Barycentremetry, spine disorders, posture and motion analysis.

PURPOSE OF THE RESEARCH: Prevention of spine disorders and their management require better understanding of related biomechanical issues. While tremendous progress has been performed for musculoskeletal modelling of the spine, subject specific modelling of the gravitational loads and their effects on the spine is still an issue. Recently, 3D reconstruction of the skeleton from biplanar head to feet X-rays in erect position has been completed by the external body envelope. An approach named "barycentremetry" has been proposed, based on density models to estimate the mass and centre of mass of each body segment, yielding a force plate less estimation of the gravity line, together with the estimation of the gravitational loads and the associated lever arm at each vertebral level.

PRINCIPAL RESULTS: Due to vertebral pose, gravitational loads effect on intervertebral disc shows wide variation. Studies exploring barycentremetry clinical relevance were analysed, particularly for adolescent idiopathic scoliosis, adult spinal deformities and osteoporosis. They progressively yield a better comprehension of the potential vicious circles linking postural disorder to increase of spine loads to increase of postural disorder. Barycentremetry was also explored within gait and motion analysis research, allowing to estimate subject specific body segments inertial parameters for patient specific dynamic analysis. Indeed, 3D musculoskeletal modelling of posture and motion could benefit from subject specific dynamic analysis based on barycentremetry.

MAJOR CONCLUSIONS: Such approaches progressively provide a better understanding of the stability of this complex system and compensation strategies that could be useful for early detection of disorders that are responsible of a biomechanical cascade.