The Anatomy of the Human Lumbar Ligamentum Flavum

Study Design An anatomic study was performed to investigate the ligamentum flavum of the human lumbar spine. Objectives To describe accurately the interlaminar portion of ligamentum flavum, and to determine if there is an insertion onto the anterosuperior surface of the caudal lamina. Summary of Background Data The insertions of the ligamentum flavum onto its adjacent laminas were classically described by Naffzinger. His description has been recounted by others. It has been the authors' observation that there is a slip of inferior ligamentum flavum that inserts onto the anterosuperior surface of the caudal lamina. Review of the literature revealed only anecdotal observations that support the authors' finding. A clear anatomic description of this structure is important to the surgeon who frequently enters the spinal canal at this anatomic site. Methods Thirty human lumbar ligamenta flava from six fresh frozen lumbar spines were studied macroscopically, with particular attention paid to the insertions onto the adjacent laminas. Results The ligamentum flavum consists of a superficial and a deep component. It is continuous in the midline. The superficial ligamentum flavum inserts onto the superior edge and posterosuperior surface of the caudal lamina. The deep ligamentum flavum inserts for a variable distance onto the anterosuperior surface of the caudal lamina. Conclusions There is an inferoventral slip of the ligamentum flavum that attaches to the anterosuperior surface of the caudal lamina. This slip is the inferior portion of the deep ligamentum flavum. When the ligamentum flavum's superficial layer is selectively released, the inferoventral slip of the ligamentum flavum's deep layer remains attached to the anterosuperior surface of the caudal lamina and remains between the surgeon and the dura.