low back pain is a highly prevalent complaint , reported to affect 26.4% of us adults at some point in the last three months , although fewer than 1% of patients proceed to undergo surgical intervention . in spite of methodical advances in surgical techniques , incidental durotomy ( iatrogenic dural tears ) during posterior spinal surgery
incidental durotomy or iatrogenic dural tears remain a relatively commonplace and potentially serious complication of lumbar spine surgery [ 35 ] .
delineating anatomical variants in the posterior lumbar spine may be crucial in reducing future rates of incidental durotomy .
the aim of this study was to investigate variations in the anatomical and histological features of the posterior epidural ligaments , passing between the dura mater and the ligamentum flavum in the lumbar spine .
seventeen lumbar spines were dissected from randomly selected soft - fixed cadavers with no known history of spinal disease or spinal surgery .
cross - sectional anatomical dissection at the levels l1-s1 via a dorsal approach was performed .
anterior retraction of the dura mater identified any connection between the dorsal surface of the dura mater and the ligamentum flavum .
any attachments between the dura and the ligamentum flavum were dissected out in their entirety , fixed in 10% formalin and stained with hematoxylin and eosin ( h&e ) and elastic van gieson ( evg ) .
a number of randomly selected control specimens from levels l1-s1 , without connection , were also stained with h&e and evg . staining with evg differentiated collagen from elastin in the tissue structure excised .
posterior epidural ligaments were identified as a connection between the dorsal surface of the dura mater and the ligamentum flavum .
nine ( 9 ) separate posterior epidural ligaments were identified in these cadavers , with 3 ( 33.3% ) at l3/l4 , 5 ( 55.6% ) at l4/l5 , and 1 ( 11.1% ) at l5/s1 ( table 1 ) .
figures 1 and 2 demonstrate the variable presentations of the ligament and its identification at different vertebral levels .
histology confirmed the presence of poorly differentiated collagen - based connective tissue , distinct from the normal anatomy ( figure 3 ) .
histological analysis highlighted variants in the presentations of the ligament ( figures 4 and 5 ) .  
figure 4 shows a ligament with a substantial coalition and fusion of fibres , which are distinct from the standard tissue plane . on other occasions ,
the ligament was observed as a discrete stranded structure with ventral - dorsal interdigitation of fibres ( figure 5 ) .
despite methodical approaches and improved surgical technique , the incidence of incidental durotomy in posterior lumbar spine surgery has not significantly decreased .
unidentified incidental durotomy has a clear postoperative risk , and the existence of variants in the lumbar spine anatomy has been hypothesised as a possible cause for the stagnant incidence rates of incidental durotomy .
previous anatomical studies have delineated ventral lumbar dural adhesions , which authors have reported them to be an adjuvant source of discogenic back pain . in the posterior spine ,
lateral ( hoffman 's ligaments ) , dorsolateral , and dorsomedial epidural attachments have been described ( reviewed by kimmel et al . ) .
the  attention to terminal attachment  ( ata ) has been described originating from the dorsal surface of the dura mater at the level of s1 projecting towards the ligamentum flavum .
this intraoperative finding had similar histological features to those identified in this anatomical study and was also described as a possible causative factor in dural tears .
however , the dorsal ligaments described here are clearly different from the ata as they were found at levels l3 to s1 and present a clear extension from the dorsal dura mater to the ligamentum flavum .
posterior decompression of lumbar neural structures often involves removal or part removal of the lumbar lamina and ligamentum flavum . in patients with severe stenosis
, surgeons regularly encounter adherent ligamentum flavum to the dura mater , where no epidural fat is present to define the surgical plane .
we observed variable ligamentous attachments between the dorsal surface of the dura mater and ligamentum flavum at levels l3-s1 .
these ventral - dorsal ligaments tethered the dura mater to the ligamentum flavum forming a substantial communication ( figures 1 and 2 ) .
the presence of such ligaments , in the anatomical plane where lumbar spine surgery is most commonly undertaken , may have a role in the aetiology of intraoperative incidental durotomy .
histology staining confirmed the presence of collagen - rich tissue that was distinct from the normal elastic structure of the ligamentum flavum ( figure 3 ) .
the variable histological presentations of the ligaments were outlined ( figures 4 and 5 ) .
the histological union of the dura mater and ligamentum flavum makes the intraoperative identification of separate tissue structures difficult , and care should be taken during surgery [ 11 , 12 ] .
with the knowledge of the existence of the posterior epidural ligament at levels l3-s1 , the authors advocate surgical caution in the region with the employment of complication avoidance techniques when approaching the ligamentum flavum .
the authors support the previous literature [ 10 , 11 ] that recommends that two - step flavotomies , using semisharp dissectors , during a posterior approach to the lumbar spine should be standard surgical practice .
furthermore , with knowledge of the features of the posterior epidural ligaments , it is recommended that in cases where movement of the dura is visualized , areas of adherent ligamentum flavum should be left in situ .
the presence of ligamentous attachments between the dorsal surface of the dura mater and the ligamentum flavum is of surgical and anatomical importance . in this paper
, we show these ligaments arising at vertebral levels l3-s1 in over half of the cadavers investigated and describe their varied anatomical and histological presentation .
the delineation of the posterior epidural ligaments in the lumbar spine is of clear clinical importance in posterior lumbar spine surgery .
 
 purpose . 
 incidental durotomy is a relatively common complication for patients undergoing posterior spinal surgery . 
 delineating anatomical variants in the posterior lumbar spinal canal is crucial in reducing future rates of incidental durotomy . 
 materials and methods . 
 the ligamentous attachments between the dura mater and ligamentum flavum in the lumbar region of 17 soft - fixed cadavers were investigated . 
 the lumbar vertebral columns were removed , and cross - sectional dissection was performed at levels l1-s1 . 
 anterior retraction of the dorsal dura mater identified attachments between the dorsal surface of the dura mater and the ligamentum flavum . 
 histological staining of the ligamentous attachments was carried out with hematoxylin and eosin ( h&e ) and elastic van gieson ( evg ) . 
 results . 
 posterior epidural ligaments were present in 9 ( 52.9% ) cadavers . 
 nine ( 9 ) separate ligaments were identified in these cadavers , with 3 ( 33.3% ) at l3/l4 , 5 ( 55.5% ) at l4/l5 , and 1 ( 11.1% ) at l5/s1 . 
 histology confirmed the presence of poorly differentiated collagen - based connective tissue , distinct from the normal anatomy . 
 conclusions . 
 this study confirms the presence of multiple dorsomedial posterior epidural ligaments at the main sites for posterior spinal surgery ( l3-s1 ) . 
 an intraoperative awareness of the variability of such connections may be an important step in reducing static rates of incidental durotomy . 
1. Introduction
2. Materials and Methods
3. Results
4. Discussion
5. Conclusion