Median nerve trauma in a rat model of work-related musculoskeletal disorder

Aberrant Neuronal Activity in a Model of Work-Related Upper Limb Pain and Dysfunction

Work-related musculoskeletal disorders associated with intense repetitive tasks are highly prevalent. Painful symptoms associated with such disorders can be attributed to neuropathy. In this study, we characterized the neuronal discharge from the median nerve in rats trained to perform an operant repetitive task. After 3-weeks of the task, rats developed pain behaviors and a decline in grip strength. Ongoing activity developed in 17.7% of slowly conducting neurons at 3-weeks, similar to neuritis. At 12-weeks, an irregular high frequency neuronal discharge was prevalent in >88.4% of slow and fast conducting neurons. At this time point, 8.3% of slow and 21.2% of fast conducting neurons developed a bursting discharge, which, combined with a reduction in fast-conducting neurons with receptive fields (38.4%), is consistent with marked neuropathology. Taken together, we have shown that an operant repetitive task leads to an active and progressive neuropathy that is characterized by marked neuropathology following 12-weeks task that mainly affects fast conducting neurons. Such aberrant neuronal activity may underlie painful symptoms in patients with work-related musculoskeletal disorders. PERSPECTIVE: Aberrant neuronal activity, similar to that reported in this study, may contribute to upper limb pain and dysfunction in patients with work-related musculoskeletal disorders. In addition, profiles of instantaneous frequencies may provide an effective way of stratifying patients with painful neuropathies.

Manual Therapy With Rest as a Treatment for Established Inflammation and Fibrosis in a Rat Model of Repetitive Strain Injury

Background: Repetitive strain injuries caused by repetitive occupational work are difficult to prevent for multiple reasons. Therefore, we examined the effectiveness of manual therapy (MT) with rest to treat the inflammation and fibrosis that develops through the performance of a repetitive task. We hypothesized that this treatment would reduce task-induced sensorimotor declines and neuromuscular inflammation. Methods: Twenty-nine female Sprague-Dawley rats performed a reaching and lever-pulling task for 14weeks. All ceased performing the task at 14weeks. Ten were euthanized at this timepoint (TASK). Nine received manual therapy to their upper extremities while resting 7weeks (MTR); 10 were assigned to rest alone (REST). Ten additional food restricted rats were included that neither performed the task nor received manual therapy (FRC). Results: Confirming previous experiments, TASK rats showed behavioral changes (forepaw mechanical hypersensitivity, reduced grip strength, lowered forelimb/forepaw agility, and noxious cold temperature sensitivity), reduced median nerve conduction velocity (NCV), and pathological tissue changes (myelin degradation, increased median nerve and muscle inflammation, and collagen production). Manual therapy with rest (MTR) ameliorated cold sensitivity seen in REST rats, enhanced muscle interleukin 10 (IL-10) more than in REST rats, lead to improvement in most other measures, compared to TASK rats. REST rats showed improved grip strength, lowered nerve inflammation and degraded myelin, and lowered muscle tumor necrosis factor alpha (TNFα) and collagen I levels, compared to TASK rats, yet maintained lowered forelimb/forepaw agility and NCV, and increased neural fibrosis. Conclusion: In our model of repetitive motion disorder, manual therapy during rest had modest effects on behavioral, histological, and physiological measures, compared to rest alone. These findings stand in contrast to the robust preventive effects of manual therapy in this same model.

Blocking CTGF/CCN2 reverses neural fibrosis and sensorimotor declines in a rat model of overuse-induced median mononeuropathy

Encapsulation of median nerves is a hallmark of overuse-induced median mononeuropathy and contributes to functional declines. We tested if an antibody against CTGF/CCN2 (termed FG-3019 or Pamrevlumab) reduces established neural fibrosis and sensorimotor declines in a clinically relevant rodent model of overuse in which median mononeuropathy develops. Young adult female rats performed a high repetition high force (HRHF) lever-pulling task for 18 weeks. Rats were then euthanised at 18 weeks (HRHF untreated), or rested and systemically treated for 6 weeks with either an anti-CCN2 monoclonal antibody (HRHF-Rest/FG-3019) or IgG (HRHF-Rest/IgG), with results compared with nontask control rats. Neuropathology was evident in HRHF-untreated and HRHF-Rest/IgG rats as increased perineural collagen deposition and degraded myelin basic protein (dMBP) in median nerves, and increased substance P in lower cervical dorsal root ganglia (DRG), compared with controls. Both groups showed functional declines, specifically, decreased sensory conduction velocity in median nerves, noxious cold temperature hypersensitivity, and grip strength declines, compared with controls. There were also increases of ATF3-immunopositive nuclei in ventral horn neurons in HRHF-untreated rats, compared with controls (which showed none). FG-3019-treated rats showed no increase above control levels of perineural collagen or dMBP in median nerves, Substance P in lower cervical DRGs, or ATF3-immunopositive nuclei in ventral horns, and similar median nerve conduction velocities and thermal sensitivity, compared with controls. We hypothesize that neural fibrotic processes underpin the sensorimotor declines by compressing or impeding median nerves during movement, and that inhibiting fibrosis using an anti-CCN2 treatment reverses these effects.

The Pelvic Girdle Pain deadlock: 2. Topics that, so far, have remained out of focus

INTRODUCTION

In our preceding paper, we concluded that Pelvic Girdle Pain (PGP) should be taken seriously. Still, we do not know its causes. Literature reviews on treatment fail to reveal a consistent pattern, and there are patients who do not respond well to treatment. We designated the lack of progress in research and in the clinic as 'deadlock', and proposed a 'deconstruction' of PGP, that is to say, taking PGP apart into its relevant dimensions.

PURPOSE

We examine the proposition that PGP may emerge as local inflammation. Inflammation would be a new dimension to be taken into account, between biomechanics and psychology. To explore the consequences of this idea, we present four different topics that, so far, have remained out of focus. One: The importance of microtrauma. Two: Ways to counteract chronification. Three: The importance of sickness behaviour when systemic inflammation turns into neuroinflammation of the brain. And Four: The mainly emotional and cognitive nature of chronic pain, and how aberrant neuroinflammation may render chronic pain intractable. For intractable pain, sleep and stress management are promising treatment options.

IMPLICATIONS

The authors hope that the present paper helps to stimulate the flexible creativity that is required to deal with the biological and psychological impact of PGP. Measuring inflammatory mediators in PGP should be a research priority. It should be understood that the boundaries between biology and psychology are becoming blurred. Clinicians must frequently monitor pain, disability, and mood, and be ready to switch treatment whenever the patient does not improve.

Forced treadmill running reduces systemic inflammation yet worsens upper limb discomfort in a rat model of work-related musculoskeletal disorders

BACKGROUND

Musculoskeletal disorders can result from prolonged repetitive and/or forceful movements. Performance of an upper extremity high repetition high force task increases serum pro-inflammatory cytokines and upper extremity sensorimotor declines in a rat model of work-related musculoskeletal disorders. Since one of the most efficacious treatments for musculoskeletal pain is exercise, this study investigated the effectiveness of treadmill running in preventing these responses.

METHODS

Twenty-nine young adult female Sprague-Dawley rats were used. Nineteen were trained for 5 weeks to pull a lever bar at high force (15 min/day). Thirteen went on to perform a high repetition high force reaching and lever-pulling task for 10 weeks (10-wk HRHF; 2 h/day, 3 days/wk). From this group, five were randomly selected to undergo forced treadmill running exercise (TM) during the last 6 weeks of task performance (10-wk HRHF+TM, 1 h/day, 5 days/wk). Results were compared to 10 control rats and 6 rats that underwent 6 weeks of treadmill running following training only (TR-then-TM). Voluntary task and reflexive sensorimotor behavioral outcomes were assessed. Serum was assayed for inflammatory cytokines and corticosterone, reach limb median nerves for CD68+ macrophages and extraneural thickening, and reach limb flexor digitorum muscles and tendons for pathological changes.

RESULTS

10-wk HRHF rats had higher serum levels of IL-1α, IL-1β and TNFα, than control rats. In the 10-wk HRHF+TM group, IL-1β and TNFα were lower, whereas IL-10 and corticosterone were higher, compared to 10-wk HRHF only rats. Unexpectedly, several voluntary task performance outcomes (grasp force, reach success, and participation) worsened in rats that underwent treadmill running, compared to untreated 10-wk HRHF rats. Examination of forelimb tissues revealed lower cellularity within the flexor digitorum epitendon but higher numbers of CD68+ macrophages within and extraneural fibrosis around median nerves in 10-wk HRHF+TM than 10-wk HRHF rats.

