Increased interleukin-1α and prostaglandin E2 expression in the spinal cord at 1 day after painful facet joint injury: evidence of early spinal inflammation

Unraveling quad fever: Severe hyperthermia after traumatic cervical spinal cord injury

PURPOSE

There are many infectious and inflammatory causes for elevated core-body temperatures, though they rarely pass 40 ℃ (104 ℉). The term "quad fever" is used for extreme hyperpyrexia in the setting of acute cervical spinal cord injuries (SCIs). The traditional methods of treating hyperpyrexia are often ineffective and reported morbidity and mortality rates approach 100%. This study aims to identify the incidence of elevated temperatures in SCIs at our institution and assess the effectiveness of using a non-invasive dry water temperature management system as a treatment modality with mortality.

METHODS

A retrospective analysis of acute SCI patients requiring surgical intensive care unit admission who experienced fevers ≥ 40 ℃ (104 ℉) were compared to patients with maximum temperatures < 40 ℃. Patients ≥18 years old who sustained an acute traumatic SCI were included in this study. Patients who expired in the emergency department; had a SCI without radiologic abnormality; had neuropraxia; were admitted to any location other than the surgical intensive care unit; or had positive blood cultures were excluded. SAS 9.4 was used to conduct statistical analysis.

RESULTS

Over the 9-year study period, 35 patients were admitted to the surgical intensive care unit with a verified SCI. Seven patients experienced maximum temperatures of ≥ 40 ℃. Six of those patients were treated with the dry water temperature management system with an overall mortality of 57.1% in this subgroup. The mortality rate for the 28 patients who experienced a maximum temperature of ≤ 40 ℃ was 21.4% (p = 0.16).

CONCLUSION

The diagnosis of quad fever should be considered in patients with cervical SCI in the presence of hyperthermia. In this study, there was no significant difference in mortality between quad fever patients treated with a dry water temperature management system versus SCI patients without quad fever. The early use of a dry water temperature management system appears to decrease the mortality rate of quad fever.

Elevated Levels of PGE2-Metabolite in Cerebrospinal Fluid and Cox-2 Gene Polymorphisms in Patients with Chronic, Post Cholecystectomy Pain and Visceral Hyperalgesia Compared to Healthy Controls. A Hypothesis-Generating Pilot Study

PURPOSE

Chronic, abdominal pain remains a problem in a subset of patients after cholecystectomy. The cause is often obscure but central sensitization may be an important component and could theoretically be mediated by spinal PGE2, which is regulated by several cytokines. The aim of the study was to examine cerebrospinal fluid (CSF) of participants with post cholecystectomy syndrome and healthy volunteers for signs of PGE2 and cytokine mediated central sensitization.

PATIENTS AND METHODS

In phase 1 of the study, 83 subjects were included for DNA analysis, eight of these subjects with post cholecystectomy syndrome. We examined the SNPs rs5275, rs16944 and rs1800795 from the Cox-2, IL-1β and IL-6 genes respectively. In phase 2 of the study, we examined concentrations of PGE2-metabolite (PGEM), IL-1β and IL-6 in CSF and plasma from 6 patients with post cholecystectomy syndrome and visceral hyperalgesia and 11 pain free volunteers.

RESULTS

We found a significant difference in distribution of the rs5275 SNP of the Cox-2 enzyme (CT-genotype=88% in pain group, 45% in pain free group, TT-genotype=0 in pain group, 41% in pain free group, p=0.05) but not in the other SNPs. PGEM, but not IL-6, was significantly elevated in CSF of the pain group (3.6 pg/mL, sd=1.9 vs 2.1 pg/mL, p=0.03), IL-1β was undetectable.

CONCLUSION

We found elevated PGEM levels in CSF of patients with post cholecystectomy syndrome and visceral hyperalgesia, suggesting a central, possibly inflammatory component to the pain, and overrepresentation of the CT-genotype in the rs5275 SNP in the Cox2 gene, suggesting overexpression of Cox2 as a possible cause for elevated PGEM levels.

Intra-articular MMP-1 in the spinal facet joint induces sustained pain and neuronal dysregulation in the DRG and spinal cord, and alters ligament kinematics under tensile loading

