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Manual and Instrument Applied Cervical Manipulation for Mechanical Neck Pain: A Randomized Controlled Trial

      Abstract

      Objective

      The purpose of this study was to compare the effects of 2 different cervical manipulation techniques for mechanical neck pain (MNP).

      Methods

      Participants with MNP of at least 1 month’s duration (n = 65) were randomly allocated to 3 groups: (1) stretching (control), (2) stretching plus manually applied manipulation (MAM), and (3) stretching plus instrument-applied manipulation (IAM). MAM consisted of a single high-velocity, low-amplitude cervical chiropractic manipulation, whereas IAM involved the application of a single cervical manipulation using an (Activator IV) adjusting instrument. Preintervention and postintervention measurements were taken of all outcomes measures. Pain was the primary outcome and was measured using visual analogue scale and pressure pain thresholds. Secondary outcomes included cervical range of motion, hand grip-strength, and wrist blood pressure. Follow-up subjective pain scores were obtained via telephone text message 7 days postintervention.

      Results

      Subjective pain scores decreased at 7-day follow-up in the MAM group compared with control (P = .015). Cervical rotation bilaterally (ipsilateral: P = .002; contralateral: P = .015) and lateral flexion on the contralateral side to manipulation (P = .001) increased following MAM. Hand grip-strength on the contralateral side to manipulation (P = .013) increased following IAM. No moderate or severe adverse events were reported. Mild adverse events were reported on 6 occasions (control, 4; MAM, 1; IAM, 1).

      Conclusion

      This study demonstrates that a single cervical manipulation is capable of producing immediate and short-term benefits for MNP. The study also demonstrates that not all manipulative techniques have the same effect and that the differences may be mediated by neurological or biomechanical factors inherent to each technique.

      Key Indexing Terms

      The annual prevalence of neck pain is estimated to range from 30% to 50%, with reports of lifetime and point prevalence values approaching those of low back pain.
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      The aim of this study was to determine whether a single application of HVLA cervical manipulation (MAM or IAM) affected MNP and, if so, whether the effect was the same for both types of manipulation.

      Methods

      The study was designed as a randomized controlled trial with 1 control and 2 intervention groups. Volunteers aged 18 to 35 years with a history of MNP of greater than 1 month were screened for contraindications to cervical spinal manipulation. Contraindications included history of a connective tissue disorder, cervical pain which was not due to mechanical dysfunction or did not originate from the lower cervical spine, current use of anticoagulant therapy, history of recent surgery and/or neck trauma, facial or intraoral anesthesia or paresthesia, visual disturbances, dizziness, and/or vertigo. In addition to this, a person was excluded if they were pregnant or had received cervical mobilization or manipulation within the preceding 1 month. A volunteer who met the inclusion criteria, passed the screening stage, and provided written consent to participate was enrolled in the trial and randomly allocated to 1 of 3 groups. Allocation was achieved using a computer-generated random number sequence created by an administrative officer not otherwise associated with the trial. Group 1 (control) received a standardized active muscle stretching routine (S); group 2 (MAM) received the same active muscle stretching routine (S) plus a single MAM; and group 3 (IAM) received the same active muscle stretching routine (S) plus a single IAM. The trial was conducted at Macquarie University’s Chiropractic Outpatient and Research Clinic in Sydney, Australia, between August and September 2014. The trial was approved by Macquarie University’s Human Research Ethics Committee (approval no.: 5201400281) and registered with the Australian and New Zealand Clinical Trials Registry (ACTRN: 12614000804684).
      All outcome assessments were performed by a single assessor. The primary outcome assessment was neck pain evaluated using subjective measures: visual analogue scale (VAS), numerical pain rating scale (NPRS), and pressure point threshold (PPT). Secondary outcome measures included cervical ROM, hand grip-strength, and wrist blood pressure. Subjective pain levels (VAS) were recorded first, followed by wrist blood pressure, hand grip-strength, PPT, and finally cervical ROM. This order was selected to minimize the effect of one measurement on any other. All outcome measurements were taken immediately preintervention and postintervention. Subjective pain levels (NPRS) were also measured 7 days postintervention by telephone text message. The NPRS used 7 days postintervention was similar to the VAS used preintervention and immediately postintervention.
      All MAMs were administered by a single practitioner with 30 years clinical experience in manual manipulation, whereas all IAMs were administered by a different practitioner with 29 years of clinical experience in instrument manipulation.
      All participants performed the same stretching routine (S) which involved flexion, extension, bilateral lateral flexion, and rotation of the cervical spine to end-range, with each position maintained for 30 seconds and repeated 3 times. The use of stretching as a standardized active control ensured that each participant had the potential for improvement, as the benefit of exercise for MNP has been previously reported in the literature.
      • Hurwitz E
      • Carragee E
      • van der Velde G
      • et al.
      Treatment of neck pain: noninvasive interventions: results of the Bone and Joint Decade 2000-2010 Task Force on Neck Pain and Its Associated Disorders.
      • Snodgrass SJ
      • Rivett DA
      • Sterling M
      • Vicenzino B
      Dose optimization for spinal treatment effectiveness: a randomized controlled trial investigating the effects of high and low mobilization forces in patients with neck pain.
      • Kay TM
      • Gross A
      • Goldsmith CH
      • et al.
      Exercises for mechanical neck disorders.
      Each participant in the MAM and IAM groups received a single application of the relevant manipulation. The choice of which level of the cervical spine to address was at the discretion of the clinician following static palpation. To maintain consistency in blinding, all participants were informed that each intervention was a recommended treatment for MNP.
      • Bryans R
      • Decina P
      • Descarreaux M
      • et al.
      Evidence-based guidelines for the chiropractic treatment of adults with neck pain.
      • Snodgrass SJ
      • Rivett DA
      • Sterling M
      • Vicenzino B
      Dose optimization for spinal treatment effectiveness: a randomized controlled trial investigating the effects of high and low mobilization forces in patients with neck pain.
      All MAMs were administered using the same technique—a lateral flexion thrust manipulation (Fig 1). In this technique, the side contacted by the hand delivering the thrust will be referred to as the ipsilateral side, whereas the opposite side is referred to as the contralateral side.
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      All IAMs were administered using an Activator IV instrument on a setting of “2” with the manipulative force delivered to the pedicle-lamina junction of the involved segment in an anterior, superior, and slightly medial line of drive (Fig 2). In this trial, the instrument was used only as a biomechanical device, and no Activator Methods protocols were used.
      Figure thumbnail gr1
      Fig 1Manually applied manipulation: lateral flexion thrust technique.
      Figure thumbnail gr2
      Fig 2Instrument-applied manipulation: Activator IV technique.

