Comparison of EMG Waveforms versus Degree of Spread in Selective Dorsal Rhizotomy

Selective dorsal rhizotomy (SDR) is a treatment for lower-extremity spasticity in disorders such as cerebral palsy (CP). "Selective" refers to sectioning nerve rootlets with the most abnormal responses on electromyography (EMG) upon intraoperative stimulation. EMG abnormalities can be classified by waveform appearance or by degree of spread throughout lower extremity muscles. We examine the relationship between different EMG waveforms and grades of spread. Intraoperative SDR EMG records from November 2009 through December 2021 were analyzed for waveform types and degrees of spread. Irregular, incremental, multiphasic, sustained, and clonic waveform patterns were considered more abnormal. Decremental, squared decremental, and squared waveforms were less abnormal. Degrees of spread were graded 0-4+, 4+ signifying the most abnormal spread. Distribution of grades of spread was compared between waveform patterns using pairwise Cochran-Armitage tests with Holm-Bonferroni correction. We hypothesized that more abnormal EMG waveform patterns would correlate with higher grades of spread. Sixty-three patients were included, with an average age of 8 years. Most had cerebral palsy (86%, n = 54). The remainder had brain malformations (8%, n = 5) and other etiologies (6%, n = 4). Higher grades of spread significantly increased the likelihood of multiphasic, sustained, or clonic patterns, compared to decremental, irregular, and squared patterns (p < .05). Squared waveforms decreased with higher grades of spread relative to other patterns (p < .05). Different EMG waveform patterns are associated with varying grades of spread in SDR, suggesting that evaluating both waveform pattern and degree of spread together can be useful in guiding rootlet sectioning.