Changes in dorsal horn neuronal responses in an experimental wrist contracture model

Static stretching of the ankle prevents cold hypersensitivity associated with limb immobilization in model mice

BACKGROUND

Limb immobilization is considered to contribute to limb pain including hyperalgesia. Approximately 50% of patients with such chronic limb pain complain that their abnormal pain worsens after exposure to cold. However, there have been few studies on the relationship between limb immobilization and cold hypersensitivity. The aim of this study was to examine whether limb immobilization induces cold hypersensitivity, and whether physical exercise such as ankle stretching prevents its induction in model mice.

METHOD

We used forty-four 8-week-old male C57Bl/6J mice, consisting of 32 immobilized mice and 12 control mice. The bilateral hind limbs of the mice were immobilized by a thermoplastic cast. After limb-immobilization for 1 week, changes in mechanical, thermal and cold hypersensitivity, and the expression levels of TRPV1, TRPA1, TRPM8, IL-1β, IL-6, and TNFα in the spinal cord, dorsal root ganglia and the affected hind paw were evaluated in comparison with those in the control mice. In addition, we examined the effect of ankle stretching on the hypersensitivity and expression levels in the limb-immobilized mice.

RESULTS

Mechanical, thermal and cold hypersensitivity were significantly increased in the limb-immobilized mice. In addition, ankle stretching during the immobilization period significantly prevented the increases in those hypersensitivities. There were no significant differences in the expression levels of TRPV1, TRPA1 and TRPM8 among the control, and limb-immobilized mice with and without ankle stretching. The expression levels of IL-1 and IL-6 were significantly increased in the immobilized hind limb paw. Furthermore, ankle stretching significantly prevented the increases in their expression levels.

CONCLUSION

Limb-immobilization induced cold hypersensitivity as well as mechanical and thermal hypersensitivity, and ankle stretching significantly prevented the hypersensitivity induction in the model mice. It would be of great interest to clarify whether a patient with limb-immobilization experiences cold hypersensitivity and whether ankle stretching might prevent hypersensitivity induction in the future.

Dysregulation of dopamine neurotransmission in the nucleus accumbens in immobilization-induced hypersensitivity

Cast immobilization causes sensory hypersensitivity, which is also a symptom of neuropathic pain and chronic pain. However, the mechanisms underlying immobilization-induced hypersensitivity remain unclear. The present study investigated the role of dopamine neurotransmission in the nucleus accumbens shell (NAcSh) of rats with cast immobilization-induced mechanical hypersensitivity using in vivo microdialysis. Cast immobilization of the hind limb decreased the paw withdrawal threshold (PWT). Mechanical stimulation of the cast-immobilized hind limb induced a decrease in dopamine in the NAcSh, and this decrease was associated with the upregulation of presynaptic D2-like receptors. A D2-like receptor antagonist infused into the NAcSh reversed the decrease in PWT in rats with cast immobilization, whereas a D2-like receptor agonist infused into the NAcSh induced a decrease in PWT in control rats. In addition, the expression of the D2 receptor (Drd2) mRNA in the NAcSh was increased by cast immobilization. Importantly, systemic administration of the D2-like receptor antagonist reversed the decrease in PWT in rats with cast immobilization. As dopamine levels regulated by presynaptic D2-like receptors did not correlate with the PWT, it is presumed that the D2-like receptor antagonist or agonist acts on postsynaptic D2-like receptors. These results suggest that immobilization-induced mechanical hypersensitivity is attributable to the upregulation of postsynaptic D2-like receptors in the NAc. Blockade of D2-like receptors in the NAcSh is a potential therapeutic strategy for immobilization-induced hypersensitivity.

Immediate curative effects of exercise therapy in patients with myalgia of the masticatory muscles

BACKGROUND

Exercise therapy is occasionally considered as an initial treatment for temporomandibular disorders. However, pain can be exacerbated during exercise therapy.

OBJECTIVE

To investigate the immediate curative effects of exercise therapy in patients with masticatory muscle myalgia.

