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

Abstract

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 our own patients, we observed a higher incidence of transient motor and sensomotor deficits after single-sitting anatomic correction of Mayerding grade IV anterolistheses and spondyloptoses. These findings are consistent with those of other authors. The deficits pertained to muscles in the innervation range of the L5 nerve root, without there being any evidence of intradural root damage or nerve compression. In vitro studies have shown distraction and translation of the nerve root to be pathogenetically relevant mechanisms, leading to damage during intraoperative reduction. Additional alteration of neuronal structures may be caused by ventral parts of the iliolumbar ligament complex during the reduction maneuver. In order to reveal extradural constrictions of the L5 nerve root that might predispose towards intra- or perioperative damage, we examined anatomic specimens to determine the course and neighboring relationships of the lumbosacral plexus, especially in relation to pelvivertebragenic ligamentous connections. In addition to the morphologic considerations, we conducted translation tests, which were designed to simulate changes in shape and size of the epineural layer, as well as in vitro measurements of the resulting pressure 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 nerve roots, we found a ligamentous connection formed by connective tissue between 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 constantly 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. The average pressure exerted on the nerve root during the distraction and translation process was over 30 mmHg in the area of this lumbosacral ligamentous connection, at a distance of greater than 20 mm. When the translation distance was further increased, perineural fatty tissue was discharged, due to increasing perineural pressure.