Effect of the L2 ramus communicans on the nociceptive pathway in lumbar intervertebral discs in rats

A Pain That is Easily Overlooked: Referred Pain Caused by OVCF

Purpose

The objective of this study was to analyze the clinical characteristics and the therapeutic effects of treatment at our spinal center in OVCF patients associated with referred pain. The underlying goals were to deepen the understanding of referred pain caused by OVCFs, improve the currently low early diagnosis rate of OVCFs, and improve the effectiveness of treatment.

Methods

The patients who had referred pain from OVCFs and met the inclusion criteria were retrospectively analyzed. All patients were treated with percutaneous kyphoplasty (PKP). Visual analog scale (VAS) scores and Oswestry Disability Index (ODI) were used to evaluate the therapeutic effect at different time points.

Results

There were 11 males (19.6%) and 45 females (80.4%). Their corresponding mean bone mineral density (BMD) value was -3.3 ± 0.4. The regression coefficient of BMD in the linear regression equation was -4.51 (P<0.001). According to the classification system for referred pain in OVCFs, there were 27 cases of type A (48.2%), 12 cases of type B (21.2%), 8 cases of type C (14.3%), 3 cases of type D (5.4%), and 6 cases of type E (10.7%). All patients were followed up for at least 6 months, and both VAS scores and ODI were found to be significantly better postoperatively than preoperatively (P<0.001). There was no significant difference in VAS scores and ODI between different types preoperatively or 6 months postoperatively (P > 0.05). Within each type, there were significant differences in VAS scores and ODI between the pre- and postoperative timepoints (P < 0.05).

Conclusion

Attention should be paid to referred pain in OVCF patients, which is not uncommon in clinical practice. Our summary of the characteristics of referred pain caused by OVCFs can improve the early diagnosis rate of OVCFs patients and provide a reference for their prognosis after PKP.

Aberrant spinal mechanical loading stress triggers intervertebral disc degeneration by inducing pyroptosis and nerve ingrowth

Aberrant mechanical factor is one of the etiologies of the intervertebral disc (IVD) degeneration (IVDD). However, the exact molecular mechanism of spinal mechanical loading stress-induced IVDD has yet to be elucidated due to a lack of an ideal and stable IVDD animal model. The present study aimed to establish a stable IVDD mouse model and evaluated the effect of aberrant spinal mechanical loading on the pathogenesis of IVDD. Eight-week-old male mice were treated with lumbar spine instability (LSI) surgery to induce IVDD. The progression of IVDD was evaluated by μCT and Safranin O/Fast green staining analysis. The metabolism of extracellular matrix, ingrowth of sensory nerves, pyroptosis in IVDs tissues were determined by immunohistological or real-time PCR analysis. The apoptosis of IVD cells was tested by TUNEL assay. IVDD modeling was successfully produced by LSI surgery, with substantial reductions in IVD height, BS/TV, Tb.N. and lower IVD score. LSI administration led to the histologic change of disc degeneration, disruption of the matrix metabolism, promotion of apoptosis of IVD cells and invasion of sensory nerves into annulus fibrosus, as well as induction of pyroptosis. Moreover, LSI surgery activated Wnt signaling in IVD tissues. Mechanical instability caused by LSI surgery accelerates the disc matrix degradation, nerve invasion, pyroptosis, and eventually lead to IVDD, which provided an alternative mouse IVDD model.

Sensory nerve ingrowth, cytokines, and instability of discogenic low back pain: A review

Introduction

Many patients suffer from discogenic low back pain. However, the mechanisms, diagnosistic strategy, and treatment of discogenic low back pain all remain controversial. The purpose of this paper was to review the pathological mechanisms of discogenic low back pain.

Methods

Many authors have investigated the pathological mechanisms of discogenic low back pain using animal models and examining human patients. Central to most investigations is understanding the innervation and instabilities of diseased intervertebral discs and the role of inflammatory mediators. We discuss three pathological mechanisms of discogenic low back pain: innervation, inflammation, and mechanical hypermobility of the intervertebral disc.