METHODS

Fifty-nine patients with masticatory muscle myalgia were included. Therapists performed exercise therapy (stretched the painful masseter and/or cervical muscles along the direction of muscle contraction) in 10 rounds of traction, each lasting 10 seconds. The patient's pain-free maximum mouth opening distance and degree of pain (VAS value) before and immediately after exercise therapy were compared using the Wilcoxon signed rank test. Mann-Whitney U test was used for the subgroup comparisons.

RESULTS

Mouth opening increased from 41 (IQR 38-43) to 46 (IQR 43-48) mm, and pain alleviation from 48 (IQR 31-56) to 21 (IQR 10-56) immediately following exercise therapy (p < 0.001 for both). None of the patients experienced pain exacerbation or reduction in mouth opening post exercise. No difference in mouth opening distance changes according to sex, painful side, painful site, and therapist were observed (p > 0.05 for all). Pain reduction was greater in patients with unilateral pain (26, IQR 12-39) than those with bilateral (13, IQR 5-25) (p = 0.019). There were no differences in the change in the degree of pain according to sex, painful site, and therapist (p > 0.05 for all).

CONCLUSION

Exercise therapy immediately enlarged the mouth opening distance and reduced myalgia; therefore, it could be helpful in managing masticatory muscle myalgia.

Responses of cutaneous C-fiber afferents and spinal microglia after hindlimb cast immobilization in rats

Previous studies have shown that persistent limb immobilization using a cast increases nociceptive behavior to somatic stimuli in rats. However, the peripheral neural mechanisms of nociception remain unclear. Using single-fiber electrophysiological recordings in vitro, we examined the general characteristics of cutaneous C-fiber afferents in the saphenous nerve and their responsiveness to mechanical and heat stimuli in a rat model of immobilization-induced pain by subjecting the rats to hindlimb cast immobilization for 4 weeks. The mechanical response of C-fibers appeared to increase in the model; however, statistical analysis revealed that neither the response threshold nor the response magnitude was altered. The general characteristics and heat responses of the C-fibers were not altered. The number of microglia and cell diameters significantly increased in the superficial dorsal horn of the lumbar spinal cord. Thus, activated microglia-mediated spinal mechanisms are associated with the induction of nociceptive hypersensitivity in rats after persistent cast immobilization.

Clipping Hind Paws Under Isoflurane Sedation as a Useful Tool for Evaluation of Chronic Pain in CCI Animals

Background

Several behavioral tests have been devised to assess pain in rodent models, one of which is the Chronic constriction injury (CCI) model of the sciatic nerve, including the sensitivity of the paw evaluated through reflex reactions to heat or mechanical stimuli. However, because of their high restless activity and responsiveness to humans, it is tough to give the moving animals consistent stimuli to get consistent and reliable reactions.

Methods

Experiments were performed on male C57BL/6J mice (aged eight weeks) and prairie voles (aged eight weeks). Sham animals (five mice and six prairie voles) and CCI animals (six mice and seven prairie voles) were tested before surgery, four days after, and seven days after surgery. Each animal was rated using a modified rating scale for the scoring of nociceptive behavior. The mechanical threshold test was administered by applying arterial clips to the base of toes under isoflurane-induced sedation.

Results

The right hind paw of the CCI administered side showed significant increases in the scores of nociceptive behavior on day 4 and day 7. The right hind paw of the CCI-administered side showed significant reductions in the mechanical threshold test on day 4 and day 7.

Conclusions

The results of the mechanical threshold test were consistent with those of the scoring of nociceptive behavior in CCI model animals, and the method of using arterial clips under sedation was useful for the mechanical threshold test.

Effect of Continuous Passive Motion Initiated After the Onset of Arthritis on Inflammation and Secondary Hyperalgesia in Rats

