Important macroscopic and microscopic differences in the bony and cartilaginous regions adjacent to the lumbar intervertebral disc between animal and man: a caveat to overinterpretation of animal experiments: comment to the article: Primary stability of anterior lumbar stabilization: interdependence of implant type and endplate retention or removal (C.H. Flamme et al.)

On how nucleus-endplate integration is achieved at the fibrillar level in the ovine lumbar disc

The intervertebral disc nucleus has traditionally been viewed as a largely unstructured amorphous gel having little obvious integration with the cartilaginous endplates (CEPs). However, recent work by the present authors has provided clear evidence of structural cohesion across the nucleus-endplate junction via a distinctive microanatomical feature termed insertion nodes. The aim of this study was to explore the nature of these insertion nodes at the fibrillar level. Specially prepared vertebra-nucleus-vertebra composite samples from ovine lumbar motion segments were extended axially and chemically fixed in this stretched state, and then decalcified. Sections taken from the samples were prepared for examination by scanning electron microscopy. A close morphological correlation was obtained between previously published optical microscopic images of the nodes and those seen using low magnification SEM. Progressively high magnifications provided insight into the fibrillar-level modes of structural integration across the nucleus-endplate junction. The closely packed fibrils of the CEP were largely parallel to the vertebral endplate and formed a dense, multi-layer substrate within which the nodal fibrils appeared to be anchored. Our idealised structural model proposes a mechanism by which this integration is achieved. The nodal fibrils, in curving into the CEP, are locked in place within its close-packed layers of transversely aligned fibrils, and probably at multiple levels. Secondly, there appears to be a subtle interweaving of the strongly aligned nodal fibrils with the multi-directional endplate fibrils. It is suggested that this structural integration provides the nucleus with a form of tethered mobility that supports physiological functions quite distinct from the primary strength requirements of the disc.

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

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 on-line 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 pre-existing 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.