CONCLUSIONS

Treadmill running was associated with lower systemic inflammation and moderate tendinosis, yet higher median nerve inflammation/fibrosis and worse task performance and sensorimotor behaviors. Continued loading of the injured tissues in addition to stress-related factors associated with forced running/exercise likely contributed to our findings.

Manual therapy prevents onset of nociceptor activity, sensorimotor dysfunction, and neural fibrosis induced by a volitional repetitive task

Painful and disabling musculoskeletal disorders remain prevalent. In rats trained to perform repetitive tasks leading to signs and dysfunction similar to those in humans, we tested whether manual therapy would prevent the development of the pathologies and symptoms. We collected behavioral, electrophysiological, and histological data from control rats, rats that trained for 5 weeks before performing a high-repetition high-force (HRHF) task for 3 weeks untreated, and trained rats that performed the task for 3 weeks while being treated 3x/week using modeled manual therapy (MMT) to the forearm (HRHF + MMT). The MMT included bilateral mobilization, skin rolling, and long axis stretching of the entire upper limb. High-repetition high-force rats showed decreased performance of the operant HRHF task and increased discomfort-related behaviors, starting after training. HRHF + MMT rats showed improved task performance and decreased discomfort-related behaviors compared with untreated HRHF rats. Subsets of rats were assayed for presence or absence of ongoing activity in C neurons and slow Aδ neurons in their median nerves. Neurons from HRHF rats had a heightened proportion of ongoing activity and altered conduction velocities compared with control and MMT-treated rats. Median nerve branches in HRHF rats contained increased numbers of CD68 macrophages and degraded myelin basic protein, and showed increased extraneural collagen deposition, compared with the other groups. We conclude that the performance of the task for 3 weeks leads to increased ongoing activity in nociceptors, in parallel with behavioral and histological signs of neuritis and nerve injury, and that these pathophysiologies are largely prevented by MMT.

Cervical Lateral Glide Neural Mobilization Is Effective in Treating Cervicobrachial Pain: A Randomized Waiting List Controlled Clinical Trial

Background

Cervicobrachial pain (CP) is a high-incidence and prevalent condition. Cervical lateral glide (CLG) is a firstline treatment of CP. There is a current lack of enough high-quality randomized controlled double-blind clinical trials that measure the effectiveness of neural tissue mobilization techniques such as the CLG and its specific effect over CP.

Objectives

The aim of the present study was to assess the effect of CLG neural mobilization in treating subjects who suffer from CP, compared with the complete absence of treatment.

Study Design

This investigation was a single-center, blinded, parallel randomized controlled clinical trial (RCT).

Setting

One hundred forty-seven individuals were screened in a medical center from July to November 2015. Fifty-eight participants were diagnosed with CP.

Methods

Participants were recruited and randomly assigned into two groups of 29 subjects. The intervention group received CLG treatment, and the control group (CG) was assigned to a six-week waiting list to receive treatment. Randomization was carried out by concealed computer software randomized printed cards. The primary outcome was pain intensity, reported through the Numeric Rating Scale for Pain (NRSP). Secondary outcomes were physical function involving the affected upper limb using the Quick DASH scale and ipsilateral cervical rotation (ICR) using a CROM device. Assessments were made at baseline and one hour after treatment.

Results

The CLG group NRSP mean value was significantly (P < 0.0001) superior to those obtained by the CG. Subjects treated with CLG reported an average NRSP decrease of 2.16 points (35%). CROM device and Quick DASH outcome values also reported significant (P < 0.0001) improvements only in the CLG group. Cohen's d showed a very large effect of the CLG intervention at subject discharge.

Limitations

Due to the lack of dipper subgroup analysis and additional reproductions of the applied protocol, the authors considered the generalization of the study results to be impossible.

Conclusions

CLG is superior to the absence of treatment in reducing pain and increasing the affected upper limb function of subjects who suffer from CP. CLG may be considered an effective treatment in specific cases of CP.

Effectiveness of median nerve neural mobilization versus oral ibuprofen treatment in subjects who suffer from cervicobrachial pain: a randomized clinical trial

INTRODUCTION

Oral ibuprofen (OI) and median nerve neural mobilization (MNNM) are first line treatments for patients who suffer cervicobrachial pain (CP). OI may produce side effects which are not tolerated by all subjects who suffer CP, whereas MNNM has no known side effects. Therefore, the aim of this study was to assess the effectiveness of both treatments (OI vs. MNNM) in CP.

MATERIAL AND METHODS

This investigation was a blinded parallel randomized clinical trial (NCT02593721). Sixty-two participants diagnosed with CP were recruited and randomly assigned to 2 groups (n = 31), which received MNNM or 1200 mg/day OI treatment for 6 weeks. The numeric rating scale for pain intensity was the primary outcome. The cervical rotation range of motion (CROM) and the upper limb function were the secondary outcomes.

RESULTS

The results showed that OI treatment (η2 = 0.612-0.755) was clearly superior to MNNM (η2 = 0.816-0.821) in all assessments (p < 0.05) except for the CROM device results, which were equivalent to those of the MNNM group (p > 0.05). Three subjects were discharged because of OI side effects.

CONCLUSIONS

Oral ibuprofen may be superior to MNNM for pain reduction and upper limb function increase of subjects with CP. Nevertheless, both treatments were effective. Median nerve neural mobilization may be considered an effective non-pharmaceutical treatment option in subjects with CP. Regarding OI adverse effects, our findings challenge the role of pharmacologic versus manual therapy as possible treatments that may improve pain intensity and upper limb functionality in subjects with CP.

Is pharmacologic treatment better than neural mobilization for cervicobrachial pain? A randomized clinical trial

Purpose: This study aim was to compare the effectiveness of the median nerve neural mobilization (MNNM) and cervical lateral glide (CLG) intervention versus oral ibuprofen (OI) in subjects who suffer cervicobrachial pain (CP). Methods: This investigation was a, multicenter, blinded, randomized controlled clinical trial (NCT02595294; NCT02593721). A number of 105 individuals diagnosed with CP were enrolled in the study and treated in 2 different medical facilities from July to November 2015. Participants were recruited and randomly assigned into 3 groups of 35 subjects. Intervention groups received MNNM or CLG neurodynamic treatments, and the (active treatment) control group received an OI treatment for 6 weeks. Primary outcome was pain intensity reported through the Numeric Rating Scale for Pain (NRSP). Secondary outcomes were physical function involving the affected upper limb using the Quick DASH scale, and ipsilateral cervical rotation (ICR) using a cervical range of motion (CROM) device. Assessments were performed before and 1 hour after treatment for NRSP (baseline, 3 and 6 weeks) and CROM (baseline and 6 weeks), as well as only 1 assessment for Quick DASH (baseline and 6 weeks). Results: Repeated-measures ANOVA intergroup statistically significant differences were shown for CP intensity (F(2,72) = 22.343; P < .001; Eta2 = 0.383) and Quick DASH (F(2,72) = 15.338; P < .001; Eta2 = 0.299), although not for CROM (F(2,72) = 1.434; P = .245; Eta2 = 0.038). Indeed, Bonferroni´s correction showed statistically significant differences for CP intensity (P < .01; 95% CI = 0.22 - 3.26) and Quick DASH reduction (P < .01; 95% CI = 8.48 - 24.67) in favor of the OI treatment at all measurement moments after baseline. Conclusions: OI pharmacologic treatment may reduce pain intensity and disability with respect to neural mobilization (MNNM and CLG) in patients with CP during six weeks. Nevertheless, the non-existence of between-groups ROM differences and possible OI adverse effects should be considered.

Effects of Median Nerve Neural Mobilization in Treating Cervicobrachial Pain: A Randomized Waiting List-Controlled Clinical Trial

BACKGROUND

There is a current lack of sufficiently high-quality randomized controlled clinical trials that measure the effectiveness of neural tissue mobilization techniques such as median nerve neural mobilization (MNNM) and their specific effects on cervicobrachial pain (CP). The aim of this study was to compare the effectiveness of MNNM in subjects with CP vs. a waiting list control group (WLCG).

METHODS

A single-blinded, parallel, randomized controlled clinical trial was performed (NCT02596815). Subjects were recruited with a medical diagnosis of CP corroborated by magnetic resonance imaging. In total, 156 individuals were screened, 60 subjects were recruited, and 51 completed the trial. Pain intensity reported using the Numeric Rating Scale for Pain (NRSP; primary outcome), cervical range of motion (CROM), and functionality using the Quick Disabilities of the Arm, Shoulder and Hand (QuickDASH) scale were the outcome measurements. Assessments were conducted at baseline and 1 hour after treatment (intervention days 1, 15, and 30). Therefore, MNNM was implemented with 30 days of follow-up.