Results

Sensory nerve fibers include C-fibers and A delta-fibers, which relay pain signals from the innervated outer layers of the intervertebral disc under normal conditions. However, ingrowth of these sensory nerve fibers into the inner layers of intervertebral disc occurs under disease conditions. Levels of neurotrophic factors and some cytokines are significantly higher in diseased discs than in normal discs. Stablization of the segmental hypermobility, which can be induced by intervertebral disc degeneration, suppresses inflammation and prevents sensitization of sensory nerve fibers innervating the disc.

Conclusions

Pathological mechanisms of discogenic low back pain include sensory nerve ingrowth into inner layers of the intervertebral disc, upregulation of neurotrophic factors and cytokines, and instability. Inhibition of these mechanisms is important in the treatment of discogenic low back pain.

Establishment and Characterization of a Novel Rat Model of Mechanical Low Back Pain Using Behavioral, Pharmacologic and Histologic Methods

Chronic low back pain (LBP), the leading cause of disability globally, is notoriously difficult to treat. Most rodent models of LBP mimic lumbar radicular pain rather than mechanical LBP. Here, we describe establishment of a new rat model of mechanical LBP that is devoid of a neuropathic component. Groups of adult male Sprague Dawley rats were anesthetized and their lumbar L4/L5 and L5/L6 intervertebral disks (IVDs) were punctured (0.5 mm outer diameter, 2mm-deep) 5 (LPB-5X), or 10 (LBP-10X) times per disk. Sham-rats underwent similar surgery, but without disk puncture. Baseline noxious pressure hyperalgesia of lumbar axial deep tissues, mechanical allodynia in the hindpaws and gait were assessed prior to surgery and once-weekly until study completion on day 49. The model was also characterized using pharmacologic and histologic methods. Good animal health was maintained for ≥ 49 days post-surgery. For LBP- but not sham-rats, there was temporal development of noxious pressure hyperalgesia in lumbar axial deep tissues at days 14–49 post-surgery. Importantly, there were no between-group differences in von Frey paw withdrawal thresholds or gait parameters until study completion. On day 49, significant histologic changes were observed in the L4/L5 and L5/L6 IVDs for LBP-10X rats, but not sham-rats. In LBP-10X rats, single bolus doses of morphine produced dose-dependent relief of primary and secondary mechanical hyperalgesia in lumbar axial deep tissues at L4/L5 and L1, respectively. In conclusion, our new rat model has considerable potential for providing novel insight on the pathobiology of mechanical LBP and for analgesic efficacy assessment of novel compounds.

Pathomechanisms of discogenic low back pain in humans and animal models

BACKGROUND CONTEXT

Although explored in humans and animal models, the pathomechanisms of discogenic low back pain (LBP) remain unknown.

PURPOSE

The aim of this study was to review the literature about the pathomechanisms of discogenic LBP.

METHODS

Animal models of discogenic pain and specimens from degenerated human intervertebral discs (IVDs) have provided clues about the pathomechanisms of discogenic LBP. Painful discs are characterized by a confluence of innervation, inflammation, and mechanical hypermobility. These three possible mechanisms are discussed in this review.

RESULTS

Animal models and specimens from humans have revealed sensory innervation of lumbar IVDs and sensory nerve ingrowth into the inner layer of IVDs. Cytokines such as tumor necrosis factor-α and interleukins induce this ingrowth. Nerve growth factor has also been recently identified as an inducer of ingrowth. Finally, disc degeneration induces several collagenases; their action results in hypermobility and pain.

CONCLUSIONS

To treat discogenic LBP, it is important to prevent sensitization of sensory nerve fibers innervating the IVD, to suppress pathogenic increases of cytokines, and to decrease disc hypermobility.

ISSLS Prize winner: Increased innervation and sensory nervous system plasticity in a mouse model of low back pain due to intervertebral disc degeneration

STUDY DESIGN

Immunohistochemical and behavioral study using the SPARC (secreted protein, acidic, rich in cysteine)-null mouse model of low back pain (LBP) associated with accelerated intervertebral disc (IVD) degeneration.

