Morphology and distribution of the intraforaminal ligaments at the L5/S1 level

English Keywords:Intraforaminal ligament  L5/S1 intervertebral foramen  Endoscopic adhesiolysis

English Abstract:

  【Abstract】 Objectives: To identify the intraforaminal ligaments in relation to the L5/S1 intervertebral foramen, and to evaluate their clinical significance. Methods: 5 embalmed cadavers and 5 fresh cadavers were studied(age: 42 to 80 years， average age, 51 years). The soft tissues around the spine were removed and the structure in median sagittally was exposed. The spinal nerve roots within the fascia were identified at their individual intervertebral foramen by meticulously removing the overlying remnants of the muscle, adipose tissue and the fascia. The quantity, morphology, origin, insertion and the spatial orientation of intraforaminal ligaments in the L5/S1 region were observed. And the length, width and diameter or thickness of ligaments were measured with a vernier caliper. Comparisons of different ligament histological types with HE staining and Masson trichrome staining were carried out and analyzed. Results: A total of 215 ligaments were found in 20 L5/S1 intervertebral foramina, and there were 90 strip-shaped ligaments and 125 trabs-shaped ligaments; there were 181 ligaments(84.2%) connecting the nerve root to the transverse or the intervertebral foraminal wall, which were characterized as radiating ligaments, and 34 ligaments(15.8%) connecting the intervertebral foramen and the organization across the intervertebral foramen, which were characterized as transforaminal ligaments; the appearance rate of radiating ligament and that of transforaminal ligament showed statistical significance(Z=-3.928, P=0.000). The IFLs could be found from the entrance zone in 73 ligaments(34.0%), mid zone in 102 ligaments(47.4%) and the exit zone in 40 ligaments(18.6%) in the L5/S1 intervertebral foramen. Ligament length varied from 1.43mm to 19.01mm; the thickest was 3.46mm. Under the microscope, eosin(HE) staining indicating the intraforaminal ligaments were composed of fibrous connective tissues and part of them contained small blood vessel tissues; Masson trichrome staining indicating intraforaminal ligaments were composed of a large amount of collagen fibers and a small amount of elastic fibers. There was no significant difference under the microscope about the histological features between intraforaminal ligaments and transforaminal ligaments. Conclusions: The intervertebral foraminal ligaments are mainly divided into strips and trabs. The appearance rate of radiating ligaments in intervertebral foramen is much higher than that of transforaminal ligaments. Therefore, surgeon should be cautious of endoscopic spinal surgery to avoid nurse root injury.