P6. Normal anatomy of the lumbar sublaminar ridge in the lateral recess with potential implications to surgical technique in degenerative spinal stenosis: a cadaveric study

BACKGROUND CONTEXT The lateral extent of the lumbar sublaminar ridge – the bony, superior insertion site of the ligamenta flava – and its topological relationship to the nerve root are not yet described in the literature. In the setting of degenerative lumbar stenosis this structure can hypertrophy and impinge the nerve root within the lateral recess even after excision of the corresponding ligamentum flavum. Failure to address this may contribute to failed lateral recess decompression. PURPOSE To provide anatomic descriptions of the normal lumbar sublaminar ridge in the lateral recess and it's potential to impact on the exiting nerve root there, with implications to surgical technique in lumbar spinal stenosis. STUDY DESIGN/SETTING This was a dissection study of preserved cadaver donor specimes from the McMaster University Department of Anatomy. PATIENT SAMPLE Fifteen donor cadavers from the McMaster University Department of Anatomy. OUTCOME MEASURES Observed anatomy of the lumbar sublaminar ridge in the lateral recess and its relations to the exiting nerve root there. METHODS Fifteen lumbar vertebrae, not obviously degenerated, were resected en bloc from three fixed adult human cadavers and then transected through the ventral base of the pedicles immediately dorsal to the floor of the central spinal canal and the PLL, leaving the posterior column and neural elements intact and articulated. The shape of the sublaminar ridge in each of these 30 lateral recesses and its relationship to the exiting nerve root were carefully examined from the ventral aspect of these specimens (ie, from the deep surface of the [laminas and] lateral recesses). RESULTS The exiting nerve root consistently crosses the sublaminar ridge immediately inferior to the mid-pedicle, lateral to the subarticular gutter and on the medial aspect of the true intervertebral foramen. A hypertrophic ridge can compress the exiting root by elevating the nerve root superiorly against the bony underside of the pedicle or displacing it anteriorly against the disc or vertebral body. CONCLUSIONS The sublaminar ridge in the lateral recess commony crosses or underscores the exiting nerve root and so if hypertrophied might potentially contribute to degenerative lumbar stenosis. Comprehensive appreciation of this anatomy and the need at surgery in the lateral recess to confirm that the exit nerve root is not compressed or elevated by the sublaminar ridge may facilitate thorough lateral recess decompression. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs.