Injury to dorsal root ganglia alters innervation of spinal cord dorsal horn lamina involved in nociception

Navigated Radiofrequency Ablation Peripheral Rhizotomy for Lumbosacral Hypertonia in a Nonambulatory Patient With Spinal Fusion: Indications, Surgical Techniques, and Lessons Learned

BACKGROUND AND OBJECTIVES

Radiofrequency ablation (RFA) is a destructive therapy which causes target tissue destruction by application of a thermal dose. Neurosurgical applications of RFA are well-described for myriad chronic pain and movement disorder diagnoses. In fact, RFA pallidotomy and thalamotomy are the initial procedures from which the field of neurosurgical management for movement disorders emerged. RFA rhizotomy for post-traumatic spasms was popular in the 1970s and 1980s, although it was largely abandoned after the invention and Food and Drug Administration approval of intrathecal baclofen therapy. RFA has not been described as a primary treatment of hypertonia in nonambulatory children.

METHODS

We report a case of computer-navigated, nonselective RFA peripheral rhizotomy for a nonambulatory child with a history of severe scoliosis and spinal fusion, where an open rhizotomy was technically impractical.

RESULTS

Navigation to and ablation of the bilateral L1-L5 peripheral nerves with this approach was successful, and the patient experienced bilateral lower extremity tone improvement.

CONCLUSION

We use this case to highlight considerations in indications, our applied operative technique, and lessons learned from this novel application of RFA peripheral rhizotomy in children.

Unique Characteristics of the Dorsal Root Ganglion as a Target for Neuromodulation

Objective

The dorsal root ganglion (DRG) is a novel target for neuromodulation, and DRG stimulation is proving to be a viable option in the treatment of chronic intractable neuropathic pain. Although the overall principle of conventional spinal cord stimulation (SCS) and DRG stimulation—in which an electric field is applied to a neural target with the intent of affecting neural pathways to decrease pain perception—is similar, there are significant differences in the anatomy and physiology of the DRG that make it an ideal target for neuromodulation and may account for the superior outcomes observed in the treatment of certain chronic neuropathic pain states. This review highlights the anatomy of the DRG, its function in maintaining homeostasis and its role in neuropathic pain, and the unique value of DRG as a target in neuromodulation for pain.

Methods

A narrative literature review was performed.

Results

Overall, the DRG is a critical structure in sensory transduction and modulation, including pain transmission and the maintenance of persistent neuropathic pain states. Unique characteristics including selective somatic organization, specialized membrane characteristics, and accessible and consistent location make the DRG an ideal target for neuromodulation. Because DRG stimulation directly recruits the somata of primary sensory neurons and harnesses the filtering capacity of the pseudounipolar neural architecture, it is differentiated from SCS, peripheral nerve stimulation, and other neuromodulation options.

Conclusions

There are several advantages to targeting the DRG, including lower energy usage, more focused and posture-independent stimulation, reduced paresthesia, and improved clinical outcomes.

Effectiveness and Safety of Dorsal Root Ganglion Stimulation for the Treatment of Chronic Pain: A Pooled Analysis

INTRODUCTION

Since it became available in the mid-2010s, dorsal root ganglion (DRG) stimulation has become part of the armamentarium to treat chronic pain. To date, one randomized controlled trial, and several studies of moderate sample size and various etiologies have been published on this topic. We conducted a pooled analysis to investigate the generalizability of individual studies and to identify differences in outcome between chronic pain etiologic subgroups and/or pain location.

MATERIALS AND METHODS

One prospective, randomized comparative trial and six prospective, single-arm, observational studies were identified that met pre-defined acceptance criteria. Pain scores and patient-reported outcome (PRO) measures were weighted by study sample sizes and pooled. Safety data are reported in aggregate form.

RESULTS

Our analysis included 217 patients with a permanent implant at 12-month follow-up. Analysis of pooled data showed an overall weighted mean pain score of 3.4, with 63% of patients reporting ≥50% pain relief. Effectiveness sub-analyses in CRPS-I, causalgia, and back pain resulted in a mean reduction in pain intensity of 4.9, 4.6, and 3.9 points, respectively. Our pooled analysis showed a pain score for primary affected region ranging from 1.7 (groin) to 3.0 (buttocks) and responder rates of 80% for foot and groin, 75% for leg, and 70% for back. A substantial improvement in all PROs was observed at 12 months. The most commonly reported procedural or device complications were pain at the IPG pocket site, lead fracture, lead migration, and infection.

CONCLUSIONS

DRG stimulation is an effective and safe therapy for various etiologies of chronic pain.

Peripheral axotomy-induced changes of motor function and histological structure of spinal anterior horn

The aim of this study was to evaluate changes of both peripheral motor function and histology of spinal anterior horn in adult rats after unilateral sciatectomy. Ten adult healthy rats served as control group, while in the ten rat experimental group the right sciatic nerve was severed. We followed-up nerve motor function using a sciatic function index and electromyography activity of the gastrocnemious muscle. The rats of the experimental group presented the expected gross locomotor deficit and leg muscle atrophy. At 12 weeks post sciatectomy, L4 and L5 spinal cord segments were removed from the twenty rats and were analysed by istological stereological methods. In the axotomized animals volume of the anterior horn and its content of motor neurons decreased, while the content of astrocytes increased (p < 0.05). Thus, in adult rats, beside the obvious peripheral nerve disfuction, the sciatic nerve axotomy have severe consequences on the soma of the injured motor neurons in the spinal anterior horn. All these quantitative analyses may be usefull to quantify changes occurring in adult animals after axotomy and eventual management to modify the final outcomes in peripheral nerve disorders.