      Subjective Pain Levels

      Participants were asked to record their neck pain using an 11-point VAS immediately preintervention and postintervention. In addition to this, a follow-up telephone text message was sent 7 days postintervention asking the participant to report their neck pain on that day. This measure used the NPRS to rate the pain following the standard question, “Out of 10, how is your neck pain today?” The minimum clinically importance difference (MCID) is 1.7cm
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      Prospective validation of clinically important changes in pain severity measured on a visual analog scale.
      for VAS and 1.3 points
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      Psychometric properties of the Neck Disability Index and Numeric Pain Rating Scale in patients with mechanical neck pain.
      for NRPS.

      Pressure Pain Threshold

      Pressure pain threshold was measured using a JTech Medical Commander Algometer (Salt Lake City, UT). The instrument was placed over the spinous process of the involved segment using a 0.5-cm2 tip, and participants were instructed to notify the examiner the moment the sensation of pressure changed to discomfort or pain. The test was then stopped and the results recorded.
      • Livingston T
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      Commander Algometer [user manual].
      This procedure was performed 3 times and included a 10-second rest between tests, with the recorded score being the average of the 3 scores. The MCID for PPT is 1.77 kg/cm2.
      • Chesterton LS
      • Sim J
      • Wright CC
      • Foster NE
      Interrater reliability of algometry in measuring pressure pain thresholds in healthy humans, using multiple raters.

      Cervical ROM

      Cervical ROM was measured using a JTech Medical Dualer IQ Pro Digital Dual Inclinometer (Salt Lake City, UT). All measurements were taken in the “dynamic dual mode”
      • J TECH Medical
      Dualer IQ Inclinometer [user manual].
      which involved a participant moving their neck to end-range.
      • Fletcher JP
      • Bandy WD
      Intrarater reliability of CROM measurement of cervical spine active range of motion in persons with and without neck pain.
      Each of the 6 movement directions (flexion, extension, left and right lateral flexion, left and right rotation) were performed 3 times, with the average of these scores recorded as the final measurement for that movement. The clinically detectable change for each of these cervical movements has been reported in the literature previously.
      • Fletcher JP
      • Bandy WD
      Intrarater reliability of CROM measurement of cervical spine active range of motion in persons with and without neck pain.
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      • Dumas JP
      • Cote JN
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      Validity and between-day reliability of the cervical range of motion (CROM) device.

      Hand Grip-Strength

      Hand grip-strength was measured using a JTech Medical Commander Grip (Salt Lake City, UT) dynamometer. Maximum isometric grip contraction was performed 3 times on each hand, alternating between hands to minimize performance fatigue. The average of the 3 measurements was recorded as the final grip-strength score for each hand. The clinically detectable change for hand grip-strength is 6 kg.
      • Nitschke JE
      • McMeeken JM
      • Burry HC
      • Matyas TA
      When is a change a genuine change? A clinically meaningful interpretation of grip strength measurements in healthy and disabled women.

      Wrist Blood Pressure

      Wrist blood pressure was measured using a digital Sigma Medical Heine Memotronic PC2 electronic sphygmomanometer (Herrsching, Germany). Blood pressure was taken 3 times, with the average of these scores recorded as the final measurement. The MCID for change in blood pressure is yet to be established in the literature because it can differ significantly between patients.
      • McAlister FA
      When should hypertension be treated? The different perspectives of Canadian family physicians and patients.

      Adverse Events

      Adverse events were recorded immediately postintervention and as part of the 7-day follow-up telephone text message.

      Statistical Analysis

      Calculation of the minimum sample size was based on detecting a difference of 0.4 units in PPT levels, a standard deviation of 0.4, comparison of 2 means, an α of .05, and power (β) of 80%.
      • de Camargo VM
      • Alburquerque-Sendin F
      • Berzin F
      • Stefanelli VC
      • de Souza DP
      • Fernandez-de-las-Penas C
      Immediate effects on electromyographic activity and pressure pain thresholds after a cervical manipulation in mechanical neck pain: a randomized controlled trial.
      These assumptions generated a minimum sample size of 21 participants per group and a total cohort size of 63. A significance level of .05 was used to assess the primary outcome measures, with a Bonferroni correction applied to correct for multiple tests for the 3 primary outcomes giving an individual significance level of .0167. No correction was applied for secondary outcomes. Data were checked for normality before statistical analysis. Baseline variables were compared between groups using one-way analysis of variance for continuous data except for VAS, Kruskal-Wallis for VAS and Pearson χ2 test for categorical data. An analysis of covariance with a factor for group and preintervention values as a covariate was performed to determine the effect of intervention on each outcome measure. For outcome measures with a significant between-group difference, Tukey honestly significantly difference test was performed to correct for multiple comparisons between groups. These statistical analyses were performed using Minitab17 software.

