The morphology and clinical significance of the intraforaminal ligaments at the L5–S1 levels

Abstract Background Context The extraforaminal ligaments between the L5 and S1 lumbar spinal nerves and the tissues surrounding the intervertebral foramina have been well studied. However, little research has been undertaken to describe the local anatomy of the intraforaminal portion of the L5–S1 spine and detailed anatomical studies of the intraforaminal ligaments (IFLs) of the L5–S1 have not been performed. Purpose The objective of this study was to identify and describe the IFLs in relation to the L5–S1 intervertebral foramen (IVF) and to determine their clinical significance. Study Design A dissection-based study of five embalmed and five fresh-frozen human cadavers was carried out. Methods Twenty L5–S1 intervertebral foramina from five embalmed cadavers and five fresh cadavers were studied, and the IFLs were identified. The quantity, morphology, origin, insertion, and spatial orientation of the IFLs in the L5–S1 region were observed. The length, width, diameter, and thickness of the ligaments were measured with a vernier caliper. This study has been supported by grants from the National Natural Science Foundation of China (Grant No. 31271286) without potential conflict of interest-associated biases in the text of the paper. Results The IFLs could be found from the entrance zone (inside) to the exit zone (outside) of the L5–S1 IVF. These ligaments were found to be of two types: a radiating ligament, which connected the nerve root sleeves that radiated to the transverse processes and wall of the IVF, and a transforaminal ligament, which connected the structures around the IVF. In our study, the radiating ligaments were found more often than the transforaminal ligaments. Conclusions The results demonstrate that IFLs are common structures in the IVF and that there are two types of IFLs: the transforaminal ligaments and the radiating ligaments. Transforaminal ligaments may be the potential cause of back pain. The radiating ligaments may contribute to dura laceration and epidural hemorrhage during endoscopic spinal adhesiolysis through the sacral hiatus, and an appreciation of this relationship might help reduce the risk of such complications.