Endoscopic spine surgery (ESS) has become popular and is the minimally invasive standard of care for the management of degenerative lumbar spinal pathologies. Especially, in disorders like lumbar canal stenosis (LCS), adequate decompression of the thecal sac and nerve roots could be achieved using a smaller skin incision and without any significant injury to the posterior spinal musculature [1]. Other potential advantages of ESS include: clear and magnified visualization of the neural structures, lesser blood loss, and cosmetically better outcomes [2,3]. In patients with LCS, thickened ligamentum flavum and hypertrophy of the medial facet are the potential sources of radicular pain owing to the compression of the traversing nerve root [4]. Patients with progressive compression of neural tissues develop neurological deficits during the course of the disease, necessitating early surgical intervention for better surgical outcomes.

Ensuring adequate decompression of the nerve root is of paramount importance to enhance optimal recovery of neural function. In addition to the bony and ligamentous compression in LCS, the role of other anatomical structures, like thickened and fibrosed epidural bands as sources of nerve root compression, has been less described in the literature. Though anatomical studies have confirmed the presence of ligamentous bands in the epidural space, their role in degenerative lumbar pathologies is less explored [5]. Our case highlights the presence of thickened fibrous bands coursing over the traversing nerve root in a patient with LCS presenting with foot drop, and the possibility of it being one of the important causative factors for symptomatology in these patients.

A 52-year-old female patient presented with low back pain for a week's duration associated with a history of right lower limb radiculopathy and difficulty in moving the toes on the right side, following a bus ride. Clinical evaluation revealed tenderness in the lower lumbar region associated with reduced lumbar range of motion. Neurological examination revealed weakness in the right ankle (L4 myotome) - 2/5 and toe extensors (L5 myotome) - 0/5 according to Medical Research Council (MRC) grading. The other myotomes were normal (5/5 MRC grading). Reflexes were 2+ without any clonus, and the plantar was flexor. On radiological evaluation, mild L4–5 degenerative listhesis was noted in the plain radiographs. Magnetic resonance imaging revealed lateral recess stenosis at the L4–5 level (Figure 1). In view of the neurological deficit, the patient was planned for L4–5 decompression by unilateral biportal endoscopy (UBE).

Under General anesthesia patient was positioned prone on a Wilson frame, and the portals for UBE decompression were planned on the left side of the patient (right-handed surgeon) at the L4–5 level. Saline irrigation using an irrigation pump with 25–40 mmHg of fluid pressure was used throughout the procedure. First, skin marking was made to identify the midline and medial pedicle line of L4 and L5 under anteroposterior fluoroscopy. Using a 0.7-cm skin incision (at the level of the medial pedicle line) at the L4 level, a dilator for the endoscope was docked. A 1-cm skin incision for the working portal was made at the L5 medial pedicle line for dilator placement, and triangulation of both dilators was performed at the spinolaminar junction (Figure 2). Using a muscle detacher, the multifidus muscle is erased from the caudal end of the L4 lamina to create the working space for ensuring optimal saline flow during the procedure. A 0° arthroscope is then inserted through the viewing portal, and a radiofrequency plasma surgical wand system (Bonss Medical, Jiangsu Medi Tech, China) is introduced through the working portal to coagulate the bleeding in the multifidus and further remove the remaining attached muscle fibers from the L4 lamina. Using a 4-mm high-speed diamond burr (Primado 2, NSK, Fukushima, Japan), ipsilateral L4 lamina burring was done till the free edge of the deep layer of ligamentum flavum is visible proximally. Drilling was continued at the spinolaminar junction and then laterally, along the ipsilateral descending facet, followed by resection of the medial part of the ipsilateral ascending facet. The superior part of ipsilateral L5 (caudal) lamina drilling was performed till the free edge of the flavum. Using an over-the-top approach, L4 laminotomy of the contralateral side was performed. The medial aspect of the contralateral ascending facet is removed. Finally, contralateral L5 (caudal) laminotomy was performed. Ligamentum flavum is then removed en bloc on the contralateral side and finally on the ipsilateral side to expose the thecal sac and bilateral L5 nerve root. Even after bony and ligamentous decompression, the traversing nerve root was pale and blanched (Figure 3). When carefully observed, fibrous tissue bands traversing over the epidural veins and the traversing L5 nerve root were visualized through the arthroscope. Using a nerve root probe and radiofrequency (RF) probe, these constriction bands were then released, and vascularity was seen over the traversing nerve root. Once adequate decompression of the nerve roots was confirmed, hemostasis was achieved and closure performed. Postoperatively, the patient gained partial neurological recovery (L4, L5: MRC grade 3/5) at 6 weeks and is under further follow-up. Informed consent was received by the authors for publication.