This study investigated the effect of continuous passive motion (CPM) initiated after the onset of arthritis in rats. Rats were injected with 3 % kaolin/carrageenan in the knee joint and randomized to the control, immobilization (IM), or CPM group. The knee joints of the IM and CPM groups were immobilized with a cast for 56 days. In the CPM group, CPM exercise was administered for 60 min/day (6 times/week). Joint transverse diameter and pressure pain threshold (PPT) were assessed as indicators of inflammation, and paw withdrawal response (PWR) was assessed as indicator of secondary hyperalgesia. Central sensitization was analyzed by measuring calcitonin gene-related peptide (CGRP) expression levels in the spinal dorsal horn. In the CPM group, the PPT was significantly increased compared with the IM group from 14 to 35 days, and PWR was significantly decreased from 14 to 56 days. Additionally, CGRP expression in the super facial layer (I-II) of the spinal dorsal horn (L4-5) in the CPM group was significantly decreased compared with the IM group. Our study found the CPM initiated after the onset of arthritis promoted the recovery of inflammation and mitigated secondary hyperalgesia

Effects of Vibration Therapy on Immobilization-Induced Hypersensitivity in Rats

BACKGROUND

Cast immobilization induces mechanical hypersensitivity, which disturbs rehabilitation. Although vibration therapy can reduce various types of pain, whether vibration reduces immobilization-induced hypersensitivity remains unclear.

OBJECTIVE

The purpose of this study was to investigate the preventive and therapeutic effects of vibration therapy on immobilization-induced hypersensitivity.

DESIGN

The experimental design of the study involved conducting behavioral, histological, and immunohistochemical studies in model rats.

METHODS

Thirty-five Wistar rats (8 weeks old, all male) were used. The right ankle joints of 30 rats were immobilized by plaster cast for 8 weeks, and 5 rats were used as controls. The immobilized rats were divided randomly into the following 3 groups: (1) immobilization-only group (Im, n=10); (2) vibration therapy group 1, for which vibration therapy was initiated immediately after the onset of immobilization (Im+Vib1, n=10); and (3) vibration therapy group 2, for which vibration therapy was initiated 4 weeks after the onset of immobilization (Im+Vib2, n=10). Vibration was applied to the hind paw. The mechanical hypersensitivity and epidermal thickness of the hind paw skin were measured. To investigate central sensitization, calcitonin gene-related peptide (CGRP) expression in the spinal cord and dorsal root ganglion (DRG) was analyzed.

RESULTS

Immobilization-induced hypersensitivity was inhibited in the Im+Vib1 group but not in the Im+Vib2 group. Central sensitization, which was indicated by increases in CGRP expression in the spinal cord and the size of the area of CGRP-positive neurons in the DRG, was inhibited in only the Im+Vib1 group. Epidermal thickness was not affected by vibration stimulation.

LIMITATIONS

A limitation of this study is that the results were limited to an animal model and cannot be generalized to humans.

CONCLUSIONS

The data suggest that initiation of vibration therapy in the early phase of immobilization may inhibit the development of immobilization-induced hypersensitivity.

Immediate effects of repetitive wrist extension on grip strength in patients with distal radial fracture

OBJECTIVE

To evaluate the immediate effect of repetitive wrist extension on grip strength in patients with distal radial fracture.

DESIGN

Interventional study.

SETTING

Patients who were admitted to a hospital department of occupational therapy.

PARTICIPANTS

Consecutive patients with a unilateral distal radial fracture (N=28).

INTERVENTION

Each patient was randomly allocated to either the experimental group (n=14) or the control group (n=14). The experimental group performed 30 repetitive wrist extensions with maximal isometric contraction of the extensors of their affected hands during a 6-minute intervention period, whereas the control group did not perform the exercise.

MAIN OUTCOME MEASURES

Grip strength was measured just before and after the intervention period. Pain during grip strength measurements was also quantified using the visual analog scale. Wrist extension strength was measured 10 minutes after the grip strength measurement.

RESULTS

Grip strength increased immediately after repetitive wrist extension in the experimental group, but it remained the same in the control group. Visual analog scale scores indicated that pain was relieved only in the experimental group. However, pain was unrelated to strength production.

CONCLUSIONS

The intervention used in this study might be useful during physical examination to reveal the potential grip strength of patients. The intervention may also be an effective warm-up training procedure in preparation for conventional grip-strengthening exercises.

[Nonspecific low back pain in young adults: associated risk factors]

OBJECTIVE

The aim of the study was to evaluate potential risk factors related to low back pain in the daily routines of two sets of youths: individuals complaining of chronic low back pain and a control group.

