The Morphology And Clinical Significance Of The Dorsal Meningovertebra Ligaments In The Lumbosacral Epidural Space

Dural laceration is one of the most common complications of spinal surgery and has been reported with an incidence as high as1%-17%; when handled incorrectly, this complication is associated with the risks of poor wound healing, meningitis, and pseudomeningocele. More in-depth consideration of how to prevent dural laceration and its complications in spinal surgery is necessary for surgeons.Lu Yu Pu hold that it is easy to damage the dura mater during biting the lamina. Dural injury mainly occurred in the course of the surgical approach, especially in the clamp injury or laceration. At present, prevention of dural tear is one of the more difficult issues in spine surgeries. Dural injury located in the dorsal lateral accounted for74.6percent according to some literatures. There are many reasons for the dural injury in spine surgery, the first of all is iatrogenic. Most pseudomeningoceles are iatrogenic and occur in the posterior lumbar region following surgery. The true incidence of iatrogenic pseudomeningoceles following laminectomy or discectomy is unknown; however, the authors of several published reports suggest that the incidence of lumbar pseudomeningoceles following laminectomy or discectomy is between0.07%and2%). Lack of experience of the surgeon, unskilled or rude surgical operation and unclear to the anatomical structures can lead to iatrogenic dural injury leading to cerebrospinal fluid leakage. Therefore, in order to prevent the occurrece of cerebrospinal fluid leakage, intraoperative identification of anatomical structures and fine operation are particularly important.Some researchers in China said that there exist normal anatomic structure between the lumbosacral dura and yellow ligament in lumbosacral region.They believe that these ligaments may be the anatomical factors of intraoperative dural tears and provide recommendations that it is better to identify these ligments and cut off them so as to avoid the dural tear.Domestic reference books mentioning the connection structure between the dura mater and yellow ligament were largely based on this study.Among the soft structures of the lumbosacral spinal canal, the meningovertebral ligaments are often neglected. These ligaments originate from the most external fibroelastic layers of the dura mater and extend to the osteofibrous walls of the spinal canal. The meningovertebral ligaments could be classified as ventral, lateral, or dorsal. Anatomical textbooks and the literature have often reported the presence of ventral connections between the dura mater and the posterior longitudinal ligament, but the existence of dorsal attachments is typically not mentioned. Blomberg (1986) conducted an anatomical study of the lumbar epidural space and found that there was a dorsal connective tissue band in the midline of the epidural space between the dura mater and the flaval ligaments; he argued that the existence of the dorsomedian connection might help explain some of the unexpected events that occur during clinical epidural anesthesia, such as accidental dural punctures as well as uneven onset and spread of anesthesia. The dorsomedian connective tissue structure observed his study with epiduroscopy was also hypothesized in1963by Luyendijk,who,in presenting the results of peridurography,described acentral defect of the contrast medium.He ascribed the defect to a dorsomedian fold of the dura mater and assumed that the fold was caused by median attachments of the dural sac to the vertebral laminae. Posterior fibrous connections have been mentioned by Anson and McVay. The dorsomedian connective tissue band demonstrated in this material may be of the same origin as the ventral connection, and may be congenital. According to Newell,fibrous bands of tissue were recognized by Meckel in1817and Humphry in1858,and later described by Trolard in1893as a series of anterior midline bands connecting dura and the PLL in the lower lumbar and sacral regions.These bands were described in detail by Hofmann in1898and have subsequently become known as Hofmann ligaments;further descriptions have been provided by von Lu"dinghausen.Hofmann’s ligaments stretch between the dura and the superficial layer of the PLL and attach the dura to the posterior longitudinal ligament. They are very narrow, almost thread-like, down at the L5level and may be missing at the S1level.There are usually two at each level, a right and a left, but there is considerable variation, and often there are many fibrows attachments. They get wider as we dissect cranially, and at L2can be1cm or more wide and often meet in the middle, so there is only one wide band. They attach to the area of the PLL above where it blends with the PLL annular complex and pass posteriorly and cranially to attach to the dura. They probably serve to hold the dura caudally as the child grows but also, to a considerable extent, hold the dura forward against the vertebra. Mother nature may not have anticipated wide midline surgical laminectomies, but these ligaments do prevent the dura from bridging across in the lumbar area, thus moving far away from the posterior surface of the vertebral body after wide posterior decompression. Spencer et al, in their excellent report published in1983, described Hofmann’s ligaments but also described lateral ligaments that bind the dural radicular sleeve complex to the vertebral canal, which they generously called "lateral Hofmann’s ligaments," although Hofmann made no mention of these ligaments. These are important, they believe, because they prevent the spinal nerve from moving posteriorly when a disc bulges against it anteriorly. Thus, pain is produced even though there is plenty of room for the nerve in the bony canal posteriorly. Spencer has argued very forcefully that because the spinal nerves are held down against the bone as they enter neurovascular canal even a relatively small bulging disc lying underneath the nerve can cause a lot of symptoms.We believe that there still exist some questions of the structure connecting the theca to the tissue lining the vertebral canal as follows:(1) Dura mater ventral and lateral connection structure, including the connection between the structure of the dura mater and the posterior longitudinal ligament (Hofmann ligaments) and the "lateral Hofmann’s ligaments which bind the dural radicular sleeve complex to the vertebral canal were identified well abroad but there is rare reports for them in domestic literature and books.