Chronic joint pain is a major healthcare challenge with a staggering socioeconomic burden. Pain from synovial joints is mediated by the innervated collagenous capsular ligament that surrounds the joint and encodes nociceptive signals. The interstitial collagenase MMP-1 is elevated in painful joint pathologies and has many roles in collagen regulation and signal transduction. Yet, the role of MMP-1 in mediating nociception in painful joints remains poorly understood. The goal of this study was to determine whether exogenous intra-articular MMP-1 induces pain in the spinal facet joint and to investigate effects of MMP-1 on mediating the capsular ligament’s collagen network, biomechanical response, and neuronal regulation. Intra-articular MMP-1 was administered into the cervical C6/C7 facet joints of rats. Mechanical hyperalgesia quantified behavioral sensitivity before, and for 28 days after, injection. On day 28, joint tissue structure was assessed using histology. Multiscale ligament kinematics were defined under tensile loading along with microstructural changes in the collagen network. The amount of degraded collagen in ligaments was quantified and substance P expression assayed in neural tissue since it is a regulatory of nociceptive signaling. Intra-articular MMP-1 induces behavioral sensitivity that is sustained for 28 days (p < 0.01), absent any significant effects on the structure of joint tissues. Yet, there are changes in the ligament’s biomechanical and microstructural behavior under load. Ligaments from joints injected with MMP-1 exhibit greater displacement at yield (p = 0.04) and a step-like increase in the number of anomalous reorganization events of the collagen fibers during loading (p ≤ 0.02). Collagen hybridizing peptide, a metric of damaged collagen, is positively correlated with the spread of collagen fibers in the unloaded state after MMP-1 (p = 0.01) and that correlation is maintained throughout the sub-failure regime (p ≤ 0.03). MMP-1 injection increases substance P expression in dorsal root ganglia (p < 0.01) and spinal cord (p < 0.01) neurons. These findings suggest that MMP-1 is a likely mediator of neuronal signaling in joint pain and that MMP-1 presence in the joint space may predispose the capsular ligament to altered responses to loading. MMP-1-mediated pathways may be relevant targets for treating degenerative joint pain in cases with subtle or no evidence of structural degeneration.

Analysis of Functional Outcomes and Risk Factors for Facet Joint Distraction During Anterior Cervical Discectomy and Fusion for Cervical Spondylotic Myelopathy

OBJECTIVE

This study aimed to clarify functional outcomes of facet joint distraction (FJD) and identify specific risk factors for excessive FJD during single-level anterior cervical discectomy and fusion (ACDF) for cervical spondylotic myelopathy (CSM).

METHODS

This study retrospectively analyzed 100 patients who underwent single-level ACDF for CSM from January 2016 to May 2020. Anteroposterior and lateral radiographs were obtained before surgery and 12 months after surgery. Radiographic parameters including anterior intervertebral height (AIH), posterior intervertebral height, facet joint gap, cage posterior depth (CPD), upper vertebral length, cervical segmental Cobb angle (CSCA), C2-C7 Cobb angle, and C2-C7 sagittal vertical axis were analyzed. Functional outcomes were evaluated using the modified Japanese Orthopedic Association Score, visual analog scale (VAS), and Neck Disability Index (NDI).

RESULTS

Comparison between the appropriate FJD and excessive FJD groups showed statistically significant differences in the NDI, VAS, CPD, and ΔAIH (P < 0.05). Multivariate logistic regression analysis showed that independent factors associated with excessive FJD were as follows: a ΔAIH > 2.28 mm (odds ratio [OR] = 6.792, 95% confidence interval [CI] = 1.885-24.470, P = 0.003), CPD > 12.45 mm (OR = 5.876, 95% CI = 1.828-18.895, P = 0.003), and post-CSCA < 0° (OR = 6.251, 95% CI = 1.275-30.633, P = 0.024). Furthermore, receiver operating characteristic curve analysis for the multilevel logistic regression model produced an area under the curve of 0.783 (P < 0.001).

CONCLUSION

Patients with an FJD of >0.905 mm had worse NDI and VAS pain scores, but not a poorer modified Japanese Orthopedic Association Score recovery rate. Our findings suggested that a ΔAIH > 2.28 mm, CPD > 12.45 mm, and post-CSCA < 0° were independent risk factors for excessive FJD after single-level ACDF for CSM.

Apremilast ameliorates IL-1α-induced dysfunction in epidermal stem cells

BACKGROUND AND PURPOSE

Skin tissue is the natural barrier that protects our body, the damage of which can be repaired by the epidermal stem cells (ESCs). However, external factors abolish the self-repair ability of ESCs by inducing oxidative stress and severe inflammation. Apremilast is a small molecular inhibitor of phosphodiesterase 4 that was approved for the treatment of psoriasis. In the present study, the protective property of Apremilast against IL-1α-induced dysfunction on epidermal stem cells, as well as the preliminary mechanism, will be investigated.

METHODS

ESCs were isolated from neonatal mice. The expression levels of TNF-α, IL-8, IL-12, MMP-2, and MMP-9 were detected using real-time PCR and ELISA. MitoSOX Red assay was used to determine the level of mitochondrial reactive oxygen species (ROS). Western blot and real-time PCR were utilized to determine the expression levels of IL-1R1, Myd88, and TRAF6. Activation of NF-κB was assessed by measuring the p-NF-κB p65 and luciferase activity. Capacities of ESCs were evaluated by measuring the gene expressions of integrin β1 and Krt19 using real-time PCR.

RESULTS

Firstly, the expression levels of TNF-α, IL-8, IL-12, MMP-2, MMP-9 and IL-1R1, as well as the ROS level, were significantly elevated by IL-1α but greatly suppressed by treatment with Apremilast. Subsequently, we found that the activated Myd88/TRAF6/NF-κB signaling pathway induced by stimulation with IL-1α was significantly inhibited by the introduction of Apremilast. As a result, Apremilast protected ESCs against IL-1α-induced impairment in capacities of ESCs, this was verified by the elevated expression levels of integrin β1 and Krt19.

