Lumbosacral Conjoined Root Anomaly: Anatomical Considerations of Exiting Angles and Root Thickness

Conjoined nerve roots (CNR) can be damaged during lumbar disc surgery and lead to neuropathic pain due to excessive retraction. The purpose of this study was to investigate the factors that facilitate the identification of CNRs that can lead to the loss of fragments in the secondary axilla, nerve root injury or unpleasant surprises during lumbar disc surgery. Accordingly, we aimed to measure the thicknesses and exit angles of the nerve roots close to the pedicle to obtain scientific data regarding rare double roots.

The data of 612 patients who were operated for lumbar disc disease in our hospital between 2012 and 2014 were reviewed retrospectively. Twenty one cases of CNR were detected in this series.

The mean nerve root thickness was 1.92 ± 0.45 mm for medially located roots and 3.33 ± 0.95 mm for laterally located roots. The comparison of medially located roots versus laterally located roots revealed a significant difference in mean values (p < 0.0001). The mean exit angle was 12.290± 4.890 for medially located roots, and 22.110 ± 5.420 for laterally located roots (p < 0.0001). In addition, the exit angles of the medially and laterally located roots increased as going down to caudal levels, (p=0.005, p=0.042).

CNRs are congenital anomalies that are usually diagnosed during the surgical procedure and affect the success of discectomy. The presence of a more medially located or thinner root during surgical exploration and the absence of the fragment in the axilla in extruded or sequestered discs usually indicate a conjoined nerve root closer to the pedicle.