Variability of the spine and pelvis location with respect to the gravity line: a three-dimensional stereoradiographic study using a force platform

Abstract

Analyzing standing posture requires a precise measure of the orientation of the various body segments with respect to the gravitational vector. We studied the posture variability of 34 healthy upright standing subjects. Using a force platform combined with a powerful stereoradiographic technique, we acquired the spine and pelvis three-dimensional (3D) geometry and located it with respect to the gravity line. For our data set, the mean 3D distance between the geometrical center of each vertebral body and the gravity line was 28 mm with a standard deviation of 5.6 mm. The vertebrae location variability, defined as plus or minus twice the mean standard deviation, was +/-40 mm in the sagittal plane and +/-25 mm in the frontal plane. The line connecting the middle of the external acoustic meatus (center of both acoustic meati: CAM) to the middle of the bi-coxo-femoral axis (hip axis: HA) was almost vertical. Its mean distance to the gravity line was 30 mm. Our data show a left lateralization, with respect to the gravity line, of the "Head-Spine-Pelvis" segments. The mean distance was 7.6 mm (SD 1.6 mm). This might be due to uneven partitioning of the body mass on each side of the sagittal plane.

3D postural balance with regard to gravity line: an evaluation in the transversal plane on 93 patients and 23 asymptomatic volunteers

“…From HA to T9, the results of the present study are consistent with the study of Gangnet et al [8]. T4, T1 and the CAM are more posterior in our study, which can be a consequence of the particular positioning of the patient (hand leaning on handle fixed at eyes' level).…”

“…Previously reported positions of elements with regard to GL on asymptomatic volunteers that adopted similar positioning of the patient during the acquisition [8,10,11] were analyzed. From HA to T9, the results of the present study are consistent with the study of Gangnet et al [8].…”

“…Figure 9 presents the mean and SD of the values already published and those evaluated in the present study. The 3D reconstructions in Gangnet et al [8] yielded reference values for the frontal and the sagittal planes and allowed the calculation of the 3D distance.…”

“…After registration, the 3D position of each element of the followings was calculated with regard to GL: -CAM, center of both acoustic meatus as defined in Gangnet et al [8]. -HA, middle of the line joining the centers of both acetabula as defined in Jackson et al [2].…”

“…Gangnet et al [8] showed that the center of acoustic meati (CAM) remains near GL and proposed evaluating the distance from CAM to HA to quantify sagittal balance. Besides, Vital and Senegas [9] underlined the proximity of this landmark to the center of gravity of the head, which role in 3D posture should be essential because of its weight, its distal location and the willing to keep a horizontal sight.…”