Abstract
BackgroundThe mechanisms subserving deep spinal pain have not been studied as well as those related to the skin and to deep pain in peripheral limb structures. The clinical phenomenology of deep spinal pain presents unique features which call for investigations which can explain these at a mechanistic level.MethodsTargeted searches of the literature were conducted and the relevant materials reviewed for applicability to the thesis that deep spinal pain is distinctive from deep pain in the peripheral limb structures. Topics related to the neuroanatomy and neurophysiology of deep spinal pain were organized in a hierarchical format for content review.ResultsSince the 1980’s the innervation characteristics of the spinal joints and deep muscles have been elucidated. Afferent connections subserving pain have been identified in a distinctive somatotopic organization within the spinal cord whereby afferents from deep spinal tissues terminate primarily in the lateral dorsal horn while those from deep peripheral tissues terminate primarily in the medial dorsal horn. Mechanisms underlying the clinical phenomena of referred pain from the spine, poor localization of spinal pain and chronicity of spine pain have emerged from the literature and are reviewed here, especially emphasizing the somatotopic organization and hyperconvergence of dorsal horn “low back (spinal) neurons”. Taken together, these findings provide preliminary support for the hypothesis that deep spine pain is different from deep pain arising from peripheral limb structures.ConclusionsThis thesis addressed the question “what is different about spine pain?” Neuroanatomic and neurophysiologic findings from studies in the last twenty years provide preliminary support for the thesis that deep spine pain is different from deep pain arising from peripheral limb structures.
Highlights
Case scenario A 45-year old male presents with chronic lumbosacral pain and some pain in the posterior thigh
Their work was motivated by the observation of what they described as a distinctive “clinical phenomenology” of spinal pain
The questions asked here are: How is deep somatic spinal pain typically experienced by people with respect to its “where?” and its “with what?” and, “Why does spinal pain so frequently refer to distal sites and why does it so frequently persist and become chronic?”
Summary
Case scenario A 45-year old male presents with chronic lumbosacral pain and some pain in the posterior thigh. Back pain and an associated, but not causally connected problem in the posterior thigh (two separate problems) Both of these options share an acceptable clinical logic; their distinction would be made on the basis of further history and examination for signs that were consistent with one or the other explanation. The primary mechanism identified by Gillette et al [8] to explain the distinctive features of spinal pain was the phenomenon of multiple convergent afferent terminations on subsets of dorsal horn neurons They termed these subsets of neurons “low back neurons” and they identified numerous sources of convergent afferent input onto these neurons from superficial cutaneous sources, deep axial somatic sources (from the tissues identified above), deep distal somatic structures (muscles and joints of the lower limb), visceral structures, spinal dura and from the sympathetic fibres in the lumbar area. Gillette et al characterized these low back neurons as “hyperconvergent”; explaining the diffuse spread and poor localization of spinal pain as well as the centrifugal (distally-directed) tendency of somatic referral of spinal pain to multiple distal sources (depending on the spinal level of origin)
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