OBJECTIVE

To determine if behavioral signs of LBP in SPARC-null mice are accompanied by sensory nervous system plasticity.

SUMMARY OF BACKGROUND DATA

IVD pathology is a significant contributor to chronic LBP. In humans and rodents, decreased expression of SPARC is associated with IVD degeneration. We previously reported that SPARC-null mice exhibit age-dependent behavioral signs of chronic axial LBP and radiating leg pain.

METHODS

SPARC-null and age-matched control young, middle-aged, and old mice (1.5, 6, and 24 mo of age, respectively) were evaluated. Cutaneous hind paw sensitivity to cold, heat, and mechanical stimuli were evaluated as measures of radiating pain. The grip force and tail suspension assays were performed to evaluate axial LBP. Motor impairment was assessed using an accelerating rotarod. IVD innervation was identified by immunohistochemistry targeting the nerve fiber marker PGP9.5 and the sensory neuropeptide calcitonin gene-related peptide (CGRP). Sensory nervous system plasticity was evaluated by quantification of CGRP- and neuropeptide-Y-immunoreactivity (-ir) in dorsal root ganglia neurons and CGRP-ir, GFAP-ir (astrocyte marker), and Iba-1-ir (microglia marker) in the spinal cord.

RESULTS

SPARC-null mice developed hypersensitivity to cold, axial discomfort, age-dependent motor impairment, age-dependent increases in sensory innervation in and around the IVDs, age-dependent upregulation of CGRP and neuropeptide-Y in dorsal root ganglia, and age-dependent upregulation of CGRP, microglia, and astrocytes in the spinal cord dorsal horn.

CONCLUSION

Increased innervation of degenerating IVDs by sensory nerve fibers and the neuroplasticity in sensory neurons and spinal cord could contribute to the underlying pathobiology of chronic discogenic LBP.

LEVEL OF EVIDENCE

N/A.

Upregulation of NaV1.7 in dorsal root ganglia after intervertebral disc injury in rats

STUDY DESIGN

Animal study.

OBJECTIVE

To investigate pain-related expression of NaV1.7 in dorsal root ganglia (DRG) innervating intervertebral discs.

SUMMARY OF BACKGROUND DATA

The pathophysiology of discogenic low back pain is not fully understood. Prostaglandins and cytokines produced by degenerated discs can cause pain, but nonsteroidal anti-inflammatory and steroid medications are often ineffective at pain reduction. Tetrodotoxin-sensitive, voltage-gated sodium (NaV) channels are associated with sensory transmission in primary sensory nerves, and the NaV1.7 channel has emerged as an attractive analgesic target. The purpose of this study was to investigate pain-related expression of NaV1.7 in DRG innervating intervertebral discs.

METHODS

Using a rodent model of disc puncture, we labeled DRG neurons innervating L5-L6 discs with FluoroGold neurotracer (n = 20). Half of the rats (n = 10) underwent intervertebral disc puncture using a 23-gauge needle (puncture group), and the other half underwent non-puncture sham surgery (non-puncture group). Seven and 14 days after surgery, DRGs from the L1 to L6 levels were harvested, sectioned, and immunostained for NaV1.7, and the proportion of NaV1.7-immunoreactive DRG neurons was evaluated.

RESULTS

NaV1.7 was expressed in DRG neurons innervating intervertebral discs from L1 to L5. The ratio of NaV1.7-expressing DRG neurons to total FG-labeled neurons was 7.2% and 7.6% at 1 and 2 weeks after surgery, respectively, in the non-puncture group and 16.2% and 16.3% at 1 and 2 weeks, respectively, in the puncture group. The upregulation of NaV1.7 after puncture was significant at both 1 and 2 weeks after surgery (P < 0.01).

CONCLUSION

We found that disc injury increases NaV1.7 expression in DRG neurons innervating injured discs. NaV1.7 may be a therapeutic target for pain control in patients with lumbar disc degeneration.

Dichotomizing sensory nerve fibers innervating both the lumbar vertebral body and the area surrounding the iliac crest: a possible mechanism of referred lateral back pain from lumbar vertebral body

STUDY DESIGN

Animal study.

