Objective
To find the correlation between dorsal root ganglion location and abnormal superficial peroneal sensory nerve action potential (SNAP) response in L5 radiculopathy. Method: This retrospective study included thirty-three patients with unilateral L5 radiculopathy, who had no peripheral polyneuropathy, focal neuropathy or other metabolic disease and were under 60 years. 33 patients were classified to two groups: group I with an abnormal superficial peroneal SNAP response and group II with a normal superficial peroneal SNAP response. Using axial view of MRI, the location of dorsal root ganglion (DRG) of the study group was classified into intraspinal, intraforaminal and extraforaminal space. Results: In group I, 71% of L4 dorsal root ganglion was located in intraforaminal space, and 14% in extraforaminal space and 64% of L5 DRG was in intraforaminal space and 14% in intraspinal. In Group II, 42% of L4 DRG was located in intraforaminal space, and 58% in extraforaminal and 26% of L5 DRG in intraforaminal space and 63% in extraforaminal space. Group I subjects were more located in the intraforaminal space than Group II subjects (p＜0.05). Conclusion: In spite of belief that "radiculopathy involves the nerve root proximal to DRG", the significant proportion of dorsal root ganglion was located inside intraforaminal space. Thus the intraspinal lesion such as disc protrusion or spondylotic encroachment may compress DRG and cause abnormal findings of SNAP in EMG study. (J Korean Acad Rehab Med 2009; 33: 309-315)