Spinal Manipulative Therapy Has an Immediate Effect on Thermal Pain Sensitivity in People With Low Back Pain: A Randomized Controlled Trial

Introduction

Injury will increase the neuronal excitability within the spinalcord, leading to the activation of pain fibers with less provocationand a heightened pain response.¹ This occurrence, known as centralsensitization, is characterized by allodynia (pain perceptionto a previously nonpainful stimulus) and hyperalgesia (increasedmagnitude of pain intensity in response to a previously painfulstimulus) and is implicated in the progression of acute painto chronic pain and in the maintenance of chronic pain.^1–3 Subsequently, acute pain resulting from peripheral input mayprovoke neuroplastic changes within the nervous system and asubsequent shift toward a centrally maintained mechanism ofpain.^1,2 Evidence for a centrally maintained mechanism of painis observed in a number of musculoskeletal conditions such asfibromyalgia,^4,5 temporomandibular joint disorder,^6,7 and whiplash-associateddisorder.^8,9 For example, compared with people who are healthy,individuals with whiplash-associated disorder and temporomandibularjoint disorder may have lower pain thresholds at sites distalfrom the region of injury.^7,9 The corresponding general hypersensitivityto pain is indicative of a central pain mechanism and suggestsneuroplastic changes in pain perception.

Mounting evidence also suggests chronic low back pain (LBP)is characterized by central sensitization.^10–12 For example,individuals experiencing chronic LBP may report greater painintensity in response to a standard pressure pain stimulus appliedto the thumbnail compared with individuals who are pain-free.¹² Consequently, the pain associated with chronic LBP is potentiallymaintained by centrally mediated mechanisms, and interventionseffective in the management of LBP either may prevent the progressionof acute pain from a peripheral to a centrally mediated mechanismor directly affect a central mechanism of pain. Consequently,interventions that favorably alter central sensitization maybe desirable in the treatment of individuals experiencing LBP.

Current evidence suggests spinal manipulative therapy (SMT)is effective in the treatment of people with LBP.^13–17Despite SMT's clinical effectiveness, its corresponding mechanismsare undetermined. Boal and Gillette¹⁸ suggested that SMT mayprovide a novel counter-irritant, resulting in inhibition ofneuroplastic changes associated with central sensitization atthe dorsal horn of the spinal cord. Prior studies have shownimmediate hypoalgesia (decreased magnitude of pain intensityin response to a standard stimulus) associated with SMT^19–23 and support such a mechanism. For example, Fernández-Carneroet al¹⁹ observed increased pain pressure threshold and pain-freegrip in response to SMT applied to the cervical spine.

Temporal summation is a specific behavioral measure of dorsalhorn cell central sensitization mediated by the C fiber afferentsin which a painful stimulus of unchanging magnitude providedat an interpulse interval frequency of less than 3 seconds isperceived as increasingly painful.^4,24 We have previously observedinhibition of temporal summation following SMT in people whowere pain-free, which was not observed following other interventionsfor LBP.²⁵ Conversely, hypoalgesia to A ${delta}$ fiber–mediatedpain perception was not unique to SMT.²⁵

Collectively, these studies support a mechanism of SMT relatedto the alteration of neuroplastic changes associated with painthat may be specific to inhibition of temporal summation. Althoughthese effects have been observed following SMT in people whowere healthy, they have not been replicated in a sample of peopleexperiencing LBP.

The purpose of this study was threefold and parallel to a previousstudy of individuals who were healthy.²⁵ First, we comparedimmediate changes in A ${delta}$ and C fiber (temporal summation)–mediatedpain perception across 3 interventions (SMT, low back extensionexercises, and use of a stationary bicycle) for individualsexperiencing LBP. Similar to the prior study,²⁵ we hypothesizedhypoalgesia to A ${delta}$ fiber–mediated pain over time regardlessof group assignment, with temporal summation inhibition greaterin participants receiving SMT. Second, we wanted to determinewhether hypoalgesia following SMT was a local effect (occurringin the lumbar innervated region) or a general effect (also occurringin the cervical innervated region). We hypothesized that, similarto our prior study,²⁵ hypoalgesia to thermal stimuli would belocalized to the lumbar innervated region. Third, we investigatedthe association between psychological factors related to painand hypoalgesia to thermal stimuli. Psychological factors havean association with clinical LBP^26–29 and with thermalpain perception in individuals with LBP.³⁰ We hypothesized asimilar relationship would be evident in changes in thermalpain perception following SMT in participants experiencing LBP.

