H reflex studies in cerebral palsy patients undergoing partial dorsal rhizotomy.

H reflex studies were performed in ten spastic children with cerebral palsy who underwent partial dorsal rhizotomy (PDR). Under anesthesia prior to PDR, H reflex amplitude evoked by percutaneous peripheral nerve stimulation gradually declined in all patients and became unobtainable in five. Motor responses could still be evoked by apparent dorsal root stimulation in these five, but since it was shown that they were M responses and not reflexes, PDR was performed randomly. In the other five patients, in whom H reflexes were still evokable, dorsal root stimulation evoked motor responses which were true reflex responses, and PDR was performed "selectively." Compared to preoperative values, postoperative Hmax/Mmax ratios declined, but no more so in selective than in random PDR. We conclude that current intraoperative methods for selection of "abnormal" dorsal rootlets for section may be invalid and may have no bearing on successful outcome, since spasticity improves even with random PDR.