Following peripheral nerve injury, there is an invasion and activation of macrophages, T-lymphocytes and satellite glial cells in the DRG. Inflammatory mediators released from these immune cells may result in ectopic activity of DRG neurons. Given the close proximity of cell bodies from different peripheral nerves within a DRG, neuro- inflammation around affected DRG neurons may also alter the firing threshold of adjacent intact neurons originating from different sites. Therefore, neuro-inflammation in the dorsal root ganglia (DRGs) is a plausible explanation for the clinically observed spread of symptoms to extraterritorial areas. For example, tarsal tunnel syndrome may induce neuro inflammation in the L4 DRG, which may lower the firing threshold not only of tibial nerve neurons, but also of the fibular and femoral nerve neurons. As a consequence, symptoms and hypersensitivity may occur in other areas than those innervated by the entrapped tibial nerve at the ankle.
Local inflammation to a peripheral nerve will create hypersensitivity. It will also provoke an inflammatory response within the dorsal root ganglion at that spinal level. This can lead to sensitization of surrounding neurons and create widespread sensitization resulting in perceived expansion of pain. So can tarsal tunnel syndrome create hip and knee pain? According to Schmid et al. 2013—Yes.
Schmid AB, Coppieters MW, Ruitenberg MJ, McLachlan EM. Local and remote immune-mediated inflammation after mild peripheral nerve compression in rats. J Neuropathol Exp Neurol 2013;72:662-80
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