Method

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Method

Participants

A sample of convenience was recruited from the University ofFlorida Health Science Center community and affiliated outpatientclinics by flyer and word of mouth. Potential participants wereintroduced to the study method and screened for eligibilityby a study representative. Individuals wanting to participatethen signed an informed consent form. Inclusion criteria werebeing 18 to 60 years of age and currently experiencing LBP.Individuals with concomitant lower-extremity complaints wereeligible for study participation. Exclusion criteria were beingnon–English speaking, systemic medical conditions (eg,diabetes, hypertension), current use of psychiatric medications,pregnancy, signs and symptoms indicative of nerve root compression(reflex change, myotomal weakness, or sensation change), anda history of surgery to the low back.

Procedure

Demographic information, psychological questionnaires, and measurementsof baseline thermal pain sensitivity were collected prior torandom assignment of participants to treatment groups. The interventionswere each applied for 5 minutes to standardize measurement timeof experimental pain testing from baseline to immediately afterintervention. The examiner was not blinded to group assignment.

Measures

Numeric rating scales.
Numeric rating scales (NRSs) were used to measure pain perception.Participants were asked to quantify the pain experienced duringexperimental pain testing using a numeric rating scale withanchors of 0 ("no pain at all") and 100 ("worst pain imaginable").The NRS is frequently used as a measure of both clinical andexperimental pain and has demonstrated sound psychometric propertiesin previous studies.^31–34

Psychological questionnaires.
Psychological measures known to influence experimental pain^35–38 and LBP^26–29 were chosen and are described below.

The Fear of Pain Questionnaire–III (FPQ-III)³⁹ is 30-itemquestionnaire, with individual items scored from 1 to 5 to measurefear of normally painful situations. Higher scores indicategreater pain-related fear. The FPQ has demonstrated sound psychometricproperties in both experimental and clinical pain studies.^37,40

The Tampa Scale of Kinesiophobia (TSK) is an 11-item questionnaire,with individual items scored from 1 to 4. The questionnairewas developed to quantify the fear of movement and of injuryor reinjury for individuals currently experiencing pain. HigherTSK scores indicate greater fear of movement and of injury orreinjury due to pain. The TSK has demonstrated acceptable psychometricproperties.⁴¹

The Coping Strategies Questionnaire (CSQ-R), commonly used inthe assessment of pain, uses a 27-item, 7-point rating scaleto measure the frequency of use for common pain coping strategies.⁴² Consistent with the previous study involving participantswho were healthy,²⁵ we included only the catastrophizing subscaleusing the currently recommended scoring system (CSQ-R).⁴³ Thevalidity of the catastrophizing subscale of the CSQ-R has beensupported in prior studies.^42–45

The State-Trait Anxiety Inventory (STAI) is commonly used toassess anxiety. It uses a 40-item, 4-point rating scale to assessdispositional (trait) and situational (state) anxiety symptoms.⁴⁶ We reported the state portion of the STAI, as this constructbetter matched the purposes of this study.

The Anxiety Sensitivity Index (ASI) uses a 16-item, 4-pointrating scale to assess anxiety sensitivity or the perceptionof harm from experiencing symptoms of anxiety. The ASI is commonlyused in pain studies and has demonstrated sound psychometricproperties.^47,48

Assessment of thermal pain sensitivity.
The same quantitative sensory testing (QST) protocol from ourprevious study²⁵ also was used in this study. The QST was performedusing the Medoc Neurosensory Analyzer (TSA 2001^*) with handheldpeltier element-based stimulator. Participants first underwenta practice session in order to familiarize themselves with thepain testing protocol.

