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Cervical Mobilizations Improve Deep Cervical Flexor Activity in Individuals With Chronic Neck Pain

Tuesday, June 6, 2023 - 3 Likes

Brent Brookbush

Brent Brookbush

DPT, PT, MS, CPT, HMS, IMT

Research Review: Cervical Mobilizations Decrease Superficial Neck Flexor Activity in Individuals With Chronic Neck Pain

By Nicholas Rolnick SPT, MS, CSCS

Edited by Brent Brookbush DPT, PT, COMT, MS, PES, CES, CSCS, ACSM H/FS

Original Citation: Sterling M, Jull G, Wright A. Cervical mobilisation: concurrent effects on pain, sympathetic nervous system activity and motor activity. Manual Therapy. 2001, 6(2): 72-81. ABSTRACT

Why the Study Is Relevant: Increased superficial neck flexor activity has been observed in individuals with chronic neck pain (2). Cervical mobilizations are commonly used to decrease patients' pain, increase range of motion and improve function (1). This 2001 Australian study, suggests grade III unilateral posterior-to-anterior mobilization to a symptomatic C5/C6 segments in individuals with neck pain, resulted in mechanical hypoalgesia (reduced sensitivity), sympathetic nervous system excitability, reduced superficial neck flexor activity and enhanced recruitment of deep neck flexors .

Illustration of the Longus Colli: Gray's Anatomy, 20th Edition
Caption: Illustration of the Longus Colli: Gray's Anatomy, 20th Edition

Gray's Anatomy - Longus Colli - By modified by Uwe Gille - Gray387.png, Public Domain, https://commons.wikimedia.org/w/index.php?curid=2526567

Study Summary

Study DesignRandomized-controlled, double-blinded, within-subject placebo-controlled group
Level of EvidenceIB Evidence from at least one randomized controlled trial

Subject Demographics

 

 

Subject Characteristics (n = 30)
  • Age (Standard deviation) years: 35.77 ± 14.92
  • Gender: 16 female, 14 male
  • Number of participants: 30

Inclusion Criteria

  • An insidious history of mid-lower cervical spine pain lasting longer than 3 months primarily from the C5/C6 segment (as assessed by a manipulative physiotherapist)

Exclusion Criteria

  • A history of cervical spine trauma or surgery
  • Radiculopathy to the arms
  • Dizziness or other upper cervical spine symptoms
  • Diabetes
  • Peripheral vascular disease

 

 Methodology

The study was carried out in a noise attenuated laboratory, with temperature and humidity controlled in order to reduce the influence of the environment on nervous system activity.

Participants took part in the study on three different days, each day separated by at least 24 hours.

Participants were randomly selected to take part in one of three procedures in each session: Spinal manual therapy (SMT), a placebo or control.

Each session including the control procedure lasted 6 minutes, with 1-minute applications followed by 1-minute rest periods.

  • SMT: A grade III postero-anterior mobilization was applied to the articular pillars of C5/C6 on the symptomatic side.
  • Control: No contact was made between the researcher and the participant
  • Placebo: Manual contact was applied over the articular pillars of C5/C6 on the symptomatic side.

Each participant’s electromyographic activity (EMG), pain pressure thresholds (PPT), visual analog scale (VAS) and thermal pain threshold (TPT) values were recorded using random selection immediately before and after all interventions.

Skin conductance (SC) and skin temperature (ST) were recorded for 2 minutes prior to and during all interventions.

  • Researcher ‘A’ recorded all pre- and post-procedure values and was blinded to the participant’s grouping.
  • Researcher ‘B’ applied the manual therapy and was blinded to the objective data collected for each participant.
  • Participants were given a standardized explanation on the effect of manual handling and positioning in physical therapy in individuals with neck pain.

A post-experiment questionnaire was given to all participants to evaluate whether or not they believed they had received the true treatment (rather than the placebo or control).

  • Three out of 30 participants correctly identified the SMT group. Their data did not influence the results of the study.
Outcomes
  • VAS Measures
    • Significant difference between SMT and control (p = 0.046), but not SMT and placebo in resting VAS scores (p = 0.091).
      • Mean resting VAS scores in SMT decreased by 0.335 ± 0.02 cm.

    • No significant differences in VAS scores at end-range cervical rotation were observed across conditions.

  • PPT Measures
    • Significant differences were observed in PPT on the symptomatic side following intervention between SMT and placebo (p = 0.0002) and SMT and control (p = 0.0001).
      • Mean increase in PPT in SMT group was 22.55 ± 2.4%.

  • TPT Measures
    • No significant differences were observed in TPT across the different conditions (p = 0.669).

  • SC Measures
    • Significant differences were observed in AUC in the SMT condition compared to placebo (p = 0.001) and control (p = 0.002).
      • Percentage increase in AUC in SMT group was 16 ± 2.96%.

    • Significant differences were observed in MAX in the SMT condition compared to placebo (p = 0.0003) and control (p = 0.002).
      • Percentage increase in MAX in SMT group was 114 ± 10.5%.