CONCLUSIONS

Apremilast might ameliorate IL-1α-induced dysfunction in ESCs by mitigating oxidative stress and inflammation through inhibiting the activation of the Myd88/TRAF6/NF-κB signaling pathway.

Predictors of Pain Recurrence After Lumbar Facet Joint Injections

Introduction

Facet joint injections (FJIs) of anesthetic and corticosteroids are useful for the diagnosis and treatment of low back pain (LBP). In the current study, we evaluated the efficacy of FJI on LBP treatment and the predictive variables of pain recurrence after FJI.

Methods

We included and followed prospectively forty-three consecutive patients with chronic LBP treated with FJI. Clinical assessments were carried out at a baseline 1 week before FJIs and after a 6-month follow-up visit using the visual analog scale (VAS) for pain, Oswestry Disability Index (ODI) for disability-specific measure and MacNab criteria for global effectiveness, and compared through analysis using paired-samples “t” tests. Multiple cox-regression analysis was used to identify the presurgical variables independently associated with pain recurrence anytime during the follow-up. In addition to the demographic, clinical, and surgical data, we also analyzed psychometric scales: Pain Catastrophizing Scale (PCS), Beck Anxiety Inventory (BAI), and Beck Depression Inventory (BDI).

Results

After a 6-month follow-up, thirty-two patients (74.4%) showed a clinically significant reduction of pain and twenty-seven (62.8%) reported a clinically significant improvement of disability. Presurgical catastrophizing (PCS score ≥ 5, adjusted HR 4.4, CI 95% 1.7–11.3, p = 0.002) and smoking (Adjusted HR 12.5, CI 95% 1.1–138.9, p = 0.04) remains associated with pain recurrence.

Conclusion

FJI reduces LBP and disability of patients with unresponsive LBP. Pain-related cognitive and behavioral factors determined by pain catastrophizing and smoking were independently associated with pain recurrence after lumbar FJI. The results support the need of a multidisciplinary approach for presurgical evaluation of patients with chronic pain.

Electroacupuncture for pain relief in labour inhibits spinal p38 MAPK-mediated prostaglandin E2 release and uterine prostaglandin E2 receptor expression in rats

BACKGROUND

p38 mitogen-activated protein kinase (p38 MAPK) activation involves the release of prostaglandin E2 (PGE2) and hyperalgesia. We have previously reported that electroacupuncture (EA) relieves labour pain, but the potential mechanisms remain unclear.

OBJECTIVE

To observe the effects of EA on labour pain intensity, serum PGE2 levels and the p38 MAPK signalling pathway in rats during labour.

METHODS

Female rats copulated with male rats to induce pregnancy, and then received castor oil to trigger labour. During labour, rats remained untreated (Control group, n=30) or were treated with remifentanil (n=30) or EA at Jiaji (n=30) or SP6+LI4 (n=30), respectively. The warm water tail-flick test was used to assess labour pain. Serum PGE2 levels were measured by ELISA. Protein expression of prostaglandin E2 receptor (PGER2), p38 MAPK and phospholipase A2 (PLA2) were analysed by Western blotting, and mRNA levels were measured by real-time PCR.

RESULTS

EA treatment at Jiaji or SP6+LI4 significantly relieved labour pain, decreased serum PGE2 levels and inhibited protein and gene expression of PGER2 in the myometrium. Moreover, EA reduced protein expression of PLA2 and p38 MAPK, and inhibited phosphorylation of p38 MAPK in the lumbar spinal cord but not in the cerebral grey matter. Additionally, EA markedly decreased mRNA levels of p38 MAPK in the lumbar spinal cord and significantly reduced PLA2-IV mRNA levels in both the lumbar spinal cord and cerebral grey matter.

CONCLUSIONS

This study indicates that EA relieves labour pain through, at least in part, inhibition of spinal p38 MAPK-mediated PGE2 release and uterine PGER2 expression in rats.

Physiologic facet capsule stretch can induce pain & upregulate matrix metalloproteinase-3 in the dorsal root ganglia when preceded by a physiological mechanical or nonpainful chemical exposure

BACKGROUND

Neck pain from cervical facet loading is common and induces inflammation and upregulation of nerve growth factor (NGF) that can sensitize the joint afferents. Yet, the mechanisms by which these occur and whether afferents can be pre-conditioned by certain nonpainful stimuli are unknown. This study tested the hypothesis that a nonpainful mechanical or chemical insult predisposes a facet joint to generate pain after a later exposure to typically nonpainful distraction.

METHODS

Rats were exposed to either a nonpainful distraction or an intra-articular subthreshold dose of NGF followed by a nonpainful distraction two days later. Mechanical hyperalgesia was measured daily and C6 dorsal root ganglia (DRG) tissue was assayed for NGF and matrix metalloproteinase-3 (MMP-3) expression on day 7.

FINDINGS

The second distraction increased joint displacement and strains compared to its first application (p = 0.0011). None of the initial exposures altered behavioral sensitivity in either of the groups being pre-conditioned or in controls; but, sensitivity was established in both groups receiving a second distraction within one day that lasted until day 7 (p < 0.024). NGF expression in the DRG was increased in both groups undergoing a pre-conditioning exposure (p < 0.0232). Similar findings were observed for MMP-3 expression, with a pre-conditioning exposure increasing levels after an otherwise nonpainful facet distraction.

