NEEDLE TIP POSITION AND INJECTION SITE IN LUMBAR SELECTIVE NERVE ROOT BLOCKS

Abstract

Aim: To study the location of injectate when diagnostic selective nerve root blockade is performed.

Method: 87 consecutive selective nerve root blocks performed by a single surgeon were assessed. A consistent surgical technique was utilised for all patients. Antero-Posterior fluoroscopy films were analysed to determine the location of injectate in relation to the foraminal and pedicle anatomy.

Results: Of needle tips positioned lateral to the middle third of the superior pedicle on the AP view, 45 of 51 flowed into the nerve sheath alone, and 6 flowed into both the nerve sheath, and spinal canal. Of these 6, 2 were due to a larger volume of contrast injected, and 2 were due to abnormal anatomy from marked lumbar degenerative scoliosis. Of needle tips located below the middle third of the pedicle, 2 of 29 flowed into the nerve sheath alone, 2 flowed into the canal alone, and 27 flowed into both. Of those placed medial to zone below the middle third of the pedicle, all seven flowed into the canal only.

Conclusion: Care must be taken to ensure that the needle tip is positioned lateral to the zone below the middle third of the pedicle if a selective nerve root block is to be used for diagnostic purposes, particularly if there is significant deformity or no contrast is used. In the absence of deformity, however, selective nerve root block may be performed reliably, with a location accuracy of 96% providing the tip of the needle lies in the lateral position described.