      Results

      Seventy-six volunteers were assessed for eligibility in the trial, with 3 failing to meet the screening criteria and subsequently being excluded (Fig 3). Eight participants did not attend the initial assessment session, leaving baseline data from 65 participants (Table 1). Table 2 describes change scores for the trial at each time point.
      Figure thumbnail gr3
      Fig 3CONSORT flow diagram. aDifferences in allocation due to failure to attend intervention session.
      Table 1Participant Baseline Characteristics
      CharacteristicControl (n = 22)MAM (n = 21)IAM (n = 22)P Value
      Age, y, SD23.8 ± 3.524.4 ± 4.025 ± 4.9.627
      Sex (male), n (%)13 (59)11 (52)13 (59).878
      Height, cm, SD174.0 ± 9.2172.3 ± 8.2174.1 ± 9.4.755
      Weight, kg, SD73.0 ± 11.471.7 ± 15.374.2 ± 10.2.810
      VAS (baseline), cm,
      Scored on a 0-10 scale.
      SD
      3.1 ± 2.03.4 ± 1.73.7 ± 2.1.598
      PPT (baseline), kg, SD5.08 ± 1.824.62 ± 1.184.72 ± 2.18.605
      Identified painful spinal level, n (%).703
       C57 (32)6 (29)7 (32)
       C66 (27)8 (38)10 (45)
       C79 (41)7 (33)5 (23)
      C5, level of fifth cervical vertebra; C6, level of sixth cervical vertebra; C7, level of seventh cervical vertebra; IAM, instrument applied cervical manipulation; MAM, manually applied cervical manipulation; PPT, pressure point threshold; SD, standard deviation; VAS, visual analogue scale.
      a Scored on a 0-10 scale.
      Table 2Change in Outcome Measures Postintervention and at 7-Day Follow-Up by Group
      Control (Mean, CI)MAM (Mean, CI)IAM (Mean, CI)P Value
      Primary outcome measures
      PainVAS
      Measured on a 0-10 scale.
      Post Rx0.50 (−1.04 to 0.04)1.48 (−2.03 to −0.92)1.32 (−1.86 to −0.78).051
      NPRS
      Measured on a 0-10 scale.
      7-d follow-up0.18 (−0.50 to 0.86)1.33 (−2.03 to −0.64)0.73 (−1.40 to −0.05).015
      PPT
      Measured in kg/cm2.
      Post Rx0.23 (−0.62 to 0.15)0.08 (−0.32 to 0.47)0.30 (−0.08 to 0.68).195
      Secondary outcome measures
      cROM (°)Flexion
      Post Rx4.33 (−0.19 to 8.86)1.32 (−5.95 to 3.32)2.83 (−1.70 to 7.36).691
      Extension
      Post Rx1.20 (−5.72 to 3.32)0.00 (−4.63 to 4.63)3.14 (−7.66 to 1.38).166
      Left rotation
      Post Rx1.56 (−6.39 to 3.27)5.11 (0.16-10.06)1.61 (−6.44 to 3.23).011
      Right rotation
      Post Rx1.52 (−5.23 to 2.20)3.94 (0.13-7.74)2.26 (−5.98 to 1.46).001
      Ipsilateral rotation
      Post Rx5.38 (−0.12 to 10.88)2.70 (−8.07 to 2.68).002
      Contralateral rotation
      Post Rx4.43 (0.35-8.51)1.17 (−5.15 to 2.81).015
      Left lateral flexion
      Post Rx0.14 (−3.25 to 3.52)0.84 (−2.62 to 4.31)4.21 (−7.60 to −0.83).037
      Right lateral flexion
      Post Rx1.00 (−1.67 to 3.66)2.82 (−5.55 to −0.10)0.53 (−3.19 to 2.13).140
      Ipsilateral
      Lateral flexion
      Post Rx0.94 (−3.56 to 5.44)3.73 (−8.12 to 0.67).060
      Contralateral lateral flexion
      Post Rx4.19 (1.33-7.05)3.01 (−5.81 to −0.22).001
      Grip-strength (kg)Ipsilateral
      Post Rx2.34 (−5.01 to 0.34)0.67 (−3.28 to 1.95).357
      Contralateral
      Post Rx3.16 (−5.60 to −0.72)1.24 (−1.14 to 3.62).013
      Left
      Post Rx4.46 (−6.82 to −2.09)2.17 (−4.60 to 0.25)1.27 (−3.64 to 1.09).188
      Right
      Post Rx2.99 (−6.08 to 0.11)3.02 (−6.19 to 0.15)0.81 (−2.29 to 3.90).146
      Blood pressure (mm Hg)Systole
      Post Rx6.48 (−11.19 to −1.78)1.10 (−5.91 to 3.72)5.67 (−10.37 to −0.97).236
      Diastole
      Post Rx1.76 (−5.40 to 1.88)2.57 (−6.30 to 1.15)2.77 (−0.87 to 6.41).093
      CI, confidence interval; cROM, cervical range of motion; IAM, instrument applied cervical manipulation; MAM, manually applied cervical manipulation; NPRS, numerical pain rating scale; PPT, pressure point threshold; Rx, treatment; SD, standard deviation; VAS, visual analogue scale.
      Values set in bold are significant.
      a Measured on a 0-10 scale.
      b Measured in kg/cm2.