INTERPRETATION

These findings suggest that nonpainful insults to the facet joint, when combined, can generate painful outcomes, possibly mediated by upregulation of MMP-3 and mature NGF.

Repeated High Rate Facet Capsular Stretch at Strains That are Below the Pain Threshold Induces Pain and Spinal Inflammation With Decreased Ligament Strength in the Rat

Repeated loading of ligamentous tissues during repetitive occupational and physical tasks even within physiological ranges of motion has been implicated in the development of pain and joint instability. The pathophysiological mechanisms of pain after repetitive joint loading are not understood. Within the cervical spine, excessive stretch of the facet joint and its capsular ligament has been implicated in the development of pain. Although a single facet joint distraction (FJD) at magnitudes simulating physiologic strains is insufficient to induce pain, it is unknown whether repeated stretching of the facet joint and ligament may produce pain. This study evaluated if repeated loading of the facet at physiologic nonpainful strains alters the capsular ligament's mechanical response and induces pain. Male rats underwent either two subthreshold facet joint distractions (STFJDs) or sham surgeries each separated by 2 days. Pain was measured before the procedure and for 7 days; capsular mechanics were measured during each distraction and under tension at tissue failure. Spinal glial activation was also assessed to probe potential pathophysiologic mechanisms responsible for pain. Capsular displacement significantly increased (p = 0.019) and capsular stiffness decreased (p = 0.008) during the second distraction compared to the first. Pain was also induced after the second distraction and was sustained at day 7 (p < 0.048). Repeated loading weakened the capsular ligament with lower vertebral displacement (p = 0.041) and peak force (p = 0.014) at tissue rupture. Spinal glial activation was also induced after repeated loading. Together, these mechanical, physiological, and neurological findings demonstrate that repeated loading of the facet joint even within physiologic ranges of motion can be sufficient to induce pain, spinal inflammation, and alter capsular mechanics similar to a more injurious loading exposure.

Inducible nitric oxide synthase inhibition by 1400W limits pain hypersensitivity in a neuropathic pain rat model

NEW FINDINGS

What is the central question of this study? Can modulation of inducible NO synthase reduce pain behaviour and pro-inflammatory cytokine signalling in a rat model of neuropathic pain? What is the main finding and its importance? Nitric oxide synthase-based therapies could be effective for the treatment of peripheral neuropathic pain.

ABSTRACT

Peripheral neuropathic pain (PNP), resulting from injury to or dysfunction of a peripheral nerve, is a major health problem that affects 7-8% of the population. It is inadequately controlled by current drugs and is characterized by pain hypersensitivity, which is believed to be attributable to sensitization of peripheral and CNS neurons by various inflammatory mediators. Here we examined, in a rat model of PNP: (i) whether reducing levels of nitric oxide (NO) with 1400W, a highly selective inhibitor of inducible NO synthase (iNOS), would prevent or attenuate pain hypersensitivity; and (ii) the effects of 1400W on plasma concentrations of several cytokines that are secreted after iNOS upregulation during chronic pain states. The L5 spinal nerve axotomy (SNA) model of PNP was used, and 1400W (20 mg kg^-1 ) was administered i.p. at 8 h intervals for 3 days starting at 18 h post-SNA. Changes in plasma concentrations of 12 cytokines in SNA rats treated with 1400W were examined using multiplex enzyme-linked immunosorbent assay. The SNA rats developed behavioural signs of mechanical and heat hypersensitivity. Compared with the vehicle/control, 1400W significantly: (i) limited development of mechanical hypersensitivity at 66 h post-SNA and of heat hypersensitivity at 42 h and at several time points tested thereafter; and (ii) increased the plasma concentrations of interleukin (IL)-1α, IL-1β and IL-10 in the SNA rats. The findings suggest that 1400W might exert its analgesic effects by reducing iNOS and altering the balance between the pro-inflammatory (IL-1β and IL-1α) and anti-inflammatory (IL-10) cytokines and that therapies targeting NO or its enzymes might be effective for the treatment of PNP.

Quad Fever: Treatment through Lowering of Ambient Temperature

Hyperpyrexia is a rare and at times fatal condition seen in an Intensive Care Unit setup. We encountered a case of a 65-year-old patient with road traffic accident presenting with dorsal spine fracture at D₁₀ level. He underwent decompression and fusion for the same. He developed hyperpyrexia of sudden onset on the 10^th day of admission with no source of infection and adequate broad-spectrum antibiotic coverage with adequate thrombo-embolic prevention in place. The patient showed no response to antipyretic agents and other cooling methods. The origin of hyperthermia was idiopathic, and we speculate that the cause was secondary to hyperthermic thermoregulatory dysfunction often quoted as “quad fever,” seen in spinal cord injury. We present a brief review of literature and the importance of early identification and treatment of this potentially fatal condition.

