Category Archives: Osteoarthritis

11Oct/13

Arthritis and pain – beyond the joints | #arthritis #pain

Arthritis and pain –> “…osteoarthritis is so common, it would make us think that we would be very good at treating it, but we aren’t”.

Why is this the case?

As with many painful conditions that persist, most of the therapies used to treat osteoarthritis (OA) primarily target the tissues. In some cases this provides relief and improves the function of the affected joint. However, there are many individuals who receive such treatments and do not experience any significant change in their pain or ability to move. So, what is happening in these folk?

The first point to understand is that we need a brain to feel pain – see Lorimer Moseley talking about this here. Of course the pain is experienced in the body tissues as this is where the sensation emerges, however, neuronal networks in the brain play a significant role in creating the feeling. Usually something happens in the body to begin the process of sensitisation such as an inflammatory process when we injure tissue or it degenerates as in arthritis when the joint structures change-worth noting is the fact that all of our tissues change as we age and this is entirely normal yet of course can be a painful process.

The brain wants to know about inflammation and does so via the danger signals sent by nociceptors from the tissues to the spinal cord before reaching the higher centres. On scrutininsing these signals, the brain has to conclude that there is a threat to the integrity of the body based on the current status, prior experiences and a prediction of what this could mean, for pain to emerge in the area deemed to be in danger. The question that the brain asks is, “how dangerous is this?”. The answer to this question will determine the response. Perceived danger triggers pain but as part of an overall protective set of measures that include changes in movement, e.g. guarding and limping, autonomic activation in ‘fright or flight’, hormonal responses and immune system activity.

All of these responses are normal, adaptive and desirable albeit accompanied by unpleasant conscious experiences such as pain and spasm. Pain is meant to be unpleasant as it drives behavioural change to promote survival. Typically, if we injure ourselves we expect the body to hurt although the intensity of the pain can vary enormously depending upon the context of the situation. There are many reports of people in casualty with significant trauma yet they describe a lack of pain. This is because pain is not an accurate indicator of tissue damage. One only has to consider phantom limb pain to see how we can experience pain in a body part that is no longer present. The representation of the limb still exists in the sensory cortex creating a conundrum for the brain as it seeks confirmative data from the periphery that does not show up. Maybe 80% of people who lose limbs will describe pain in the space once occupied. Something similar can happen following a joint replacement. Some patients report feeling on-going pain in the joint as if it is still present rather than the shiny new titanium joint surfaces actually in situ. Therefore, it has become apparent that to feel pain, the brain does not even need to receive danger signals but rather determines a threat value for a particular situation or context.

Many people experience relief once they have a joint replacement but some do not. Prior to a replacement, the sensitivity that arises can cause changes throughout the nervous system similar to other persisting pain states. This is called central sensitisation, the term defined by plastic remodelling of neurons in the central nervous system that underpin widespread pain, amplified responses to normal stimuli and a reduced ability to inhibit the process of nociception. There are clinical ways in which we can test for this mechanism alongside listening to the clues from the patient’s narrative that is usually very revealing. On detecting this form of sensitivity, a different approach is required to tackle the pain and influencing factors.

So, we need the brain to feel pain that emerges from the body. What does this mean for OA? In particular, those who continue to suffer with joint pain and stiffness despite treatment or surgery need to be considered as having a more centralised aspect although all pain patients should be thought about in terms of the brain’s perception of threat. The bottom line: reduce the threat, reduce the pain; and conversely, increased threat, increased pain. Therapies and strategies must bear this in mind in order to change the pain experience and improve the functioning of the joint.

All too often patients are told that a joint is degenerate and that there is nothing that they can do. Of course we have acknowledged that some people will need surgery, but either way, there is plenty that they can do to proactively seek to gain control and change their experience. The fact that we have identified the role of the brain in pain, that the brain is plastic and designed to change (neuroplasticity) and that we have techniques that target the known changes (e.g. cortical reorganisation) and mechanisms provides great optimism.