Briefly, the practice session included a continuous heat pulsedelivered to the volar part of the dominant forearm startingat 35°C and increased at a rate of 0.5°C/s. Participantswere instructed to indicate when the stimulus first changedfrom warmth to pain and the heat pulse was terminated at thispoint. This procedure was performed twice, with the mean ofthe 2 temperatures at which the participant reported pain servingas a measure of pain threshold. Participants then underwentseparate protocols to measure A ${delta}$ fiber–mediated pain sensitivityand temporal summation^4,24 in both the upper and lower extremities.These sites were chosen to observe the treatment response ina dermatome specific to the application site of the SMT (lowerextremity) and a dermatome separate from the application siteof the SMT (upper extremity). Participants were blinded to thetemperature of the thermal stimuli, as well as to whether theA ${delta}$ fiber–mediated pain sensitivity or temporal summationprotocol was being applied.

A ${delta}$ fiber–mediated pain sensitivity was assessed on thevolar part of the nondominant forearm and the nondominant calfof each participant through the application of heat stimuliof 3 seconds’ duration. The thermode was applied witha baseline temperature of 35°C, which rose rapidly (10°C/s)to a peak of 45°, 47°, 49°, or 50°C. The sequenceof testing the extremity (ie, calf and forearm) and the sequenceof application of the finishing temperatures were determinedrandomly to prevent an order effect. Participants were askedto rate their "first" pain intensity using a 0 to 100 NRS. Theseratings are believed to be mediated primarily by the A ${delta}$ fibers.^4,24 The protocol was performed 2 times at each temperatureat each extremity, with the average rating of each temperatureanalyzed. The thermode was moved slightly, and the researcherwaited 60 seconds between trials in order to prevent habituation.

Temporal summation was assessed on the plantar surface of thenondominant foot and the palmar surface of the nondominant handusing a train of 10 consecutive heat pulses of less than 1 secondduration at an inter-stimulus frequency of 0.33 Hz. The baselinetemperature of each pulse was 35°C, and temperature peakedat 51°C. Participants were asked to rate their delayed (second)pain for each of the 10 pulses using an NRS. The sequence oftesting was counterbalanced to prevent an order effect.

Interventions

Participants were instructed, as part of the informed consentprocess, that they would be randomly assigned to receive 1 of3 interventions commonly used in the management of LBP.⁴⁹ Randomizationwas computer generated, with group assignments maintained insealed, opaque, sequentially numbered envelopes. The envelopeswere opened in sequential order based on entry in the studyand after all baseline measures were completed for the participant.We elected to not incorporate a true control group in this studybecause we wanted all participants to have some form of interventionfor their LBP. Furthermore, changes in temporal summation didnot seem biologically plausible in a true control group, butwas biologically plausible from performing other activity. Allinterventions were performed under the supervision of researchstaff to ensure adherence to the described parameters.

Stationary bicycle.
Hypoalgesia has been reported in response to general exercise.^50,51 Participants rode a stationary bicycle and served as thenonspecific activity comparison group. The treatment dosagewas 5 minutes at 60 to 70 rpm and 1 KPa.

Lumbar extension exercise.
Participants performed a prone low back extension exercise andserved as a specific activity comparison group. The exercisehas been described previously in the literature for treatmentof people with LBP,^52,53 and several studies have demonstratedfavorable outcomes in participants with LBP after performingthis exercise.^54–58 Although not specific to this exercise,hypoalgesia has been reported in response to specific exercisein the cervical spine.⁵⁹ The treatment dosage was 3 sets of15 repetitions within a 5-minute period.

Spinal manipulative therapy.
This technique has been well described in the literature^15,17and was used in our prior studies of the immediate effects ofSMT.^25,60 Spinal manipulative therapy has been shown to be effectivein the management of LBP in participants meeting a clinicalprediction rule.^15,17 The treatment dosage was performance ofthe SMT 2 times on each side of the pelvis, for a total of 4manipulations in the 5-minute period, regardless of whethercavitation was experienced. Immediately following the assignedintervention, the previously described QST protocol was repeated.