METHODS

The sample consisted of 198 university-age students (male and female) aged between 18 and 29. In accordance with back pain diagnoses, they were separated into two groups: with or without nonspecific chronic low back pain. Both groups were evaluated by a "blinded" observer with no knowledge to the presence or otherwise of lower back pain. Questionnaires concerning clinical-demographic characteristics, life style, quality of life (SF-36 questionnaire), pain visual analogical scales (VAS), and physical examination were applied.

RESULTS

A univariate analysis showed a statistically significant association (P<0.05) with the presence of low back pain and some factors. There was a negative association between low back pain and the following variables: BMI, health self-assessment, VAS and some SF-36 domains (physical functioning, body pain, general health, vitality, social functioning). There was a positive correlation with the following variables: global pain by VAS, presence of diffuse pain and number of tender points. However, the multivariate analysis showed statistically significant correlations (P<0.05) between low back pain and few variables: global pain VAS and number of tender points.

CONCLUSION

Some variables related to chronic diffuse pain and lower quality of life might be associated to chronic low back pain in young adults. However, longitudinal studies are necessary.

Immobilization-induced hypersensitivity associated with spinal cord sensitization during cast immobilization and after cast removal in rats

This study examined mechanical and thermal hypersensitivity in the rat hind paw during cast immobilization of the hind limbs for 4 or 8 weeks and following cast removal. Blood flow, skin temperature, and volume of the rat hind paw were assessed in order to determine peripheral circulation of the hind limbs. Sensitization was analyzed by measuring the expression of the calcitonin gene-related peptide (CGRP) in the spinal dorsal horn following cast immobilization. Two weeks post immobilization, mechanical and thermal sensitivities increased significantly in all rats; however, peripheral circulation was not affected by immobilization. Cast immobilization for 8 weeks induced more serious hypersensitivity compared to cast immobilization for 4 weeks. Moreover, CGRP expression in the deeper lamina layer of the spinal dorsal horn increased in the rats immobilized for 8 weeks but not in those immobilized for 4 weeks. These findings suggest that immobilization-induced hypersensitivity develops during the immobilization period without affecting peripheral circulation. Our results also highlight the possibility that prolonged immobilization induces central sensitization in the spinal cord.

Sensory innervation of rat contracture shoulder model

BACKGROUND

To date, few studies have investigated the cause of pain experienced by patients with frozen shoulder. The purposes of this study were to establish a rat contracture model and clarify the innervation pattern of the glenohumeral (GH) joint and subacromial bursa (SAB) using immunohistochemistry in the dorsal root ganglion (DRG) neurons.

MATERIALS AND METHODS

The rat contracture models were made by tying the animal's humerus and scapula with No. 2-0 FiberWire (Arthrex, Naples, FL, USA). Contracture was confirmed on x-ray images taken 8 weeks after the operation. Subsequently, two kinds of neurotracers, Fluoro-Gold (FG) (Fluorochrome, Denver, CO, USA) and 1,1'-dioctadecyl-3,3,3',3'-tetramethyl-indocarbocyanine perchlorate (DiI) (Molecular Probes, Eugene, OR, USA), were used to detect the GH joints and SAB separately. FG tracers were injected into GH joints, and DiI tracers were injected into the SAB. At 7 days after injection, DRGs were harvested between C1 and T1. Immunohistochemistry by use of calcitonin gene-related peptide (CGRP) was performed. CGRP is thought to be one of the causes of pain sensation in joint disease. We evaluated the percentages of FG-labeled CGRP-immunoreactive (CGRP-ir) neurons in the total number of FG-labeled neurons and of DiI-labeled CGRP-ir neurons in the total number of DiI-labeled neurons.

RESULTS

Abduction and total arc of the rotation were statistically significantly decreased in the contracture group. Furthermore, the percentage of CGRP-ir DRG neurons was significantly higher in the contracture group in both the GH joint and SAB.

CONCLUSION

These results show that pain sensation in rat shoulder contracture may be induced by the up-regulation of CGRP expression in DRG neurons.