RESULTS

The NRSP values of the MNNM group were significantly (P < 0.0001; 95% confidence interval [CI]) superior to those obtained in the WLCG. Subjects treated with MNNM reported an NRSP decrease of 3.08 points at discharge. CROM and QuickDASH outcome values were significantly (P ˂ 0.0001; 95% CI) improved only in the MNNM group. Hedges' g showed a very large effect of the MNNM intervention.

CONCLUSION

MNNM may be superior to no treatment in reducing pain and increasing function in the affected upper limbs of subjects with CP.

Decreased grip strength, muscle pain, and atrophy occur in rats following long-term exposure to excessive repetitive motion

Work‐related musculoskeletal disorders (WMSD) are caused by the overuse of muscles in the workplace. Performing repetitive tasks is a primary risk factor for the development of WMSD. Many workers in highly repetitive jobs exhibit muscle pain and decline in handgrip strength, yet the mechanisms underlying these dysfunctions are poorly understood. In our study, rats performed voluntary repetitive reaching and grasping tasks (Task group), while Control group rats did not perform these activities. In the Task group, grip strength and forearm flexor withdrawal threshold declined significantly from week 2 to week 6, compared with these values at week 0 (P < 0.05). Relative muscle weight and muscle fiber cross‐sectional area of flexor digitorum superficialis (FDS) muscles decreased significantly in the Task group, compared with the Control group, at 6 weeks (P < 0.05 and P < 0.01, respectively). Nerve growth factor, glial cell line‐derived neurotrophic factor, and tumor necrosis factor α‐expression in FDS muscles were not significantly different in Control and Task groups at 3 and 6 weeks. At 6 weeks, the Task group had elevated MuRF1 protein levels (P = 0.065) and significant overexpression of the autophagy‐related (Atg) proteins, Beclin1 and Atg5–Atg12, compared with in the Control group (both P < 0.05). These data suggested that long‐term exposure to excessive repetitive motion causes loss of grip strength, muscle pain, and skeletal muscle atrophy. Furthermore, this exposure may enhance protein degradation through both the ubiquitin‐proteasome and autophagy‐lysosome systems, thereby decreasing skeletal muscle mass.

Increases in human motoneuron excitability after cervical spinal cord injury depend on the level of injury

After human spinal cord injury (SCI), motoneuron recruitment and firing rate during voluntary and involuntary contractions may be altered by changes in motoneuron excitability. Our aim was to compare F waves in single thenar motor units paralyzed by cervical SCI to those in uninjured controls because at the single-unit level F waves primarily reflect the intrinsic properties of the motoneuron and its initial segment. With intraneural motor axon stimulation, F waves were evident in all 4 participants with C₄-level SCI, absent in 8 with C₅ or C₆ injury, and present in 6 of 12 Uninjured participants (P < 0.001). The percentage of units that generated F waves differed across groups (C₄: 30%, C₅ or C₆: 0%, Uninjured: 16%; P < 0.001). Mean (±SD) proximal axon conduction velocity was slower after C₄ SCI [64 ± 4 m/s (n = 6 units), Uninjured: 73 ± 8 m/s (n = 7 units); P = 0.037]. Mean distal axon conduction velocity differed by group [C₄: 40 ± 8 m/s (n = 20 units), C₅ or C₆: 49 ± 9 m/s (n = 28), Uninjured: 60 ± 7 m/s (n = 45); P < 0.001]. Motor unit properties (EMG amplitude, twitch force) only differed after SCI (P ≤ 0.004), not by injury level. Motor units with F waves had distal conduction velocities, M-wave amplitudes, and twitch forces that spanned the respective group range, indicating that units with heterogeneous properties produced F waves. Recording unitary F waves has shown that thenar motoneurons closer to the SCI (C₅ or C₆) have reduced excitability whereas those further away (C₄) have increased excitability, which may exacerbate muscle spasms. This difference in motoneuron excitability may be related to the extent of membrane depolarization following SCI.

NEW & NOTEWORTHY

Unitary F waves were common in paralyzed thenar muscles of people who had a chronic spinal cord injury (SCI) at the C₄ level compared with uninjured people, but F waves did not occur in people that had SCI at the C₅ or C₆ level. These results highlight that intrinsic motoneuron excitability depends, in part, on how close the motoneurons are to the site of the spinal injury, which could alter the generation and strength of voluntary and involuntary muscle contractions.

Motoneuron Death after Human Spinal Cord Injury

The severe muscle weakness and atrophy measured after human spinal cord injury (SCI) may relate to chronic muscle denervation due to motoneuron death and/or altered muscle use. The aim of this study was to estimate motoneuron death after traumatic human SCI. The diameter and number of myelinated axons were measured in ventral roots post-mortem because ventral roots contain large diameter (> 7 μm) myelinated axons that typically arise from motoneurons and innervate skeletal muscle. In four cases (SCI levels C7, C8, T4, and L1) involving contusion (n = 3) or laceration (n = 1), there was a significant reduction in the number of large diameter myelinated axons at the lesion epicenter (mean ± standard error [SE]: 45 ± 11% Uninjured), one level above (51 ± 14%), and one (27 ± 12%), two (45 ± 40%), and three (54 ± 23%) levels below the epicenter. Reductions in motoneuron numbers varied by side and case. These deficits result from motoneuron death because the gray matter was destroyed at and near the lesion epicenter. Muscle denervation must ensue. In seven cases, ventral roots at or below the epicenter had large diameter myelinated axons with unusually thin myelin, a sign of incomplete remyelination. The mean ± SE g ratio (axon diameter/fiber diameter) was 0.60 ± 0.01 for axons of all diameters in five above-lesion ventral roots, but increased significantly for large diameter fibers (≥ 12 μm) in three roots at the lesion epicenter. Motoneuron death after human SCI will coarsen muscle force gradation and control, while extensive muscle denervation will stifle activity-based treatments.

Manual therapy as an effective treatment for fibrosis in a rat model of upper extremity overuse injury

Key clinical features of carpal tunnel syndrome and other types of cumulative trauma disorders of the hand and wrist include pain and functional disabilities. Mechanistic details remain under investigation but may involve tissue inflammation and/or fibrosis. We examined the effectiveness of modeled manual therapy (MMT) as a treatment for sensorimotor behavior declines and increased fibrogenic processes occurring in forearm tissues of rats performing a high repetition high force (HRHF) reaching and grasping task for 12 weeks. Young adult, female rats were examined: food restricted control rats (FRC, n=12); rats that were trained for 6 weeks before performing the HRHF task for 12 weeks with no treatment (HRHF-CON, n=11); and HRHF task rats received modeled manual therapy (HRHF-MMT, n=5) for 5 days/week for the duration of the 12-week of task. Rats receiving the MMT expressed fewer discomfort-related behaviors, and performed progressively better in the HRHF task. Grip strength, while decreased after training, improved following MMT. Fibrotic nerve and connective tissue changes (increased collagen and TGF-β1 deposition) present in 12-week HRHF-CON rats were significantly decreased in 12-week HRHF-MMT rats. These observations support the investigation of manual therapy as a preventative for repetitive motion disorders.

Increased CCN2, substance P and tissue fibrosis are associated with sensorimotor declines in a rat model of repetitive overuse injury

Key clinical features of cumulative trauma disorders include pain, muscle weakness, and tissue fibrosis, although the etiology is still under investigation. Here, we characterized the temporal pattern of altered sensorimotor behaviors and inflammatory and fibrogenic processes occurring in forearm muscles and serum of young adult, female rats performing an operant, high repetition high force (HRHF) reaching and grasping task for 6, 12, or 18 weeks. Palmar mechanical sensitivity, cold temperature avoidance and spontaneous behavioral changes increased, while grip strength declined, in 18-week HRHF rats, compared to controls. Flexor digitorum muscles had increased MCP-1 levels after training and increased TNFalpha in 6-week HRHF rats. Serum had increased IL-1beta, IL-10 and IP-10 after training. Yet both muscle and serum inflammation resolved by week 18. In contrast, IFNγ increased at week 18 in both muscle and serum. Given the anti-fibrotic role of IFNγ, and to identify a mechanism for the continued grip strength losses and behavioral sensitivities, we evaluated the fibrogenic proteins CCN2, collagen type I and TGFB1, as well as the nociceptive/fibrogenic peptide substance P. Each increased in and around flexor digitorum muscles and extracellular matrix in the mid-forearm, and in nerves of the forepaw at 18 weeks. CCN2 was also increased in serum at week 18. At a time when inflammation had subsided, increases in fibrogenic proteins correlated with sensorimotor declines. Thus, muscle and nerve fibrosis may be critical components of chronic work-related musculoskeletal disorders. CCN2 and substance P may serve as potential targets for therapeutic intervention, and CCN2 as a serum biomarker of fibrosis progression.