      Subjective Pain Levels (VAS and NPRS)

      There was no immediate change in subjective pain levels for any of the 3 groups (F2,62 = 3.13, P = .051). However, there was a between-group difference in subjective pain levels at 7-day follow-up (F2,62 = 4.47, P = .015) for the MAM group which reported a decrease in pain compared with control of −1.40 points (P = .015; 95% confidence interval [CI], −2.52 to −0.27). There were no other between-group differences for subjective pain levels at 7-day follow-up: IAM to control (P = .235), and MAM to IAM (P = .367).

      Pressure Pain Threshold

      There were no between-group differences for PPT (F2,62 = 1.68, P = .195).

      Cervical ROM

      There was an immediate change in rotation bilaterally (ipsilateral: F1,41 = 11.17, P = .002; contralateral: F1,41 = 6.44, P = .015). This change was an increase for the MAM group of 10.35° on the ipsilateral side (P = .002; 95% CI, −16.60 to −4.09) and 6.32° on the contralateral side to manipulation (P = .015; 95% CI, −11.36 to −1.29) compared with the IAM group.
      There was a between-group difference for lateral flexion on the contralateral side to manipulation (F1,41 = 12.44, P = .001) for the MAM group of 6.40° (P = .001; 95% CI, −10.06 to −2.73) compared with the IAM group (Fig 4). There was no difference in lateral flexion between the MAM and IAM groups on the ipsilateral side to manipulation (F1,41 = 3.73, P = .060). There were no between-group differences reported for flexion (F2,62 = 0.37, P = .691) or extension (F2,62 = 1.85, P = .166).
      Figure thumbnail gr4
      Fig 4Change in mean differences between manual (MAM) and instrument (IAM) manipulation. ●: Contralateral grip strength, IAM; ▲: contralateral lateral flexion, MAM; ■: contralateral rotation, MAM; ♦: ipsilateral rotation, MAM.

      Hand Grip-Strength

      There was a between-group difference reported in hand grip-strength on the contralateral side to manipulation (F1,41 = 6.77, P = .013). This difference was an increase of 4.43 kg (P = .013; 95% CI, 0.99-7.86) in the IAM group compared with MAM (Fig 4). There was no between-group difference on the ipsilateral side to manipulation (F1,41 = 0.87, P = .357).

      Wrist Blood Pressure

      There were no changes in wrist blood pressure reported in this trial: systole (F2,62 = 2.44, P = .096) or diastole (F2,62 = 2.53, P = .088).

      Adverse Events

      There were no moderate or severe adverse events following any of the interventions. There were 6 mild adverse events reported at 7-day follow-up: 4 in the control group and 1 each in the MAM and IAM groups. These reports included stiffness, mild soreness, and pain during neck movement. Two participants in the IAM group reported reactions which, although not classified as adverse events, have been included here for completeness. These reactions were “feeling unbalanced due to manipulation of only one side of the neck” and “increased clicking in the cervical spine following manipulation.”

      Discussion

      The findings reported in this study show that a single application of cervical manipulation increases cervical ROM and decreases subjective pain levels in people with MNP. The study also shows that cervical manipulation produces remote effects. However, these effects are noticeably different for each type of manipulation. MAM produced immediate increases in rotation bilaterally and lateral flexion on the contralateral side to manipulation compared with IAM and a decrease in subjective pain levels 7 days postintervention when compared with control. IAM did not produce equivalent changes. Our results support the findings of a recent large study comparing MAM, IAM, and usual care in a cohort with low back pain which reported greater reductions in short-term self-reported disability and pain scores following MAM.
      • Schneider M
      • Haas M
      • Glick R
      • Stevans J
      • Landsittel D
      Comparison of spinal manipulation methods and usual medical care for acute and subacute low back pain: a randomized clinical trial.
      However, our results contradict the findings from other smaller studies which reported that MAM and IAM were equally effective in the treatment of MNP.
      • Yurkiw D
      • Mior S
      Comparison of two chiropractic techniques on pain and lateral flexion in neck pain patients: a pilot study.
      • Gemmell H
      • Miller P
      Relative effectiveness and adverse effects of cervical manipulation, mobilisation and the activator instrument in patients with sub-acute non-specific neck pain: results from a stopped randomised trial.
      • Wood TG
      • Colloca CJ
      • Matthews R
      A pilot randomized clinical trial on the relative effect of instrumental (MFMA) versus manual (HVLA) manipulation in the treatment of cervical spine dysfunction.
      In the absence of a control group, it is possible that performance bias may have affected the results from these smaller studies.
      • Budgell BS
      Reflex effects of subluxation: the autonomic nervous system.
      • Furlan AD
      • Pennick V
      • Bombardier C
      • van Tulder M
      2009 Updated method guidelines for systematic reviews in the Cochrane Back Review Group.
      • Jüni P
      • Altman DG
      • Egger M
      Assessing the quality of controlled clinical trials.
      • Rubinstein SM
      • van Eekelen R
      • Oosterhuis T
      • de Boer MR
      • Ostelo RWJG
      • van Tulder MW
      The risk of bias and sample size of trials of spinal manipulative therapy for low back and neck pain: analysis and recommendations.
      • Vernon H
      • Puhl A
      • Reinhart C
      Systematic review of clinical trials of cervical manipulation: control group procedures and pain outcomes.
      In addition, given that these studies reported on small sample sizes (14-47 participants), it is possible that a series of type II errors may have occurred, resulting in incorrect acceptance of the hypothesis that there is no difference between MAM and IAM.
      • Jones SR
      • Carley S
      • Harrison M
      An introduction to power and sample size estimation.
      • Ioannidis JPA
      Why most published research findings are false.
      Given the quality of previous studies investigating manipulation for MNP, we will compare our results with studies of higher quality that investigated the effects of spinal mobilization because the forces used in those studies are similar to those used in our study.
      • Downie AS
      • Vemulpad S
      • Bull PW
      Quantifying the high-velocity, low-amplitude spinal manipulative thrust: a systematic review.
      • Snodgrass SJ
      • Rivett DA
      • Robertson VJ
      Manual forces applied during posterior-to- anterior spinal mobilization: a review of the evidence.