Sample Size Estimates

This study, to our knowledge, was the first to use thermal painsensitivity as an outcome measure for SMT for participants withLBP. Therefore, limited data were available for a priori samplesize calculation. We set a minimum recruitment threshold of30 participants based on observed effect sizes from the previousstudy of participants who were healthy.²⁵

Data Analysis

All statistical analysis was performed using SPSS for Windowsversion 16.0. Significance was set at P $≤$ .05 for all analysesbecause we were attempting to confirm an observation made inprior studies.^25,60

Descriptive statistics were generated for continuous and categoricalmeasures. Univariate analysis of variance (ANOVA) was used toassess post-randomization differences in continuous variablesof demographic, psychological, and baseline thermal testingmeasures. Chi-square analysis was used to assess for post-randomizationdifferences in categorical demographic variables.

Our primary outcome of interest was change in thermal pain sensitivityover time (prior to and immediately following the assigned intervention).We used separate repeated-measures ANOVAs with group assignmentas the between-subject factor and preintervention and postinterventionmeasures of A ${delta}$ fiber–mediated pain sensitivity and temporalsummation as the within-subject factor to assess for group differencesin pain sensitivity. We included the ratings from only the 47°Cand 49°C temperatures from the A ${delta}$ fiber–mediated painto match the parameters of our previous study. Furthermore,45°C is not a suprathreshold stimulus for all participants,and 50°C tends to be at tolerance, causing concerns forfloor and ceiling effects, respectively. We performed this analysisin both the upper and lower extremities in order to observefor local and general effects of SMT. We used pair-wise comparisons,as indicated by the repeated-measures ANOVA results, to explorespecific group changes.

Next, we wanted to observe for significant associations betweenpsychological factors and changes in pain perception. Pearsoncorrelation coefficients were calculated to observe for significantassociations among psychological factors, measures of clinicalpain, and changes in temporal summation.

Role of the Funding Source

The project was supported by grant AT002796 from the NationalInstitutes of Health, National Center for Complementary andAlternative Medicine, awarded to Dr Bishop, Dr Robinson, andDr George (principal investigator). Dr Bialosky also receivedsupport from grant AT002796 and from the National Institutesof Health T-32 Neural Plasticity Research Training Fellowship(T32HD043730). This work also was supported with resources fromthe Brain Rehabilitation Research Center, a VA RehabilitationResearch and Development Center of Excellence at the MalcomRandall VA Medical Center in Gainesville, Florida.

Results

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Results

Thirty-six individuals met the criteria for the study and agreedto participate, and all individuals completed the study (Fig. 1). Number of excluded individuals and reasons for study exclusionwere not tracked as part of this study. Group comparisons ofbaseline questionnaire and demographic information are presentedin Table 1. Significant group differences were observed forsex and fear in baseline measures. Further exploration for covariateconsideration indicated fear and sex were not significantlycorrelated with change in A ${delta}$ fiber–mediated pain sensitivityor temporal summation in either the upper or lower extremity(P>.05). Subsequently, we elected to exclude fear and sexas covariates in the subsequent analyses, as neither variablemet the assumptions for covariance analysis.

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Figure 1. Summary of recruitment, enrollment, randomization, allocation, follow-up, and analysis for the study.

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Table 1. Baseline Measures of Demographic Variables and Clinical Pain, Pain Sensitivity, and Psychological Variables^{^a}

Pain Response in Lumbar Innervated Region (Local Response)

A ${delta}$ fiber–mediated pain sensitivity.
The intervention groups did not differ in A ${delta}$ fiber–mediatedpain sensitivity in the lower extremity to heat pulses of 47°C(P=.73) and 49°C (P=.96). Additionally, a main effect fortime was not observed at 47°C (P=.31) or 49°C (P=.94),suggesting no change in A ${delta}$ fiber–mediated pain sensitivityoccurred over time.

Temporal summation.
A significant group (randomization) x time (preinterventionto postintervention) interaction was observed for pain sensitivityto the temporal summation protocol in the lower extremity (F_2,33=3.41,P=.05, partial ${eta}$ ²=0.17), suggesting changes in temporal summationdiffered by group assignment (Tab. 2, Fig. 2). Pair-wise comparisonsindicated a significant hypoalgesic effect of temporal summationin the lower extremity of participants who received the SMT(mean decrease in pain perception=–8.5, SD=11.8; P=.03,Cohen d=0.37). Inhibition of temporal summation was not observedin those riding a stationary bicycle (mean increase in painperception=3.7, SD=9.2; P=.19, Cohen d=0.16) or performing lumbarextension exercises (mean decrease in pain perception=–2.5,SD=13.1; P=.52, Cohen d=0.08).