Role of inflammation in the aging bones

Chronic inflammation in aging is characterized by increased inflammatory cytokines, bone loss, decreased adaptation, and defective tissue repair in response to injury. Aging leads to inherent changes in mesenchymal stem cell (MSC) differentiation, resulting in impaired osteoblastogenesis. Also, the pro-inflammatory cytokines increase with aging, leading to enhanced myelopoiesis and osteoclastogenesis. Bone marrow macrophages (BMMs) play pivotal roles in osteoblast differentiation, the maintenance of hematopoietic stem cells (HSCs), and subsequent bone repair. However, during aging, little is known about the role of macrophages in the differentiation and function of MSC and HSC. Aged mammals have higher circulating pro-inflammatory cytokines than young adults, supporting the hypothesis of increased inflammation with aging. This review will aid in the understanding of the potential role(s) of pro-inflammatory (M1) and anti-inflammatory (M2) macrophages in differentiation and function of osteoblasts and osteoclasts in relation to aging.

Altered median nerve deformation and transverse displacement during wrist movement in patients with carpal tunnel syndrome

RATIONALE AND OBJECTIVES

Carpal tunnel syndrome (CTS) is the most common peripheral nerve entrapment syndrome. Strong pinch or grip with wrist flexion has been considered a risk factor for CTS. Studying median nerve displacement during wrist movements may provide useful information about median nerve kinematic changes in patients with CTS. The purpose of this study was to evaluate the deformability and mobility of the median nerve in patients with CTS compared to healthy subjects.

MATERIALS AND METHODS

Dynamic ultrasound images were obtained in 20 affected wrists of 13 patients with CTS. Results were compared to complementary data obtained from both wrists of 10 healthy subjects reported in a previous study. Shape and position of initial and final median nerve were measured and analyzed for six defined wrist movements. The deformation ratios for each movement were defined as the median nerve area, perimeter, and circularity of the final position normalized by respective values assessed in the initial position. The median nerve displacement vector and magnitude were also calculated.

RESULTS

The deformation ratio for circularity was significantly less in patients with CTS compared to healthy subjects during wrist flexion (P < .05). The mean vector of median nerve displacement during wrist flexion was significantly different between patients with CTS and healthy subjects (P < .05). The displacement magnitude of the median nerve was found to be less in patients with CTS compared to healthy subjects during most movements, with the exception of wrist extension with fingers extended.

CONCLUSIONS

Patients with CTS differ from normal subjects with regard to mobility and deformability of the median nerve.

Bone loss from high repetitive high force loading is prevented by ibuprofen treatment

We examined roles of loading and inflammation on forearm bones in a rat model of upper extremity overuse. Trabecular structure in distal radius and ulna was examined in three groups of young adult rats: 1) 5% food-restricted that underwent an initial training period of 10 min/day for 5 weeks to learn the repetitive task (TRHF); 2) rats that underwent the same training before performing a high repetition high force task, 2 hours/day for 12 weeks (HRHF); and 3) food-restricted only (FRC). Subsets were treated with oral ibuprofen (IBU). TRHF rats had increased trabecular bone volume and numbers, osteoblasts, and serum osteocalcin, indicative of bone adaptation. HRHF rats had constant muscle pulling forces, showed limited signs of bone adaptation, but many signs of bone resorption, including decreased trabecular bone volume and bone mineral density, increased osteoclasts and bone inflammatory cytokines, and reduced median nerve conduction velocity (15%). HRHF+IBU rats showed no trabecular resorptive changes, no increased osteoclasts or bone inflammatory cytokines, no nerve inflammation, preserved nerve conduction, and increased muscle voluntary pulling forces. Ibuprofen treatment preserved trabecular bone quality by reducing osteoclasts and bone inflammatory cytokines, and improving muscle pulling forces on bones as a result of reduced nerve inflammation.

Transverse ultrasound assessment of median nerve deformation and displacement in the human carpal tunnel during wrist movements

The symptoms of carpal tunnel syndrome, a compression neuropathy of the median nerve at the wrist, are aggravated by wrist motion, but the effect of these motions on median nerve motion are unknown. To better understand the biomechanics of the abnormal nerve, it is first necessary to understand normal nerve movement. The purpose of this study was to evaluate the deformation and displacement of the normal median nerve at the proximal carpal tunnel level on transverse ultrasound images during different wrist movements, to have a baseline for comparison with abnormal movements. Dynamic ultrasound images of both wrists of 10 asymptomatic volunteers were obtained during wrist maximal flexion, extension and ulnar deviation. To simplify the analysis, the initial and final shape and position of the median nerve were measured and analyzed. The circularity of the median nerve was significantly increased and the aspect ratio and perimeter were significantly decreased in the final image compared with the first image during wrist flexion with finger extension, wrist flexion with finger flexion and wrist ulnar deviation with finger extension (p < 0.01). There were significant differences in median nerve displacement vector between finger flexion, wrist flexion with finger extension and wrist ulnar deviation with finger extension (all p's < 0.001). The mean amplitudes of median nerve motion in wrist flexion with finger extension (2.36 ± 0.79 normalized units [NU]), wrist flexion with finger flexion (2.46 ± 0.84 NU) and wrist ulnar deviation with finger extension (2.86 ± 0.51 NU) were higher than those in finger flexion (0.82 ± 0.33 NU), wrist extension with finger extension (0.77 ± 0.46 NU) and wrist extension with finger flexion (0.81 ± 0.58 NU) (p < 0.0001). In the normal carpal tunnel, wrist flexion and ulnar deviation could induce significant transverse displacement and deformation of the median nerve.

Longitudinal design for sonographic measurement of median nerve swelling with controlled exposure to physical work using an animal model

In the study described here, we examined the feasibility of a longitudinal design to measure sonographically swelling of the median nerve caused by controlled exposure to a work task and to evaluate the relationship of changes in morphology to diagnostic standards. Fifteen macaques, Macaca fascicularis, pinched a lever in various wrist positions at a self-regulated pace (8 h/d, 5 d/wk, 18-20 wk). Nerve conduction velocity (NCV) and cross-sectional area (CSA) were measured every 2 wk from baseline through working and a 6-wk recovery. Trending across all subjects revealed that NCV slowed and CSA at the carpal tunnel increased in the working arm, whereas no changes were observed in CSA either at the forearm or for any measure in the non-working arm. There was a small negative correlation between NCV and CSA in the working arm. This study provides validation that swelling can be observed using a longitudinal design. Longitudinal human studies are needed to describe the trajectory of nerve swelling for early identification of median nerve pathology.

The interaction of force and repetition on musculoskeletal and neural tissue responses and sensorimotor behavior in a rat model of work-related musculoskeletal disorders

Background

We examined the relationship of musculoskeletal risk factors underlying force and repetition on tissue responses in an operant rat model of repetitive reaching and pulling, and if force x repetition interactions were present, indicative of a fatigue failure process. We examined exposure-dependent changes in biochemical, morphological and sensorimotor responses occurring with repeated performance of a handle-pulling task for 12 weeks at one of four repetition and force levels: 1) low repetition with low force, 2) high repetition with low force, 3) low repetition with high force, and 4) high repetition with high force (HRHF).

Methods

Rats underwent initial training for 4–6 weeks, and then performed one of the tasks for 12 weeks, 2 hours/day, 3 days/week. Reflexive grip strength and sensitivity to touch were assayed as functional outcomes. Flexor digitorum muscles and tendons, forelimb bones, and serum were assayed using ELISA for indicators of inflammation, tissue stress and repair, and bone turnover. Histomorphometry was used to assay macrophage infiltration of tissues, spinal cord substance P changes, and tissue adaptative or degradative changes. MicroCT was used to assay bones for changes in bone quality.

Results

Several force x repetition interactions were observed for: muscle IL-1alpha and bone IL-1beta; serum TNFalpha, IL-1alpha, and IL-1beta; muscle HSP72, a tissue stress and repair protein; histomorphological evidence of tendon and cartilage degradation; serum biomarkers of bone degradation (CTXI) and bone formation (osteocalcin); and morphological evidence of bone adaptation versus resorption. In most cases, performance of the HRHF task induced the greatest tissue degenerative changes, while performance of moderate level tasks induced bone adaptation and a suggestion of muscle adaptation. Both high force tasks induced median nerve macrophage infiltration, spinal cord sensitization (increased substance P), grip strength declines and forepaw mechanical allodynia by task week 12.