      Subjective Pain Levels (VAS and NPRS)

      Our results are consistent with previous reports that MAM is more effective than mobilization in reducing subjective pain levels for MNP.
      • Carlesso L
      • MacDermid J
      • Gross A
      • Walton D
      • Santaguida P
      Treatment preferences amongst physical therapists and chiropractors for the management of neck pain: results of an international survey.
      • Martinez-Segura R
      • de-la-Llave-Rincon AI
      • Ortega-Santiago R
      • Cleland JA
      • Fernandez-de-las-Penas C
      Immediate changes in widespread pressure pain sensitivity, neck pain, and cervical range of motion after cervical or thoracic thrust manipulation in patients with bilateral chronic mechanical neck pain: a randomized clinical trial.
      • Saavedra-Hernandez M
      • Arroyo-Morales M
      • Cantarero-Villanueva I
      • et al.
      Short-term effects of spinal thrust joint manipulation in patients with chronic neck pain: a randomized clinical trial.
      • Dunning JR
      • Cleland JA
      • Waldrop MA
      • et al.
      Upper cervical and upper thoracic thrust manipulation versus nonthrust mobilization in patients with mechanical neck pain: a multicenter randomized clinical trial.
      As in our study, time appears to be a factor, with these studies reporting improvements at 2,
      • Dunning JR
      • Cleland JA
      • Waldrop MA
      • et al.
      Upper cervical and upper thoracic thrust manipulation versus nonthrust mobilization in patients with mechanical neck pain: a multicenter randomized clinical trial.
      4,
      • Carlesso L
      • MacDermid J
      • Gross A
      • Walton D
      • Santaguida P
      Treatment preferences amongst physical therapists and chiropractors for the management of neck pain: results of an international survey.
      and 7
      • Saavedra-Hernandez M
      • Arroyo-Morales M
      • Cantarero-Villanueva I
      • et al.
      Short-term effects of spinal thrust joint manipulation in patients with chronic neck pain: a randomized clinical trial.
      days postintervention. In contrast, Martinez-Segura et al
      • Martinez-Segura R
      • de-la-Llave-Rincon AI
      • Ortega-Santiago R
      • Cleland JA
      • Fernandez-de-las-Penas C
      Immediate changes in widespread pressure pain sensitivity, neck pain, and cervical range of motion after cervical or thoracic thrust manipulation in patients with bilateral chronic mechanical neck pain: a randomized clinical trial.
      reported an immediate decrease in subjective pain levels following a single cervical HVLA manipulation compared with mobilization in participants with MNP.
      Our results contradict the findings of 2 studies comparing the effectiveness of cervical MAM with mobilization in patients with neck pain.
      • Hurwitz EL
      • Morgenstern H
      • Harber P
      • Kominski GF
      • Yu F
      • Adams AH
      A randomized trial of chiropractic manipulation and mobilization for patients with neck pain: clinical outcomes from the UCLA neck-pain study.
      • Leaver AM
      • Maher CG
      • Herbert RD
      • et al.
      A randomized controlled trial comparing manipulation with mobilization for recent onset neck pain.
      However, this contradiction may be explained by the heterogeneous nature of their designs compared with our study. In the first trial, patients with radiculopathy were included as well as treatment to the thoracic spine,
      • Hurwitz EL
      • Morgenstern H
      • Harber P
      • Kominski GF
      • Yu F
      • Adams AH
      A randomized trial of chiropractic manipulation and mobilization for patients with neck pain: clinical outcomes from the UCLA neck-pain study.
      whereas in the second trial, treatment to the thoracic and lumbar regions was included, randomization only occurred after several treatments, and the type of MAM and mobilization procedures was not reported.
      • Leaver AM
      • Maher CG
      • Herbert RD
      • et al.
      A randomized controlled trial comparing manipulation with mobilization for recent onset neck pain.
      As none of the groups in the current study reported changes that were above the MCID for either VAS or NPRS, the results should not strictly be interpreted as clinically significant. As our cohort displayed relatively low pain levels at baseline, it is possible that a “floor effect” may have contributed to this lack of clinical significance.
      • Langley GB
      • Sheppeard H
      The visual analogue scale: its use in pain measurement.
      • Paul-Dauphin A
      • Guillemin F
      • Virion JM
      • Briancon S
      Bias and precision in visual analogue scales: a randomized controlled trial.
      This floor effect may have been avoided by excluding participants who reported a baseline pain level less than 3 of 10.
      • Hegedus EJ
      • Goode A
      • Butler RJ
      • Slaven E
      The neurophysiological effects of a single session of spinal joint mobilization: does the effect last?.
      Furthermore, interpretation of subjective pain scores can vary between individuals. For example, some patients interpret the minimum end point on the scale (labeled “0”) as indicative of “normal” or “manageable” pain. These patients often exclude the lower half of the rating scale, considering such levels of pain as outside their experience. Interpretation of subjective pain scales in this way can result in distorted scores because these patients only use part of the range, that is, 6-10, leading some authors to question the validity of subjective pain scales.
      • Myles PS
      • Urquhart N
      The linearity of the visual analogue scale in patients with severe acute pain.
      • Ferreira-Valente MA
      • Pais-Ribeiro JL
      • Jensen MP
      Validity of four pain intensity rating scales.
      • Leininger BD
      • Evans R
      • Bronfort G
      Exploring patient satisfaction: a secondary analysis of a randomized clinical trial of spinal manipulation, home exercise, and medication for acute and subacute neck pain.
      • Hjermstad MJ
      • Fayers PM
      • Haugen DF
      • et al.
      Studies comparing Numerical Rating Scales, Verbal Rating Scales, and Visual Analogue Scales for assessment of pain intensity in adults: a systematic literature review.
      • Williams ACdC
      • Davies HTO
      • Chadury Y
      Simple pain rating scales hide complex idiosyncratic meanings.
      In addition, based on the change scores reported immediately postintervention, it is hypothesized that the MCID may have been achieved at 7-day follow-up had a second manipulation been applied such as would usually occur in clinical practice.

