Background: Selective lumbar nerve root blocks (SLNRB) are widely used as a diagnostic tool. The usefulness of this technique depends on the ability to accurately infiltrate the desired nerve root without blocking the traversing nerve root to the next level. The aim of this retrospective study was to ascertain the accuracy of SLNRB’s in adult deformity.

Method: 30 SLNRB’s were performed by one surgeon on patients with adult deformity.Pre-operative AP + lateral lumbar films were used to quantify the degree of deformity using the Schwab grading system. An AP fluoroscopic film was taken and analysed to determine the flow of injectate in relation to pedicle anatomy. The results were analysed to determine the accuracy of SLN-RB’s in adult deformity.

Results: Of the 30 patients with deformity 17 needle tips were positioned lateral to the middle third of the pedicle and 13 under the middle third of the pedicle. Of the 17 needle tips placed laterally 8 (47%) had flow into the nerve root sheath, 6 (35%) into the nerve root sheath + canal and 3 (17%) into the canal alone. Overall accuracy with no epidural spread was 40% compared the published standard of 61%.

Conclusions: The accuracy of SLNRB in adult deformity was significantly less than the published standard in patients without deformity. In addition the accuracy of SLNRB with needle tip position lateral to the pedicle was only 47% compared to 96% in previous studies. The suggestion of this author is that contrast is used in all SLNRB’s in patients with deformity in order to allow accurate clinical interpretation of results.