economic standing position.

The standing posture of 17 young men and women were studied using Barycentremeter measurements and full spine radiograph with a single referential system. These procedures provide in vivo measurements of the weight and center of weight supported by each vertebra and the coxofemoral joints. The relationship between the vertebra, the sacrum or the coxofemoral rotation axis and the center of weight they support, is displayed. The moment of the corresponding force may also be assessed. Mean values were computed and the relation with spine sagittal curves and pelvic parameters were studied. The position of the center of weight, in front of or behind the vertebra or the coxofemoral joints, requires an opposing muscle force to ensure mechanical stability. The load exerted on the vertebra cannot be precisely evaluated, but we can describe the way in which these loads vary when the spinal curves and the pelvic slope change. This study provides basic data suggesting that there is a tendency to maintain the body in the most economical position in terms of muscle fatigue and vertebral strain. Individual anatomical shapes and pelvic parameters of the pelvis induce corresponding specific sagittal curves of the spine. This concept is very useful for analysing pathological situations and devising appropriate treatment.