Below, Dr Tasha Stanton talking about osteoarthritis and the brain, describing the mechanisms and highlighting the altered sense of the affected area that is so common. The change in body schema, that is how the brain constructs the sense of self, is often part of a persisting pain state yet many patients do not volunteer the experince for fear of disbelief. Knowing that the area feels bigger, smaller, missing or detached is a vital clue that reveals features of the conidion that must be targeted with therapy and hence patients should be encouraged to fully express their story using their own language and metaphors.

With the knowledge of these mechanisms we are making headway in treating conditions such as arthritis. We are all going to experience joint and tissue changes in our bodies as we age, so it is vital that we improve the way in which we tackle the issues.

 

29Oct/12

The brain changes

The nervous system is plastic meaning that it changes and moulds according to the stimuli presented. Norman Doidge wrote about the ‘brain that changes itself’ and we have seen over the past 10 years or so an increasing number of studies that show this in a range of conditions, some painful and others not. Our ability to change and adapt have been a vital characteristics for our survival and to learn new skills. The same principles apply when we think about rehabilitation and treatment of painful conditions. We need to tap into these properties and stimulate the brain and other body systems (e.g. immune system, neuroendocrine) so that we are creators of health manifesting physically through normal movement, function and optimal performance.

Here are some examples of studies that have shown brain changes using functional MRI. You will note the variety that includes rheumatoid arthritis, osteoarthritis, pain, chronic pelvic pain, schizophrenia and fibromyalgia. This has serious implications for treatment in that we need brain focused therapies as well as those that target the tissues and end-organs. This includes the absolute need to explain pain and symptoms from a neuroscience perspective.

Arthritis Rheum. 2012 Feb;64(2):371-9. doi: 10.1002/art.33326.

Structural changes of the brain in rheumatoid arthritis.

Wartolowska K, Hough MG, Jenkinson M, Andersson J, Wordsworth BP, Tracey I.

Abstract

OBJECTIVE: To investigate whether structural changes are present in the cortical and subcortical gray matter of the brains of patients with rheumatoid arthritis (RA).

METHODS: We used two surface-based style morphometry analysis programs and a voxel-based style analysis program to compare high-resolution structural magnetic resonance imaging data obtained for 31 RA patients and 25 age- and sex-matched healthy control subjects.

RESULTS: We observed an increase in gray matter content in the basal ganglia of RA patients, mainly in the nucleus accumbens and caudate nucleus. There were no differences in the cortical gray matter. Moreover, patients had a smaller intracranial volume.

CONCLUSION: Our results suggest that RA is associated with changes in the subcortical gray matter rather than with cortical gray matter atrophy. Since the basal ganglia play an important role in motor control as well as in pain processing and in modulating behavior in response to aversive stimuli, we suggest that these changes may result from altered motor control or prolonged pain processing. The differences in brain volume may reflect either generalized atrophy or differences in brain development.

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Am J Psychiatry. 2002 Feb;159(2):244-50.

Volume changes in gray matter in patients with schizophrenia.

Hulshoff Pol HE, Schnack HG, Bertens MG, van Haren NE, van der Tweel I, Staal WG, Baaré WF, Kahn RS.

Abstract

OBJECTIVE: Schizophrenia is generally characterized by a progressive decline in functioning. Although structural brain abnormalities, particularly decrements in gray matter volume, are considered important to the pathology of schizophrenia, it is not resolved whether the brain abnormalities become more prominent over time.

METHOD: Magnetic resonance brain images from 159 patients with schizophrenia and 158 healthy comparison subjects between 16 and 70 years of age were compared. Using linear regression analysis, the authors analyzed the relationship between the volumes of the total brain, gray and white matter, cerebellum, and lateral and third ventricles with patient age.

RESULTS: Total brain (-2.2%), cerebral gray matter (-3.3%), prefrontal gray matter (-4.4%), and prefrontal white matter (-3.5%) volumes were smaller, and lateral (27%) and third (30%) ventricle and peripheral CSF (11%) volumes were larger in schizophrenia patients. A significant group-by-age interaction for gray matter volume was found, as shown by a steeper regression slope between age and gray matter volume in patients (-3.43 ml/year) than in healthy comparison subjects (-2.74 ml/year).

CONCLUSIONS: The smaller brains of the patients with schizophrenia can be explained by decreases in gray matter volume. Moreover, the finding that the smaller gray matter volume was more pronounced in older patients with schizophrenia may suggest progressive loss of cerebral gray matter in schizophrenia patients.