Sciatic nerve injury alters the spatial arrangement of neurons and glial cells in the anterior horn of the spinal cord

The spatial arrangement of the cell is important and considered as underlying mechanism for mathematical modeling of cell to cell interaction. The ability of cells to take on the characteristics of other cells in an organism, it is important to understand the dynamical behavior of the cells. This method implements experimental parameters of the cell-cell interaction into the mathematical simulation of cell arrangement. The purpose of this research was to explore the three-dimensional spatial distribution of anterior horn cells in the rat spinal cord to examine differences after sciatic nerve injury. Sixteen Sprague-Dawley male rats were assigned to control and axotomy groups. Twelve weeks after surgery, the anterior horn was removed for first- and second-order stereological studies. Second-order stereological techniques were applied to estimate the pair correlation and cross-correlation functions using a dipole probe superimposed onto the spinal cord sections. The findings revealed 7% and 36% reductions in the mean volume and total number of motoneurons, respectively, and a 25% increase in the neuroglial cell number in the axotomized rats compared to the control rats. In contrast, the anterior horn volume remained unchanged. The results also indicated a broader gap in the pair correlation curve for the motoneurons and neuroglial cells in the axotomized rats compared to the control rats. This finding shows a negative correlation for the distribution of motoneurons and neuroglial cells in the axotomized rats. The cross-correlation curve shows a negative correlation between the motoneurons and neuroglial cells in the axotomized rats. These findings suggest that cellular structural and functional changes after sciatic nerve injury lead to the alterations in the spatial arrangement of motoneurons and neuroglial cells, finally affecting the normal function of the central nervous system. The experimental protocol was reviewed and approved by the Animal Ethics Committee of Shahid Beheshti University of Medical Sciences (approval No. IR.SBMU.MSP.REC1395.375) on October 17, 2016.

Postinjury Induction of Activated ErbB2 Selectively Hyperactivates Denervated Schwann Cells and Promotes Robust Dorsal Root Axon Regeneration

Following nerve injury, denervated Schwann cells (SCs) convert to repair SCs, which enable regeneration of peripheral axons. However, the repair capacity of SCs and the regenerative capacity of peripheral axons are limited. In the present studies we examined a potential therapeutic strategy to enhance the repair capacity of SCs, and tested its efficacy in enhancing regeneration of dorsal root (DR) axons, whose regenerative capacity is particularly weak. We used male and female mice of a doxycycline-inducible transgenic line to induce expression of constitutively active ErbB2 (caErbB2) selectively in SCs after DR crush or transection. Two weeks after injury, injured DRs of induced animals contained far more SCs and SC processes. These SCs had not redifferentiated and continued to proliferate. Injured DRs of induced animals also contained far more axons that regrew along SC processes past the transection or crush site. Remarkably, SCs and axons in uninjured DRs remained quiescent, indicating that caErbB2 enhanced regeneration of injured DRs, without aberrantly activating SCs and axons in intact nerves. We also found that intraspinally expressed glial cell line-derived neurotrophic factor (GDNF), but not the removal of chondroitin sulfate proteoglycans, greatly enhanced the intraspinal migration of caErbB2-expressing SCs, enabling robust penetration of DR axons into the spinal cord. These findings indicate that SC-selective, post-injury activation of ErbB2 provides a novel strategy to powerfully enhance the repair capacity of SCs and axon regeneration, without substantial off-target damage. They also highlight that promoting directed migration of caErbB2-expressing SCs by GDNF might be useful to enable axon regrowth in a non-permissive environment.SIGNIFICANCE STATEMENT Repair of injured peripheral nerves remains a critical clinical problem. We currently lack a therapy that potently enhances axon regeneration in patients with traumatic nerve injury. It is extremely challenging to substantially increase the regenerative capacity of damaged nerves without deleterious off-target effects. It was therefore of great interest to discover that caErbB2 markedly enhances regeneration of damaged dorsal roots, while evoking little change in intact roots. To our knowledge, these findings are the first demonstration that repair capacity of denervated SCs can be efficaciously enhanced without altering innervated SCs. Our study also demonstrates that oncogenic ErbB2 signaling can be activated in SCs but not impede transdifferentiation of denervated SCs to regeneration-promoting repair SCs.

Percutaneous transforaminal endoscopic surgery (PTES) for symptomatic lumbar disc herniation: a surgical technique, outcome, and complications in 209 consecutive cases

Background

We designed an easy posterolateral transforaminal endoscopic decompression technique, termed PTES, for radiculopathy secondary to lumbar disc herniation. The purpose of the study is to describe the technique of PTES and evaluate the efficacy and safety for treatment of lumbar disc herniation including primary herniation, reherniation, intracanal herniation, and extracanal herniation and to report outcome and complications.

Methods

PTES was performed to treat 209 cases of intracanal or extracanal herniations with or without extruding or sequestrated fragment, high iliac crest, scoliosis, calcification, or cauda equina syndrome including recurrent herniation after previous surgical intervention at the index level or adjacent disc herniation after decompression and fusion. Preoperative and postoperative leg pain was evaluated using the 10-point visual analog scale (VAS) and the results were determined to be excellent, good, fair, or poor according to the MacNab classification at 2-year follow-up.

Results

The patients were followed for an average of 26.3 ± 2.3 months. The VAS score of leg pain significantly dropped from 9 (6–10) before operation to 1 (0–3) (P < 0.001) immediately after the operation and to 0 (0–3) (P < 0.001) 2 years after operation. At 2-year follow-up, 95.7% (200/209) of the patients showed excellent or good outcomes, 2.9% (6/209) fair and 1.4% (3/209) poor. No patients had any form of permanent iatrogenic nerve damage and a major complication, although there were one case of infection and one case of recurrence.

Conclusions

PTES for lumbar disc herniation is an effective and safe method with simple orientation, easy puncture, reduced steps, and little X-ray exposure, which can be applied in almost all kinds of lumbar disc herniation, including L5/S1 level with high iliac crest, herniation with scoliosis or calcification, recurrent herniation, and adjacent disc herniation after decompression and fusion. The learning curve is no longer steep for surgeons.

Pulsed electrical stimulation protects neurons in the dorsal root and anterior horn of the spinal cord after peripheral nerve injury

Most studies on peripheral nerve injury have focused on repair at the site of injury, but very few have examined the effects of repair strategies on the more proximal neuronal cell bodies. In this study, an approximately 10-mm-long nerve segment from the ischial tuberosity in the rat was transected and its proximal and distal ends were inverted and sutured. The spinal cord was subjected to pulsed electrical stimulation at T₁₀ and L₃, at a current of 6.5 mA and a stimulation frequency of 15 Hz, 15 minutes per session, twice a day for 56 days. After pulsed electrical stimulation, the number of neurons in the dorsal root ganglion and anterior horn was increased in rats with sciatic nerve injury. The number of myelinated nerve fibers was increased in the sciatic nerve. The ultrastructure of neurons in the dorsal root ganglion and spinal cord was noticeably improved. Conduction velocity of the sciatic nerve was also increased. These results show that pulsed electrical stimulation protects sensory neurons in the dorsal root ganglia as well as motor neurons in the anterior horn of the spinal cord after peripheral nerve injury, and that it promotes the regeneration of peripheral nerve fibers.