      Pressure Pain Threshold

      Our finding of no between-group differences in PPT immediately postintervention is consistent with results from other studies that found no differences in PPT following high -and low-force mobilization in people with chronic, nonspecific neck pain
      • Carlesso L
      • MacDermid J
      • Gross A
      • Walton D
      • Santaguida P
      Treatment preferences amongst physical therapists and chiropractors for the management of neck pain: results of an international survey.
      or whiplash.
      • Sterling M
      • Pedler A
      • Chan C
      • Puglisi M
      • Vuvan V
      • Vicenzino B
      Cervical lateral glide increases nociceptive flexion reflex threshold but not pressure or thermal pain thresholds in chronic whiplash associated disorders: a pilot randomised controlled trial.
      Furthermore, none of the reported changes in the current trial were above the MCID for PPT. This finding is also consistent with Martinez-Segura et al
      • Martinez-Segura R
      • de-la-Llave-Rincon AI
      • Ortega-Santiago R
      • Cleland JA
      • Fernandez-de-las-Penas C
      Immediate changes in widespread pressure pain sensitivity, neck pain, and cervical range of motion after cervical or thoracic thrust manipulation in patients with bilateral chronic mechanical neck pain: a randomized clinical trial.
      who reported nonsignificant increases in PPT following both cervical and thoracic manipulation for MNP. As PPT is a self-reported measure of pain, it is possible that our results may have been influenced by participants who had varying pain thresholds, specifically where a sensitive participant may have reported pain earlier than a more stoic participant. In addition, the control group was not blinded, and it is possible that participants in this group may have had a falsely lowered pain threshold.

      Cervical ROM

      The immediate increase in cervical rotation and lateral flexion following MAM reported in this study contradicts findings from other studies where no change to cervical ROM was reported following cervical mobilization or manipulation in populations with MNP.
      • Carlesso L
      • MacDermid J
      • Gross A
      • Walton D
      • Santaguida P
      Treatment preferences amongst physical therapists and chiropractors for the management of neck pain: results of an international survey.
      • Martinez-Segura R
      • de-la-Llave-Rincon AI
      • Ortega-Santiago R
      • Cleland JA
      • Fernandez-de-las-Penas C
      Immediate changes in widespread pressure pain sensitivity, neck pain, and cervical range of motion after cervical or thoracic thrust manipulation in patients with bilateral chronic mechanical neck pain: a randomized clinical trial.
      Furthermore, 2 recent systematic reviews concluded that there was uncertainty as to whether spinal manipulation improved cervical ROM.
      • Snodgrass SJ
      • Cleland JA
      • Haskins R
      • Rivett DA
      The clinical utility of cervical range of motion in diagnosis, prognosis, and evaluating the effects of manipulation: a systematic review.
      • Millan M
      • Leboeuf-Yde C
      • Budgell B
      • Descarreaux M
      • Amorim MA
      The effect of spinal manipulative therapy on spinal range of motion: a systematic literature review.
      In explaining our findings, consideration must be given to the fact that we used an MAM technique which facilitated distraction and displacement of the cervical spine. As preload manipulative forces are capable of eliciting changes in paraspinal muscle activation,
      • Huggins T
      • Boras AL
      • Gleberzon BJ
      • Popescu M
      • Bahry LA
      Clinical effectiveness of the activator adjusting instrument in the management of musculoskeletal disorders: a systematic review of the literature.
      • Descarreaux M
      • Nougarou F
      • Dugas C
      Standardization of spinal manipulation therapy in humans: development of a novel device designed to measure dose-response.
      • Nougarou F
      • Dugas C
      • Deslauriers C
      • Page I
      • Descarreaux M
      Physiological responses to spinal manipulation therapy: investigation of the relationship between electromyographic responses and peak force.
      • Nougarou F
      • Dugas C
      • Deslauriers C
      • Page I
      • Descarreaux M
      The role of preload forces in spinal manipulation: experimental investigation of kinematic and electromyographic responses in healthy adults.
      it is suggested that the chosen technique exerted a preload force that achieved this activation, thereby facilitating a change in cervical ROM. This may explain the lack of change to cervical ROM seen subsequent to IAM, as different preload forces are generated using this technique.

