The Electromyographic Responses to Dorsal Rootlet Stimulation during Partial Dorsal Rhizotomy Are Inconsistent

Abstract

Concerns have arisen regarding the ability of physiologic techniques to select rootlets mediating spasticity in children undergoing partial dorsal rhizotomy (PDR) for the treatment of spastic gait from cerebral palsy. To determine whether these physiologic responses are reproducible, 60 rootlets in 6 patients were graded from 0 to 4+ according to the system first reported by Phillips and Park, and then retested and graded using a randomized, blinded paradigm. Two thirds of the rootlets had one or more grade difference between the two trials, and 25% had a grade change of 3 or more. Only 4 of 23 rootlets with a ‘normal’ response (grade 0) on one test were also graded normal on the other test. Only 2 of 14 rootlets with a bilateral response (grade 4+) had a bilateral response on both trials. Statistical analysis demonstrated no correlation and poor agreement between trials. Regardless of whether responses are reflex in origin with technical or physiologic variability, or the consequence of stimulus spread to ventral roots, we found inconsistent responses with commonly used methods and the criteria most agreed upon. These findings suggest that currently used techniques are not reliable for rootlet ‘selection’ and result only in a random partial rhizotomy.

Selective dorsal rhizotomy: efficacy and safety in an investigator‐masked randomized clinical trial

“…1994Steinbok et 11. , 1995Ojemann et al 1997). experimental (Riven et al 1994, Warf andNelson 1996), and conceptual grounds (Pollack 1994, Burke 1995, Logigianet al 1996.…”

Gentle dorsal root retraction and dissection can cause areflexia: Implications for intraoperative monitoring during “selective” partial dorsal rhizotomy

“…Although skepticism about this time‐intensive monitoring technique has grown over the last decade, it is still routinely performed, even in the most recent controlled trials 17, 26, 33. It is our hope that this study, in the context of others,10, 13, 14, 21, 25, 31, 32 will help the intraoperative electrophysiologist to both escape the intuitive traps set by this monitoring technique and to recognize its significant limitations.…”

“…For example, extrasegmental spread to other ipsilateral leg muscles can be found in normal human subjects,25 and even to contralateral muscles in the decerebrate, spinalized cat 21. It has also been shown that there is marked variability of the responses from trial to trial,31, 32 and that there is poor correlation between the proportion of “abnormal” rootlets found intraoperatively and clinical measures of spasticity and motor function 10…”

Nonselective Partial Dorsal Rhizotomy: A Clinical Experience with 1-Year Follow-Up

“…Spatial facilitation, in which a nerve root demonstrates an abnormal response, while no individual rootlet can be identified as contributing to that response, has been documented [23, 24]. Furthermore, experimental studies have shown that intraoperative electromyographic responses of individual rootlets are inconsistent and not reproducible, further suggesting that current techniques are not reliable for rootlet selection [25]. …”