• Jean Legaye and Ginette Duval-Beaupere.
• Department of Orthopaedic Surgery, University Hospital UCL Mont-Godinne, 5530, Yvoir, Belgium. jean.legaye@uclouvain.be.
• Eur Spine J. 2017 Nov 1; 26 (11): 2828-2833.

PurposeTo evaluate the influence of the position of the arms on the location of the body's gravity line.Previous DataThe sagittal balance of the pelvi-spinal unit is organized so that the gravity line is localized in a way that limits the mechanical loads and the muscle efforts. This position of the gravity line was analyzed in vivo, in standing position, the arms dangling, by the barycentremeter, a gamma rays scanner. Then, several teams had the same purpose but using a force platform combined with radiographies. Their results differed significantly among themselves and with the data of the barycentremetry. However, in these studies, the positions of the arms varied noticeably, either slightly bent forwards on a support, or the fingers on the clavicles or on the cheeks.MethodsWe estimated, for each varied posture of the arms, the sagittal coordinates of the masses of the upper limbs and their influence on the anatomical position of the gravity line of the whole body.ResultsUsing a simple equation and the data of the barycentremeter, we observed that the variations in the location of the gravity line were proportionally connected to the changes of the sagittal position of the mass of the upper limbs induced by the various positions of the arms.ConclusionsWe conclude in a validation of the data of the barycentremeter, as well as of the data obtained by the force platforms as long as the artifact of the position of the arms is taken into account.

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