Development of heat hyperalgesia and changes of TRPV1 and NGF expression in rat dorsal root ganglion following joint immobilization

The aim of this study was to examine whether threshold to heat stimuli, and expression of transient receptor potential vanilloid1 (TRPV1) and nerve growth factor (NGF) in dorsal root ganglion (DRG) altered under conditions of long-term limb immobilization. A plastic cast was wrapped around the right limb from the forearm to the forepaw to keep wrist joint at 90° of flexion for 5 weeks. Heat hyperalgesia was tested using the plantar test at 6 h after removing cast. The rats were perfused transcardially with 4 % paraformaldehyde and DRGs were excised at 24 h after removing cast. For size distributions of the TRPV1-IR and NGF-IR neuronal profile, the DRG area measurements over 1000 DRG neurons per animal were measured in each side, on both the immobilized (ipsilateral) and contralateral sides. Ipsilateral withdrawal latency was significantly shorter than contralateral sides. Ipsilateral percentage of immunoreactive neurons in the total DRG neurons was significantly higher than contralateral sides in TRPV1-IR and NGF-IR. Long-term casting induced heat hyperalgesia, and up-regulation and phenotypic change of TRPV1-IR and NGF-IR in DRGs on the immobilized side. These DRG alterations may involve heat hyperalgesia after long-term limb immobilization.

Changes in hind paw epidermal thickness, peripheral nerve distribution and mechanical sensitivity after immobilization in rats

This study was designed to investigate histological changes in skin tissue accompanying immobilization-induced hypersensitivity. Changes in mechanical sensitivity, epidermal thickness, and peripheral nerve profiles in the upper dermis were examined in glabrous skin of rat hind paw after 1, 2, and 4 weeks of ankle joint immobilization by plaster casts. Induction of mechanical hypersensitivity was confirmed after 2 and 4 weeks of joint immobilization. Epidermal thinning and increase in peripheral nerve profiles were observed in skin tissues in immobilized rats. The time course of epidermal thinning and increase in peripheral nerve profiles were similar closely to that of hypersensitivity, with significant differences between the immobilized and control rats after 2 weeks of immobilization, which became even more remarkable at 4 weeks of immobilization. These findings suggest that joint immobilization by cast induces epidermal thinning and increases peripheral nerve profiles in the upper dermis and that these changes might be partly responsible for immobilization-induced hypersensitivity.

Peripheral pain mechanisms in chronic widespread pain

Clinical symptoms of chronic widespread pain (CWP) conditions like fibromyalgia (FM), include pain, stiffness, subjective weakness, and muscle fatigue. Muscle pain in CWP is usually described as fluctuating and often associated with local or generalised tenderness (hyperalgesia and/or allodynia). This tenderness related to muscle pain depends on increased peripheral and/or central nervous system responsiveness to peripheral stimuli, which can be either noxious (hyperalgesia) or non-noxious (allodynia). For example, patients with muscle hyperalgesia will rate painful muscle stimuli higher than normal controls, whereas patients with allodynia may perceive light touch as painful, something that a 'normal' individual will never describe as painful. The pathogenesis of such peripheral and/or central nervous system changes in CWP is unclear, but peripheral soft tissue changes have been implicated. Indirect evidence from interventions that attenuate tonic peripheral nociceptive impulses in patients with CWP syndromes like FM suggest that overall FM pain is dependent on peripheral input. More importantly, allodynia and hyperalgesia can be improved or abolished by removal of peripheral impulse input. Another potential mechanism for CWP pain is central disinhibition. However, this pain mechanism also depends on tonic impulse input, even if only inadequately inhibited. Thus, a promising approach to understanding CWP is to determine whether abnormal activity of receptors in deep tissues is fundamental to the development and maintenance of this chronic pain disorder.

CONCLUSIONS

Most CWP patients present with focal tissue abnormalities including myofascial trigger points, ligamentous trigger points or osteoarthritis of the joints and spine. While not predictive for the development of CWP, these changes nevertheless represent important pain generators that may initiate or perpetuate chronic pain. Local chemical mediators, including lactic acid, adenosine triphosphate (ATP) and cytokines, seem to play an important role in sensitising deep tissue nociceptors of CWP patients. Thus, the combination of peripheral impulse input and increased central pain sensitivity may be responsible for widespread chronic pain disorders including FM.