OBJECTIVE

To determine the existence of dichotomizing sensory nerve fibers innervating both the lumbar vertebral body and the area surrounding the iliac crest (ASIC).

SUMMARY OF BACKGROUND DATA

Elderly patients with osteoporosis sometimes experience lumbar vertebral fracture and may feel diffuse nonlocalized pain in the back, the lateral portion of the trunk, and the ASIC. The pattern of sensory innervation of vertebral bodies remains unclear. DRG neurons with dichotomizing axons have been reported and are thought to be related to referred pain. The purpose of this study was to investigate the existence of dichotomizing axons to the lumbar vertebral bodies and the ASIC in rats.

METHODS

Two kinds of neurotracers (1,1´-dioctadecyl-3,3,3´,3´-tetramethylindocarbocyanine perchlorate [DiI] and Fluoro-Gold [FG]) were used. DiI crystals were placed in the left ASIC, and FG was applied into the L2 vertebral body in 10 rats. Four weeks later, left DRGs from L1 to L6 were resected, sectioned, and observed under a fluorescence microscope.

RESULTS

DiI-labeled DRG neurons innervating the ASIC and FG-labeled DRG neurons innervating the vertebral L2 body were distributed from L1 to L6. The ratio of total double-labeled per total DiI-labeled DRG neurons was 10.2%, and that of total double-labeled per total FG-labeled DRG neurons was 14.7%. These double-labeled DRG neurons innervating the L2 vertebral body had other axons that extended to the ASIC.

CONCLUSION

This finding provides a possible neuroanatomical explanation for referred pain in the ASIC from vertebral bodies.

Is section of the sympathetic rami communicantes by laparoscopy in patients with refractory low back pain efficient?

OBJECTIVE

The objective of this prospective innovative treatment is to section the pain pathways carried by sympathetic lumbar rami communicantes to achieve lasting pain relief of refractory low back pain.

METHODS

From December 2005 to September 2008, nine patients were operated by bilateral section of rami communicantes for a refractory low back pain. As a diagnostic and predictive test, all patients had, before surgery, a local anaesthetic infiltration of the sympathetic trunk at L2 performed with computed tomography guidance. Surgery is indicated if the tests lead to a reduction in pain of at least 50 %. The procedure, using a retroperitoneal laparoscopic approach, consisted to identify the sympathetic trunk and to section all lumbar rami communicantes from L1 to L2.

RESULTS

No intraoperative complications were observed. The mean postoperative follow-up was 29 ± 15 months. At the last follow-up, only 22 % (2/9) patients had an improvement of their low back pain with this surgery but with a minimal effect (30 and 50 % reduction of pain). An improvement of quality of life was observed in 33 % (3/9) of cases. Due to persistent pain, four patients had a spinal cord stimulation after this surgery.

CONCLUSIONS

Section the pain pathways carried by sympathetic lumbar rami communicantes for refractory low back pain improved 22 % of patients at the last follow-up of 29 months.

Lumbar disc degeneration induces persistent groin pain

STUDY DESIGN

Prospective study of 212 patients with groin pain but without low back pain.

OBJECTIVE

To evaluate discogenic groin pain without low back pain or radicular pain.

SUMMARY OF BACKGROUND DATA

Patients feel low back pain originating from discogenic disease. It has been reported that the rat lower lumbar discs are innervated mainly by L2 dorsal root ganglion neurons. Thus, it is possible that patients feel referred groin pain corresponding to the L2 dermatome originating from intervertebral discs; however, the referred pain has not been fully clarified in humans.

METHODS

We selected 5 patients with groin pain alone for investigation. The patients suffered from groin pain and showed disc degeneration only at 1 level (L4-L5 or L5-S1) on magnetic resonance imaging. Patients did not show any hip joint abnormality on radiography or magnetic resonance imaging. To prove that their groin pain originated in degenerated intervertebral discs, we evaluated changes in groin pain after infiltration of lidocaine into hip joints and examined pain provocation on discography, pain relief by anesthetic discoblock, and finally anterior lumbar interbody fusion surgery.