Conclusions

Although not consistent in all tissues, we found several significant interactions between the critical musculoskeletal risk factors of force and repetition, consistent with a fatigue failure process in musculoskeletal tissues. Prolonged performance of HRHF tasks exhibited significantly increased risk for musculoskeletal disorders, while performance of moderate level tasks exhibited adaptation to task demands.

Increased serum and musculotendinous fibrogenic proteins following persistent low-grade inflammation in a rat model of long-term upper extremity overuse

We examined the relationship between grip strength declines and muscle-tendon responses induced by long-term performance of a high-repetition, low-force (HRLF) reaching task in rats. We hypothesized that grip strength declines would correlate with inflammation, fibrosis and degradation in flexor digitorum muscles and tendons. Grip strength declined after training, and further in weeks 18 and 24, in reach limbs of HRLF rats. Flexor digitorum tissues of reach limbs showed low-grade increases in inflammatory cytokines: IL-1β after training and in week 18, IL-1α in week 18, TNF-α and IL-6 after training and in week 24, and IL-10 in week 24, with greater increases in tendons than muscles. Similar cytokine increases were detected in serum with HRLF: IL-1α and IL-10 in week 18, and TNF-α and IL-6 in week 24. Grip strength correlated inversely with IL-6 in muscles, tendons and serum, and TNF-α in muscles and serum. Four fibrogenic proteins, TGFB1, CTGF, PDGFab and PDGFbb, and hydroxyproline, a marker of collagen synthesis, increased in serum in HRLF weeks 18 or 24, concomitant with epitendon thickening, increased muscle and tendon TGFB1 and CTGF. A collagenolytic gelatinase, MMP2, increased by week 18 in serum, tendons and muscles of HRLF rats. Grip strength correlated inversely with TGFB1 in muscles, tendons and serum; with CTGF-immunoreactive fibroblasts in tendons; and with MMP2 in tendons and serum. Thus, motor declines correlated with low-grade systemic and musculotendinous inflammation throughout task performance, and increased fibrogenic and degradative proteins with prolonged task performance. Serum TNF-α, IL-6, TGFB1, CTGF and MMP2 may serve as serum biomarkers of work-related musculoskeletal disorders, although further studies in humans are needed.

Aging contributes to inflammation in upper extremity tendons and declines in forelimb agility in a rat model of upper extremity overuse

We sought to determine if tendon inflammatory and histopathological responses increase in aged rats compared to young rats performing a voluntary upper extremity repetitive task, and if these changes are associated with motor declines. Ninety-six female Sprague-Dawley rats were used in the rat model of upper extremity overuse: 67 aged and 29 young adult rats. After a training period of 4 weeks, task rats performed a voluntary high repetition low force (HRLF) handle-pulling task for 2 hrs/day, 3 days/wk for up to 12 weeks. Upper extremity motor function was assessed, as were inflammatory and histomorphological changes in flexor digitorum and supraspinatus tendons. The percentage of successful reaches improved in young adult HRLF rats, but not in aged HRLF rats. Forelimb agility decreased transiently in young adult HRLF rats, but persistently in aged HRLF rats. HRLF task performance for 12 weeks lead to increased IL-1beta and IL-6 in flexor digitorum tendons of aged HRLF rats, compared to aged normal control (NC) as well as young adult HRLF rats. In contrast, TNF-alpha increased more in flexor digitorum tendons of young adult 12-week HRLF rats than in aged HRLF rats. Vascularity and collagen fibril organization were not affected by task performance in flexor digitorum tendons of either age group, although cellularity increased in both. By week 12 of HRLF task performance, vascularity and cellularity increased in the supraspinatus tendons of only aged rats. The increased cellularity was due to increased macrophages and connective tissue growth factor (CTGF)-immunoreactive fibroblasts in the peritendon. In conclusion, aged rat tendons were overall more affected by the HRLF task than young adult tendons, particularly supraspinatus tendons. Greater inflammatory changes in aged HRLF rat tendons were observed, increases associated temporally with decreased forelimb agility and lack of improvement in task success.

Performance of repetitive tasks induces decreased grip strength and increased fibrogenic proteins in skeletal muscle: role of force and inflammation

BACKGROUND

This study elucidates exposure-response relationships between performance of repetitive tasks, grip strength declines, and fibrogenic-related protein changes in muscles, and their link to inflammation. Specifically, we examined forearm flexor digitorum muscles for changes in connective tissue growth factor (CTGF; a matrix protein associated with fibrosis), collagen type I (Col1; a matrix component), and transforming growth factor beta 1 (TGFB1; an upstream modulator of CTGF and collagen), in rats performing one of two repetitive tasks, with or without anti-inflammatory drugs.

METHODOLOGY/RESULTS

To examine the roles of force versus repetition, rats performed either a high repetition negligible force food retrieval task (HRNF), or a high repetition high force handle-pulling task (HRHF), for up to 9 weeks, with results compared to trained only (TR-NF or TR-HF) and normal control rats. Grip strength declined with both tasks, with the greatest declines in 9-week HRHF rats. Quantitative PCR (qPCR) analyses of HRNF muscles showed increased expression of Col1 in weeks 3-9, and CTGF in weeks 6 and 9. Immunohistochemistry confirmed PCR results, and also showed greater increases of CTGF and collagen matrix in 9-week HRHF rats than 9-week HRNF rats. ELISA, and immunohistochemistry revealed greater increases of TGFB1 in TR-HF and 6-week HRHF, compared to 6-week HRNF rats. To examine the role of inflammation, results from 6-week HRHF rats were compared to rats receiving ibuprofen or anti-TNF-α treatment in HRHF weeks 4-6. Both treatments attenuated HRHF-induced increases in CTGF and fibrosis by 6 weeks of task performance. Ibuprofen attenuated TGFB1 increases and grip strength declines, matching our prior results with anti-TNFα.

CONCLUSIONS/SIGNIFICANCE

Performance of highly repetitive tasks was associated with force-dependent declines in grip strength and increased fibrogenic-related proteins in flexor digitorum muscles. These changes were attenuated, at least short-term, by anti-inflammatory treatments.

Exposure to repetitive tasks induces motor changes related to skill acquisition and inflammation in rats

The authors elucidate exposure-response relationships between repetitive tasks, inflammation, and motor changes with work-related musculoskeletal disorders. Using a rat model of reaching and handle pulling, they examined effects of performing a high-repetition, low-force (HRLF); low-repetition, high-force (LRHF); or high-repetition, high-force (HRHF) task (2 hr/day, 3 days/week, 12 weeks) on reach rate and force, percentage of successful reaches, duration of participation, and grip strength. Reach rate and reach force improved with HRLF, and percentage success increased in all groups in Week 9, and in HRLF and HRHF in Week 12, indicative of skill acquisition. Duration and grip strength showed force-dependent declines with task performance. A subset of HRHF rats received ibuprofen in Weeks 5-12. Ibuprofen significantly improved reach rate, reach force, and duration in treated rats, indicative of an inflammatory influence on reach performance. Ibuprofen improved percentage of successful reaches in Week 9, although this increase was not sustained. However, declines in grip strength, a nocifensive behavior, were not prevented by ibuprofen. Examination of cervical spinal cords of untreated and ibuprofen treated HRHF rats showed increased IL-1beta, an inflammatory cytokine, in neurons. These findings suggest that only a preventive intervention could have addressed all motor declines.

Aging enhances serum cytokine response but not task-induced grip strength declines in a rat model of work-related musculoskeletal disorders

Background

We previously reported early tissue injury, increased serum and tissue inflammatory cytokines and decreased grip in young rats performing a moderate demand repetitive task. The tissue cytokine response was transient, the serum response and decreased grip were still evident by 8 weeks. Thus, here, we examined their levels at 12 weeks in young rats. Since aging is known to enhance serum cytokine levels, we also examined aged rats.

Methods

Aged and young rats, 14 mo and 2.5 mo of age at onset, respectfully, were trained 15 min/day for 4 weeks, and then performed a high repetition, low force (HRLF) reaching and grasping task for 2 hours/day, for 12 weeks. Serum was assayed for 6 cytokines: IL-1alpha, IL-6, IFN-gamma, TNF-alpha, MIP2, IL-10. Grip strength was assayed, since we have previously shown an inverse correlation between grip strength and serum inflammatory cytokines. Results were compared to naïve (grip), and normal, food-restricted and trained-only controls.

Results

Serum cytokines were higher overall in aged than young rats, with increases in IL-1alpha, IFN-gamma and IL-6 in aged Trained and 12-week HRLF rats, compared to young Trained and HRLF rats (p < 0.05 and p < 0.001, respectively, each). IL-6 was also increased in aged 12-week HRLF versus aged normal controls (p < 0.05). Serum IFN-gamma and MIP2 levels were also increased in young 6-week HRLF rats, but no cytokines were above baseline levels in young 12-week HRLF rats. Grip strength declined in both young and aged 12-week HRLF rats, compared to naïve and normal controls (p < 0.05 each), but these declines correlated only with IL-6 levels in aged rats (r = -0.39).