Thickened ligamentum flavum and hypertrophy of the medial facets are well-established causes of the pathogenesis of LCS. However, the presence and role of the epidural periradicular fibrous tissue in LCS remain less explored in the literature. Our case report highlights the significant advantages of the application of endoscopy in clearly visualizing the anatomy of these fibrous tissues and their course in the epidural space in patients with LCS. Even after ligamentous and bony decompression, the traversing nerve root appeared pale till the epidural fibrous band was removed. We believe that these fibrous bands were constricting the vascularity of the traversing nerve root, and decompressing these structures could contribute to the neurological recovery of our patient, who presented with foot drop. This is an important anatomical consideration, as even after the removal of ligamentum flavum and hypertrophied ascending facet, neurological recovery could be guarded in patients with motor weakness, due to various factors like the duration and severity of neural compression. Decompressing these periradicular fibrous tissues could be another important factor in improving the prognosis in such patients, as adequate vascularity is essential for optimal function of the neural tissues.

Several anatomical and cadaveric studies have shown the presence of fibro-ligamentous structures in the epidural space, including the peridural membrane and the meningovertebral ligaments [6-8]. The peridural membrane was initially identified in the cervical spine, and a pathological variant causing radicular symptoms has been previously reported. Similarly, dorsal and ventral bands of the meningovertebral ligaments connect the dural sac to the ligamentum flavum and posterior longitudinal ligament, respectively, and have been noted in the lumbar spine. Forceful release of these ligaments has been linked to a higher risk of causing dural lacerations during flavectomy. However, there is limited literature on any fibrous connective tissue bands over the traversing nerve roots and epidural veins, as observed in our case [6-8]. Miyauchi et al. [9,10], in their study of 134 patients with LCS, identified the morphology of structures such as neural compressive epidural membrane and periradicular fibrous tissues, noting that their anatomy may vary from fibrous loose tissues in the form of strands or fragile venous plexus to a thicker membranous structure. The authors also postulated that these structures initially develop as delicate fibrous tissues, which progressively transform into substantial fibrous bands adherent to surrounding neural structures. This transformation is thought to result from repeated cycles of damage and repair under both dynamic and static compression during the progression of degenerative stenosis. We employed an RF probe to coagulate and gently release the fibrous tissue bands over the L5 nerve root. Any attempt at forceful removal could lead to bleeding from the epidural veins and increase the risk of postoperative hematoma formation.

In patients with LCS, periradicular fibrous tissues in the epidural space are significant anatomical structures that could contribute to the patient's symptomatology and should not be overlooked (Figure 4). However, their exact role in the recovery of patients with LCS is less explored, and our case highlights the importance of surgically removing such constrictive bands. Spinal endoscopy facilitates careful evaluation of the nerve root, allowing the surgeon to assess the restoration of vascularity before completing the surgical procedure. This is particularly important in patients with significant canal stenosis and neurological deficits. This signifies the role of endoscopy in spinal decompression procedures compared to open and tubular surgeries. Although tubular decompression is a minimally invasive surgical technique, clear visualization of thin fibrous structures in the thecal sac can be challenging. The magnification provided by the endoscope allows for a clear understanding of the surgical anatomy and all the potential sites of neural compression. With the broader application of spine endoscopy, locating anatomical aspects such as constriction bands and compression points in the epidural space is crucial for improving patient outcomes. The adequacy of neural decompression can also be confirmed under endoscopic guidance by confirming the vascularity of the traversing nerve root and its pulsations.

Periradicular fibrous tissues in the epidural space are potentially one of the important structures to be carefully looked at in patients with LCS. UBE provides superior anatomical visualization with improving the safety and overall precision in the decompression of these structures. The magnification offered by spine endoscopy also enhances the surgeon's ability to identify and decompress such constrictive bands to ensure better clinical outcomes.