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Psychosom Med. 2009 Jun;71(5):566-73. Epub 2009 May 4.

Decreased gray matter volumes in the cingulo-frontal cortex and the amygdala in patients with fibromyalgia.

Burgmer M, Gaubitz M, Konrad C, Wrenger M, Hilgart S, Heuft G, Pfleiderer B.

Abstract

OBJECTIVE: Studies in fibromyalgia syndrome with functional neuroimaging support the hypothesis of central pain augmentation. To determine whether structural changes in areas of the pain system are additional preconditions for the central sensitization in fibromyalgia we performed voxel based morphometry in patients with fibromyalgia and healthy controls.

METHODS: We performed 3 Tesla magnetic resonance imaging of the brain in 14 patients with fibromyalgia and 14 healthy controls. Regional differences of the segmented and normalized gray matter volumes in brain areas of the pain system between both groups were determined. In those areas in which patients structurally differed from healthy controls, the correlation of disease-related factors with gray matter volumes was analyzed.

RESULTS: Patients presented a decrease in gray matter volume in the prefrontal cortex, the amygdala, and the anterior cingulate cortex (ACC). The duration of pain or functional pain disability did not correlate with gray matter volumes. A trend of inverse correlation of gray matter volume reduction in the ACC with the duration of pain medication intake has been detected.

CONCLUSIONS: Our results suggest that structural changes in the pain system are associated with fibromyalgia. As disease factors do not correlate with reduced gray matter volume in areas of the cingulo-frontal cortex and the amygdala in patients, one possible interpretation is that volume reductions might be a precondition for central sensitization in fibromyalgia.

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Brain. 2008 Dec;131(Pt 12):3222-31. Epub 2008 Sep 26.

Working memory performance is correlated with local brain morphology in the medial frontal and anterior cingulate cortex in fibromyalgia patients: structural correlates of pain-cognition interaction.

Luerding R, Weigand T, Bogdahn U, Schmidt-Wilcke T.

Abstract

Fibromyalgia (FM) is a disorder of unknown aetiology, characterized by chronic widespread pain, stiffness and sleep disturbances. In addition, patients frequently complain of memory and attention deficits. Accumulating evidence suggests that FM is associated with CNS dysfunction and with an altered brain morphology. However, few studies have specifically investigated neuropsychological issues in patients suffering from FM. We therefore sought to determine whether neuropsychological deficits found in FM patients may be correlated with changes in local brain morphology specifically in the frontal, temporal or cingulate cortices. Twenty FM patients underwent extensive testing for potential neuropsychological deficits, which demonstrated significantly reduced working memory and impaired non-verbal long-term memory (limited to free recall condition) in comparison with normative data from age- and education-matched control groups. Voxel-based morphometry (VBM) was used to evaluate for potential correlations between test results and local brain morphology. Performance on non-verbal working memory was positively correlated with grey matter values in the left dorsolateral prefrontal cortex, whereas performance on verbal working memory (digit backward) was positively correlated with grey matter values in the supplementary motor cortex. On the other hand, pain scores were negatively correlated with grey matter values in the medial frontal gyrus. White matter analyses revealed comparable correlations for verbal working memory and pain scores in the medial frontal and prefrontal cortex and in the anterior cingulate cortex. Our data suggest that, in addition to chronic pain, FM patients suffer from neurocognitive deficits that correlate with local brain morphology in the frontal lobe and anterior cingulate gyrus, which may be interpreted to indicate structural correlates of pain-cognition interaction.

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Pain. 2012 May;153(5):1006-14. Epub 2012 Mar 2.

Changes in regional gray matter volume in women with chronic pelvic pain: a voxel-based morphometry study.

As-Sanie S, Harris RE, Napadow V, Kim J, Neshewat G, Kairys A, Williams D, Clauw DJ, Schmidt-Wilcke T.