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Table 2. Summary of Comparisons of Within-Group and Between-Group Changes in Temporal Summation^{^a}

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Figure 2. Change in temporal summation in the lumbar innervated region following randomly assigned intervention. A significant group (intervention) x time (preintervention to postintervention) interaction was present for hypoalgesia to temporal summation in the lumbar innervated region (F_2,33=3.41, P=.05, partial ${eta}$ ²=0.17). Pair-wise comparison indicated significant hypoalgesia in the participants who received spinal manipulative therapy (SMT), which was not observed in the participants who rode a stationary bicycle or performed lumbar extension exercises. Positive numbers along the Y axis indicate hypoalgesia. Error bars represent one standard error of the mean. Asterisk indicates significant at P $≤$ .05. NRS=numeric rating scale, with anchors of 0 ("no pain at all") and 100 ("worst pain imaginable")

Pain Response in Cervical Innervated Region (General Response)

A ${delta}$ fiber–mediated pain sensitivity.
The intervention groups did not differ in A ${delta}$ fiber–mediatedpain sensitivity in the upper extremity to heat pulses of 47°C(P=.37) and 49°C (P=.53). Additionally, a main treatmenteffect for time was not observed at 47°C (P=.26) or 49°C(P=.49), suggesting no change in A ${delta}$ fiber–mediated painsensitivity occurred over time.

Temporal summation.
A significant group (randomization) x time (preinterventionto postintervention) interaction (P=.40) was not observed inthe upper extremity, indicating the lack of a group-dependentchange in temporal summation. Instead, a main treatment effectfor time (F_1,31=6.78, P=.01, partial ${eta}$ ²=0.18) was observed fortemporal summation in the upper extremity (mean decrease inpain perception=–6.1, SD=13.5; Cohen d=0.22), suggestingall participants had a decrease in temporal summation.

Association Between Psychological Factors and Changes in Thermal Pain Sensitivity

Both pain catastrophizing (r=–.67, P=.02) and state anxiety(r=–.62, P=.04) were significantly associated with changesin A ${delta}$ fiber–mediated pain sensitivity in the lower extremityin participants who received SMT (Tab. 3). Psychological variableswere not correlated with the change in temporal summation inthe lower extremity observed in participants who received theSMT (P>.05). The largest association was a small to mediumassociation with pain catastrophizing (r=.32).

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Table 3. Associations (Pearson r) Between Change in Lumbar Innervated Thermal Pain Sensitivity and Baseline Measures of Psychological Variables, Low Back Pain Duration, and Thermal Pain Sensitivity in Participants Who Received Spinal Manipulative Therapy^{^a}

Discussion

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Discussion

Spinal manipulative therapy is hypothesized to inhibit painat the dorsal horn of the spinal cord through the alterationsof neuroplastic changes consistent with central sensitization.¹⁸ We have previously observed inhibition of temporal summationfollowing SMT in participants who were healthy.^25,60 We investigatedthe same phenomenon in the current study in participants experiencingLBP to determine the relevance of this observation in clinicalpopulations. Similar to our prior study in participants whowere healthy,²⁵ we observed inhibition of temporal summationin participants with LBP associated with SMT that was greaterthan the changes observed in response to riding a stationarybicycle or performing lumbar extension exercises. Inhibitionof temporal summation appeared to be a local effect, as it wasobserved primarily in lumbar innervated areas (lower extremity)and was not strongly correlated with psychological variables.Furthermore, this effect did not appear to be a general bluntedresponse to the QST protocol because it was not observed inthe A ${delta}$ fiber–mediated pain perception.