RESULTS

All patients were negative for hip joint block, positive for pain provocation on discography, and positive for pain relief by anesthetic discoblock. Furthermore, bony union was achieved 1 year after anterior interbody fusion surgery in all patients, and visual analogue scale score of groin pain was significantly improved at 1 year after surgery in all patients (P < 0.05).

CONCLUSION

In the current study, we diagnosed discogenic groin pain, using magnetic resonance imaging, infiltration of lidocaine into the hip joint, pain provocation on discography, pain relief by anesthetic discoblock, and lumbar surgery. It is important to consider the existence of discogenic groin pain if patients do not show low back pain.

Effectiveness of L2 spinal nerve infiltration for selective discogenic low back pain patients

BACKGROUND

It has been reported that rat L5/6 lumbar discs are innervated mainly by L2 dorsal root ganglion neurons. We previously reported that L2 spinal nerve infiltration was effective for discogenic low back pain (DLBP) patients, although the diagnosis was based only on the results of physical examination, plain films, and magnetic resonance imaging (MRI). The purpose of the current study was to evaluate L2 spinal nerve block for DLBP patients retrospectively based on MRI findings and surgical results.

METHODS

A total of 62 patients with only LBP and no accompanying radicular pain were investigated. Patients had only one level of disc degeneration on MRI. When pain was provoked during discography, we performed surgery at the next stage (40 patients). In all, 22 patients were excluded owing to negative discography results. Of the 40 patients, we evaluated 25 strictly selected patients suffering from DLBP. DLBP was diagnosed when the patient experienced pain relief at least 2 years after anterior lumbar interbody fusion. Fifteen patients who did not show pain relief after surgery were used for the non-DLBP group. L2 spinal nerve infiltration using 1.5 ml of lidocaine was performed in all 40 patients before surgery. The visual analogue scale (VAS) score after L2 spinal nerve infiltration was recorded, and an association of L2 spinal nerve infiltration and DLBP was explored.

RESULTS

Low back pain scores assessed using the VAS score, the Japanese Orthopedic Association score, and the Oswestry Disability Index score in the two groups were not significantly different. L 2 spinal nerve infiltration was effective for 27 patients but not effective for 13 patients; the VAS score after 15 min and 2 h improved in the DLBP group compared with that of the non-DLBP group (P < 0. 05). L2 spinal nerve infiltration was more effective in DLBP patients (21 patients, 84%) than in the non-DLBP group (6 patients, 40%) (P < 0.05).

CONCLUSIONS

In the current study, L2 spinal nerve infiltration was effective in 84% of selected DLBP patients and is thought to be a useful tool for diagnosing DLBP. However, we should take into consideration that the L2 spinal nerve infiltration was effective in 40% of non-DLBP patients as well.

[Neurostimulation techniques in the therapeutic management of chronic pelvic and perineal pain]

INTRODUCTION

Neuromodulation is a nonspecific analgesic treatment whose mechanism of action has not yet been elucidated. The purpose of this article is to review the techniques and results of neuromodulation in the management of chronic pelvic and perineal pain.

MATERIAL AND METHODS

A comprehensive review of the literature was performed by searching PUBMED for articles on the various neuromodulation techniques used in the management of chronic pelvic and perineal pain.

RESULTS

Several levels of neuromodulation of the somatic nervous system have been evaluated in the management of pelvic pain: transcutaneous electrical nerve stimulation (TENS), percutaneous nerve stimulation (PNS), nerve root or nerve trunk stimulation, spinal cord stimulation. An improvement was obtained in an average of two thirds of cases, but with declining efficacy over time. The various studies were difficult to compare due to the heterogeneous study populations and very diverse endpoints. Interesting studies on the value of autonomic nervous system intervention have been described, but with no specific trials of neuromodulation.

CONCLUSION

The place of neuromodulation in the management of patients with chronic pelvic and perineal pain has yet to be defined, as it is too frequently used as a last resort. It appears important to develop and analyse this treatment modality in large-scale, randomized, prospective studies.