Ablation of IB4 non-peptidergic afferents in the rat facet joint prevents injury-induced pain and thalamic hyperexcitability via supraspinal glutamate transporters

The facet joint is a common source of neck pain, particularly after excessive stretch of its capsular ligament. Peptidergic afferents have been shown to have an important role in the development and maintenance of mechanical hyperalgesia, dysregulated nociceptive signaling, and spinal hyperexcitability that develop after mechanical injury to the facet joint. However, the role of non-peptidergic isolectin-B4 (IB4) cells in mediating joint pain is unknown. Isolectin-B4 saporin (IB4-SAP) was injected into the facet joint to ablate non-peptidergic cells, and the facet joint later underwent a ligament stretch known to induce pain. Behavioral sensitivity, thalamic glutamate transporter expression, and thalamic hyperexcitability were evaluated up to and at day 7. Administering IB4-SAP prior to a painful injury prevented the development of mechanical hyperalgesia that is typically present. Intra-articular IB4-SAP also prevented the upregulation of the glutamate transporters GLT-1 and EAAC1 in the ventral posterolateral nucleus of the thalamus and reduced thalamic neuronal hyperexcitability at day 7. These findings suggest that a painful facet injury induces changes extending to supraspinal structures and that IB4-positive afferents in the facet joint may be critical for the development and maintenance of sensitization in the thalamus after a painful facet joint injury.

Cytokine and chemokine profile changes in patients with lower segment lumbar degenerative spondylolisthesis

BACKGROUND

Lumbar degenerative spondylolisthesis (DS) develops as a result of inflammatory and remodeling processes in facet joints (FJs). Several inflammatory cytokines are involved in the osteoarthritic and remodeling changes that occur and in low-back and/or radicular pain, the most prevalent clinical symptom of disease. This study improves knowledge related to the roles that 27 cytokines, chemokines and growth factors play in the pathophysiology of lumbar DS.

MATERIAL AND METHODS

Cytokine levels were examined using capture sandwich immunoassay using the Bio-Plex^® 200 System and the Bio-PlexTM Human Cytokine Standard 27-Plex, Group I (Bio-Rad, Hercules, California, USA) separately in intervertebral discs (IVDs) and FJ bone tissue. The samples were obtained during primary spinal surgery from 9 patients suffering from lower segment lumbar DS. The pain intensity was assessed using a visual analog scale. The controls were tissue samples collected from both lower lumbar segment levels of 6 male subjects during a multiorgan procurement procedure.

RESULTS

The Bio-Plex^® assay revealed significant differences between the patients and controls in cytokines, chemokines and growth factor profiles: i, The elevated interleukin-6 (IL-6), IL-7, IL-13, tumor necrosis factor α (TNF-α), interferon γ and platelet-derived growth factor levels in lumbar DS samples of subchondral FJ bone. These indicated ongoing inflammation, bone formation and increased fibroblasts activity in the FJ bone. ii, The elevated levels of IL-6, IL-8, TNF-α, granulocyte-macrophage colony-stimulating factor and monocyte chemoattractant protein-1 in anulus fibrosus together with increased IL-6, IL-8, TNF-α and eotaxin and decreased IL-1-receptor antagonist in nucleus pulposus confirmed advanced IVD degeneration in the patient samples.

CONCLUSION

This study identified, for the first time, protective levels of cytokines, chemokines and growth factors in healthy subjects and supported their significant involvement in the pathogenesis of lumbar DS. The control samples and analytical methods used avoided any false changes in the cytokine levels due to secondary factors (e.g., death of donor and limited cytokine stability).

IL1A rs1800587 associates with chronic noncrisis pain in sickle cell disease

AIM

Pain is prevalent in sickle cell disease (SCD) patients who display great heterogeneity in pain severity and frequency. Hypothesizing that inflammatory factors are involved in the pathogenesis of SCD pain, we focused on the IL1A C/T polymorphism rs1800587 that is an SNP located in a cis-transcriptional regulatory region.

METHODS

We genotyped IL1A rs1800587 and performed association studies with phenotype data obtained by a multidimensional pain assessment tool using the PAINReportIt^® Questionnaire.

RESULTS

Each T allele was associated with a 3.9 increase in composite pain index score (p = 0.04) as determined by multiple linear regression.

CONCLUSION

IL1A rs1800587 may influence chronic pain in SCD.

Upper Cervical Spine Loading Simulating a Dynamic Low-Speed Collision Significantly Increases the Risk of Pain Compared to Quasi-Static Loading With Equivalent Neck Kinematics

Dynamic cervical spine loading can produce facet capsule injury. Despite a large proportion of neck pain being attributable to the C2/C3 facet capsule, potential mechanisms are not understood. This study replicated low-speed frontal and rear-end traffic collisions in occiput-C3 human cadaveric cervical spine specimens and used kinematic and full-field strain analyses to assess injury. Specimens were loaded quasi-statically in flexion and extension before and after dynamic rotation of C3 at 100 deg/s. Global kinematics in the sagittal plane were tracked at 1 kHz, and C2/C3 facet capsule full-field strains were measured. Dynamic loading did not alter the kinematics from those during quasi-static (QS) loading, but maximum principal strain (MPS) and shear strain (SS) were significantly higher (p = 0.028) in dynamic flexion than for the same quasi-static conditions. The full-field strain analysis demonstrated that capsule strain was inhomogeneous, and that the peak MPS generally occurred in the anterior aspect and along the line of the C2/C3 facet joint. The strain magnitude in dynamic flexion continued to rise after the rotation of C3 had stopped, with a peak MPS of 12.52 ± 4.59% and a maximum SS of 5.34 ± 1.60%. The peak MPS in loading representative of rear-end collisions approached magnitudes previously shown to induce pain in vivo, whereas strain analysis using linear approaches across the facet joint was lower and may underestimate injury risk compared to full-field analysis. The time at which peak MPS occurred suggests that the deceleration following a collision is critical in relation to the production of injurious strains within the facet capsule.