Regulation of peripheral blood flow in complex regional pain syndrome: clinical implication for symptomatic relief and pain management

BACKGROUND

During the chronic stage of Complex Regional Pain Syndrome (CRPS), impaired microcirculation is related to increased vasoconstriction, tissue hypoxia, and metabolic tissue acidosis in the affected limb. Several mechanisms may be responsible for the ischemia and pain in chronic cold CPRS.

DISCUSSION

The diminished blood flow may be caused by either sympathetic dysfunction, hypersensitivity to circulating catecholamines, or endothelial dysfunction. The pain may be of neuropathic, inflammatory, nociceptive, or functional nature, or of mixed origin.

SUMMARY

The origin of the pain should be the basis of the symptomatic therapy. Since the difference in temperature between both hands fluctuates over time in cold CRPS, when in doubt, the clinician should prioritize the patient's report of a persistent cold extremity over clinical tests that show no difference. Future research should focus on developing easily applied methods for clinical use to differentiate between central and peripheral blood flow regulation disorders in individual patients.

Enhanced central pain processing of fibromyalgia patients is maintained by muscle afferent input: a randomized, double-blind, placebo-controlled study

Fibromyalgia (FM) syndrome is characterized by pain and widespread hyperalgesia to mechanical, thermal, and electrical stimuli. Despite convincing evidence for central sensitization of nociceptive pain pathways, the role of peripheral tissue impulse input in the initiation and maintenance of FM is unclear. Therefore this randomized, double-blind, placebo-controlled trial of 22 female normal controls (NCs) and 28 female FM subjects tested the effects of trapezius muscle (TrapM) tender point injections with 1% lidocaine on local pain thresholds as well as on remote heat hyperalgesia at the forearm. Prior to muscle injections shoulder pain was standardized by tonic mechanical muscle stimulation, resulting in local pain ratings of 4.0+/-0.5 VAS units. Tonic muscle stimulation was interrupted for the TrapM injections but was continued afterwards at the same level. NC as well as FM subjects experienced significant increases of TrapM pressure pain thresholds from lidocaine injections but not from placebo injections (p<0.001). Additionally, heat hyperalgesia of FM participants was significantly reduced at areas remote from the injection site (forearm) by lidocaine but not by placebo (p=0.02). Neither lidocaine nor saline injections significantly affected clinical FM pain ratings, a result most likely due to the very low dose of lidocaine (50mg) used in this trial.

CONCLUSION

Lidocaine injections increased local pain thresholds and decreased remote secondary heat hyperalgesia in FM patients, emphasizing the important role of peripheral impulse input in maintaining central sensitization in this chronic pain syndrome; similar to other persistent pain conditions such as irritable bowel syndrome and complex regional pain syndrome.

Changes in calcitonin gene-related peptide expression following joint immobilization in rats

Long-term immobilization by casting can occasionally cause pathologic pain states in the immobilized side. The underlying neurophysiological mechanisms of immobilization-related pain are not well understood. For this reason, we specifically examined changes of calcitonin gene-related peptide (CGRP) expression in the dorsal root ganglion (DRG), spinal dorsal horn and posterior nuclei (cuneate nuclei) in a long-term immobilization model following casting for 5 weeks. A plastic cast was wrapped around the right limb from the forearm to the forepaw to keep wrist joint at 90 degrees of flexion. In this model, CGRP in immobilized (ipsilateral) side was distributed in larger DRG neurons compared with contralateral side, even though the number of CGRP-immunoreactive (CGRP-IR) neurons did not differ. Spinal laminae III-V, not laminae I-II in ipsilateral side showed significantly high CGRP expression relative to contralateral side. CGRP expression in cuneate nuclei was not significantly different between ipsilateral and contralateral sides. Long-term immobilization by casting may induce phenotypic changes in CGRP expression both in DRG and spinal deep layers, and these changes are partly responsible for pathological pain states in immobilized side.

