Introduction. The lateral extent of the sublaminar ridge – the bony, superior insertion site of the ligamenta flava – and its topological relationship to the nerve root are not described in the literature. Through anatomic dissection of healthy specimens we 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. 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.

Methods. Fifteen lumbar vertebrae, not obviously degenerated, were resected en bloc from three fixed adult human cadavers and then transected through the pedicles, leaving the posterior column and neural elements intact and articulated. The shape of the sublaminar ridge in the lateral recess and its relationship to the exiting nerve root were carefully examined.

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.

Conclusion. The sublaminar ridge in the lateral recess may contribute to degenerative lumbar stenosis, and failure to address it at surgery may account for the frequent clinical failure of spinal stenosis surgery. Comprehensive appreciation of this anatomy may facilitate thorough lateral recess decompression.