The frequency of intradural conjoined lumbosacral dorsal nerve roots found during selective dorsal rhizotomy.

The frequency of occurrence of conjoined nerve roots (CR) in the cauda equina has been reported to range from 0.3% to 2%. We found intradural conjoined nerve roots in 13 of 123 (10.6%) patients undergoing selective dorsal rhizotomy for spasticity due to cerebral palsy. The anomaly occurred most commonly at L5-S1 and S1-S2. There was no consistent relationship to other anomalies of segmental anatomy. Our finding of a significantly higher number of conjoined nerve roots in these patients is primarily due to the surgical exposure of the entire cauda equina. This anomaly is more common than previous reports have indicated.