Conclusion

Aging enhanced a serum cytokine response in general, a response that was even greater with repetitive task performance. Grip strength was adversely affected by task performance in both age groups, but was apparently influenced by factors other than serum cytokine levels in young rats.

Joint inflammation and early degeneration induced by high-force reaching are attenuated by ibuprofen in an animal model of work-related musculoskeletal disorder

We used our voluntary rat model of reaching and grasping to study the effect of performing a high-repetition and high-force (HRHF) task for 12 weeks on wrist joints. We also studied the effectiveness of ibuprofen, administered in the last 8 weeks, in attenuating HRHF-induced changes in these joints. With HRHF task performance, ED1+ and COX2+ cells were present in subchondral radius, carpal bones and synovium; IL-1alpha and TNF-alpha increased in distal radius/ulna/carpal bones; chondrocytes stained with Terminal deoxynucleotidyl Transferase- (TDT-) mediated dUTP-biotin nick end-labeling (TUNEL) increased in wrist articular cartilages; superficial structural changes (e.g., pannus) and reduced proteoglycan staining were observed in wrist articular cartilages. These changes were not present in normal controls or ibuprofen treated rats, although IL-1alpha was increased in reach limbs of trained controls. HRHF-induced increases in serum C1,2C (a biomarker of collagen I and II degradation), and the ratio of collagen degradation to synthesis (C1,2C/CPII; the latter a biomarker of collage type II synthesis) were also attenuated by ibuprofen. Thus, ibuprofen treatment was effective in attenuating HRHF-induced inflammation and early articular cartilage degeneration.

Role of TNF alpha and PLF in bone remodeling in a rat model of repetitive reaching and grasping

We have previously developed a voluntary rat model of highly repetitive reaching that provides an opportunity to study effects of non-weight bearing muscular loads on bone and mechanisms of naturally occurring inflammation on upper limb tissues in vivo. In this study, we investigated the relationship between inflammatory cytokines and matricellular proteins (Periostin-like-factor, PLF, and connective tissue growth factor, CTGF) using our model. We also examined the relationship between inflammatory cytokines, PLF and bone formation processes. Rats underwent initial training for 5 weeks, and then performed a high repetition high force (HRHF) task (12 reaches/min, 60% maximum grip force, 2 h/day, 3 days/week) for 6 weeks. We then examined the effect of training or task performance with or without treatment with a rat specific TNFalpha antibody on inflammatory cytokines, osteocalcin (a bone formation marker), PLF, CTGF, and behavioral indicators of pain or discomfort. The HRHF task decreased grip strength and induced forepaw mechanical hypersensitivity in both trained control and 6-week HRHF animals. Two weeks of anti-TNFalpha treatment improved grip strength in both groups, but did not ameliorate forepaw hypersensitivity. Moreover, anti-TNFalpha treatment attenuated task-induced increases in inflammatory cytokines (TNFalpha, IL-1alpha, and MIP2 in serum; TNFalpha in forelimb bone and muscles) and serum osteocalcin in 6-week HRHF animals. PLF levels in forelimb bones and flexor digitorum muscles increased significantly in 6-week HRHF animals, increases attenuated by anti-TNFalpha treatment. CTGF levels were unaffected by task performance or anti-TNFalpha treatment in 6-week HRHF muscles. In primary osteoblast cultures, TNFalpha, MIP2 and MIP3a treatment increased PLF levels in a dose dependent manner. Also in primary osteoblast cultures, increased PLF promoted proliferation and differentiation, the latter assessed by measuring Runx2, alkaline phosphatase (ALP) and osteocalcin mRNA levels; ALP activity; as well as calcium deposition and mineralization. Increased PLF also promoted cell adhesion in MC3T3-E1 osteoblast-like cell cultures. Thus, tissue loading in vivo resulted in increased TNFalpha, which increased PLF, which then induced anabolic bone formation, the latter results confirmed in vitro.

Serum biomarkers as signals for risk and severity of work-related musculoskeletal injury

Work-related musculoskeletal disorders (MSDs) have accounted for a significant proportion of work injuries and workers' compensation claims in industrialized nations since the late 1980s. Despite epidemiological evidence for the role of repetition and force in the onset and progression of work-related MSDs, complete understanding of these important occupational health problems requires further elucidation of the underlying pathogenesis. Results from several clinical and experimental studies indicate that pathological and/or adaptive tissue changes occur as a consequence of performing repetitive and/or forceful tasks. Here, we review evidence of these tissue changes as revealed by the testing of serum biomarkers. Biomarkers of inflammation (inflammatory cytokines and C-reactive protein), cell stress or injury (malondialdehyde and creatine kinase), and collagen synthesis and degradation (collagen I carboxy-terminal propeptide and type-I collagen cross-linked C-telopeptide, respectively) and their association with MSDs will be reviewed.

Comparative study of carpal tunnel compliance in the human, dog, rabbit, and rat

The purpose of this study was to measure the compliance of the carpal tunnel in candidate animal models of carpal tunnel syndrome (CTS), by measuring the resistance when passing a tapered metal rod through the carpal tunnel. Forepaws from 10 dogs, 10 rabbits, and 10 rats with intact carpal tunnels, and 10 fresh frozen human wrist cadavers were used. The slopes of the linear part of the force-displacement curve (a measure of stiffness), normal force, and increasing area ratio (InAR) were significantly different among the four species (p<0.05). Post hoc analysis indicated that the mean slopes for the human carpal tunnel were the largest, indicating the least compliance, whereas those of the rat were the least (p<0.05). The features of the compliance for the dog carpal tunnel were closest to the human. The development of animal models of CTS should consider the compliance of the carpal tunnel, as it will be more difficult to increase pressure in a more compliant tunnel.

Peripheral and central changes combine to induce motor behavioral deficits in a moderate repetition task

Repetitive motion disorders, such as carpal tunnel syndrome and focal hand dystonia, can be associated with tasks that require prolonged, repetitive behaviors. Previous studies using animal models of repetitive motion have correlated cortical neuroplastic changes or peripheral tissue inflammation with fine motor performance. However, the possibility that both peripheral and central mechanisms coexist with altered motor performance has not been studied. In this study, we investigated the relationship between motor behavior changes associated with repetitive behaviors and both peripheral tissue inflammation and cortical neuroplasticity. A rat model of reaching and grasping involving moderate repetitive reaching with negligible force (MRNF) was used. Rats performed the MRNF task for 2 h/day, 3 days/week for 8 weeks. Reach performance was monitored by measuring reach rate/success, daily exposure, reach movement reversals/patterns, reach/grasp phase times, grip strength and grooming function. With cumulative task exposure, reach performance, grip strength and agility declined while an inefficient food retrieval pattern increased. In S1 of MRNF rats, a dramatic disorganization of the topographic forepaw representation was observed, including the emergence of large receptive fields located on both the wrist/forearm and forepaw with alterations of neuronal properties. In M1, there was a drastic enlargement of the overall forepaw map area, and of the cortex devoted to digit, arm-digits and elbow-wrist responses. In addition, unusually low current amplitude evoked digit movements. IL-1 beta and TNF-alpha increased in forearm flexor muscles and tendons of MRNF animals. The increases in IL-1 beta and TNF-alpha negatively correlated with grip strength and amount of current needed to evoke forelimb movements. This study provides strong evidence that both peripheral inflammation and cortical neuroplasticity jointly contribute to the development of chronic repetitive motion disorders.

Induction of periostin-like factor and periostin in forearm muscle, tendon, and nerve in an animal model of work-related musculoskeletal disorder

Work-related musculoskeletal disorders (WMSDs), also known as repetitive strain injuries of the upper extremity, frequently cause disability and impairment of the upper extremities. Histopathological changes including excess collagen deposition around myofibers, cell necrosis, inflammatory cell infiltration, and increased cytokine expression result from eccentric exercise, forced lengthening, exertion-induced injury, and repetitive strain-induced injury of muscles. Repetitive tasks have also been shown to result in tendon and neural injuries, with subsequent chronic inflammatory responses, followed by residual fibrosis. To identify mechanisms that regulate tissue repair in WMSDs, we investigated the induction of periostin-like factor (PLF) and periostin, proteins induced in other pathologies but not expressed in normal adult tissue. In this study, we examined the level of PLF and periostin in muscle, tendon, and nerve using immunohistochemistry and Western blot analysis. PLF increased with continued task performance, whereas periostin was constitutively expressed. PLF was located in satellite cells and/or myoblasts, which increased in number with continued task performance, supporting our hypothesis that PLF plays a role in muscle repair or regeneration. Periostin, on the other hand, was not present in satellite cells and/or myoblasts.