Identification of potential therapeutic targets in a model of neuropathic pain

Neuropathic pain (NP) is caused by damage to the nervous system, resulting in dysfunction and aberrant pain. The cellular functions (e.g., peripheral neuron spinal cord innervation, neuronal excitability) associated with NP often develop over time and are likely associated with gene expression changes. Gene expression studies on the cells involved in NP (e.g., sensory dorsal root ganglion neurons) are publically available; the mining of these studies may enable the identification of novel targets and the subsequent development of therapies that are essential for improving quality of life for the millions of individuals suffering with NP. Here we analyzed a publically available microarray dataset (GSE30165) in order to identify new RNAs (e.g., messenger RNA (mRNA) isoforms and non-coding RNAs) underlying NP. GSE30165 profiled gene expression in dorsal root ganglion neurons (DRG) and in sciatic nerve (SN) after resection, a NP model. Gene ontological analysis shows enrichment for sensory and neuronal processes. Protein network analysis demonstrates DRG upregulated genes typical to an injury and NP response. Of the top changing genes, 34 and 36% are associated with more than one protein coding isoform in the DRG and SN, respectively. The majority of genes are receptor and enzymes. We identified 15 long non-coding RNAs (lncRNAs) targeting these genes in LNCipedia.org, an online comprehensive lncRNA database. These RNAs represent new therapeutic targets for preventing NP development and this approach demonstrates the feasibility of data reanalysis for their identification.

Evaluation of pain behavior and calcitonin gene-related peptide immunoreactive sensory nerve fibers in the spinal dorsal horn after sciatic nerve compression and application of nucleus pulposus in rats

STUDY DESIGN

Animal study.

OBJECTIVE

To evaluate pain behavior and neuropeptide changes in the spinal dorsal horn after sciatic nerve compression and application of nucleus pulposus (NP) in rats.

SUMMARY OF BACKGROUND DATA

The pathomechanisms of lumbar disc herniation pain have not been fully elucidated. Pain-associated neuropeptides, including substance P and calcitonin gene-related peptide (CGRP), are produced in dorsal root ganglion neurons and transported to spinal dorsal horn nerve terminals where they function in pain transmission. However, changes in CGRP-immunoreactive (IR) sensory nerve terminals have not been reported in models of disc herniation. This study evaluated pain-related behavior and changes in CGRP-IR terminals in the spinal dorsal horn after combined sciatic nerve compression and NP application.

METHODS

Five groups of rats underwent either sciatic nerve compression with NP (n = 20), application of NP only (n = 20), nerve compression only (n = 20), and sham operation with neither compression nor NP (n = 20) or no operation (controls, n = 20). Mechanical hyperalgesia was measured every second day for 3 weeks. CGRP-IR terminals in each spinal dorsal horn lamina were examined 7 and 14 days postsurgery. Pain behavior and CGRP immunoreactivity were compared among the 5 groups.

RESULTS

Mechanical hyperalgesia was found in the NP only, nerve compression only, and the NP with nerve compression groups (P ≤ 0.05). CGRP-IR nerve terminals in the superficial laminae (I and II) and the deep laminae (III-VI) significantly increased in the NP only, nerve compression only, and NP with nerve compression groups compared with control and sham groups (P ≤ 0.05). Significant mechanical hyperalgesia and increased CGRP-IR nerve terminals were found in the NP with nerve compression group compared with the NP only and nerve compression only groups (P ≤ 0.05).

CONCLUSION

Our results indicate that nerve compression plus NP application produces the most pain-related behavior. CGRP-IR nerve terminals increased in laminae I and II that transmit pain and in laminae III to VI that transmit proprioception. Findings suggest that nerve compression plus NP application induces changes in CGRP expression in the superficial and deep laminae, and these changes are partly responsible for disc herniation pain.

Functional up-regulation of Nav1.8 sodium channel in Aβ afferent fibers subjected to chronic peripheral inflammation

Background

Functional alterations in the properties of Aβ afferent fibers may account for the increased pain sensitivity observed under peripheral chronic inflammation. Among the voltage-gated sodium channels involved in the pathophysiology of pain, Na_v1.8 has been shown to participate in the peripheral sensitization of nociceptors. However, to date, there is no evidence for a role of Na_v1.8 in controlling Aβ-fiber excitability following persistent inflammation.

Methods

Distribution and expression of Na_v1.8 in dorsal root ganglia and sciatic nerves were qualitatively or quantitatively assessed by immunohistochemical staining and by real time-polymerase chain reaction at different time points following complete Freund’s adjuvant (CFA) administration. Using a whole-cell patch-clamp configuration, we further determined both total I_Na and TTX-R Na_v1.8 currents in large-soma dorsal root ganglia (DRG) neurons isolated from sham or CFA-treated rats. Finally, we analyzed the effects of ambroxol, a Na_v1.8-preferring blocker on the electrophysiological properties of Na_v1.8 currents and on the mechanical sensitivity and inflammation of the hind paw in CFA-treated rats.

Results

Our findings revealed that Na_v1.8 is up-regulated in NF200-positive large sensory neurons and is subsequently anterogradely transported from the DRG cell bodies along the axons toward the periphery after CFA-induced inflammation. We also demonstrated that both total I_Na and Na_v1.8 peak current densities are enhanced in inflamed large myelinated Aβ-fiber neurons. Persistent inflammation leading to nociception also induced time-dependent changes in Aβ-fiber neuron excitability by shifting the voltage-dependent activation of Na_v1.8 in the hyperpolarizing direction, thus decreasing the current threshold for triggering action potentials. Finally, we found that ambroxol significantly reduces the potentiation of Na_v1.8 currents in Aβ-fiber neurons observed following intraplantar CFA injection and concomitantly blocks CFA-induced mechanical allodynia, suggesting that Na_v1.8 regulation in Aβ-fibers contributes to inflammatory pain.