Tissue Strain Reorganizes Collagen With a Switchlike Response That Regulates Neuronal Extracellular Signal-Regulated Kinase Phosphorylation In Vitro: Implications for Ligamentous Injury and Mechanotransduction

Excessive loading of ligaments can activate the neural afferents that innervate the collagenous tissue, leading to a host of pathologies including pain. An integrated experimental and modeling approach was used to define the responses of neurons and the surrounding collagen fibers to the ligamentous matrix loading and to begin to understand how macroscopic deformation is translated to neuronal loading and signaling. A neuron-collagen construct (NCC) developed to mimic innervation of collagenous tissue underwent tension to strains simulating nonpainful (8%) or painful ligament loading (16%). Both neuronal phosphorylation of extracellular signal-regulated kinase (ERK), which is related to neuroplasticity (R2 ≥ 0.041; p ≤ 0.0171) and neuronal aspect ratio (AR) (R2 ≥ 0.250; p < 0.0001), were significantly correlated with tissue-level strains. As NCC strains increased during a slowly applied loading (1%/s), a "switchlike" fiber realignment response was detected with collagen reorganization occurring only above a transition point of 11.3% strain. A finite-element based discrete fiber network (DFN) model predicted that at bulk strains above the transition point, heterogeneous fiber strains were both tensile and compressive and increased, with strains in some fibers along the loading direction exceeding the applied bulk strain. The transition point identified for changes in collagen fiber realignment was consistent with the measured strain threshold (11.7% with a 95% confidence interval of 10.2-13.4%) for elevating ERK phosphorylation after loading. As with collagen fiber realignment, the greatest degree of neuronal reorientation toward the loading direction was observed at the NCC distraction corresponding to painful loading. Because activation of neuronal ERK occurred only at strains that produced evident collagen fiber realignment, findings suggest that tissue strain-induced changes in the micromechanical environment, especially altered local collagen fiber kinematics, may be associated with mechanotransduction signaling in neurons.

Management of lumbar zygapophysial (facet) joint pain

AIM: To investigate the diagnostic validity and therapeutic value of lumbar facet joint interventions in managing chronic low back pain.

METHODS: The review process applied systematic evidence-based assessment methodology of controlled trials of diagnostic validity and randomized controlled trials of therapeutic efficacy. Inclusion criteria encompassed all facet joint interventions performed in a controlled fashion. The pain relief of greater than 50% was the outcome measure for diagnostic accuracy assessment of the controlled studies with ability to perform previously painful movements, whereas, for randomized controlled therapeutic efficacy studies, the primary outcome was significant pain relief and the secondary outcome was a positive change in functional status. For the inclusion of the diagnostic controlled studies, all studies must have utilized either placebo controlled facet joint blocks or comparative local anesthetic blocks. In assessing therapeutic interventions, short-term and long-term reliefs were defined as either up to 6 mo or greater than 6 mo of relief. The literature search was extensive utilizing various types of electronic search media including PubMed from 1966 onwards, Cochrane library, National Guideline Clearinghouse, clinicaltrials.gov, along with other sources including previous systematic reviews, non-indexed journals, and abstracts until March 2015. Each manuscript included in the assessment was assessed for methodologic quality or risk of bias assessment utilizing the Quality Appraisal of Reliability Studies checklist for diagnostic interventions, and Cochrane review criteria and the Interventional Pain Management Techniques - Quality Appraisal of Reliability and Risk of Bias Assessment tool for therapeutic interventions. Evidence based on the review of the systematic assessment of controlled studies was graded utilizing a modified schema of qualitative evidence with best evidence synthesis, variable from level I to level V.

RESULTS: Across all databases, 16 high quality diagnostic accuracy studies were identified. In addition, multiple studies assessed the influence of multiple factors on diagnostic validity. In contrast to diagnostic validity studies, therapeutic efficacy trials were limited to a total of 14 randomized controlled trials, assessing the efficacy of intraarticular injections, facet or zygapophysial joint nerve blocks, and radiofrequency neurotomy of the innervation of the facet joints. The evidence for the diagnostic validity of lumbar facet joint nerve blocks with at least 75% pain relief with ability to perform previously painful movements was level I, based on a range of level I to V derived from a best evidence synthesis. For therapeutic interventions, the evidence was variable from level II to III, with level II evidence for lumbar facet joint nerve blocks and radiofrequency neurotomy for long-term improvement (greater than 6 mo), and level III evidence for lumbosacral zygapophysial joint injections for short-term improvement only.

