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Scoliosis - Mechanical or Neurological?

Scoliosis is a condition that chiropractors are often called upon to identify and then manage. While there is significant awareness of scoliosis in the general population, it is not accompanied by much understanding of the underlying mechanisms that bring about spinal curvature. As such, there has been considerable room for unproven, or even disproven, treatment strategies - as well as theories of aetiology that just don't make sense. Is scoliosis a mechanical condition? Or is there something else at play?

In recent times there has been a shift in research attention towards brain-based models of scoliosis development. In particular, intriguing evidence has amassed that suggests a sensory disorder might underpin the problem of abnormal spinal curvature. Proprioception appears compromised in idiopathic scoliosis sufferers, leading to impaired static balance and postural control (1). Furthermore, these somatosensory inputs need to be combined with visual and vestibular sensation to provide an accurate three-dimensional perception of our bodies' positioning in space. This process of integration also seems compromised in scoliosis patients, leading to problems with dynamic control when our balance is challenged (2).
So is scoliosis a vestibular disorder?
Perhaps not. Children with hearing abnormalities are known to have a higher incidence of vestibular dysfunction, yet a lower rate of scoliosis than normal. More recent studies have homed in upon the {ulcortexPerhaps not. Children with hearing abnormalities are known to have a higher incidence of vestibular dysfunction, yet a lower rate of scoliosis than normal. More recent studies have homed in upon the cortex as the central player in scoliosis, even suggesting that the condition might actually be a form of dystonia (5). Indeed, many of the abnormalities in cortical processing that are seen in other forms of dystonia can be found in idiopathic scoliosis (IS) Authors Domenech et al point out;

The inappropriately increased motor activity, which is characteristic of dystonic patients, has been related to an unbalanced cortico-cortical modulation with decreased intracortical motor inhibition. Our results support the hypothesis that a dystonic disorder might underlay the pathogenesis of IS. A deregulation with hemispheric asymmetry in the modulation of the motor activity controlling spine posture at intracortical level could be the cause of progressive scoliotic deformity."

Functional MRI studies have also demonstrated over-activity of secondary motor areas of the cortex when compared to control subjects (6).
"Patients with IS showed a significant overactivation of the supplementary motor area (SMA) while performing the motor task as compared to healthy controls. SMA has a major role in selection, preparation, initiation and execution of voluntary movements, and also in posture control”So it just might be that scoliosis occurs when sensory information from all sources is inappropriately combined at a cortical level, with subsequent over-activation of motor circuits involved in postural control. If this is the case, then what of treatment strategies that view scoliosis through a purely mechanical paradigm? Does this mean that they have nothing to offer?  

As our understanding of spinal deformity grows, so too does our appreciation for the central neurological effects of spinal manipulation. Far from being a simple mechanical 'realignment', manipulation of the spine appears to influence the neuraxis at many levels. Heidi Haavik Taylor and colleagues have begun to assemble an impressive series of studies that look at changes to sensorimotor integration after cervical spine manipulation (7,8,9,10,11). Perhaps the clinical improvements that we sometimes observe in idiopathic scoliosis following spinal manipulation represent enhancements in sensorimotor control? After all, a chiropractic adjustment appears to offer a ‘novel’ blend of sensory input that might modulate central function in a positive fashion, enabling greater control posture, balance and symmetry of the spinal musculature. The difficulty we face, however, is the lack of predictability that comes with this approach.
In any case, I think that the time has come to finally put the ‘carrying the school bag on one shoulder’ theory to rest...
Dr Matthew D. Long - BSc. M.Chiro

(This article has been reprinted with permission  from Dr Matthew D Long .The numbers throughout this article refer to a full list of references available at reception on request)

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