Periostin-like-factor and Periostin in an animal model of work-related musculoskeletal disorder

Work-related musculoskeletal disorders (WMSDs), also known as overuse injuries, account for a substantial proportion of work injuries and workers' compensation claims in the United States. However, the pathophysiological mechanisms underlying WMSDs are not well understood, especially the early events in their development. In this study we used an animal model of upper extremity WMSD, in which rats perform a voluntary repetitive reaching and pulling task for a food reward. This innovative model provides us an opportunity to investigate the role of molecules which may be used either as markers of early diagnosis of these disorders, and/or could be targeted for therapeutic purposes in the future. Periostin-like-factor (PLF), and Periostin were examined in this study. Both belong to a family of vitamin K-dependent gamma carboxylated proteins characterized by the presence of conserved Fasciclin domains and not detected in adult tissues except under conditions of chronic overload, injury, stress or pathology. The spatial and temporal pattern of PLF and Periostin localization was examined by immunohistochemistry and western blot analysis in the radius and ulna of animals performing a high repetition, high force task for up to 12 weeks and in controls. We found that PLF was present primarily in the cellular periosteum, articular cartilage, osteoblasts, osteocytes and osteoclasts at weeks 3 and 6 in all distal bone sites examined. This increase coincided with a transient increase in serum osteocalcin in week 6, indicative of adaptive bone formation at this time point. PLF immunoexpression decreased in the distal periosteum and metaphysis by week 12, coincided temporally with an increase in serum Trap5b, thinning of the growth plate and reduced cortical thickness. In contrast to PLF, once Periostin was induced by task performance, it continued to be present at a uniformly high level between 3 and 12 weeks in the trabeculae, fibrous and cellular periosteum, osteoblasts and osteocytes. In general, the data suggest that PLF is located in tissues during the early adaptive stage of remodeling but not during the pathological phase and therefore might be a marker of early adaptive remodeling.

Spinal substance P and neurokinin-1 increase with high repetition reaching

Musculoskeletal injury and inflammation is associated with performance of repetitive and forceful tasks. In this study, we examined the effects of performing a voluntary, highly repetitive, negligible force (HRNF) reaching task on spinal cord neurochemicals involved in nociception. To our knowledge, no other laboratories are examining spinal cord nociceptive neurochemicals in response to repetitive motion-induced injury and inflammation. The purpose of this study was to extend our earlier findings related to central neurotransmitters from a low demand task to a higher demand task. Specifically, this study determined immunoreactivity of a peptidergic pro-nociceptive transmitter (substance P) and one of its receptors, neurokinin-1 (NK-1) receptor, in spinal cord dorsal horns in rats performing a HRNF reaching task for 6-10 weeks. The relationship of these spinal cord changes with the number of TNFalpha immunopositive cells in flexor forelimb muscles and with previously observed forearm grip strength changes from these same rats were examined. Performance of the HRNF task resulted in significantly increased substance P and NK-1 receptor immunoreactivity in the superficial lamina of spinal cord dorsal horns at 6 and 10 weeks compared to trained controls (p<0.01). The increased substance P and NK-1 receptor immmunoreactivity were positively correlated with declines in forearm grip strength, an assay of movement-related hyperalgesia (r=0.70, p<0.01 and r=0.64, p<0.05, respectively). The increased substance P and NK-1 receptor immmunoreactivity were also positively correlated with increased TNF immunopositive cells in forelimb flexor muscles (r=0.85, p<0.001 and r=0.88, p<0.001, respectively). Thus, our highly repetitive task leads to increased spinal cord pro-nociceptive neurochemicals that are most likely directed by forelimb muscle inflammation and pain.

Longitudinal sliding of the median nerve in patients with non-specific arm pain

In patients with non-specific arm pain (NSAP; also known as repetitive strain injury), there are clinical signs of altered median nerve sliding. It is possible that a restriction along the nerve course will lead to abnormal increases in local strain during limb movements, possibly contributing to symptoms. The present study uses ultrasound imaging to examine median nerve sliding through the proximal and distal nerve segments in 18 NSAP patients. Longitudinal nerve sliding was measured during metacarpophalangeal, wrist and elbow movements. During elbow movements, the angle of elbow extension at which the nerve begins to move was determined, since this was expected to decrease with a restriction through the shoulder. The results from this study were compared with previously reported data. Nerve movements ranged from 1.26 to 4.73 mm in patients compared with 1.43-5.57 mm in controls. There was no significant difference in nerve sliding (p>0.05) or in the angle of elbow extension at which the nerve began to move (mean=53.4 degrees in patients, 52.0 degrees in controls; p>0.05). In summary, restriction of median nerve sliding is unlikely to play a major role in NSAP. Therefore, painful responses during limb movements which tension the nerve are unlikely to result from abnormal increases in nerve strain.

High force reaching task induces widespread inflammation, increased spinal cord neurochemicals and neuropathic pain

Repetitive strain injuries (RSI), which include several musculoskeletal disorders and nerve compression injuries, are associated with performance of repetitive and forceful tasks. In this study, we examined in young, adult Sprague-Dawley rats, the effects of performing a voluntary, moderate repetition, high force (MRHF; nine reaches/min; 60% maximum pulling force) task for 12 weeks on motor behavior and nerve function, inflammatory responses in forearm musculoskeletal and nerve tissues and serum, and neurochemical immunoexpression in cervical spinal cord dorsal horns. We observed no change in reach rate, but reduced voluntary participation and grip strength in week 12, and increased cutaneous sensitivity in weeks 6 and 12, the latter indicative of mechanical allodynia. Nerve conduction velocity (NCV) decreased 15% in the median nerve in week 12, indicative of low-grade nerve compression. ED-1 cells increased in distal radius and ulna in week 12, and in the median nerve and forearm muscles and tendons in weeks 6 and 12. Cytokines IL-1alpha, IL-1beta, TNF-alpha, and IL-10 increased in distal forearm bones in week 12, while IL-6 increased in tendon in week 12. However, serum analysis revealed only increased TNF-alpha in week 6 and macrophage inflammatory protein 3a (MIP3a) in weeks 6 and 12. Lastly, Substance P and neurokinin-1 were both increased in weeks 6 and 12 in the dorsal horns of cervical spinal cord segments. These results show that a high force, but moderate repetition task, induced declines in motor and nerve function as well as peripheral and systemic inflammatory responses (albeit the latter was mild). The peripheral inflammatory responses were associated with signs of central sensitization (mechanical allodynia and increased neurochemicals in spinal cord dorsal horns).

Serum and tissue cytokines and chemokines increase with repetitive upper extremity tasks

We investigated inflammation in rats performing a low repetition, negligible force (LRNF) or high repetition, negligible force (HRNF) task of reaching and retrieving food pellets at target rates of two or four reaches/min for 2 h/day, for 6-8 weeks. Serum was assayed for 11 cytokines and chemokines; forelimb tissues for four cytokines. Macrophages were counted in forelimb tissues of LRNF rats to add to results from our previous studies of HRNF rats. In HRNF rats, serum IL-1 alpha, IL-1 beta, TNFalpha, MIP2, MIP3a, and RANTES were elevated in weeks 6 and 8. In contrast, only MIP2 and MIP3a increased in serum of LRNF rats. In 8 week HRNF reach limb tissues, IL-1 alpha, IL-1beta, TNFalpha, and IL-10 increased in distal bones, IL-1 alpha and -beta in muscles, and TNFalpha in tendons. Only IL-10 increased in LRNF reach limb muscles in week 8. Serum IL-1 alpha and MIP2 correlated with macrophages in LRNF loose connective tissues, serum MIP3a and MIP2 correlated negatively with grip strength, while serum TNFalpha, MIP3a, and MIP2 correlated positively with total number of reaches. Thus, several tissue and circulating cytokines/chemokines increase in an exposure dependent manner following short-term performance of repetitive reaching tasks and correlate with macrophage infiltration and decreasing grip strength.