Treatment of fibromyalgia and its symptoms

The main symptoms of fibromyalgia syndrome (FM) are pain, stiffness, subjective weakness and muscle fatigue. Pain in FM usually fluctuates, as well as being 'deep' and is always associated with local or generalized tenderness (hyperalgesia and allodynia). The pathogenesis of such peripheral and/or CNS changes in FM is unclear, but peripheral tissue changes, specifically in muscles, have been implicated. Indirect evidence from interventions that attenuate tonic peripheral impulse input in patients with FM suggest that overall FM pain is dependent on nociception. More importantly, FM-associated widespread mechanical hyperalgesia and allodynia can also be improved or abolished by removal of peripheral pain impulse input. In addition, FM patients show evidence of abnormal stress reactivity, including blunting of the hypothalamic-pituitary-adrenal axis and increased autonomic nervous system responsiveness. Thus, therapeutic interventions in FM should target not only pain reductions, but also improvements of peripheral/central sensitization and neuroendocrine/autonomic abnormalities. Despite the complexity of FM, there are pharmacologic and non-pharmacologic interventions that are available that have clinical benefit. Present evidence indicates efficacy of antidepressants, cardiovascular exercise and cognitive behavioral therapy. Based on this evidence, a stepwise program emphasizing education, medications, exercise and cognitive therapy can be recommended.

Future perspectives: pathogenesis of chronic muscle pain

Chronic painful muscle conditions include non-inflammatory and inflammatory illnesses. This review is focused on chronic non-inflammatory pain conditions such as myofascial pain syndrome (MPS) and fibromyalgia syndrome (FM), and will not discuss metabolic, genetic or inflammatory muscle diseases such as McArdle's disease, muscular dystrophy, polymyositis, dermatomyositis, or inclusion body myositis.

Mechanisms underlying development of spatially distributed chronic pain (fibromyalgia)

Chronic fibromyalgia (FM) pain is prevalent (estimated as high as 13%), predominantly affects women, and is associated with a variety of focal pain conditions. Ongoing FM pain is referred to deep tissues and is described as widespread but usually is maximally located within a restricted region such as the shoulders. Palpation of deep tissues reveals an enhanced nociceptive sensitivity that is not restricted to regions of clinical pain. Similarly, psychophysical testing reveals allodynia and hyperalgesia for cutaneous stimulation at locations beyond regions of clinical pain referral. The combination of widely distributed clinical pain and generalized hypersensitivity is highly disabling, but no satisfactory treatment is regularly prescribed. A thorough understanding of mechanisms will likely be required to develop and document adequate therapies. The generalized hypersensitivity associated with FM has focused considerable interest on central (CNS) mechanisms for the disorder. These include central sensitization, central disinhibition and a dysfunctional hypothalamic-pituitary-adrenal (HPA) axis. However, the central effects associated with FM can be produced by a peripheral source of pain. Chronic nociceptive input induces central sensitization, magnifying pain, and it activates the HPA and the sympathetic nervous system. Chronic sympathetic activation indirectly sensitizes peripheral nociceptors and sets up a vicious cycle. Thus, it appears that central mechanisms of FM pain are dependent on abnormal peripheral input(s) for development and maintenance of this condition. A substantial literature defines peripheral-CNS-peripheral interactions that are integral to FM pain. These reciprocal actions and related phenomena of relevance to FM pain are reviewed here, leading to suggestions for testing of therapeutic approaches.

Joint capsule matrix turnover in a rabbit model of chronic joint contractures: Correlation with human contractures

To evaluate changes in matrix molecules of the joint capsule, the right knees of 24 skeletally mature female NZW rabbits were immobilized while the contralateral limb served as an unoperated control. The immobilization was discontinued at 8 weeks and the rabbits were divided among four groups (n = 6) based on the number of weeks the right knees were remobilized: 0, 8, 16, or 32. Three rabbits (six knees) that did not have operations provided normal control joint capsules. The mRNA levels for collagen types I, II, and III, and MMP-1 and -13 were significantly increased in the joint capsules of the contracture knees in all groups when compared to normal and contralateral limb joint capsules. In contrast, the mRNA levels for TIMP-1, -2, and -3 were decreased in the joint capsules of the contracture knees in all groups when compared to normal and contralateral limb joint capsules. The mRNA levels for lumican and decorin were increased in the joint capsules of the contracture knees in all groups when compared to normal capsules. Many of the changes observed in this animal model are similar to those observed in human joint capsules from posttraumatic elbow contractures, supporting the value of this rabbit model.