This is the first study, to our knowledge, to observe SMT-associatedalterations in temporal summation in a clinical sample. Recentrehabilitation interventions for individuals experiencing neurologicalimpairments, such as those observed following a stroke or spinalcord injury, have attempted to influence neuroplasticity ofthe central nervous system to regain motor function.^61–64 For example, rather than prioritizing dysfunctions such asspecific strength (force-generating capacity) and range-of-motiondeficits, some rehabilitation protocols now attempt to promoteneuroplastic changes in motor control through repetitive orforced use of an involved extremity.^62,64,65 Similarly, theobserved inhibition of temporal summation suggests SMT may workthrough a neurophysiological mechanism specific to the alterationof neuroplastic changes associated with pain. Clinically, SMTfrequently is applied in response to a biomechanical dysfunctionsuch as decreased range of motion or a hypomobile joint. Forexample, an evaluative process is used to localize a dysfunctionalvertebral segment followed by the application of a specificSMT technique to correct the noted problem. Despite this focus,the evaluative process for SMT generally is unreliable,^66,67and prior studies have documented a poor relationship betweenphysical factors such as strength and range of motion and LBP-relatedoutcomes.^68–70 Subsequently, clinical application of SMTmay be better guided by the goal of decreasing pain than bythe correction of a biomechanical lesion. Our findings of temporalsummation inhibition specific to SMT (in comparison with ridinga stationary bicycle and performing press-up exercises) suggestSMT may provide a novel stimulus effective in altering the neuroplasticchanges associated with central sensitization and support currenthypotheses about the counter-irritant properties of SMT.¹⁸ Consequently,our findings provide preliminary support for the clinical useof SMT as a means to inhibit neuroplastic changes (eg, centralsensitization) associated with LBP. The potential specificityof SMT's effect is corroborated by a lack of inhibition forA ${delta}$ fiber–mediated pain perception for participants withLBP.

Our findings of a local effect of SMT further suggest a focusedneurophysiological response. Similar to our prior study,²⁵ weobserved a localized hypoalgesic effect for SMT in participantsexperiencing LBP in which inhibition of temporal summation occurredin the dermatomes related to the area of SMT (leg) and not toan unrelated dermatome (upper extremity). Similarly, Dishmanet al⁷¹ observed changes in lumbar motoneuron pool excitabilityfollowing SMT to the low back but not the cervical spine. Collectively,these studies suggest a local effect of SMT specific to theregion of application. The current findings in a clinical sampleand prior observations in participants who were healthy²⁵ suggestthe neurophysiological responses associated with SMT to thelow back are specific to the lumbar innervated regions.

Our findings of hypoalgesia to C fiber–mediated pain throughthe assessment of temporal summation suggest a spinal cord–mediatedeffect of SMT. Psychological factors are known to influenceboth outcomes associated with LBP^26–29 and response toexperimental pain.^30,37,38 Subsequently, we wanted to observethe association of these factors to our outcome measure. Significantcorrelations between psychological factors and inhibition oftemporal summation could suggest a descending, supraspinal mechanismof SMT related to fear, catastrophizing, or negative cognitions.Psychological associations with A ${delta}$ fiber–mediated painperception were expected and parallel a previous study of thermalpain and LBP.³⁰ However, changes in temporal summation did notsignificantly correlate to any of the psychological measures,and all associations were relatively small, the largest beingpain catastrophizing (r=.32). We have not observed a significantcorrelation between psychological factors and SMT-related changesin temporal summation in participants who were healthy²⁵ andnow participants experiencing LBP. Collectively, these findingssuggest the immediate inhibition of temporal summation relatedto SMT is independent of descending inhibition related to psychologicalfactors or only minimally influenced by these factors.

Limitations

The current study represented our first investigation into theeffects of SMT on temporal summation in a clinical sample andhas several limitations. First, we made no attempt to blindthe examiner to the intervention received by the individualparticipant. As a result, we cannot be certain that examinerbias did not play a role in our findings.

As this study was exploratory, we incorporated a sample of convenienceand obtained a sample of participants with chronic LBP withlower pain intensity ratings than those typically enrolled inclinical trials. As a result, our findings may not be applicableto individuals with acute LBP or to those with a higher intensityof LBP.

