The Morphology And Clinical Significance Of The Intraforaminal Ligaments At The L5-S1 Level

Endoscopy is micro-invasive progress in spinal surgery.From the percutaneous endoscopic assisted lumbar discectomy,to endoscopy into the spinal canal,under direct vision through the epidural space directly removing the nucleus pulposus or loosing the compression of nerve root,has become a safer and more effective minimally invasive surgical procedure.As the L5-S1 intervertebral foramen is located between the highly mobile lumbar segment and the relatively immobile sacrum,a special spinal region with structural and functional changes,which easily leads to a herniated disk,ligament degeneration or lumbar degeneration,resulting in L5 nerve root compression.Percutaneous endoscopic through intervertebral foramen is more difficult and easily damage the nerve root or dura mater to operate because of the obstruction of the iliac crest and tough lumbosacral ligament,lumbosacral arch fascia and other anatomical factors.For this reason,some scholars have invented a new operation,endoscopic spinal adhesiolysis through the sacral hiatus under the guidance of X-ray images,to release the nerve root from intraforaminal areas of the L5-S1 intervertebral foramen and achieve some certain curative effect.Previous studies on L5-S1 intervertebral foramen mostly concentrated on the distribution of the extraforaminal transforaminal ligaments and structure adjacent to the spinal nerves,while the distribution of radiating ligament which connecting the nerve root sleeves that radiate to the transverse processes and wall of the exit zone and the intraforaminal ligaments in the L5-S1 intervertebral foramen and its relation with the nerve roots were rarely mentioned.The distribution of intraforaminal ligaments in the entrance zone and its relation with the nerve root are rarely described in detail,and surgeons could not understand its anatomical structures and imaging features before the operation,and the lack of knowledge about position and adjacency of these structures could lead to misunderstanding the dept of device placement,probably causing cerebrospinal fluid leakage,dural tears or damage of nerve roots.Therefore,the aim of this study is to elucidate the position,shape and distribution of L5-S1 intervertebral foramen ligament and its relationship with the nerve root sleeves,which could help surgeons with the construction of a safe working channel,the identification of ligaments and nerves and the safe implementation of the precise endoscopic nerve release program as anatomical basis.The specific studies are summarized as follows:Objective:To investigate the traits and distribution of intraforaminal ligaments in L5-S1 intervertebral foramen and to evaluate their clinical significance,in order to provide the spine surgeon with more detailed anatomical data.Methods:30 embalmed and 15 fresh frozen lumbosacral specimens(aged 40 to 85 years,mean age 56 years)were taken.The arteries are perfused with red latex.Carefully remove the soft tissue around the spine,and open the spine in the median sagittal plane.Identify the L5-S1 nerve root and carefully remove the surrounding fat,fascia and other soft tissue along the intervertebral foramen.The shape,distribution,origin,insertion,and spatial orientation of the ligaments were observed under naked eyes and a surgical microscope.The length,width and diameter or thickness were measured under a surgical microscope with a vernier caliper.Different types of IFLs in the entrance zones were removed from the IVFs,which were subject to eosin staining and Masson trichrome staining before the histological properties were examined under a microscope.Results:A total of 818 ligaments were found in 90 L5-S1 intervertebral foramen,including strap type(350 ligaments)and the trabs type(468 ligaments).There were 699 radiating ligaments(85.45%)that connected the nerve root sleeves and radiated to the transverse process or wall of IVFs,and 119(14.55%)TFLs that connected the structures around the IVFs.Of these,270(33.01%)ligaments were distributed in the entrance zone of L5-S1 intervertebral foramen;381(46.58%)ligaments were in the middle zone and 167(20.42%)ligaments were in the exit zone.The lengths of ligament are variable,raging from 1.43mm to 19.01mm;the thickest one was 3.46mm.Intraforaminal ligaments under the intervertebral foramen ligament by a large number of collagen fibers and a small amount of elastic fibers.There was no significant difference in histological findings between radial ligament and transverse ligament.Under a light microscope,the intraforaminal ligaments consisted mostly of collagen fibers and a few elastic fibers.According to histological properties,there was no significant difference between radiating ligaments and TFLs.Conclusions:The ligaments are divided into two types:strap type and the trabs type.All ligaments in entrance zone were radiating ligaments,and the incidence of radiating ligaments in the intervertebral foramen is higher than that of the TFLs.Understanding the distribution and characteristic of IVFs before surgery and identifying IVFs and properly releasing nerve root during the surgery may properly reduce the incidence of complications.