Abstract

Chronic pelvic pain (CPP) is a highly prevalent pain condition, estimated to affect 15%-20% of women in the United States. Endometriosis is often associated with CPP, however, other factors, such as preexisting or concomitant changes of the central pain system, might contribute to the development of chronic pain. We applied voxel-based morphometry to determine whether women with CPP with and without endometriosis display changes in brain morphology in regions known to be involved in pain processing. Four subgroups of women participated: 17 with endometriosis and CPP, 15 with endometriosis without CPP, 6 with CPP without endometriosis, and 23 healthy controls. All patients with endometriosis and/or CPP were surgically confirmed. Relative to controls, women with endometriosis-associated CPP displayed decreased gray matter volume in brain regions involved in pain perception, including the left thalamus, left cingulate gyrus, right putamen, and right insula. Women with CPP without endometriosis also showed decreases in gray matter volume in the left thalamus. Such decreases were not observed in patients with endometriosis who had no CPP. We conclude that CPP is associated with changes in regional gray matter volume within the central pain system. Although endometriosis may be an important risk factor for the development of CPP, acting as a cyclic source of peripheral nociceptive input, our data support the notion that changes in the central pain system also play an important role in the development of chronic pain, regardless of the presence of endometriosis.

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Arthritis Rheum. 2010 Oct;62(10):2930-40.

Thalamic atrophy associated with painful osteoarthritis of the hip is reversible after arthroplasty: a longitudinal voxel-based morphometric study.

Gwilym SE, Filippini N, Douaud G, Carr AJ, Tracey I.

Abstract

OBJECTIVE: Voxel-based morphometry (VBM) is a method of assessing brain gray matter volume that has previously been applied to various chronic pain conditions. From this previous work, it appears that chronic pain is associated with altered brain morphology. The present study was undertaken to assess these potential alterations in patients with painful hip osteoarthritis (OA).

METHODS: We studied 16 patients with unilateral right-sided hip pain, before and 9 months after hip arthroplasty. This enabled comparison of gray matter volume in patients with chronic musculoskeletal pain versus healthy controls, as well as identification of any changes in volume following alleviation of pain (after surgery). Assessment involved self-completion questionnaires to assess pain, function, and psychosocial variables, and magnetic resonance imaging scanning of the brain for VBM analysis.

RESULTS: Significant differences in brain gray matter volume between healthy controls and patients with painful hip arthritis were seen. Specifically, areas of the thalamus in patients with chronic OA pain exhibited decreased gray matter volume. Furthermore, when these preoperative changes were compared with the brain morphology of the patients 9 months after surgery, the areas of reduced thalamic gray matter volume were found to have “reversed” to levels seen in healthy controls.

CONCLUSION: Our findings confirm that gray matter volume decreases within the left thalamus in the presence of chronic pain and disability in patients with hip OA. The results also show that these thalamic volume changes reverse after hip arthroplasty and are associated with decreased pain and increased function. These findings have potential implications with regard to optimizing the timing of orthopedic interventions such as arthroplasty

21Jan/12

Central sensitisation is more common than you may think

Clifford Woolf recently said this about central sensitisation:

Nociceptor inputs can trigger a prolonged but reversible increase in the excitability and synaptic efficacy of neurons in central nociceptive pathways, the phenomenon of central sensitization. Central sensitization manifests as pain hypersensitivity, particularly dynamic tactile allodynia, secondary punctate or pressure hyperalgesia, aftersensations, and enhanced temporal summation. It can be readily and rapidly elicited in human volunteers by diverse experimental noxious conditioning stimuli to skin, muscles or viscera, and in addition to producing pain hypersensitivity, results in secondary changes in brain activity that can be detected by electrophysiological or imaging techniques. Studies in clinical cohorts reveal changes in pain sensitivity that have been interpreted as revealing an important contribution of central sensitization to the pain phenotype in patients with fibromyalgia, osteoarthritis, musculoskeletal disorders with generalized pain hypersensitivity, headache, temporomandibular joint disorders, dental pain, neuropathic pain, visceral pain hypersensitivity disorders and post-surgical pain. The comorbidity of those pain hypersensitivity syndromes that present in the absence of inflammation or a neural lesion, their similar pattern of clinical presentation and response to centrally acting analgesics, may reflect a commonality of central sensitization to their pathophysiology. An important question that still needs to be determined is whether there are individuals with a higher inherited propensity for developing central sensitization than others, and if so, whether this conveys an increased risk in both developing conditions with pain hypersensitivity, and their chronification. Diagnostic criteria to establish the presence of central sensitization in patients will greatly assist the phenotyping of patients for choosing treatments that produce analgesia by normalizing hyperexcitable central neural activity. We have certainly come a long way since the first discovery of activity-dependent synaptic plasticity in the spinal cord and the revelation that it occurs and produces pain hypersensitivity in patients. Nevertheless, discovering the genetic and environmental contributors to and objective biomarkers of central sensitization will be highly beneficial, as will additional treatment options to prevent or reduce this prevalent and promiscuous form of pain plasticity.

