The Morphology and Possible Clinical Significance of the Intraforaminal Ligaments in the Entrance Zones of the L1-L5 Levels.

BACKGROUND: The extraforaminal ligaments between the L1-L5 lumbar spinal nerves and the tissues surrounding the intervertebral foramina (IVF) have been well studied. However, little research has been performed to describe the local anatomy of the entrance zones at the L1-L5 level. Detailed anatomic studies of the intraforaminal ligaments (IFLs) in the entrance zones at the L1-L5 levels have not been performed.

OBJECTIVES: The objective of this study is to identify and describe the IFLs in the entrance zones of the L1-L5 IVF and to determine their possible clinical significance.

STUDY DESIGN: A dissection-based study of 10 fresh-frozen human cadavers.

SETTING: Guangdong Provincial Key Laboratory of Medical Biomechanics in Anatomy Department of Southern Medical University.

METHODS: Eighty L1-L5 IVF from 10 fresh cadavers were studied, and the IFLs in the entrance zones were identified. The quantities, morphologies, origins, insertions, and spatial orientations of the IFLs in the entrance zones of the L1-L5 IVF were observed. The lengths, widths, diameters, and thicknesses of the ligaments were measured using a vernier caliper. Ten intraforaminal radiating ligaments were removed for histological examination.

RESULTS: A total of 197 ligaments were identified in the entrance zones of the 80 L1-L5 IVF, including 191 (96.95%) radiating ligaments and 6 (3.05%) transforaminal ligaments. The thickest ligaments were observed at the L3-L4 IVF. The lengths of the ligaments varied from 0.59 to 11.92 mm. There were 66 (33.50%) ligaments in the superior aspect of the entrance zone of the IVF, 58 (29.44%) ligaments at the anterior aspect, 43 (21.83%) ligaments at the posterior aspect, and 30 (15.23%) ligaments at the inferior aspect. The morphologies of the IFLs were divided into 2 types: the strap type and the trabs type. Histological examination of the meningovertebral ligaments revealed fibrous connective tissue.

LIMITATIONS: The major limitation of this study is the lack of actual clinical data from live patients. In addition, future medical biomechanics experiments are expected to contribute more objective data on the strength of the IFLs.

CONCLUSIONS: In the lumbar spine, IFLs are common structures in the entrance zones of the L1-L5 IVF, and radiating ligaments are more likely to be present.

KEY WORDS: Clinical Anatomy, microdissection, intraforaminal ligament, the entrance zone, L1-L5 intervertebral foramen, endoscopic spinal adhesiolysis, sacral hiatus, cerebrospinal fluid leakage, dural laceration.