      Hand Grip-Strength

      This is the first study to report immediate increases in hand grip-strength following IAM and contradicts other reports of changes following manipulation.
      • Botelho MB
      • Andrade BB
      Effect of cervical spine manipulative therapy on judo athletes' grip strength.
      • Humphries KM
      • Ward J
      • Coats J
      • Nobert J
      • Amonette W
      • Dyess S
      Immediate effects of lower cervical spine manipulation on handgrip strength and free-throw accuracy of asymptomatic basketball players: a pilot study.
      • Fernandez-Carnero J
      • Fernandez-de-las-Penas C
      • Cleland JA
      Immediate hypoalgesic and motor effects after a single cervical spine manipulation in subjects with lateral epicondylalgia.
      • Fernandez-Carnero J
      • Cleland JA
      • Arbizu RL
      Examination of motor and hypoalgesic effects of cervical vs thoracic spine manipulation in patients with lateral epicondylalgia: a clinical trial.
      Notwithstanding this, the finding of increased hand grip-strength on the contralateral side to manipulation is supported by Humphries et al
      • Humphries KM
      • Ward J
      • Coats J
      • Nobert J
      • Amonette W
      • Dyess S
      Immediate effects of lower cervical spine manipulation on handgrip strength and free-throw accuracy of asymptomatic basketball players: a pilot study.
      who reported increases in a population of asymptomatic basketball players. Furthermore, other authors have reported an immediate increase in hand grip-strength on both the affected side (ipsilateral)
      • Fernandez-Carnero J
      • Fernandez-de-las-Penas C
      • Cleland JA
      Immediate hypoalgesic and motor effects after a single cervical spine manipulation in subjects with lateral epicondylalgia.
      • Fernandez-Carnero J
      • Cleland JA
      • Arbizu RL
      Examination of motor and hypoalgesic effects of cervical vs thoracic spine manipulation in patients with lateral epicondylalgia: a clinical trial.
      as well as bilaterally
      • Botelho MB
      • Andrade BB
      Effect of cervical spine manipulative therapy on judo athletes' grip strength.
      following cervical MAM. The current findings are congruent with previous studies reporting excitatory effects on motor activity subsequent to spinal manipulation.
      • Keller TS
      • Colloca CJ
      Mechanical force spinal manipulation increases trunk muscle strength assessed by electromyography: a comparative clinical trial.
      • Colloca CJ
      • Keller TS
      Electromyographic reflex responses to mechanical force, manually assisted spinal manipulative therapy.
      • Dishman JD
      • Cunningham BM
      • Burke J
      Comparison of tibial nerve H-reflex excitability after cervical and lumbar spine manipulation.
      • Dishman JD
      • Burke J
      Spinal reflex excitability changes after cervical and lumbar spinal manipulation: a comparative study.
      More specifically, Dunning and Rushton
      • Dunning J
      • Rushton A
      The effects of cervical high-velocity low-amplitude thrust manipulation on resting electromyographic activity of the biceps brachii muscle.
      demonstrated that a single cervical manipulation can elicit an immediate increase in resting electromyographic activity in an area distal and not directly connected to the cervical spine. Other studies investigating the effects of cervical manipulation on lateral epicondylalgia have described both sensory and motor changes including an increased hand grip-strength following manipulation.
      • Fernandez-Carnero J
      • Fernandez-de-las-Penas C
      • Cleland JA
      Immediate hypoalgesic and motor effects after a single cervical spine manipulation in subjects with lateral epicondylalgia.
      • Fernandez-Carnero J
      • Cleland JA
      • Arbizu RL
      Examination of motor and hypoalgesic effects of cervical vs thoracic spine manipulation in patients with lateral epicondylalgia: a clinical trial.
      • Vicenzino B
      • Paungmali A
      • Buratowski S
      • Wright A
      Specific manipulative therapy treatment for chronic lateral epicondylalgia produces uniquely characteristic hypoalgesia.
      It has also been reported that multiple sessions of cervical manipulation may produce a cumulative effect on hand grip-strength, supporting the concept of a dose-response mechanism.
      • Botelho MB
      • Andrade BB
      Effect of cervical spine manipulative therapy on judo athletes' grip strength.
      • Fernandez-Carnero J
      • Fernandez-de-las-Penas C
      • Cleland JA
      Immediate hypoalgesic and motor effects after a single cervical spine manipulation in subjects with lateral epicondylalgia.
      As the increases in hand grip-strength reported in this trial were not above the MCID, any interpretation of their clinical significance should be restrained.

      Wrist Blood Pressure

      Previous studies have reported mixed results when measuring changes in blood pressure following spinal manipulation.
      • Budgell BS
      Reflex effects of subluxation: the autonomic nervous system.
      • Carrick FR
      Changes in brain function after manipulation of the cervical spine.
      • Eingorn AM
      • Muhs GJ
      Rationale for assessing the effects of manipulative therapy on autonomic tone by analysis of heart rate variability.
      • Bolton PS
      • Kerman IA
      • Woodring SF
      • Yates BJ
      Influences of neck afferents on sympathetic and respiratory nerve activity.
      Two systematic reviews reflect this observation, with one reporting that spinal manipulation produced a nonsignificant, minimal clinical effect on blood pressure,
      • Mangum K
      • Partna L
      • Vavrek D
      Spinal manipulation for the treatment of hypertension: a systematic qualitative literature review.
      whereas the other reported strong evidence for a positive change in blood pressure in healthy populations following manipulation.
      • Kingston L
      • Claydon L
      • Tumilty S
      The effects of spinal mobilizations on the sympathetic nervous system: a systematic review.
      To the authors’ best knowledge, this is the first study to investigate the effect of cervical manipulation on blood pressure in a population with MNP.