And Latremolier

Central sensitization represents an enhancement in the function of neurons and circuits in nociceptive pathways caused by increases in membrane excitability and synaptic efficacy as well as to reduced inhibition and is a manifestation of the remarkable plasticity of the somatosensory nervous system in response to activity, inflammation, and neural injury. The net effect of central sensitization is to recruit previously subthreshold synaptic inputs to nociceptive neurons, generating an increased or augmented action potential output: a state of facilitation, potentiation, augmentation, or amplification. Central sensitization is responsible for many of the temporal, spatial, and threshold changes in pain sensibility in acute and chronic clinical pain settings and exemplifies the fundamental contribution of the central nervous system to the generation of pain hypersensitivity. Because central sensitization results from changes in the properties of neurons in the central nervous system, the pain is no longer coupled, as acute nociceptive pain is, to the presence, intensity, or duration of noxious peripheral stimuli. Instead, central sensitization produces pain hypersensitivity by changing the sensory response elicited by normal inputs, including those that usually evoke innocuous sensations. PERSPECTIVE: In this article, we review the major triggers that initiate and maintain central sensitization in healthy individuals in response to nociceptor input and in patients with inflammatory and neuropathic pain, emphasizing the fundamental contribution and multiple mechanisms of synaptic plasticity caused by changes in the density, nature, and properties of ionotropic and metabotropic glutamate receptors.

In essence we are talking about changes within the central nervous system that underpin the widespread, unpredictable and varied nature of persisting pain.

When I am listening to a patient, observing their movements and performing a ‘multi-system’ examination, I am in part looking for the pain mechanisms at play, including central sensitisation. Several of my questions are: ‘what is going on here to create this experience for the person in front of me?’, ‘why are the nervous and other systems responding in such a way?’ and ‘what is influencing the behaviour of those systems?’. I really need to know what it is that is prolonging this protection and is it really worthwhile for the individual.

Suspecting that there is a component of central sensitisation at play in many cases of chronic pain that I see, it is pleasing to see a group looking at this closely and finding evidence to support this thinking:

J Bone Joint Surg Br. 2011 Apr;93(4):498-502.

Evidence that central sensitisation is present in patients with shoulder impingement syndrome and influences the outcome after surgery.

Gwilym SE, Oag HC, Tracey I, Carr AJ.

Source

Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences, Nuffield Orthopaedic Centre, Windmill Road, Headington, Oxford OX3 7LD, UK. [email protected]

Abstract

Impingement syndrome in the shoulder has generally been considered to be a clinical condition of mechanical origin. However, anomalies exist between the pathology in the subacromial space and the degree of pain experienced. These may be explained by variations in the processing of nociceptive inputs between different patients. We investigated the evidence for augmented pain transmission (central sensitisation) in patients with impingement, and the relationship between pre-operative central sensitisation and the outcomes following arthroscopic subacromial decompression. We recruited 17 patients with unilateral impingement of the shoulder and 17 age- and gender-matched controls, all of whom underwent quantitative sensory testing to detect thresholds for mechanical stimuli, distinctions between sharp and blunt punctate stimuli, and heat pain. Additionally Oxford shoulder scores to assess pain and function, and PainDETECT questionnaires to identify ‘neuropathic’ and referred symptoms were completed. Patients completed these questionnaires pre-operatively and three months post-operatively. A significant proportion of patients awaiting subacromial decompression had referred pain radiating down the arm and had significant hyperalgesia to punctate stimulus of the skin compared with controls (unpaired t-test, p < 0.0001). These are felt to represent peripheral manifestations of augmented central pain processing (central sensitisation). The presence of either hyperalgesia or referred pain pre-operatively resulted in a significantly worse outcome from decompression three months after surgery (unpaired t-test, p = 0.04 and p = 0.005, respectively). These observations confirm the presence of central sensitisation in a proportion of patients with shoulder pain associated with impingement. Also, if patients had relatively high levels of central sensitisation pre-operatively, as indicated by higher levels of punctate hyperalgesia and/or referred pain, the outcome three months after subacromial decompression was significantly worse.

