How reliable is lumbar nerve root sheath infiltration?

To determine the reliability of lumbar nerve root sheath infiltration, a prospective study was performed. Ninety-four patients were randomized into three groups. In the first group of 33 patients, 0.5 cc of dye (Telebrix N, 30 g) was applied at nerve root L4, in the second group of 30 patients, 1.0 cc, and in the third group of 31 patients, 2.0 cc. The infiltration was guided by computer tomography. The diffusion of the dye was documented with computed tomography of the affected segment L4-5. The images were evaluated by an unbiased observer. The results showed that in the first group the dye diffused to the adjacent ipsilateral nerve roots L3 and/or L5 in nine patients. In the second and third groups this diffusion was seen in 9 and 11 patients, respectively. A diffusion into the psoas muscle was documented in 4, 10 and 22 patients, respectively. These latter differences were statistically significant (P < 0.01). Diffusion into the psoas muscle is especially important because the nerve roots converge in this muscle to become a plexus, and they are no longer surrounded by their dural sheaths. Diagnostic lumbar nerve root sheath infiltration should be performed by an experienced examiner. To guarantee high reliability, the tip of the needle should be placed as near as possible to the affected nerve root. The amount of local anaesthetic should be as small as possible, 0.5 cc or preferably less.