Does microcurrent stimulation increase the range of movement of ankle dorsiflexion in children with cerebral palsy?

AIM

To determine whether microcurrent stimulation (MENS) increases the range of motion (ROM) of the ankle joint in children with cerebral palsy.

DESIGN

Twelve children with spastic hemiplegia (age range 4.5 to 16 years) with moderate myocontracture of the triceps surae, received MENS for 1 h five times a week for 4 weeks. An equally long baseline period was preceded. The assessments were: active and passive ROM of ankle dorsiflexion, popliteal flexion and ankle dorsiflexion in maximal flexion of knees in standing position while maintaining the heels in contact with the floor, one foot standing and hopping on one foot.

RESULTS

After the treatment with MENS, the passive ROM of ankle dorsiflexion with both knees flexed and extended (p<0.001) increased significantly. Increases were also observed in popliteal flexion (p<0.001) and ankle dorsiflexion (p=0.0012) during maximal flexion of the knees in a standing position. The ROM of active dorsiflexion with the knee flexed (p<0.05) and one foot standing (p<0.05) also improved. Children and parents found this treatment easy to carry out.

CONCLUSIONS

MENS relieves myocontracture and can enhance conventional rehabilitation programmes for children with cerebral palsy.

Rabbit knee model of post-traumatic joint contractures: the long-term natural history of motion loss and myofibroblasts

Our objective is to describe the natural history of motion loss with time and myofibroblast numbers in a rabbit knee model of post-traumatic joint contractures. Twenty-eight skeletally mature New Zealand White female rabbits had five-mm-squares of cortical bone removed from the medial and lateral femoral condyles of the right knee. A Kirschner wire (K-wire) was used to immobilize the knee joint in maximum flexion. A second operation was performed 8 weeks later to remove the K-wire. The rabbits were divided into four groups depending on the time of remobilization; 0, 8, 16 or 32 weeks. The average flexion contracture of the experimental knees in the 0-week and 8-week remobilization groups (38 degrees and 33 degrees, respectively) were significantly greater when compared with the values of the unoperated contralateral knees (8 degrees). The average flexion contractures of the experimental knees in the 16-week and 32-week remobilization groups were also greater than the unoperated contralateral knees, although they were not statistically significant. The average flexion contractures of the 16-week and 32-week groups were 19 degrees and 18 degrees, respectively, indicating a stabilization of the motion loss. Myofibroblast numbers in the posterior joint capsules were elevated 4-5x in the knees with contractures when compared to the contralateral knees. The initial decrease in severity followed by stabilization of motion loss and the association of motion loss with myofibroblasts mimics the human scenario of permanent post-traumatic joint contractures.

Changes of wide dynamic range neuronal responses to mechanical cutaneous stimuli following acute compression of the rat sciatic nerve

To investigate the changes in central neuronal activity in response to cutaneous stimulation following acute nerve compression, the responses of wide dynamic range dorsal horn neurons (n = 13) to graded mechanical cutaneous stimuli (brush, press, pinch, and squeeze) were recorded in anesthetized male Sprague-Dawley rats before and during compression, and after the release of the compression. A small vascular clip (pinching force, 120 g) was applied to compress the sciatic nerve for 30 min. In 12 neurons, background activities increased transiently for 1.5 to 4 min after nerve compression. Similarly, after the release of the compression, 7 neurons showed a transient increase in background activities. The responses to brush, press, and pinch were inhibited significantly 10 min after the nerve compression. The responses to press and pinch recovered gradually after the release of the compression. Responses to squeeze were little affected throughout the experimental period. Acute compression of the rat sciatic nerve can cause short periods of continuous increased spontaneous firing and can attenuate the dorsal horn neuronal responses to cutaneous stimuli. In particular, the neuronal responses to innocuous stimuli were more susceptible to compression of the nerve than the responses to noxious stimuli.