Conclusions

Collectively, these findings support a key role for Na_v1.8 in controlling the excitability of Aβ-fibers and its potential contribution to the development of mechanical allodynia under persistent inflammation.

Pain-related sensory innervation in monoiodoacetate-induced osteoarthritis in rat knees that gradually develops neuronal injury in addition to inflammatory pain

Background

The exact mechanism of knee osteoarthritis (OA)-associated pain is unclear, whereas mixed evidence of inflammatory pain and neuropathic pain has been noted. We aimed to investigate pain-related sensory innervation in a monoiodoacetate (MIA)-induced model of OA.

Methods

Sixty of seventy female Sprague Dawley rats of six week-old underwent intra-articular MIA and fluorogold (FG) retrograde neurotracer injection into their right (ipsilateral) knee, while their left knees were treated with FG in saline as a control (contralateral knee). Other rats were treated with FG only bilaterally, and used as controls. Rats were evaluated for tactile allodynia using von Frey hairs. Proinflammatory mediators in the knee soft tissues, including tumor necrosis factor (TNF)-α, interleukin (IL)-6, and nerve growth factor (NGF), were quantified using ELISAs to evaluate inflammation in the knee after 1, 4, 7,14,21, and 28 days post injection:. Dorsal root ganglia (DRG) were immunostained for three molecules after 7,14,21, and 28 days post injection: calcitonin gene-related peptide (CGRP), a marker of inflammatory pain; and activating transcription factor-3 (ATF3) and growth associated protein-43 (GAP43), as markers for nerve injury and regenerating axons. The distribution of microglia in the spinal cord were also evaluated, because they have been reported to increase in neuropathic pain states. These evaluations were performed up to 28 days postinjection. P < 0.05 was considered significant.

Results

Progressive tactile allodynia and elevated cytokine concentrations were observed in ipsilateral knees. CGRP-immunoreactive (-ir) ipsilateral DRG neurons significantly increased, peaking at 14 days postinjection, while expression of FG-labeled ATF3-ir or ATF3-ir GAP43-ir DRG neurons significantly increased in a time-dependent manner. Significant proliferation of microglia were found with time in the ipsilateral dorsal horn.

Conclusions

Pain-related characteristics in a MIA-induced rat OA model can originate from an inflammatory pain state induced by the local inflammation initiated by inflammatory cytokines, and that state will be followed by gradual initiation of neuronal injury, which may induce the neuropathic pain state.

PATHOANATOMIC BASIS FOR STRETCH-INDUCED LUMBAR NERVE ROOT INJURY WITH A REVIEW OF THE LITERATURE

OBJECTIVE

Persistent pain originating from a dysfunctional lumbar motion segment poses significant challenges in the clinical arena. Although the predominance of the existing spine literature has addressed nerve root compression as the principal cause of pain, it is equally likely that a stretch mechanism may be responsible for all or part of the pathology.

METHODS

The literature supporting the role of stretch damage as a primary cause of nerve root injury and pain was systematically reviewed. Pathoanatomic considerations between nerve roots and juxtaposed environment are described and correlated with the available literature. Potential anatomic relationships that may lead to stretch-induced injury are delineated.

RESULTS

A dynamic lumbar functional spinal unit that encloses a tethered nerve root can create significant stretch and/or compression. This phenomenon may be present in a variety of pathological conditions. These include anterior, posterior, and rotatory olisthesis as well as degenerative conditions such as the loss of disc interspace height and frank multisegment spinal deformity. Although numerous studies have demonstrated that stretch can result in nerve damage, the pathophysiology that may associate nerve stretch with chronic pain has yet to be determined.

CONCLUSION

The current literature concerning stretch-related injury to nerve roots is reviewed, and a conceptual framework for its diagnosis and treatment is proposed and graphically illustrated using cadaveric specimens. The dynamic biomechanical and functional interrelationships between neural structures and adjacent connective tissue elements are particularly important in the face of spinal deformity.

Dorsal root compression produces myelinated axonal degeneration near the biomechanical thresholds for mechanical behavioral hypersensitivity

Increased sensitivity to mechanical stimuli produced by transient cervical nerve root compression is dependent on the severity of applied load. In addition, trauma in the nervous system induces local inflammation, Wallerian degeneration, and a host of other degenerative processes leading to axonal dysfunction. Here, axonal degeneration and inflammation were assessed following transient dorsal root compression to establish a relationship between conditions for dorsal root axonal changes and those previously established for the onset and maintenance of mechanical behavioral hypersensitivity (26.3 mN and 38.2 mN, respectively). Compression loads were applied over a range (0-110 mN) known to produce sustained behavioral hypersensitivity. CD68- and NF200-immunoreactivity, as well as axonal pathological changes, were assessed in the dorsal root to investigate the load thresholds requisite for inducing macrophage infiltration and axonal degeneration relative to those thresholds for producing the onset and persistence of behavioral hypersensitivity. Neurofilament accumulation and the depletion of NF200-immunoreactivity in the region of compressed tissue were produced for loads that produce mechanical behavioral hypersensitivity. A 50th-percentile load threshold was determined (31.6 mN) governing the onset of NF200 depletion. However, CD68-immunoreactivity was increased for nearly all loads, suggesting that macrophage recruitment may not be directly related to nerve root-mediated behavioral hypersensitivity. This study provides new evidence for threshold-mediated degenerative changes in the context of behavioral hypersensitivity following nerve root compression.

Increase of 200-kDa neurofilament-immunoreactive afferents in the substantia gelatinosa in allodynic rats induced by compression of the dorsal root ganglion

STUDY DESIGN

An experimental study on mechanical allodynia, c-Fos expression, and 200-kDa-neurofilament immunoreactive (IR) afferent expression in the substantia gelatinosa related to compression of dorsal root ganglion (DRG).

OBJECTIVES

To evaluate the presence of allodynia in DRG compression model and to demonstrate that the structural changes of spinal dorsal horn related to DRG compression.

SUMMARY OF BACKGROUND DATA

A previous experimental report has demonstrated that the peripheral nerve injury may trigger some structural changes of the superficial spinal dorsal horn. These changes of the spinal dorsal horn were thought to be important for the modulation of pain sensations such as allodynia.