  • ST Measures
    • Significant differences were observed in AUC between SMT and control (p = 0.017), but not SMT and placebo (p = 0.154).
      • Percentage decrease in AUC in SMT group was -1.3 ± 0.4%.

    • Significant differences were observed in MIN in the SMT condition compared to placebo (p = 0.022) and control (p = 0.016).
      • Percentage decrease in MIN in SMT group was -2.5 ± 0.5%.

  • Cranio-cervical Flexion Test EMG Measures
    • Significant differences were observed in the cranio-cervical flexion test EMG values between SMT and placebo and SMT and control groups in the 22 mm Hg, 24 mm Hg and 26 mm Hg conditions (all conditions, p = 0.0001).
      • SMT group decreased superficial neck flexor activity (as a percentage of change from baseline) -28 ± 3.2% at 22 mm Hg, -34 ± 2.6% at 23 mm Hg and -21 ± 1.8% at 26 mm Hg.

    • No significant differences were observed between any groups in the 28 mm Hg and 30 mm Hg conditions.
    • There was a trend for increased superficial neck flexor muscle activity in the placebo condition greater than the control.
      • Significance between placebo and control groups were seen in 22 mm Hg (p = 0.044) and 26 mm Hg (p = 0.019).
      • Placebo group increased superficial neck flexor activity (as a percentage of change from baseline) 40 ± 2.1% at 22 mm Hg and 27 ± 1.7% at 26 mm Hg.

Our ConclusionsCervical mobilizations may reduce superficial neck flexor recruitment in those with chronic neck pain. Performing cervical mobilizations (if within the scope of practice of the professional) prior to performing deep cervical flexor isolated activation may aid in reducing superficial neck flexor activity, enhance deep neck flexor recruitment and improve neuromuscular control.
Conclusions of the Researchers

A grade III unilateral postero-anterior mobilization to the symptomatic C5/C6 segments in individuals with neck pain resulted in mechanical hypoalgesia, sympathetic nervous system excitability and reduced superficial neck flexor activity. Based on the activation patterns in the 22-26 mm Hg cranio-cervical flexion test, it appears that SMT increases the low-load tonic activation of the deep cervical neck flexors. SMT does not appear to increase the strength of the deep neck flexors (as 28-30 mm Hg was not significantly different across the testing conditions, indicating that the force needed to produce cranio-cervical flexion was greater than the force generating capabilities of the deep neck flexors without increased contribution from the superficial neck flexors).

Pain reduction patterns in the SMT group indicate that pain may not be the major reason for the observed decreased superficial neck flexor activity.

Image of individual performing a unilateral posterior to anterior cervical mobilization at about the C6/C7 level
Caption: Image of individual performing a unilateral posterior to anterior cervical mobilization at about the C6/C7 level

Cervical Mobilization

Review & Commentary:

Spinal manual therapy (SMT) is used by human movement professionals (primarily physical therapists and chiropractors) working in rehab, fitness and performance settings to increase range of motion, reduce pain and/or improve neuromuscular control (1). Current research suggests that the acute effects of SMT are primarily neurophysiological through modulation of mechanical nociceptive receptors, both proximal and distal to the site of SMT (1, 3-4). One recent study hypothesized that spinal and supraspinal-mediated pathways were most likely responsible for changes in central nervous system activity following SMT (4); however, the exact mechanism of action remains unclear. Refer to the appendix below for additional background information about the context of the study design.

In consideration of the neurophysiological effects of mobilization, an interesting finding in this study was increased activity in the superficial neck flexors following the placebo intervention, but a decrease in activity of the superficial neck flexors in the experimental group. The placebo intervention was manual touch to the C5/C6 area without joint mobilization, where as the experimental group received joint mobilization to the same segment. It appears that specificity of manual therapy has an effect on the resulting changes in muscle activity. This may have important implications on practice, but more research is needed.

The study had many methodological strengths, including:

  • This study used a condition randomized, placebo-controlled, double-blinded, repeated-measures, within-subject design. This minimized the effects of bias within the study. In manual therapy interventions, the probability for observer bias to influence results increases due to the inability to blind the experimental condition; however, this study attempted to minimize observer bias by blinding the researcher collecting the data and the researcher performing the manual therapy. A placebo group was also used, which is important because it recognizes the effect of manual touch alone on the outcomes of interest. The within-subjects design also strengthens the results of the study, as all subjects underwent each procedure.
  • The use of clinically relevant exercises. The cranio-cervical flexion test performed in this study is a variation of a commonly used assessment known as the deep cervical flexor endurance test .
  • The use of multiple outcome measures provides additional information about the acute systemic effects of a 6-minute cervical spine mobilization. Research has shown that the acute effects of SMT are not exclusively mechanical (1,3-4). This study builds on that data, providing supporting evidence, and ideas for future research on the multi-faceted affects of SMT.

Weaknesses that should be noted prior to clinical integration of the findings include:

  • The reliability of the grade III postero-anterior mobilization was not established. Although the same clinician performed the mobilization throughout the study, intra-rater reliability measures would strengthen the results. Future studies should include a reliability assessment of the intervention used.
  • The participants had chronic neck pain. Findings may not be generalizable to other populations. Future research should replicate this study in other populations,
  • The acute nature of the study does not provide any information about long-term outcomes. It is unknown whether or not acute decreases in superficial neck flexor activity will produce long-term increases in deep neck flexors activity, motor control, and function. Future research should include longitudinal data.

