Topographic relations between the neural and ligamentous structures of thelumbosacral junction: in-vitro investigation

Transient or persistent alterations in the. L5 lumbar nerve root have been described as a complication after the reduction of spondylolistheses. In a retrospective analysis of om: own patients, we observed a higher incidence of transient motor and sensomotor deficits after single-sitting anatomic co rrection of Mayerding grade IV anterolistheses and spondyloptoses. These fi ndings are consistent with those of other authors. The deficits pertained t o muscles in the innervation range of the L5 nerve root, without there bein g any evidence of intradural root damage or nerve compression. In vitro stu dies have shown distraction and translation of the nerve root to be pathoge netically relevant mechanisms, leading to damage during intraoperative redu ction. Additional alteration of neuronal structures may be caused by ventra l parts of the iliolumbar ligament complex during the reduction maneuver. I n order to reveal extradural constrictions of the LS nerve root that might predispose towards intra- or perioperative damage, we examined anatomic spe cimens to determine the course and neighboring relationships of the lumbosa cral plexus, especially in relation to pelvivertebragenic ligamentous conne ctions. In addition to the morphologic considerations, we conducted transla tion tests, which were designed to simulate changes in shape and size of th e epineural layer, as well as in vitro measurements of the resulting pressu re on the nerve. In addition to a range of variations in the attachment of the iliolumbar ligament complex, which was always located dorsally to the n erve roots, we found a ligamentous connection formed bu connective tissue b etween the sacrum and the fifth lumbar vertebral body on the caudal margin of the ligament apparatus in 14 out of 30 specimens. Its course was constan tly ventral to the L5 nerve root, which was also adherent to the periosteum of the sacrum distal to this constriction in one-fifth of the specimens. T he average pressure exerted on the nerve root during the distraction and tr anslation process was over 30 mmHg in the area of this lumbosacral ligament ous connection, at a distance of greater than 20 mm. When the translation d istance. was further increased, perineural fatty tissue was discharged. due to increasing perineural pressure.