Piotr Godek

Sutherland Medical Center, Warsaw, 04-036 Poland, ORCID ID: 0000-0001-7809-1289

*Corresponding Author: Piotr Godek, Sutherland Medical Center, Warsaw, 04-036 Poland, ORCID ID: 0000-0001-7809-1289

Abstract
Background: Lumbar foraminal stenosis (LFS) is a common form of spinal spondylosis, especially in the lower segments of the spine. It is usually a consequence of degenerative disc disease (DDD) leading to intervertebral instability and secondary hypertrophy of the intervertebral joints (facet joints) and ligamentous elements, creating a significant obstacle in the path of nerve roots leaving the spinal canal. The consequence of this entity is a mixed form of axial and radicular pain in patients with LFS. The prevalence of LFS has been reported to be 8–11 %. While the diagnosis of LFS based on imaging studies is not difficult, its conservative treatment causes considerable difficulties, not only because of the mechanical obstacle but most of all the perineural adhesions which are the cause of disturbed neurodynamic of the nerve roots and frequent pain chronification. The hyaluronic acid (HA) can be a new option for LFS symptomatic treatment as an interposing agent preventing perineural friction and the formation of adhesions around nerve roots.

Results: A 66-year-old, male patient, without a history of spine surgery, a blue-collar worker with pain in the lumbar region radiating to the left buttock and hip in the course of LFS, was referred by a physiotherapist due to ineffective manual therapy. The pain intensified after exertion, especially after working on a forklift, without any traumatic background. In a physical examination, positive Kemp's sign significantly reduced Straight Leg Raise (SLR) and positive Slump test on the left, no neurological deficiency symptoms. Radiography of the hip joints - no pathologies were found. In MRI, multi-level discopathy, foraminal stenosis of L4/L5 and L5/S1 segments predominately on the left. Due to severe pain, an ultrasound-guided steroid was administered around facet joints at the L5/S1 and L4/L5 levels. A month later, the patient came for a check-up reporting only a few days' improvements after administration of the steroid. In the medical survey, his condition did not differ from before the injection. Under ultrasound guidance, HA was administered epidurally (interlaminar approach) into the lateral recess at the L5/S1 level on the left side, and the patient was instructed how to perform neural mobilization exercises in the unloaded position. Follow-up after 4, 8 and 12 weeks confirmed sustained improvement in the Numeric Rating Scale, NRS (0-10), Oswestry Disability Index, ODI (0-50), Rolland-Morris Questionnaire, RM (0-24), and pain-free elevation angle in SLR test. There were no signs of intolerance to the HA and no administration complications.

Conclusion: Epidural hyaluronic acid injection combined with an exercise program can be an interesting way to improve nerve root neurodynamics in LFS and an alternative to steroid administration.

Keywords: Hyaluronic Acid; Spondylosis; Injections, Epidural.

Introduction
Lumbar foraminal stenosis (LFS) is a quite common form of spinal spondylosis, especially in the lower segments of the spine and it is the phenomenon of limited space of the lateral part of the spinal canal leading to compression of the root and dorsal root ganglion. In 1976, a definition and classification of LFS were proposed as an extension of the concept of spinal canal stenosis [1].
Anatomically, LFS describes the diameter of the intervertebral foramen and the volume of the lateral part of the spinal canal called the lateral recess, where several sensitive zones are distinguished. The anatomical boundaries for foramen are composed of multiple anatomical components: the adjacent vertebra pedicles, the posterior margins of adjacent vertebral bodies, the intervertebral disc (IVD), the ligamentum flavum, and superior and inferior articular facets as the posterior boundaries. The lateral canal is segmented into the lateral recess, vertical interpedicular (foraminal), and extraforaminal zone. The foraminal area varies from 40 to 160 mm ² but not all space is available for the root because trans- or intra-foraminal ligaments are present in the inferior foraminal aspect. Thus, the exiting nerve root or dorsal root ganglion (DRG) surrounded by fat and radicular vessels is often located in the superior and anterior region of the foramen or in the subpedicular notch, normally occupying approximately 30 % of the available foraminal area. The most sensitive zone is where the arc of bending root in the subpedicular notch adheres to the cortical bone of the pedicle and where the root rubbing against its bone boundary is exposed to ischemia. In the course of degenerative spondylosis, the intervertebral foramen and the lateral recess decrease not only due to the hypertrophy of the facet joints, the ligamentum flavum, and the base of the arch but also due to the instability causing articular subluxation so the irregular course of the intervertebral foramen, changes its shape from vertical to oblique or even horizontal [2].

The prevalence of lumbar foraminal stenosis has been reported to be 8–11 %, specifically L5 nerve root disorders due to L5/S1 foraminal stenosis have been reported to account for 75 % of all cases of foraminal stenoses [3].