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Arthritis Rheum. 2009 Sep 15;61(9):1226-34.

Psychophysical and functional imaging evidence supporting the presence of central sensitization in a cohort of osteoarthritis patients.

Gwilym SE, Keltner JR, Warnaby CE, Carr AJ, Chizh B, Chessell I, Tracey I.

Source

University of Oxford, Oxford, UK. [email protected]

Abstract

OBJECTIVE:

The groin pain experienced by patients with hip osteoarthritis (OA) is often accompanied by areas of referred pain and changes in skin sensitivity. We aimed to identify the supraspinal influences that underlie these clinical manifestations that we consider indicative of possible central sensitization.

METHODS:

Twenty patients with hip OA awaiting joint replacement and displaying signs of referred pain were recruited into the study, together with age-matched controls. All subjects completed pain psychology questionnaires and underwent quantitative sensory testing (QST) in their area of referred pain. Twelve of 20 patients and their age- and sex-matched controls underwent functional magnetic resonance imaging (MRI) while the areas of referred pain were stimulated using cold stimuli (12 degrees C) and punctate stimuli (256 mN). The remaining 8 of 20 patients underwent punctate stimulation only.

RESULTS:

Patients were found to have significantly lower threshold perception to punctate stimuli and were hyperalgesic to the noxious punctate stimulus in their areas of referred pain. Functional brain imaging illustrated significantly greater activation in the brainstem of OA patients in response to punctate stimulation of their referred pain areas compared with healthy controls, and the magnitude of this activation positively correlated with the extent of neuropathic-like elements to the patient’s pain, as indicated by the PainDETECT score.

DISCUSSION:

Using psychophysical (QST) and brain imaging methods (functional MRI), we have identified increased activity with the periaqueductal grey matter associated with stimulation of the skin in referred pain areas of patients with hip OA. This offers a central target for analgesia aimed at improving the treatment of this largely peripheral disease.

18Jan/12

Contemporary understanding of factors in joint pain

Recent research has identified biological reasons for joint pain in arthritis:

  • Interleukin-6, a pro-inflammatory cytokine released both locally at the joint and in the spinal cord, consequently plays a role in the widespread nature of the pain via its role in central sensitisation.
  • Sprouting of sensory and sympathetic fibres at the joint may well have a role in sensitisation
  • Angiogenesis, the growth of new blood vessels, at the joint, perhaps having a role in inflammation

Some of this may sound familiar. IL-6 is known to play a role in the spinal cord following nerve injury, sprouting of the sympathetic fibres at the DRG and in tendinopathy, and angiogenesis also seen in tendinopathy. All are clearly responses by the body and are involved in pain–remembering that pain is a brain experience 100% of the time of course.

Spinal interleukin-6 is an amplifier of arthritic pain (Vazquez et al. 2011)

Objective.

Significant joint pain is usually widespread beyond the afflicted joint which results from the sensitization of nociceptive neurons in the central nervous system (central sensitization). In the present study we explored (a) whether the proinflammatory cytokine interleukin-6 (IL-6) in the joint induces central sensitization, (b) whether joint inflammation causes IL-6 release in the spinal cord, and (c) whether spinal IL-6 contributes to central sensitization.

Methods.

In anesthetized rats electrophysiological recordings were made from spinal cord neurons with sensory input from the knee joint. Neuronal responses to mechanical stimulation of the knee and the leg were monitored. IL-6 and its soluble receptor sIL-6R were applied to the knee joint or the spinal cord. Spinal release of IL-6 was measured by ELISA. Sgp130 which neutralizes IL-6/sIL-6R was spinally applied during development of joint inflammation or during established inflammation.

