Lab resource Extraforaminal compression of the L5 nerve: An anatomical study with application to failed posterior decompressive procedures R. Shane Tubbs a,b , Joe Iwanaga a,⇑ , Islam Aly b , Marc D. Moisi c , David R. Hanscom c , Jens R. Chapman c , Marios Loukas b , Rod J. Oskouian a,c a Seattle Science Foundation, 550 17th Ave, James Tower, Suite 600, Seattle, WA 98122, USA b Department of Anatomical Sciences, St. George’s University, St. George’s, Grenada c Swedish Neuroscience Institute, Swedish Medical Center, 550 17th Avenue, Suite 500, Seattle, WA 98122, USA article info Article history: Received 22 September 2016 Accepted 13 March 2017 Available online xxxx Keywords: Far lateral syndrome Lumbosacral Nerve compression Radiculopathy abstract This anatomical study was performed to elucidate the pertinent foraminal and lateral L5 nerve anatomy to enhance our understanding of possible neurologic causes of failed decompression surgery. Persistent extraforaminal L5 nerve compression is a possible cause of persistent symptoms following lumbosacral surgery. The amount of extraforaminal space for the L5 ventral ramus was examined in fifty adult human skeletons (100 sides). Based on morphology, the specimens were then categorized (types I–IV) on the basis of the bony space available for the nerve at this location. Next, 25 embalmed adult cadavers (50 sides) underwent bilateral dissection of the lower lateral lumbar region. The type of bony extraforaminal outlet was documented for each cadaver on the basis of our skeletal analysis. Lastly, segments (intra- and extra-foraminal) of the L5 ventral ramus were excised and examined histologically. Types I–IV outlets were found in 43, 31, 20 and 6 skeletal sides, respectively. For cadavers, 22,15, 10 and 3 sides were found to have types I–IV bony outlets, respectively. In cadavers, all type IV outlets and 70% of the type III bony configurations adjacent to the L5 ventral ramus had signs of neural irritation/injury including vascular hyalinization and increased fibrosis distal to the intervertebral foramen. No distal segments of type I and type II outlets showed histological signs of neural compromise. Patients with symptoms referable to L5 nerve compression for whom no proximal pathology is identified could warrant investigation of the more distal extraforaminal segment of this nerve. Ó 2017 Elsevier Ltd. All rights reserved. 1. Introduction Persistent extraforaminal L5 nerve compression is a possible cause of persistent symptoms following lumbosacral surgery and this is not uncommon. For example, in 1971, Macnab [12] reported a series of 842 patients who had undergone surgical exploration of the lumbar spine. In 68 of them, no disc herniation was identified despite irrefutable clinical evidence of continuing intractable root irritation, and in 18 of these, no other intraspinal pathology was observed that could have resulted in such symptoms. On post- mortem examination, one of these patients was found to have extraforaminal compression of the L5 spinal nerve. Various find- ings have been used to explain continuing symptomatology follow- ing lumbar disc surgery. For example, Amonoo-Kuofi et al. [2] and others [17,20] described tethering ligaments within the lumbar intervertebral foramen. Some have attributed this to disc desicca- tion at L5 with subsequent bony compression of the extraforaminal L5 nerve root [21] or anterior osteophytes at this level [7,9]. Mat- sumoto et al. [13] also mentioned extraforaminal stenosis at the lumbosacral junction as a cause of compression of the L5 nerve root with resultant pain, motor deficits, neurogenic claudication and sensory disturbances of the L5 dermatome. However, these authors also commented on the difficulty of making such a diagno- sis. Other causes of extraformainal compression include Bar- tolotti’s syndrome and lumbosacral tunnel compression. As extraforaminal L5 nerve compression is a possible though uncommon location, the following anatomical study was per- formed to elucidate this segmental nerve’s anatomic surroundings and their possible implications in causing pertinent neurologic symptoms. Therefore, the current study investigated the anatomy and histology of the L5 ventral ramus at the lumbosacral junction to better elucidate these relationships seen in various bony morphologies. http://dx.doi.org/10.1016/j.jocn.2017.03.051 0967-5868/Ó 2017 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. Fax: +1 2067326599. E-mail address: joei@seattlesciencefoundation.or (J. Iwanaga). Journal of Clinical Neuroscience xxx (2017) xxx–xxx Contents lists available at ScienceDirect Journal of Clinical Neuroscience journal homepage: www.elsevier.com/locate/jocn Please cite this article in press as: Tubbs RS et al. Extraforaminal compression of the L5 nerve: An anatomical study with application to failed posterior decompressive procedures. J Clin Neurosci (2017), http://dx.doi.org/10.1016/j.jocn.2017.03.051