The LFS is often difficult to diagnose, contributing to an unfavorable prognosis after routine surgical treatment of lumbar spinal canal stenosis. In their review of failed back surgery syndrome, Burton et al. considered foraminal stenosis to be the cause of pain in nearly 60% of patients with persistent postoperative symptoms [4]. Although there are differences in clinical features of LFS, the clinical picture includes mixed axial and radial pain of the sciatica type, occurring not only during exercise but also at rest, and much more often than in the central form of spinal stenosis (76 vs. 35%) as confirmed by an intraoperative study by Yamada et al [5].

Conventional radiography is highly insufficient to assess the morphology and degree of lateral recess stenosis, therefore MRI is the best imaging modality in combination with CT, as the bone proliferative changes, soft tissue hypertrophy, and an accurate assessment of the degree of intervertebral disc degeneration are possible. The vacuum phenomenon and late stage of IVD pathology are encountered in the L5/S1 segment in 95.2% of the LSFS patients [6].

Due to the prolonged adherence of the root nerve to the bone boundaries and overgrown ligamentous elements, without the possibility of its natural movement in the physiological range, a few dangerous processes can occur that threaten the neurotrophy. Direct pressure exerted on the vasa nervorum with a blood supply deficit slows down the cytoplasmic transport and consequently promotes the neurodegenerative processes. On the other hand, the swelling and increased intra-nerve pressure due to the venous and lymphatic stasis of the root leads to further root ischemia because of increased vascular resistance. An additional unfavourable consequence of prolonged adherence is perineural adhesions, which arise especially abundantly in the inflammatory environment and can be visible in epiduroscopy images. All those mechanisms disturb the neurodynamics of the root and its dural sheet, leading to the formation of pernicious vicious circle: pressure => ischemia => swelling => inflammation => adhesion formation => ischemia => pressure [7].

The cause-oriented treatment of LFS is the removal of the mechanical obstacle, the release of adhesions, and the prevention of secondary stenosis using implants widening not only the diameter of the intervertebral foramen but also the volume of the lateral recesses (resections of the facet joints and ligaments).

In the symptomatic treatment of LFS, the attempt of mechanical widening of the lateral recess by traction procedures and manual therapy or local and systemic anti-inflammatory treatments (epidural and periradicular steroid injections) are commonly used. The conservative treatment faces however significant obstacles due to the rapid pain chronification because DRG located in the vicinity is prone to secreting from glial cells many substances that promote neuropathic pain like substance P and proinflammatory cytokines [8]. 

The concept of hyaluronic acid (HA) administration in the epidural space was initially introduced in animal studies. Its purpose was to interpose a dural sac with a slip layer to prevent adhesions and enable it to slide properly during normal movement.

In the case report presented here, the rationale for HA epidural administration assumes its contribution for regaining of normal nerve root neurodynamic, spontaneous resolution of radicular edema subjected to neural mobilization processes with the recovery of proper blood supply which will relieve the neuropathic pain in the long-term perspective.

Case report
A 66-year-old, male patient, with a normal BMI, without a history of spine surgery, a blue-collar worker with pain in the lumbar region and its radiation to the left buttock and hip in the course of LFS, was referred by a physiotherapist due to ineffective manual therapy. The pain intensifies after exertion, especially after working on a forklift, without any traumatic background. In a physical examination, positive Kemp's sign on the left, significantly reduced SLR on the left side (45 degrees), on the right side 70 degrees, and positive Slump test. No neurological deficiency symptoms. Radiography of the hip joints - no pathologies. In MRI, multi-level discopathy, foraminal stenosis of L4/L5 and L5/S1 segments predominately on the left [Figure 1].

Figure 1: Lumbar spine MRI sagittal and transverse scan - foraminal stenosis of L4/L5 and L5/S1 segments.

Due to severe pain, ultrasound-guided injection of steroid (Dexaven, 4 mg) was administered around the facet joints at L5/S1 and L4/L5 levels. A month later, the patient came for a check-up visit reporting only a few days' improvements, and in the medical survey, his condition did not differ from that before the injection. The patient was thoroughly informed about the possible reasons for the ineffectiveness of the current treatment and the options of further treatment were thoroughly explained to him, including the unconventional solution of HA ultrasound-guided epidurally in the area of the entrapped root as preparation for neural mobilization exercises. The patient accepted this option, reluctantly thinking about surgical treatment and continuing to take high doses of analgesics. Under ultrasound guidance, a single dose of HA (Synovial HL, IBSA) was administered epidurally (interlaminar approach, BD Spinal needle, 20G x 3,5’’) into the lateral recess at the L5/S1 level on the left side after the initial injection of 10 ml saline according to the loss of resistance method [Figure 2,3].

Figure 2: Ultrasound image of L5/S1 interlaminar acoustic window for epidural injection technique. Parasagittal long axis scan.

Figure 3: Ultrasound-guided L5/S1 interlaminar epidural injection. In-plane technique, starting point from caudal direction.

The injection was performed very slowly and gradually with constant monitoring of foot active movement for which the patient was encouraged. After 30 min observation, the patient was instructed how to exercise neural mobilization of the ischial nerve in the unloaded position of the spine (lateral decubitus with lumbar flexion) using a skateboard daily [Figure 4].

Figure 4: Neural mobilisation of the L5 root in autotherapy.