METHODS

Sixty-eight male rats were used. The left L5 lamina was exposed and a drill hole was made in it. A stainless rod was placed close to the left L5 DRG through the drill hole. Behavioral testing with von Frey filament was performed. On day 28 after surgery, c-Fos expression in the spinal dorsal horn by non-noxious stimulation was examined. L5 spinal cord and bilateral L5 DRG specimens were stained with antibody for 200-kDa neurofilament (RT97). In addition, 2 or 3 spinal cord sections per rats were processed for immunoelectron microscopy.

RESULTS

In the DRG compression group, the mechanical withdrawal threshold was decreased, c-Fos expression by non-noxious stimulation was observed in the spinal dorsal horn, and there were many RT97-IR afferents in the superficial spinal dorsal horn. Immunoelectron microscopic observations showed that RT97-IR terminals made synaptic contact with neurons in the superficial spinal dorsal horn. There were no significant differences in the distribution of RT97-IR neurons in DRG between compression and sham group.

CONCLUSIONS

DRG compression induced allodynia and that RT97-IR afferents increased in the superficial dorsal horn of the spinal cord. The increase of RT97-IR afferents may be related to the mechanisms for the observed allodynia.

Transforaminal posterolateral endoscopic discectomy with or without the combination of a low-dose chymopapain: a prospective randomized study in 280 consecutive cases

STUDY DESIGN

A prospective randomized study involving 280 consecutive cases of lumbar disc herniation managed either by an endoscopic discectomy alone or an endoscopic discectomy combined with an intradiscal injection of a low dose (1000 U) of chymopapain.

OBJECTIVE

To compare outcome, complications, and reherniations of both techniques.

SUMMARY OF BACKGROUND DATA

Despite a low complication rate, posterolateral endoscopic nucleotomy has made a lengthy evolution because of an assumed limited indication. Chemonucleolysis, however, proven to be safe and effective, has not continued to be accepted by the majority in the spinal community as microdiscectomy is considered to be more reliable.

METHOD

A total of 280 consecutive patients with a primary herniated, including sequestrated, lumbar disc with predominant leg pain, was randomized. A clinical follow-up was performed at 3 months, and at 1 and 2 years after the index operation with an extensive questionnaire, including the visual analog scale for pain and the MacNab criteria. The cohort integrity at 3 months was 100%, at 1 year 96%, and at 2 years 92%.

RESULTS

At the 3-month evaluation, only minor complications were registered. At 1-year postoperatively, group 1 (endoscopy alone) had a recurrence rate of 6.9% compared to group 2 (the combination therapy), with a recurrence rate of 1.6%, which was a statistically significant difference in favor of the combination therapy (P = 0045). At the 2-year follow-up, group 1 reported that 85.4% had an excellent or good result, 6.9% a fair result, and 7.7% were not satisfied. At the 2-year follow-up, group 2 reported that 93.3% had an excellent or good result, 2.5% a fair result, and 4.2% were not satisfied. This outcome was statistically significant in favor of the group including chymopapain. There were no infections or patients with any form of permanent iatrogenic nerve damage, and no patients had a major complication.

CONCLUSIONS

A high percentage of patient satisfaction could be obtained with a posterior lateral endoscopic discectomy for lumbar disc herniation, and a statistically significant improvement of the results was obtained when an intradiscal injection of 1000 U of chymopapain was added. There was a low recurrence rate with no major complications. The method can be applied in any type of lumbar disc herniation, including the L5-S1 level.

Head-turned rear impact causing dynamic cervical intervertebral foramen narrowing: implications for ganglion and nerve root injury

OBJECT

A rotated head posture at the time of vehicular rear impact has been correlated with a higher incidence and greater severity of chronic radicular symptoms than accidents occurring with the occupant facing forward. No studies have been conducted to quantify the dynamic changes in foramen dimensions during head-turned rear-impact collisions. The objectives of this study were to quantify the changes in foraminal width, height, and area during head-turned rear-impact collisions and to determine if dynamic narrowing causes potential cervical nerve root or ganglion impingement.

METHODS

The authors subjected a whole cervical spine model with muscle force replication and a surrogate head to simulated head-turned rear impacts of 3.5, 5, 6.5, and 8 G following a noninjurious 2-G baseline acceleration. Continuous dynamic foraminal width, height, and area narrowing were recorded, and peaks were determined during each impact; these data were then statistically compared with those obtained at baseline. The authors observed significant increases (p < 0.05) in mean peak foraminal width narrowing values greater than baseline values, of up to 1.8 mm in the left C5-6 foramen at 8 G. At the right C2-3 foramen, the mean peak dynamic foraminal height was significantly narrower than baseline when subjected to rear-impacts of 5 and 6.5 G, but no significant increases in foraminal area were observed. Analysis of the results indicated that the greatest potential for cervical ganglion compression injury existed at C5-6 and C6-7. Greater potential for ganglion compression injury existed at C3-4 and C4-5 during head-turned rear impact than during head-forward rear impact.

CONCLUSIONS

Extrapolation of present results indicated potential ganglion compression in patients with a non-stenotic foramen at C5-6 and C6-7; in patients with a stenotic foramen the injury risk greatly increases and spreads to include the C3-4 through C6-7 as well as C4-5 through C6-7 nerve roots.

Dynamic intervertebral foramen narrowing during simulated rear impact

STUDY DESIGN

A biomechanical study of intervertebral foraminal narrowing during simulated automotive rear impacts.

OBJECTIVES

To quantify foraminal width, height, and area narrowing during simulated rear impact, and evaluate the potential for nerve root and ganglion impingement in individuals with and without foraminal spondylosis.

SUMMARY OF BACKGROUND DATA

Muscle weakness and paresthesias, documented in whiplash patients, have been associated with neural compression within the cervical intervertebral foramen. To our knowledge, no studies have comprehensively examined dynamic changes in foramen dimensions.

METHODS

There were 6 whole cervical spine specimens (average age 70.8 years) with muscle force replication and surrogate head that underwent simulated rear impact at 3.5, 5, 6.5, and 8 g, following noninjurious baseline 2 g acceleration. Peak dynamic narrowing of foraminal width, height, and area were determined during each impact and statistically compared to baseline narrowing.