CONCLUSION: This review provides significant evidence for the diagnostic validity of facet joint nerve blocks, and moderate evidence for therapeutic radiofrequency neurotomy and therapeutic facet joint nerve blocks in managing chronic low back pain.

Intra-articular nerve growth factor regulates development, but not maintenance, of injury-induced facet joint pain & spinal neuronal hypersensitivity

OBJECTIVE

The objective of the current study is to define whether intra-articular nerve growth factor (NGF), an inflammatory mediator that contributes to osteoarthritic pain, is necessary and sufficient for the development or maintenance of injury-induced facet joint pain and its concomitant spinal neuronal hyperexcitability.

METHOD

Male Holtzman rats underwent painful cervical facet joint distraction (FJD) or sham procedures. Mechanical hyperalgesia was assessed in the forepaws, and NGF expression was quantified in the C6/C7 facet joint. An anti-NGF antibody was administered intra-articularly in additional rats immediately or 1 day following facet distraction or sham procedures to block intra-articular NGF and test its contribution to initiation and/or maintenance of facet joint pain and spinal neuronal hyperexcitability. NGF was injected into the bilateral C6/C7 facet joints in separate rats to determine if NGF alone is sufficient to induce these behavioral and neuronal responses.

RESULTS

NGF expression increases in the cervical facet joint in association with behavioral sensitivity after that joint's mechanical injury. Intra-articular application of anti-NGF immediately after a joint distraction prevents the development of both injury-induced pain and hyperexcitability of spinal neurons. Yet, intra-articular anti-NGF applied after pain has developed does not attenuate either behavioral or neuronal hyperexcitability. Intra-articular NGF administered to the facet in naïve rats also induces behavioral hypersensitivity and spinal neuronal hyperexcitability.

CONCLUSION

Findings demonstrate that NGF in the facet joint contributes to the development of injury-induced joint pain. Localized blocking of NGF signaling in the joint may provide potential treatment for joint pain.

Whole-body Vibration at Thoracic Resonance Induces Sustained Pain and Widespread Cervical Neuroinflammation in the Rat

BACKGROUND

Whole-body vibration (WBV) is associated with back and neck pain in military personnel and civilians. However, the role of vibration frequency and the physiological mechanisms involved in pain symptoms are unknown.

QUESTIONS/PURPOSES

This study asked the following questions: (1) What is the resonance frequency of the rat spine for WBV along the spinal axis, and how does frequency of WBV alter the extent of spinal compression/extension? (2) Does a single WBV exposure at resonance induce pain that is sustained? (3) Does WBV at resonance alter the protein kinase C epsilon (PKCε) response in the dorsal root ganglia (DRG)? (4) Does WBV at resonance alter expression of calcitonin gene-related peptide (CGRP) in the spinal dorsal horn? (5) Does WBV at resonance alter the spinal neuroimmune responses that regulate pain?

METHODS

Resonance of the rat (410 ± 34 g, n = 9) was measured by imposing WBV at frequencies from 3 to 15 Hz. Separate groups (317 ± 20 g, n = 10/treatment) underwent WBV at resonance (8 Hz) or at a nonresonant frequency (15 Hz). Behavioral sensitivity was assessed throughout to measure pain, and PKCε in the DRG was quantified as well as spinal CGRP, glial activation, and cytokine levels at Day 14.

RESULTS

Accelerometer-based thoracic transmissibility peaks at 8 Hz (1.86 ± 0.19) and 9 Hz (1.95 ± 0.19, mean difference [MD] 0.290 ± 0.266, p < 0.03), whereas the video-based thoracic transmissibility peaks at 8 Hz (1.90 ± 0.27), 9 Hz (2.07 ± 0.20), and 10 Hz (1.80 ± 0.25, MD 0.359 ± 0.284, p < 0.01). WBV at 8 Hz produces more cervical extension (0.745 ± 0.582 mm, MD 0.242 ± 0.214, p < 0.03) and compression (0.870 ± 0.676 mm, MD 0.326 ± 0.261, p < 0.02) than 15 Hz (extension, 0.503 ± 0.279 mm; compression, 0.544 ± 0.400 mm). Pain is longer lasting (through Day 14) and more robust (p < 0.01) after WBV at the resonant frequency (8 Hz) compared with 15 Hz WBV. PKCε in the nociceptors of the DRG increases according to the severity of WBV with greatest increases after 8 Hz WBV (p < 0.03). However, spinal CGRP, cytokines, and glial activation are only evident after painful WBV at resonance.

CONCLUSIONS

WBV at resonance produces long-lasting pain and widespread activation of a host of nociceptive and neuroimmune responses as compared with WBV at a nonresonance condition. Based on this work, future investigations into the temporal and regional neuroimmune response to resonant WBV in both genders would be useful.

CLINICAL RELEVANCE

Although WBV is a major issue affecting the military population, there is little insight about its mechanisms of injury and pain. The neuroimmune responses produced by WBV are similar to other pain states, suggesting that pain from WBV may be mediated by similar mechanisms as other neuropathic pain conditions. This mechanistic insight suggests WBV-induced injury and pain may be tempered by antiinflammatory intervention.

