Biomechanical spinal growth modulation and progressive adolescent scoliosis – a test of the 'vicious cycle' pathogenetic hypothesis: Summary of an electronic focus group debate of the IBSE

Abstract

There is no generally accepted scientific theory for the causes of adolescent idiopathic scoliosis (AIS). As part of its mission to widen understanding of scoliosis etiology, the International Federated Body on Scoliosis Etiology (IBSE) introduced the electronic focus group (EFG) as a means of increasing debate on knowledge of important topics. This has been designated as an online Delphi discussion. The text for this debate was written by Dr Ian A Stokes. It evaluates the hypothesis that in progressive scoliosis vertebral body wedging during adolescent growth results from asymmetric muscular loading in a "vicious cycle" (vicious cycle hypothesis of pathogenesis) by affecting vertebral body growth plates (endplate physes). A frontal plane mathematical simulation tested whether the calculated loading asymmetry created by muscles in a scoliotic spine could explain the observed rate of scoliosis increase by measuring the vertebral growth modulation by altered compression. The model deals only with vertebral (not disc) wedging. It assumes that a preexisting scoliosis curve initiates the mechanically-modulated alteration of vertebral body growth that in turn causes worsening of the scoliosis, while everything else is anatomically and physiologically 'normal' The results provide quantitative data consistent with the vicious cycle hypothesis. Dr Stokes' biomechanical research engenders controversy. A new speculative concept is proposed of vertebral symphyseal dysplasia with implications for Dr Stokes' research and the etiology of AIS. What is not controversial is the need to test this hypothesis using additional factors in his current model and in three-dimensional quantitative models that incorporate intervertebral discs and simulate thoracic as well as lumbar scoliosis. The growth modulation process in the vertebral body can be viewed as one type of the biologic phenomenon of mechanotransduction. In certain connective tissues this involves the effects of mechanical strain on chondrocytic metabolism a possible target for novel therapeutic intervention.

Does Removing the Spinal Tether in a Porcine Scoliosis Model Result in Persistent Deformity?: A Pilot Study

“…The mechanical modulation of vertebral body growth through asymmetric loading in the tethered spine is governed by the Hueter-Volkmann principle [2] (growth is retarded by increased mechanical compression and accelerated by reduced loading). Our observations are consistent with the ''vicious cycle'' theory proposed by Stokes et al [20][21][22]. We suspect the necessary initial bony dysplasia needed to obtain a mechanically ''self-progressive'' curve was not obtained in the autocorrective group.…”

“…When asymmetric mechanical loading was removed with release of the spinal tether, vertebral growth continued although at a slightly altered rate on the curve concavity as evidenced by the increase in coronal wedging between the tether release and tether intact groups. Continued progression of vertebral asymmetry after tether release again is consistent with the vicious cycle theory [21]. The induced vertebral asymmetry sets the stage for an altered mechanical environment leading to continued growth modulation.…”

Emerging Technology and Analytical Techniques for the Clinical Assessment of Scoliosis

“…Evidence from computational [26] and animal models [8] have supported the hypothesis that asymmetric loading of the spinal elements influences the development of vertebral deformities, and consequently progression of the spinal curve [7]. These models are in agreement with emerging evidence from biomechanical and neurophysiologic measures that suggest dysfunction of the neuromuscular system may be an additional factor and indicator of progression risk in IS.…”

Stretching Versus Mechanical Traction of the Spine in Treatment of Idiopathic Scoliosis

“…Although its ultimate cause is unknown, there is evidence to support that there are two types of pathogenic factors called initiating factors and progression factors for AIS 2) . There is consensus that curve progression involves a mechanical process called torsion with eccentric loading of the spine and vertebral growth modulation (vicious cycle model) 3).…”