RESULTS

Significant increases (P < 0.05) in average peak foraminal width narrowing above baseline were observed at C5-C6 beginning with 3.5 g impact. No significant increases in average peak foraminal height narrowing were observed, while average peak foraminal areas were significantly narrower than baseline at C4-C5 at 3.5, 5, and 6.5 g.

CONCLUSIONS

Extrapolation of the present results indicated that the highest potential for ganglia compression injury was at the lower cervical spine, C5-C6 and C6-C7. Acute ganglia compression may produce a sensitized neural response to repeat compression, leading to chronic radiculopathy following rear impact.

Extracellular signal-regulated kinase mitogen-activated protein kinase activation in the dorsal root ganglion (DRG) and spinal cord after DRG injury in rats

STUDY DESIGN

We investigated the extracellular signal-regulated kinase (ERK) activation by immunohistochemically detecting phosphorylated ERK (pERK) in the dorsal root ganglion (DRG) and spinal cord.

OBJECTIVE

To clarify the ERK activation in the rat nervous system following DRG injury.

SUMMARY OF BACKGROUND DATA

Radicular pain is known to be associated with DRG injury caused by intervertebral disc herniation. ERK is activated by phosphorylation in the DRG and spinal cord by noxious stimuli, which are related to pain hypersensitivity.

METHODS

From 2 minutes to 24 hours after the left L4 DRG crush injury, L4 DRGs and spinal cords were resected to prepare serial sections, which were investigated immunohistochemically.

RESULTS

In the DRG, ERK activation was detected in neurons and satellite cells at 2 minutes; the former was maintained at increased levels for 20 minutes, and the latter for 4 hours. At 30 minutes, pERK immunoreactivity was observed in Schwann cells, which continued for up to 24 hours. In the spinal cord, pERK-positive neurons were detected at 2 minutes, and the pERK levels were maintained at increased levels for 20 minutes.

CONCLUSIONS

Profiles of pERK induction in neurons after DRG injury were similar between the DRG and spinal cord, whereas pERK induction in the satellite cells was more long lasting. The pERK induction in Schwann cells in the DRG was late onset and the most long lasting.

Alteration of sensorineural circuits in spinal cord by chronic contact dermatitis

In the present study, eczema-induced alteration of sensorineural circuits of the spinal dorsal horn was investigated. Eczematous lesions resembling atopic dermatitis were induced by repeated application of diphenylcyclopropenone (DCP) onto murine right hind paws. Immunohistochemical labeling of calcitonin gene-related peptide and substance P was increased in the dorsal horn on the DCP-treated side. Expression of calcium binding proteins, calretinin and calbindin-D28K, normally widely seen in dorsal horn interneurons, was up-regulated on the DCP-treated side. E-Cadherin and alpha-N-catenin, synapse-related molecules, were intensely expressed in the spinal dorsal horn of the DCP-treated side. Interestingly, c-Fos positive cells were also significantly increased in laminae I and III of the DCP-treated side. These results suggest an enhanced release of neuropeptides from peripheral afferents and alterations in the sensorineural circuitry of the dorsal horn. These changes may account for the enhanced sensory sensitivity recognized in patients with chronic eczema and atopic dermatitis.

Transient cervical nerve root compression in the rat induces bilateral forepaw allodynia and spinal glial activation: mechanical factors in painful neck injuries

STUDY DESIGN

An in vivo rat model of transient cervical nerve root compression.

OBJECTIVES

To investigate the potential for cervical nerve root compression to produce behavioral hypersensitivity and examine its dependence on compression.

SUMMARY OF BACKGROUND DATA

Clinically, nerve root injury has been hypothesized as a potential source of neck pain, particularly because cervical nerve roots are at mechanical risk for injury during neck loading. Lumbar radiculopathy models of nerve root ligation show that mechanical allodynia and spinal glial changes depend on nerve root deformation magnitude. However, no investigation has been performed to examine cervical nerve root compression as a cause of pain.

METHODS

Two compressive forces (10 and 60 grams force [gf]) were transiently applied to the C7 nerve roots unilaterally using microvascular clips in separate groups (n = 12 each). Sham procedures were also performed in a separate group of rats (n = 12). Bilateral forepaw mechanical allodynia was monitored after surgery for 7 days. On day 7, spinal glial activation was assessed using immunohistochemistry to investigate its dependence on nerve root compressive force, in the context of behavioral hypersensitivity.

RESULTS

Bilateral allodynia was observed following injury, which was significantly (P < 0.042) increased over sham and baseline responses. No difference in allodynia was found between the 10 and 60 gf injuries. Astrocytic and microglial activation were observed in the ipsilateral dorsal horn following compression, with only astrocytic activation paralleling allodynia patterns.

CONCLUSIONS

Results imply a force threshold exists less than 10 gf for persistent pain symptoms following transient cervical nerve root compression. Findings also suggest that spinal glial activation may be related to behavioral sensitivity and may modulate cervical nerve root mediated pain.

Posterolateral transforaminal selective endoscopic discectomy and thermal annuloplasty for chronic lumbar discogenic pain: a minimal access visualized intradiscal surgical procedure

BACKGROUND CONTEXT

Chronic lumbar discogenic pain (CLDP) impairs the patient's physical abilities to function within the normal physiologic loading ranges of activities of daily living. The pathogenesis of CLDP is multifactorial and not well understood. Conservative therapeutic regimens often fail to achieve sufficient pain relief. Surgical options vary greatly in surgical invasiveness as well as outcome. Definitive surgical treatment is often 360-degree fusion. The morbidity associated with this approach is significant, considering that only 65% to 80% of patients obtain satisfactory clinical results. This has spawned interest in minimally invasive surgical options, such as intradiscal electrothermal therapy (IDET; ORATEC Interventions, Inc., Menlo Park, CA), but results are conflicting.

PURPOSE

The authors describe their surgical technique of minimal access posterolateral transforaminal selective endoscopic discectomy (SED) and bipolar radiofrequency thermal annuloplasty to treat CLDP. The procedure's rationale is based on the hypothesis that annular defects are the focal points of chronic exposure between neural sensory receptors in the defect and the inflammatogenic nucleus pulposus. In contrast to other percutaneous procedures, this technique allows direct visualization and targeting of the disc nucleus and annular fissures. Our 2-year clinical result is reported.

