Spinal Manipulation Reduces Pain and Hyperalgesia After Lumbar Intervertebral Foramen Inflammation in the Rat

To document potential mediating effects of the Activator-assisted spinal manipulative therapy (ASMT) on pain and hyperalgesia after acute intervertebral foramen (IVF) inflammation. The IVF inflammation was mimicked by in vivo delivery of inflammatory soup directly into the L5 IVF in adult male Sprague-Dawley rats. Thermal hyperalgesia and mechanical allodynia were determined by the shortened latency of foot withdrawal to radiant heat and von Frey filament stimulation to the hind paw, respectively. Intracellular recordings were obtained in vitro from L5 dorsal root ganglion (DRG) somata. DRG inflammation was examined by observation of the appearance and hematoxylin and eosin staining. ASMT was applied to the spinous process of L4, L5, and L6. A series of 10 adjustments were initiated 24 hours after surgery and subsequently applied daily for 7 consecutive days and every other day during the second week. (1) ASMT applied on L5, L6, or L5 and L6 spinous process significantly reduced the severity and duration of thermal and mechanical hyperalgesia produced by the IVF inflammation. However, ASMT applied on L4 did not affect the response in rats with IVF inflammation or the controls; (2) electrophysiological studies showed that hyperexcitability of the DRG neurons produced by IVF inflammation was significantly reduced by ASMT; (3) pathological studies showed that manifestations of the DRG inflammation, such as the increased vascularization and satellitosis, were significantly reduced 2 to 3 weeks after ASMT. These studies show that ASMT can significantly reduce the severity and shorten the duration of pain and hyperalgesia caused by lumbar IVF inflammation. This effect may result from ASMT-induced faster elimination of the inflammation and recovery of excitability of the inflamed DRG neurons by improving blood and nutrition supplement to the DRG within the affected IVF. Manipulation of a specific spinal segment may play an important role in optimizing recovery from lesions involving IVF inflammation.