Threshold testing of lumbosacral pedicle screws: a reappraisal

Older reports of unmonitored pedicle screw implantation during spine decompression/fusion suggest a low but finite additional clinical risk when compared with decompression/fusion without the use of pedicle screws. Intraoperative and/or postoperative computed tomography imaging has advanced our understanding of the key spatial relationships between screws, pedicle wall, and nerve roots. These combined data underpin and background reported series of monitored pedicle screw insertion. "Predicates" for well-done pedicle screw threshold test recordings are based on these data and newer knowledge of proper free-run and stimulated electromyography technique. The sum of the evidence indicates a continuous (rather than dichotomous) relationship between pedicle screw threshold test sensitivity versus specificity for breach. Also, there is a dubious connection between breach and clinical risk. Therefore, in the setting of healthy root and bone, it is suggested that alerts should be restricted to the lowest (most-specific) range of pedicle screw threshold test results.