STUDY DESIGN/SETTING

This is a retrospective review of consecutive surgical cases performed by one surgeon (ATY). The procedures were carried out from January 1997 to December 1999. Each patient has a minimum postoperative follow-up of 2 years.

PATIENT SAMPLE

A total of 113 patients met the generally accepted clinical criteria for chronic lumbar discogenic pain and were selected for the procedure.

OUTCOME MEASURES

Two outcome measures were used for clinical assessment: a surgeon-based modified MacNab method and a patient-based questionnaire. A mandatory poor result was given to any patient who had repeat spine surgery at the same level or has indicated dissatisfaction with the surgical result on the questionnaire response.

METHOD

After meeting CLDP selection criteria, provocation contrast/indigo carmine dye discography was performed. This test was used to confirm the suspected discs as pain generators. The subject surgery then followed. Only cases with one and two levels of confirmed painful discs were entered into the study. The nonoperating author (PMT) analyzed the data.

RESULTS

Using the surgeon assessment method, 17 patients (15%) had excellent results, 32 patients (28.3%) had good results, 34 patients (30.1%) had fair results and 30 patients (26.5%) had poor results. Of the 30 patients in the poor result group, 12 reported either no improvement or worsening, and refused further surgical treatment. Of the remaining 18 patients in the poor group, 8 had spinal fusion, 3 had laminectomy and 7 had repeat spinal endoscopic surgery. The patient-based questionnaire yielded similar percentages in each category. However, only 73.5% of the 113 patients returned the survey questionnaire. There were no aborted procedures, unexpected hemorrhage, device-related complications, neurologic deficits, perioperative deaths or late instability.

CONCLUSIONS

Posterolateral transforaminal SED and radiofrequency thermal annuloplasty were used to interrupt the purported annular defect pain sensitization process, thought to be necessary in the genesis of chronic lumbar discogenic pain. Lack of clinical benefit from the subject procedure did not degrade any subsequent surgical or nonsurgical treatment options. The experience gained from this study warrants further investigation into the cellular and molecular processes that provided back pain relief in these patients.

Spinal Manipulation Postepidural Injection for Lumbar and Cervical Radiculopathy: A Retrospective Case Series

OBJECTIVE

To describe the safety and potential therapeutic benefit of spinal manipulation postepidural injection in the nonsurgical treatment of patients with cervical and lumbar radiculopathy.

METHODS

The study design was a retrospective review of outcomes of 20 cervical and 60 lumbar radiculopathy patients who underwent spinal manipulation postepidural injection in a hospital setting. Patients received either fluoroscopically guided or computed tomography (CT)-guided epidural injection of a combination of lidocaine and Depo-Medrol. The manual therapy consisted of an immediate postepidural application of flexion distraction mobilization and then high-velocity, low-amplitude spinal manipulation to the affected spinal regions. Outcome criteria were empirically defined as significant improvement, temporary improvement, or no change. The minimum follow-up time for all patients was 1 year.

RESULTS

There were no complications associated with spinal manipulation, whereas 3 complications associated with the epidural injection procedure were noted. Of lumbar spine patients, 36.67% (n = 22) noted significant improvement, 41.67% (n = 25) experienced temporary improvement, and 21.67% (n = 13) reported no change. Of the patients undergoing spinal manipulation after cervical epidural injection, 50% (n = 10) noted significant improvement, 30% (n = 6) experienced temporary improvement, whereas 20% (n = 4) exhibited no change.

CONCLUSIONS

These data suggest that spinal manipulation postepidural injection is a safe nonsurgical procedure to use in the treatment of the patient with radiculopathy of spinal origin. This is also the first report of the use of spinal manipulation postepidural injection in the cervical spine.

Lumbar nerve root injury induces central nervous system neuroimmune activation and neuroinflammation in the rat: relationship to painful radiculopathy

STUDY DESIGN

These studies were designed to examine the role of central neuroimmune activation and neuroinflammation in a rat model of lumbar radiculopathy.

OBJECTIVES

In the present study the authors investigated the role of neuroimmune activation using immunocytochemistry to detect expression of major histocompatibility complex Class II, cluster determinant 4, intracellular adhesion molecule-1 (ICAM-1), and platelet endothelial cellular adhesion molecule-1 (PECAM-1). The role of central neuroinflammation was investigated using radiation bone marrow chimeric rats.

SUMMARY OF BACKGROUND DATA

The pathologic mechanisms resulting in painful lumbar radiculopathy secondary to nerve root injury remain obscure. There is a growing body of evidence that central neuroimmune activation and neuroinflammation may play a key role in the initiation and maintenance of various pain states, including lumbar radiculopathy.

METHODS

Male Holtzman rats undergoing mechanical sensitivity testing were divided into two groups: a sham group and a chromic gut suture group. Animals were killed on day 14 post surgery. Male Holtzman rats, used to detect cluster determinant 4, major histocompatibility complex Class II, and CAM spinal expression, were divided into three groups: a normal group, a sham surgery group, and a chromic group. The male Brown Norway rats used to make the radiation bone marrow chimeras were divided into two groups: a sham group and a chromic group. Animals were killed at 1, 3, 7 or 14 days following surgery.

RESULTS

Nerve root injury in the rat produced increased spinal major histocompatibility complex Class II, cluster determinant 4, ICAM-1, and PECAM-1 immunoreactivity and increased bilateral sensitivity to tactile stimuli. Leukocyte trafficking into the spinal parenchyma was observed, which increased over time after nerve root injury.

CONCLUSIONS

The presence of bilateral mechanical allodynia and spinal neuroimmune changes following nerve root injury supports the hypothesis that central sensitization through activation of immune mediators, coupled with macrophage traffic across the blood-brain barrier, plays a key role in the development and maintenance of radicular pain.

The vascular pattern of the human dorsal root ganglion and its probable bearing on a compartment syndrome

STUDY DESIGN

A descriptive anatomic investigation of the vasculature of the dorsal root ganglions.

OBJECTIVES

To determine whether the blood supply of the various spinal ganglions is sufficiently consistent to derive a "generic" description and illustration that would be applicable to all spinal levels, and to ascertain whether this vascular pattern is inherently predisposed to the development of a closed compartment syndrome.