Why This Study Is Important

This study suggests that unilateral grade III cervical mobilizations may decrease superficial neck flexor activity. This may be evidence that mobilizations not only affect joint motion, but alter motor unit recruitment. The results of this study also highlight the acute systemic neurophysiological effects of mobilizations. These include reductions in resting pain levels (although statistically significant, were small) and skin temperature, along with increases in the mechanical pain pressure threshold and skin conductance. Based on the findings of this study, it would appear that cerviccal mobilizations are effective and their impact is multi-factorial.

How the Findings Apply to Practice

Increased superficial neck flexor activity has been observed in individuals with chronic neck pain (6). Further, under-activity of the deep neck flexors is a proposed mechanism for pain and loss of function in this group (2). Human movement professionals may use deep cervical flexor activation techniques to facilitate recruitment of these muscles. However, the findings of this study suggest that cervical mobilizations may aid in optimizing recruitment. Human movement professionals whose scope of practice includes manual therapy (DPTs, ATCs, DCs) should consider using mobilization techniques prior to deep cervical flexor activation techniques .

Related Brookbush Institute Content

The results of this study support the Brookbush Institute’s (BI) use of mobilizations and the assertion that the various systems responsible for human movement are integrated (articular, neural, fascial and muscular). Further, the study supports BI's recommended order of intervention, implying that mobilizations alter muscle activity and should be performed prior to activation techniques. Cervical facet joint stiffness, over-activity of the superficial cervical flexors and inhibition of deep cervical flexors is commonly noted in cervical dysfunction, and upper body dysfunction (UBD) , implying that cervical mobilizations may be appropriate for both. In addition to the Overhead Squat Assessment and Goniometry , BI recommends the use of the the deep cervical flexor endurance test (as used in this study), in place of other traditional Manual Muscle Tests used for cervical muscles. Human movement professionals whose scope of practice includes manual therapy should consider mobilization of cervical facets, prior to deep cervical flexor activation  to improve the effectiveness of the intervention.

The following videos show deep cervical flexor activation  exercises and progressions, mobilization videos are in development.

Brookbush Institute Videos

Lewit Deep Neck Flexor Activation

Deep Cervical Flexor Isolated Activation:

Deep Cervical Flexor Activation Progressions for Stabilization:

Deep Cervical Flexor Activation Progressions for Range of Motion (ROM):

Appendix:

The dorsal periaqueductal gray matter (dPAG) is a group of structures within the brain that is thought to be responsible for the favorable outcomes of SMT (5). In one animal study, stimulation of the dPAG produced movements of the musculoskeletal system (5). Taken in context, if dPAG is the primary area responsible for the acute effects of SMT, it stands to reason that a concomitant effect on neuromuscular control exists in humans. No studies have yet clearly defined the relationship between the dPAG, SMT and its acute effect on muscle activity in human subjects.

Cervical mobilizations are a common form of SMT used to reduce pain and restore movement in individuals with neck pain (6). A common clinical finding in neck pain is decreased endurance of the deep cervical neck flexors and overactivity of the superficial neck flexors to stabilize the cervical spine (2). The authors of this 2001 study attempted to indirectly define the relationship between SMT, dPAG and the muscle activity in human subjects. This study investigated the acute effects of SMT on pain, sympathetic nervous system activity and superficial neck flexor muscle activity in individuals with chronic neck pain. The results of the study do not rule out the potential influence of the dPAG on producing the positive effects of SMT.

Bibiliography:

  1. Millan M, Leboeuf-Yde C, Budgell B, Amorim MA. The effect of spinal manipulative therapy on experimentally induced pain: a systematic literature review. Chiropr Man Therap. 2012, 20(1): 26
  2. Jull G, Falla D. Does increased superficial neck flexor activity in the craniocervical flexion test reflect reduced deep flexor activity in people with neck pain? Man Ther. 2016, 25:43-47.
  3. Bialosky JE, George SZ, Horn ME, Price DD, Staud R, Robinson ME. Spinal Manipulative Therapy Specific Changes In Pain Sensitivity In Individuals With Low Back Pain (NCT01168999). The journal of pain : official journal of the American Pain Society. 2014, 15(2):136-148.
  4. Coronado RA, Gay CW, Bialosky JE, et al. Changes in pain sensitivity following spinal manipulation: a systematic review and meta-analysis. J Electromyogr Kinesiol. 2012, 22(5): 752-767.
  5. Lovick T. Interactions between descending pathways from the dorsal and ventrolateral periaqueductal gray matter in the rat. In: Depaulis A, Bandler R. The midbrain periaqueductal gray matter. Plenum Press, New York. 101-134.
  6. Chu J, Allen DD, Pawlowsky S, Smoot B. Peripheral response to cervical or thoracic spine manual therapy: an evidence-based review with meta analysis. J Man Manip Ther. 2014, 22(4): 220-229.

© 2017 Brent Brookbush

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