Obstetrical lumbosacral plexus injury.

Injuries to the lumbosacral plexus during labor and delivery have been reported in the literature for years, but have lacked electrophysiologic testing to substantiate the location of the nerve injury. We report 2 cases with comprehensive electrophysiologic testing which localizes the site of this obstetrical paralysis to the lumbosacral trunk (L4-5) and S-1 root where they join and pass over the pelvic rim. The paralysis may be mild or severe. Small maternal size, a large fetus, midforceps rotation, and fetal malposition may place the mother at risk for this nerve injury.