(2) The naming of connection ligaments of the dosal part of dura mater is not yet unified.Foreign literature and books used to call the ventral ligaments of dura mater as "Hofmann ligaments". The40th edition of Gray’s Anatomy reported that the "meningovertebral ligaments "connected the theca to the tissue lining the vertebral canal.(3) The research of the lumbosacral dural back connection structure has not yet reached a consensus. There is less relevant reports of anatomy books mentioning them at home and abroad, and further study and discussion are necessary. The impact of these structure to epidural anesthesia was mentioned abroad, while the possible anatomical reason for dural injury in the lumbar spine surgery was mentioned only in china but not yet taken seriously.(4) Various reports’discussions of the physiological and pathological role of the dura mater of the ventral ligaments or dorsal ones are isolated, the result is inevitable one-sidedness and limitations.(5) The clinical significance of the ligaments of the dura mater around the spinal canal wall, especially the dorsal ligaments in the lumbosacral epidural space and related damage caused by these ligments are not yet clear.To solve the above problem, we performed depth and detailed study to fully reveal these ligaments’traits and clarify their clinical significance in the lumbar spine surgery. Expect this structure to add new knowledge to these structures, provide clinicians with more detailed anatomical information in order to reduce related complications.This study includes the two parts as follws:Chapter1The anatomical observation of the dorsal meningovertebra ligaments in the lumbosacral epidural space based on endoscopicObjective:Endoscopic observation of the dorsal meningovertebra ligaments in the lumbosacral epidural space without opening the vertebral canal in order to reveal its true colors and to provide a basis for further research.Methods:A total of30healthy adult cadavers that were fixed in10%formalin were used (20male and10female; age range,52-70years; mean age,64years). The spine was transected at the level of the intervertebral disc between T12and L1. All findings were documented with photography.Results:The appearance of the meningovertebral ligaments varied from strands of connective tissue to a complete membrane. According to the morphology observed on endoscopy, the meningovertebral ligaments were divided into five types:strip-type (47%), cord-type (25%),"Y"-shaped type (14%), grid type (8%), and thin slice type (6%).Conclusion:The dorsal meningovertebral ligaments in the lumbosacral epidural space are normal structures of human bodys, which may play an important role in the dural suspension and fixation. This kind of ligaments can be divided into five types according to their morphology.Chaper2The observation of the dorsal meningovertebral ligaments in the lumbosacral epidural space performed by naked eye and surgical microscopeObjective:Tofully reveal the character of the dorsal meningovertebral ligaments in the lumbosacral epidural space and their role of resulting in the dural injury in order to provide clearer data of these ligaments for clinicians.Methods:A total of30healthy adult cadavers that were fixed in10%formalin were used (20male and10female).The posterior aspect of the vertebral column was exposed from L1to S1by dissecting the post-vertebral muscles.After epiduroscopy, the vertebral bodies were carefully removed to expose the dural sac while leaving the attachments between the dural sac and the laminae or ligamentum flavum intact. The ventral aspect of the lumbosacral vertebrae was divided into10segments:L1laminae, L1/L2ligamenta flava, L2laminae, L2/L3ligamenta flava, L3laminae, L3/L4ligamenta flava, L4laminae, L4/L5ligamenta flava, L5laminae, and L5/S1ligamenta flava. Each spinal nerve was identified and followed laterally to the intervertebral foramen, where it was sectioned as far laterally as possible to free the dura from lateral attachments. The dura mater was then carefully reflected ventrally to expose and isolate the meningovertebral ligaments from the peridural membrane using blunt dissection. Then, the extradural fat was removed. The dural sac was elevated free to identify the meningovertebral ligaments. The distribution, morphology, number, orientation and sites of origin and insertion of the meningovertebral ligaments were observed and recorded. The length, width or diameter and thickness of the ligaments were measured using vernier calipers (accurate to0.01mm) under the surgical microscope. Statistical analysis on the measurements was performed using SPSS13.0(SPSS Inc., Chicago, IL, USA). The measurement data were expressed in the form of "x±S(min-max)", and the qualitativedata were tested with the chi-squared test.Results:The dorsal meningovertebral ligaments in the lumbosacral region connect the dura to the ligamenta flava or lamina. The data showed that the dorsal meningovertebral ligaments are associated more often with the ligamenta flava than the laminae (χ2=14.810, P=0.000),and the occurrence rate of dorsal meningovertebral ligaments was97%at L5/S1. The meningovertebral ligaments were very closely connected to the ligamenta flava, and these connections were difficult to separate. However, the connections between the meningovertebral ligaments and the vertebral laminae were not secure. Under the surgical microscope, we determined that the inner surface of the vertebral laminae was covered with a thin layer of membrane. The membrane was loosely connected to the vertebral laminae and was easily separated. Vascular structures were also observed at the ends of some of the meningovertebral ligamentsThe thickest ligaments were observed at the L5and S1vertebrae. The length of the ligaments varied from5.16to40.24mm, and the orientation of the ligaments was craniocaudal.Conclusion:The ligaments connecting the dura and yellow ligament as well as lamina exist in dorsal lumbosacralepidural space. Inadvertent management of these ligaments has potential risk for inducing dural lacerations andepidural hemorrahage. Dissecting the meningovertebral ligaments before the discectomy may reduce postoperative cerebrospinal fluid leakage.