TNFα transport induced by dynamic loading alters biomechanics of intact intervertebral discs

Objective

Intervertebral disc (IVD) degeneration is an important contributor to the development of back pain, and a key factor relating pain and degeneration are the presence of pro-inflammatory cytokines and IVD motion. There is surprisingly limited understanding of how mechanics and inflammation interact in the IVD. This study investigated interactions between mechanical loading and pro-inflammatory cytokines in a large animal organ culture model to address fundamental questions regarding (i.) how inflammatory mediators arise within the IVD, (ii.) how long inflammatory mediators persist, and (iii.) how inflammatory mediators influence IVD biomechanics.

Methods

Bovine caudal IVDs were cultured for 6 or 20-days under static &amp; dynamic loading with or without exogenous TNFα in the culture medium, simulating a consequence of inflammation of the surrounding spinal tissues. TNFα transport within the IVD was assessed via immunohistochemistry. Changes in IVD structural integrity (dimensions, histology &amp; aggrecan degradation), biomechanical behavior (Creep, Recovery &amp; Dynamic stiffness) and pro-inflammatory cytokines in the culture medium (ELISA) were assessed.

Results

TNFα was able to penetrate intact IVDs when subjected to dynamic loading but not static loading. Once transported within the IVD, pro-inflammatory mediators persisted for 4–8 days after TNFα removal. TNFα exposure induced changes in IVD biomechanics (reduced diurnal displacements &amp; increased dynamic stiffness).

Discussion

This study demonstrated that exposure to TNFα, as might occur from injured surrounding tissues, can penetrate healthy intact IVDs, induce expression of additional pro-inflammatory cytokines and alter IVD mechanical behavior. We conclude that exposure to pro-inflammatory cytokine may be an initiating event in the progression of IVD degeneration in addition to being a consequence of disease.

Thrombospondin-4 and excitatory synaptogenesis promote spinal sensitization after painful mechanical joint injury

Facet joint injury induces persistent pain that may be maintained by structural plasticity in the spinal cord. Astrocyte-derived thrombospondins, especially thrombospondin-4 (TSP4), have been implicated in synaptogenesis and spinal sensitization in neuropathic pain, but the TSP4 response and its relationship to synaptic changes in the spinal cord have not been investigated for painful joint injury. This study investigates the role of TSP4 in the development and maintenance of persistent pain following injurious facet joint distraction in rats and tests the hypothesis that excitatory synaptogenesis contributes to such pain. Painful facet joint loading induces dorsal horn excitatory synaptogenesis along with decreased TSP4 in the DRG and increased astrocytic release of TSP4 in the spinal cord, all of which parallel the time course of sustained tactile allodynia. Blocking injury-induced spinal TSP4 expression with antisense oligonucleotides or reducing TSP4 activity at its neuronal receptor in the spinal cord with gabapentin treatment both attenuate the allodynia and dorsal horn synaptogenesis that develop after painful facet joint loading. Increased spinal TSP4 also facilitates the development of allodynia and spinal hyperexcitability, even after non-painful physiological loading of the facet joint. These results suggest that spinal TSP4 plays an important role in the development and maintenance of persistent joint-mediated pain by inducing excitatory synaptogenesis and facilitating the transduction of mechanical loading of the facet joint that leads to spinal hyperexcitability.

Early afferent activity from the facet joint after painful trauma to its capsule potentiates neuronal excitability and glutamate signaling in the spinal cord

Cervical facet joint injury induces persistent pain and central sensitization. Preventing the peripheral neuronal signals that initiate sensitization attenuates neuropathic pain. Yet, there is no clear relationship among facet joint afferent activity, development of central sensitization, and pain, which may be hindering effective treatments for this pain syndrome. This study investigates how afferent activity from the injured cervical facet joint affects induction of behavioral sensitivity and central sensitization. Intra-articular bupivacaine was administered to transiently suppress afferent activity immediately or 4 days after facet injury. Mechanical hyperalgesia was monitored after injury, and spinal neuronal hyperexcitability and spinal expression of proteins that promote neuronal excitability were measured on day 7. Facet injury with saline vehicle treatment induced significant mechanical hyperalgesia (P<.027), dorsal horn neuronal hyperexcitability (P<.026), upregulation of pERK1/2, pNR1, mGluR5, GLAST, and GFAP, and downregulation of GLT1 (P<.032). However, intra-articular bupivacaine immediately after injury significantly attenuated hyperalgesia (P<.0001), neuronal hyperexcitability (P<.004), and dysregulation of excitatory signaling proteins (P<.049). In contrast, intra-articular bupivacaine at day 4 had no effect on these outcomes. Silencing afferent activity during the development of neuronal hyperexcitability (4 hours, 8 hours, 1 day) attenuated hyperalgesia and neuronal hyperexcitability (P<.045) only for the treatment given 4 hours after injury. This study suggests that early afferent activity from the injured facet induces development of spinal sensitization via spinal excitatory glutamatergic signaling. Peripheral intervention blocking afferent activity is effective only over a short period of time early after injury and before spinal modifications develop, and is independent of modulating spinal glial activation.