Development of an in-vivo method to estimate the personalized 3D mass moment of inertia of the scoliotic trunk

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The general objectives of this proposal are to 1) develop a clinical method for estimating the in vivo personalized three-dimensional (3D) moment of inertia of the scoliotic trunk using an inverse dynamic approach and to 2) validate it. In adolescent idiopathic scoliosis (AIS), changes in the spine and rib cage develop progressively leading to a serious trunk deformity. Since spinal deformity often progresses, the moment of inertia is constantly changing at each clinical visit. This has a repercussion on the mobility of the trunk and its rigidity. Presently there is no clinical method for estimating the in vivo personalized moment of inertia of the ever changing scoliotic trunk though different methods have been proposed to estimate the body segment inertial properties. Anthropometric tables derived from cadavers do not truly represent the adolescent female population or scoliotic girls and can not be adapted for changing trunk shape. The first specific objective is to adapt our 3D inverse dynamic pendulum model to estimate the moment of inertia of the whole body when the subject willingly oscillates about the ankles. Normally, the muscle moment is the unknown value in an inverse dynamic calculation but can be eliminated using substitution leaving only the moment of inertia as the unknown. The parallel axis theorem can then be used to estimate the moment of inertia of the scoliotic trunk since that of the whole body and that of the un-deformed body segments are known. The second specific objective is to apply a similar approach using the angular momentum equation. The third specific objective is to compare our results with other accepted methods such video-based systems, our universe pendulum method or that of an oscillating table, etc. This work addresses for the first time the personalized in vivo mass moment of inertia of the scoliotic spine. Because scoliosis is a 3D deformation of the spine leading to changes in the trunk and that body morphology strongly affects standing stability and trunk mobility. It is reasonable to advance that modifications in the moment of inertia may be link to standing imbalance in scoliotic patient.