      Adverse Events

      Although the absence of any moderate or severe adverse events following 21 MAMs and 22 IAMs in a young population with MNP is welcomed, it should not be interpreted as an unequivocal endorsement of the safety of cervical manipulation. Reports of this kind are evidence of the “relative” safety of cervical manipulation and add to the body of evidence in the field. Furthermore, reporting the rate of minor adverse events (4.7% in the current study) promotes evidence-based discussion on the risks associated with this type of intervention.

      Limitations

      There are a number of limitations which should be considered when interpreting the results of this study. Firstly, the trial was designed as a “proof of concept” with the choice to use a single manipulation as the intervention driven by the desire to directly measure dose-response, an approach previously recommended by several authors.
      • Descarreaux M
      • Nougarou F
      • Dugas C
      Standardization of spinal manipulation therapy in humans: development of a novel device designed to measure dose-response.
      • Nougarou F
      • Dugas C
      • Deslauriers C
      • Page I
      • Descarreaux M
      Physiological responses to spinal manipulation therapy: investigation of the relationship between electromyographic responses and peak force.
      • Nougarou F
      • Dugas C
      • Deslauriers C
      • Page I
      • Descarreaux M
      The role of preload forces in spinal manipulation: experimental investigation of kinematic and electromyographic responses in healthy adults.
      • Kawchuk GN
      • Prasad NG
      • McLeod RC
      • Liddle T
      • Li T
      • Zhu Q
      Variability of force magnitude and force duration in manual and instrument-based manipulation techniques.
      The results should therefore not be interpreted as indicative of clinical practice. Secondly, as participants in the trial were young with low baseline levels of pain, the results may not be generalizable to older patients or those with other cervical complaints such as neck trauma or radiculopathy. Thirdly, we attempted to reduce interoperator inconsistencies by using a single clinician for each type of manipulation; therefore, it is possible that similar studies using multiple practitioners may have difficulty replicating our results. Fourthly, the reliability and validity of VAS
      • Gallagher EJ
      • Liebman M
      • Bijur PE
      Prospective validation of clinically important changes in pain severity measured on a visual analog scale.
      • Paul-Dauphin A
      • Guillemin F
      • Virion JM
      • Briancon S
      Bias and precision in visual analogue scales: a randomized controlled trial.
      and NPRS
      • Bijur PE
      • Latimer CT
      • Gallagher EJ
      Validation of a verbally administered numerical rating scale of acute pain for use in the emergency department.
      have been reported separately; however, this does not extend to inclusion in the same analysis. To maintain consistency across measures, the average of a multiple-question NPRS could have been used at all time points to report subjective pain levels. In addition, it is possible that as numerous multiple comparisons were performed, a type I error may have occurred.
      • Feise R
      Do multiple outcome measures require p-value adjustment?.
      Furthermore, as there was no interexaminer validation of the diagnosis, it is also possible that the initial diagnosis may have been incorrect and therefore influenced the results. Notwithstanding, a recent study supports the use of a targeted physical examination involving pain provocation with manual palpation for accurate diagnosis of MNP.
      • Triano J
      • Budgell B
      • Bagnulo A
      • et al.
      Review of methods used by chiropractors to determine the site for applying manipulation.

      Conclusion

      This study demonstrates that a single cervical manipulation is capable of producing both immediate and short-term benefits for MNP. The study also demonstrates that not all manipulative techniques have the same effect. The results reported in this study are consistent with the hypothesis that the biomechanical characteristics of different spinal manipulation techniques may be responsible for varying clinical effects. However, the results are not definitive, and further research investigating the nature of these changes is warranted.

      Funding Sources and Potential Conflicts of Interest

      No funding sources or conflicts of interest were reported for this study.

      Contributorship Information

      • Concept development (provided idea for the research): L.G., R.E.
      • Design (planned the methods to generate the results): L.G., R.E.
      • Supervision (provided oversight, responsible for organization and implementation, writing of the manuscript): R.E.
      • Data collection/processing (responsible for experiments, patient management, organization, or reporting data): L.G.
      • Analysis/interpretation (responsible for statistical analysis, evaluation, and presentation of the results): L.G., K.B., R.E.
      • Literature search (performed the literature search): L.G.
      • Writing (responsible for writing a substantive part of the manuscript): L.G., R.E.
      • Critical review (revised manuscript for intellectual content; this does not relate to spelling and grammar checking): L.G., K.B., R.E.
      • Other (list other specific novel contributions): R.E.—provided all MAM in trial.

      Practical Applications

      • A single application of MAM increased rotation and lateral flexion movements and decreased pain levels in people with mechanical neck pain.
      • A single application of IAM increased hand grip-strength on the contralateral side to manipulation.
      • There was no change in PPT following either type of manipulation.
      • Following 21 MAMs and 22 IAMs, there were no moderate or severe adverse events and 2 mild adverse events reported in this trial.

      Acknowledgements

      The authors thank Mr Tim Wade-Ferrell and Mr Aron Downie for their assistance during the project.

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