149 THE “THREE JOINT COMPLEX” MODEL FOR PROGRESSION OF IDIOPATHIC SCOLIOSIS

Abstract

It was previously postulated that the IV disc wedging is a significant progressive factor for mild IS curves. The present report introduces an innovative comprehensive model of IS curves progression based on intervertebral disc (IV) diurnal variation and the subsequent patho-biomechanics of the deforming “three joint complex”, where vertebral growth occurs.

Throughout day and night, due to sustained loading and unloading, the scoliotic wedged IV disc expels fluid and imbibes it more convex-wise. The convex side of the IV sustains a greater amount of cyclic expansion than the concave side. Consequently the imposed, convex-wise, asymmetrical concentrated cyclical loads to the adjacent immature vertebral end plates and posterior elements of the spine lead to asymmetrical vertebral growth. More specifically the loading on the two facet-joins asymmetrically increases during the day, as the wedged IV space narrows due to expelled water and it asymmetrically decreases during the night, as the IV space swells due to imbibed water.

This 24 hour period cyclic asymmetric loading leads both to asymmetric growth of the end plates and wedging of the vertebral bodies, and to similarly asymmetric growth of the pedicles and arches posteriorly as an effect of Hüeter-Volkmann law. This model explains the well described anatomical findings of the more elongated pedicles and the larger facet joints in the convex side than in the concave in scoliotic spines