Peripheral neuritis and increased spinal cord neurochemicals are induced in a model of repetitive motion injury with low force and repetition exposure

Performance of high repetition tasks with or without force is associated with peripheral tissue inflammation, decreased nerve function and motor dysfunction. Here, we examined whether a low repetition task with negligible force (LRNF) produces fewer tissue and behavioral pathologies than previously observed with high repetition tasks using our rat model of repetitive motion injury (RMI). Thirty-seven rats were randomized into control or LRNF groups, the latter reaching and grasping a 45 mg food pellet at a rate of 3 reaches/min. This task was performed in 4, 0.5 5 h sessions with 1.5 5 h rest periods for 3 days/week for up to 12 weeks. Examination of distal median nerve, forelimb flexor tendons and bones for ED1-positive cells (macrophages and osteoclasts) revealed increases in nerve and bone in week 12. The nerve also contained increased TNF-alpha expressing cells in week 12. Examination of spinal cord dorsal horns revealed increased immunoexpression of Substance P in week 8 and neurokinin-1 in weeks 8 and 12 in the superficial lamina. Motor behavioral analyses showed no changes in reach rate across weeks, slightly reduced task duration (a measurement of voluntary task participation) in week 12, but significantly increased extra arm movement reversals during reaching in week 8. These extra movement reversals were corrections for missed food pellets during a reach. Thus, performance of even a low repetition, negligible force upper extremity task for 3 months can induce mild peripheral tissue inflammation, neurochemical increases in spinal cord dorsal horns, and declines in fine motor control.

Learning-based animal models: task-specific focal hand dystonia

Dystonia is a disabling, involuntary disorder of movement that leads to writhing, twisting end-range movements or abnormal postures. Inadequate inhibition could account for excessive excitation and near synchronous co-contractions of agonists and antagonists. Dystonia may be generalized or specific, affecting only one part of the body or involving only a well-learned task (e.g., writing, keyboarding, golfing, playing a musical instrument). Task-specific and other focal dystonias are considered idiopathic, with multiple factors such as genetics, anatomy, physiology, psychology, environment, and behavioral characteristics contributing to the development of symptoms. This article provides detailed descriptions of two behavioral animal models (a primate [owl monkey] model and a rodent [Sprague-Dawley rat] model) developed to study the effect of excessive repetition as a potential etiology of focal hand dystonia (FHd). The hypothesis is that repetitive, near simultaneous hand movements can degrade the topographic representations of the hand on the somatic sensory and motor cortices, creating the involuntary movements characteristic of dystonia. While animal studies permit the opportunity for greater control to determine efficacy, the findings must always be confirmed by clinical studies to evaluate sensitivity and specificity of diagnosis and effectiveness of treatment in the home, work, and personal environment. This article presents a review of the etiology and clinical implications for intervention strategies from animal and clinical studies that support learning-based mechanisms for FHd. Other animal models are also briefly reviewed.

Towards development of a nonhuman primate model of carpal tunnel syndrome: performance of a voluntary, repetitive pinching task induces median mononeuropathy in Macaca fascicularis

This study investigated changes in median sensory nerve conduction velocity (SNCV) over several weeks of exposure to a voluntary, moderately forceful, repetitive pinching task performed for food rewards by a small sample of young adult female monkeys (Macaca fascicularis). SNCV, derived from peak latency, decreased significantly in the working hands of three of the four subjects. The overall decline in NCV was 25%-31% from baseline. There was no decrease in SNCV in the contralateral, nonworking hands. Several weeks after being removed from the task, SNCV returned to within 87%-100% of baseline. MRI showed enlargement of the affected nerves near the proximal end of the carpal tunnel, at the time of maximal SNCV slowing. This new animal model demonstrates a temporally unambiguous relationship between exposure to a moderately forceful, repetitive manual task and development of median mononeuropathy at the wrist, and recovery of SNCV following termination of task exposure. This study contributes to the pattern of evidence of a causal relationship between manual work, median mononeuropathy, and carpal tunnel syndrome in humans. In the future, this new animal model could be used to characterize dose-response relationships between risk factors and carpal tunnel syndrome.

Management of radial tunnel syndrome: a therapist's clinical perspective

Current best evidence for the conservative management of radial tunnel syndrome (RTS) consists primarily of expert opinion and inferences taken from studies on other nerve compressions and related syndromes. There are limited data reported in the literature of this particular disorder. This article reviews literature on modalities, therapeutic exercise, ergonomic interventions, and cortical reorganization, and how they may be considered for intervention with RTS. The author's preferred method of treatment, as based on theoretical constructs, for RTS is presented. Definitive evidence in the literature to support the conservative interventions suggested is lacking. Suggestions for clinical management and study are included in this therapist's clinical perspective.

Functional reinnervation of the canine bladder after spinal root transection and immediate end-on-end repair

The goal of this study was to transect and immediately repair ventral roots, selected by their ability to stimulate bladder contraction, to assess the feasibility of bladder reinnervation in a canine model. Brain-derived neurotrophic factor (BDNF) was delivered via an osmotic pump (0.5 or 5 mg/mL) to a cuff surrounding the reanastomosis site to the two root bundles on one side. Electrodes were implanted bilaterally immediately proximal to the site of surgical reanastomosis. Results were compared to four root-intact, control animals that also received bilateral electrode implantation. At 6-12 months post-surgery, five of eight nerve transected and repaired animals showed increased pressure and bladder emptying during electrical stimulation of the repaired ventral roots contralateral to the BDNF delivery side. Nerve tracing studies one year postoperatively determined the repaired roots to be S1 and S2 and showed regrowth of axons from the spinal cord to nerve sites proximal to the repair site and to the bladder, and the presence of neurofilament-labeled axons growing across the ventral root repair site. In conclusion, transected ventral and dorsal roots in the sacral spine can be repaired and are capable of functionally reinnervating the urinary bladder. This feasibility study paves the way for future studies utilizing other more proximal motor nerves to bypass the transection site for bladder reinnervation.

Inflammation and the pathophysiology of work-related musculoskeletal disorders

Work-related musculoskeletal disorders (MSDs) have accounted for a significant proportion of work injuries and workers' compensation claims in industrialized nations since the late 1980s. Despite epidemiological evidence for the role of repetition and force in the onset and progression of work-related MSDs, complete understanding of these important occupational health problems requires further elucidation of pathophysiological mechanisms of the tissue response, particularly in the early stage of these disorders. Results from several clinical and experimental studies indicate that tissue microtraumas occur as a consequence of performing repetitive and/or forceful tasks, and that this mechanical tissue injury leads to local and perhaps even systemic inflammation, followed by fibrotic and structural tissue changes. Here we review work linking inflammation and the development of work-related MSDs. We also propose a conceptual framework suggesting the potential roles that inflammation may play in these disorders, and how inflammation may contribute to pain, motor dysfunction, and to puzzling psychological symptoms that are often characteristic of patients with work-related MSDs.

Twitch and Tetanic Properties of Human Thenar Motor Units Paralyzed by Chronic Spinal Cord Injury

Little is known about how human motor units respond to chronic paralysis. Our aim was to record surface electromyographic (EMG) signals, twitch forces, and tetanic forces from paralyzed motor units in the thenar muscles of individuals ( n = 12) with chronic (1.5–19 yr) cervical spinal cord injury (SCI). Each motor unit was activated by intraneural stimulation of its motor axon using single pulses and trains of pulses at frequencies between 5 and 100 Hz. Paralyzed motor units ( n = 48) had small EMGs and weak tetanic forces ( n = 32 units) but strong twitch forces, resulting in half-maximal force being achieved at a median of only 8 Hz. The distributions for cumulative twitch and tetanic forces also separated less for paralyzed units than for control units, indicating that increases in stimulation frequency made a smaller relative contribution to the total force output in paralyzed muscles. Paralysis also induced slowing of conduction velocities, twitch contraction times and EMG durations. However, the elevated ratios between the twitch and the tetanic forces, but not contractile speed, correlated significantly with the extent to which unit force summated in response to different frequencies of stimulation. Despite changes in the absolute values of many electrical and mechanical properties of paralyzed motor units, most of the distributions shifted uniformly relative to those of thenar units obtained from control subjects. Thus human thenar muscles paralyzed by SCI retain a population of motor units with heterogeneous contractile properties because chronic paralysis influenced all of the motor units similarly.

Structure and biomechanics of peripheral nerves: nerve responses to physical stresses and implications for physical therapist practice

The structural organization of peripheral nerves enables them to function while tolerating and adapting to stresses placed upon them by postures and movements of the trunk, head, and limbs. They are exposed to combinations of tensile, shear, and compressive stresses that result in nerve excursion, strain, and transverse contraction. The purpose of this appraisal is to review the structural and biomechanical modifications seen in peripheral nerves exposed to various levels of physical stress. We have followed the primary tenet of the Physical Stress Theory presented by Mueller and Maluf (2002), specifically, that the level of physical stress placed upon biological tissue determines the adaptive response of the tissue. A thorough understanding of the biomechanical properties of normal and injured nerves and the stresses placed upon them in daily activities will help guide physical therapists in making diagnoses and decisions regarding interventions.