SUMMARY OF BACKGROUND DATA

The few previous descriptions of spinal ganglionic vasculature do not include photographic evidence showing uniformity in the arterial distribution plan at all ganglionic levels. The venous drainage, although verbally reconstructed from microscopic sections, lacks any indication of its probable role in the etiology of a compartment syndrome.

METHODS

Three perinatal cadavers received latex/India ink injections, and their removed radiculomedullary systems were cleared, transilluminated, and macroscopically photographed. Paravertebral sections were grossly removed from the spines of two adult anatomic cadavers and received retrograde venous injections of a fine suspension of barium sulfate. The intervertebral foraminal tissues were then dissected from the bone, and radiographs of them were made. For comparative reference, a nerve root/ganglion complex of a rabbit was arterially injected with a more dilute preparation of the latex/India ink suspension.

RESULTS

Macroscopic photographs of perinatal dorsal root ganglions showed that the pattern of the intraganglionic arterial distribution was sufficiently consistent to allow a graphic rendering and labeling of a "generic" ganglion. The series of incomplete retrograde venous injections adequately indicated the pressure labile location of a periganglionic venous plexus.

CONCLUSIONS

The common development, structure, and function of the human dorsal root ganglions have resulted in the evolution of a uniform nutritional vascular pattern that can be conceptualized in a single visual image. Its plan of a primarily internal arterialization with a superficial venous drainage renders it vulnerable to the ischemic conditions consequent on external pressures and/or internal edematous swelling. This vascular arrangement may contribute to a propensity for the ganglion to develop a compartment syndrome when subjected to compression by periforaminal degenerative or neoplastic space-occupying lesions.

How does neuropathophysiology affect the signs and symptoms of spinal disease?

A complex relationship exists between back pain and the presence of spinal disease. Particularly in chronic situations, back pain and its behavioural and emotional consequences are as likely to reflect the influence of psychosocial factors as any underlying spinal pathology. Nevertheless, physical factors are clearly important and it is significant that whereas in normal discs only the outer third of the annulus fibrosus is innervated, a much more extensive innervation develops in the presence of degeneration. Inflammation, as evidenced by leukocyte infiltration and expression of inflammatory mediators, is associated with disc degeneration and serves to alter the neural responses resulting in local and referred pain. It is probable that similar inflammatory processes, as well as direct root compression, contribute to radicular symptoms following disc herniation. An appreciation of these mechanisms encourages the search for novel treatments and permits a more rational and effective use of existing strategies for relieving pain.

Repeated injury to the lumbar nerve roots produces enhanced mechanical allodynia and persistent spinal neuroinflammation

STUDY DESIGN

A lumbar radiculopathy model investigated pain behavioral responses after nerve root reinjury.

OBJECTIVES

To gain a further understanding of central sensitization and neuroinflammation associated with chronic lumbar radiculopathy after repeated nerve root injury.

SUMMARY OF BACKGROUND DATA

The pathophysiologic mechanisms associated with chronic radicular pain remain obscure. It has been hypothesized that lumbar root injury produces neuroimmunologic and neurochemical changes, sensitizing the spinal cord and causing pain responses to manifest with greater intensity and longer duration after reinjury. However, this remains untested experimentally.

METHODS

Male Holtzman rats were divided into two groups: a sham group having only nerve root exposure, and a chromic group in which the nerve root was ligated loosely with chromic gut suture. Animals underwent a second procedure at 42 days. The chromic group was further divided into a reinjury group and a chromic-sham group, in which the lumbar roots were only re-exposed. Bilateral mechanical allodynia was continuously assessed throughout the study. Qualitative assessment of spinal cord glial activation and IL-beta expression was performed.

RESULTS

Mechanical allodynia was significantly greater on both the ipsilateral and contralateral sides after reinjury (P < 0.001), and the response did not return to baseline after reinjury, as it did with the initial injury. There were also persistent spinal astrocytic and microglial activation and interleukin-1beta expression.

CONCLUSIONS

The bilateral responses support central modulation of radicular pain after nerve root injury. An exaggerated and more prolonged response bilaterally after reinjury suggests central sensitization after initial injury. Neuroinflammatory activation in the spinal cord further supports the hypothesis that central neuroinflammation plays an important role in chronic radicular pain.

Whiplash syndrome: kinematic factors influencing pain patterns

STUDY DESIGN

The overall, local, and segmental kinematic responses of intact human cadaver head-neck complexes undergoing an inertia-type rear-end impact were quantified. High-speed, high-resolution digital video data of individual facet joint motions during the event were statistically evaluated.

OBJECTIVES

To deduce the potential for various vertebral column components to be exposed to adverse strains that could result in their participation as pain generators, and to evaluate the abnormal motions that occur during this traumatic event.

SUMMARY OF BACKGROUND DATA

The vertebral column is known to incur a nonphysiologic curvature during the application of an inertial-type rear-end impact. No previous studies, however, have quantified the local component motions (facet joint compression and sliding) that occur as a result of rear-impact loading.

METHODS

Intact human cadaver head-neck complexes underwent inertia-type rear-end impact with predominant moments in the sagittal plane. High-resolution digital video was used to track the motions of individual facet joints during the event. Localized angular motion changes at each vertebral segment were analyzed to quantify the abnormal curvature changes. Facet joint motions were analyzed statistically to obtain differences between anterior and posterior strains.

RESULTS

The spine initially assumed an S-curve, with the upper spinal levels in flexion and the lower spinal levels in extension. The upper C-spine flexion occurred early in the event (approximately 60 ms) during the time the head maintained its static inertia. The lower cervical spine facet joints demonstrated statistically greater compressive motions in the dorsal aspect than in the ventral aspect, whereas the sliding anteroposterior motions were the same.

CONCLUSIONS

The nonphysiologic kinematic responses during a whiplash impact may induce stresses in certain upper cervical neural structures or lower facet joints, resulting in possible compromise sufficient to elicit either neuropathic or nociceptive pain. These dynamic alterations of the upper level (occiput to C2) could impart potentially adverse forces to related neural structures, with subsequent development of a neuropathic pain process. The pinching of the lower facet joints may lead to potential for local tissue injury and nociceptive pain.