Results.

A single injection of IL-6/sIL-6R into the knee joint as well as spinal application of IL-6/sIL-6R significantly increased the responses of spinal neurons to mechanical stimulation of the knee and ankle joint, i.e. induced central sensitization. Spinally applied sgp130 attenuated this IL-6 effect. Development of knee inflammation caused spinal release of IL-6. Spinal application of spg130 attenuated the development of inflammation-evoked central sensitization but did not reverse it.

Conclusions.

Not only IL-6 in the joint is involved in the generation of joint pain but also IL-6 which is released in the spinal cord. Spinal IL-6 contributes to central sensitization and thus promotes the widespread hyperalgesia in the course of joint disease.

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Neuroplasticity of sensory and sympathetic nerve fibers in the painful arthritic joint (Ghilardi et al. 2011)

Objective.

Many forms of arthritis are accompanied by significant chronic joint pain. Here we studied whether there is significant sprouting of sensory and sympathetic nerve fibers in the painful arthritic knee joint and whether nerve growth factor (NGF) drives this pathological reorganization.

Methods.

A painful arthritic knee joint was produced by injection of complete Freund’s adjuvant (CFA) into the knee joint of young adult mice. CFA-injected mice were then treated systemically with vehicle or anti-NGF antibody. Pain behaviors were assessed and at 28 days following the initial CFA injection, the knee joints were processed for immunohistochemistry using antibodies raised against calcitonin gene-related peptide (CGRP; sensory nerve fibers), neurofilament 200 kDa (NF200; sensory nerve fibers), growth associated protein-43 (GAP43; sprouted nerve fibers), tyrosine hydroxylase (TH; sympathetic nerve fibers), CD31 (endothelial cells) or CD68 (monocytes/macrophages).

Results.

In CFA-injected mice, but not vehicle-injected mice, there was a significant increase in the density of CD68+ macrophages, CD31+ blood vessels, CGRP+, NF200+, GAP43+, and TH+ nerve fibers in the synovium as well as joint pain-related behaviors. Administration of anti-NGF reduced these pain-related behaviors and the ectopic sprouting of nerve fibers, but had no significant effect on the increase in density of CD31+ blood vessels or CD68+ macrophages.

Conclusions.

Ectopic sprouting of sensory and sympathetic nerve fibers occurs in the painful arthritic joint and may be involved in the generation and maintenance of arthritic pain.

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Contributions of angiogenesis to inflammation, joint damage, and pain in a rat model of osteoarthritis (Ashraf et al. 2011)

Objective

To determine the contributions of angiogenesis to inflammation, joint damage, and pain behavior in a rat meniscal transection model of osteoarthritis (OA).

Methods

OA was induced in male Lewis rats (n = 8 per group) by meniscal transection. Animals were orally dosed with dexamethasone (0.1 mg/kg/day), indomethacin (2 mg/kg/day), or the specific angiogenesis inhibitor PPI-2458 (5 mg/kg every other day). Controls consisted of naive and vehicle-treated rats. Synovial inflammation was measured as the macrophage fractional area (expressed as the percentage), thickness of the synovial lining, and joint swelling. Synovial angiogenesis was measured using the endothelial cell proliferation index and vascular density. Channels positive for vessels at the osteochondral junction were assessed (osteochondral angiogenesis). Medial tibial plateaus were assessed for chondropathy, osteophytosis, and channels crossing the osteochondral junction. Pain behavior was measured as weight-bearing asymmetry.

Results

Dexamethasone and indomethacin each reduced pain behavior, synovial inflammation, and synovial angiogenesis 35 days after meniscal transection. Dexamethasone reduced, but indomethacin had no significant effect on, the total joint damage score. PPI-2458 treatment reduced synovial and osteochondral angiogenesis, synovial inflammation, joint damage, and pain behavior.

Conclusion

Our findings indicate that synovial inflammation and joint damage are closely associated with pain behavior in the meniscal transection model of OA. Inhibition of angiogenesis may reduce pain behavior both by reducing synovitis and by preventing structural change. Targeting angiogenesis could therefore prove useful in reducing pain and structural damage in OA.