We used temporal summation as an indirect measure of centralsensitization. Animal studies have directly observed activityat the dorsal horn of the spinal cord with similar methods toinduce temporal summation.^72–74 However, we currentlyare unable to directly visualize the spinal cord in human participants.Consequently, we cannot be certain that the associated findingsof the current study were due to a direct effect mediated bythe dorsal horn of the spinal cord. Additionally, pain is amultifaceted sensation relying on the peripheral nervous systemin combination with the spinal cord and supraspinal centers,and the effect of SMT on pain likely results from an interactionof sites across the nervous system.⁷⁵ Spinal manipulative therapyhas been suggested to influence pain through mechanisms relatedto the peripheral nervous system^76,77 and the supraspinal centers.^78–80 Although our findings of diminished temporal summationsuggest a spinal cord–mediated effect, other than assessingcommonly reported psychological factors, we did not accountfor potential peripheral and supraspinal influences on our findings.

Our primary outcome in the current study was inhibition of temporalsummation, and we did not assess clinical pain ratings followingtreatment. The study was intended to investigate a specificmechanism of SMT, and the benefit of studying an experimentalpain model was the ability to control the magnitude of the painfulstimulus. The study was not intended to measure immediate changesin clinical pain intensity because we did not plan to trackoutcomes past immediate follow-up. Our protocol provided anindirect measure of a particular pain pathway believed to beimportant in the development of chronic pain conditions, butwe are unable to comment upon the relationship between our findingsand changes in clinical pain, as we did not include clinicalpain ratings as an outcome measure.

Future Studies

The current study focused on a potential spinal cord–mediatedmechanism of SMT. The mechanisms through which SMT influencemusculoskeletal pain are likely related to multiple interactionsthroughout the nervous system.⁷⁵ Subsequently, future studiesshould attempt to replicate the current findings while controllingfor or manipulating additional potential factors such as thoserelated to peripheral mechanisms and descending inhibition fromsupraspinal levels. Researchers in future studies also may wantto include multiple sessions in order to assess dose responseto SMT and to observe for longitudinal relationships betweenchanges in temporal summation and clinical pain. Prior reviews^13,14 suggest SMT is effective in the treatment of people withLBP; however, the evidence is stronger when homogeneous samplesare included based on signs and symptoms suggesting a positiveresponse.^15–17 In future studies, researchers may wantto include a sample of participants meeting a clinical predictionrule suggesting the likelihood of a positive clinical response.

Conclusions

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Conclusions

There were no differences in inhibition of A ${delta}$ fiber–mediatedpain sensitivity for SMT in comparison with lumbar exerciseand riding a stationary bicycle. The current study is the firstto report that SMT specifically inhibits temporal summationin individuals with LBP. Additionally, this inhibition appearsto be local, as it was observed only in the lower extremityand psychological factors were not strongly associated withresultant inhibition of temporal summation. These findings suggestthat inhibition of temporal summation is a potential mechanismfor pain relief following SMT for individuals with LBP.

Footnotes

Dr Bialosky, Dr Bishop, Dr Robinson, and Dr George providedconcept/idea/research design and writing. Dr Bialosky and MrZeppieri provided data collection. Dr Bialosky provided dataanalysis. Dr George provided fund procurement. All authors providedconsultation (including review of manuscript before submission).

This study was approved by the Institutional Review Board ofthe University of Florida.

A platform presentation of this research was given at the CombinedSections Meeting of the American Physical Therapy Association;February 6–9, 2008; Nashville, Tennessee.

The project was supported by grant AT002796 from the NationalInstitutes of Health, National Center for Complementary andAlternative Medicine, awarded to Dr Bishop, Dr Robinson, andDr George (principal investigator). Dr Bialosky also receivedsupport from grant AT002796 and from the National Institutesof Health T-32 Neural Plasticity Research Training Fellowship(T32HD043730). This work also was supported with resources fromthe Brain Rehabilitation Research Center, a VA RehabilitationResearch and Development Center of Excellence at the MalcomRandall VA Medical Center in Gainesville, Florida.

This study was registered at www.clinicaltrials.gov under theidentifier of NCT00922220 [ClinicalTrials.gov] .

^* Medoc Ltd, Ha'dekel St, Ramat Yishai, Israel 30095.

SPSS Inc, 233 S Wacker Dr, Chicago, IL 60606.

References

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