Patients With Neck Pain Demonstrate Reduced Electromyographic
Activity of the Deep Cervical Flexor Muscles During
Performance of the Craniocervical Flexion Test

This section is compiled by Frank M. Painter, D.C.
Send all comments or additions to:    Frankp@chiro.org

FROM:   Spine (Phila Pa 1976). 2004 (Oct 1); 29 (19): 2108–2114 ~ FULL TEXT

Deborah L. Falla, Gwendolen A. Jull, and Paul W. Hodges

Division of Physiotherapy,
The University of Queensland,
Brisbane, Queensland, Australia.
d.falla@shrs.uq.edu.au

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STUDY DESIGN:   Cross-sectional study.

OBJECTIVE:   The present study compared activity of deep and superficial cervical flexor muscles and craniocervical flexion range of motion during a test of craniocervical flexion between 10 patients with chronic neck pain and 10 controls.

SUMMARY OF BACKGROUND DATA:   Individuals with chronic neck pain exhibit reduced performance on a test of craniocervical flexion, and training of this maneuver is effective in management of neck complaints. Although this test is hypothesized to reflect dysfunction of the deep cervical flexor muscles, this has not been tested.

METHODS:   Deep cervical flexor electromyographic activity was recorded with custom electrodes inserted via the nose and fixed by suction to the posterior mucosa of the oropharynx. Surface electrodes were placed over the superficial neck muscles (sternocleidomastoid and anterior scalene). Root mean square electromyographic amplitude and craniocervical flexion range of motion was measured during five incremental levels of craniocervical flexion in supine.

RESULTS:   There was a strong linear relation between the electromyographic amplitude of the deep cervical flexor muscles and the incremental stages of the craniocervical flexion test for control and individuals with neck pain (P = 0.002). However, the amplitude of deep cervical flexor electromyographic activity was less for the group with neck pain than controls, and this difference was significant for the higher increments of the task (P < 0.05). Although not significant, there was a strong trend for greater sternocleidomastoid and anterior scalene electromyographic activity for the group with neck pain.

CONCLUSIONS:   These data confirm that reduced performance of the craniocervical flexion test is associated with dysfunction of the deep cervical flexor muscles and support the validity of this test for patients with neck pain.

Key words:   electromyography, neck muscles, neck pain, clinical evaluation.

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From the FULL TEXT Article:

Background

Chronic cervical spine disease is becoming increasingly prevalent in society. Estimations indicate that 67% of individuals will suffer neck pain at some stage of life. [1] With an increasingly sedentary population, especially with reliance on computer technology in the workplace, it is predicated that the prevalence rate will continue to rise. Effective management of this condition is vital, not only for the relief of symptoms but perhaps more importantly, for the prevention of recurrent episodes of cervical pain, personal suffering, and lost work productivity.

Craniocervical flexion exercise has been shown to be effective in the management of cervicogenic headache. [2] This intervention was based on research that indicates inferior ability to increase and hold progressively inner range positions of craniocervical flexion in individuals with neck pain of traumatic and nontraumatic origin [3, 4] and the proposal that this maneuver provides a strategy to test and retrain the activity of the deep cervical flexor muscles, [3] which are considered important for control of stability of the cervical spine. [5-8] However, to date, no study has been undertaken to directly measure this deep muscle group to substantiate whether activity of these muscles is impaired in individuals with cervical pain and whether such a deficit is reflected by this maneuver.

The cervical spine is surrounded by a complex arrangement of muscles that contribute to static and dynamic control of the head and neck. However, because of morphologic differences between the muscle layers that encapsulate the spine, [9] there is variation in their mechanical effect on the spine. Within the anterior muscles, it has been argued that the deep cervical flexor muscles, longus capitis and colli, subserve an important role in control of spinal elements, which cannot be replicated by the more superficial anterior muscles. Anatomically, the deep flexor muscles are related intimately with the cervical osseous and articular elements, whereas the sternocleidomastoid has no attachments to the cervical vertebrae. [9] The longus colli is the principle muscle to support and control the cervical curve6 against the tendency towards buckling of the spine induced by head weight and with the contraction of the powerful extensor muscles. [8, 10] The deep cervical flexors are also vital for control of the cervical segments. In a computer model, Winters and Peles [8] showed regions of local segmental instability if only the large, more superficial muscles of the neck were simulated to produce movement, particularly in near upright or neutral postures. Deep muscle activity was required in conjunction with activity of the larger muscles to stiffen or stabilize the segments, especially in functional midranges.

Previous studies have demonstrated a loss of strength and endurance in the neck flexor synergy in patients with neck pain. [11-14] Because of the functional differentiation in the neck flexors, the craniocervical flexion test was developed as an indirect measure for the clinical evaluation of the deep cervical flexor muscles and the longus capitus and colli muscles. [3] The craniocervical flexion test, which is performed in supine lying, involves the two main actions of these deep cervical muscles, i.e., upper cervical flexion and slight flattening of the cervical spine. [6, 15, 16] Previous research has demonstrated significantly inferior performance on the craniocervical flexion test in patients with traumatic and nontraumatic origin neck pain, [3, 4] characterized by a lesser ability to increase and hold progressively inner range positions of craniocervical flexion (monitored by an air-filled pressure sensor placed behind the neck to detect progressive flattening of the cervical lordosis with the longus colli contraction [6]). This was concomitant with increased electromyographic (EMG) activity in the superficial cervical flexors. Although this infers a deficit in the deep cervical flexor muscles, [4] as yet there has been no direct quantification of deep cervical flexor muscle activity in a patient population. However, recording from deep cervical flexor muscles has been problematic. Recent studies using surface electrodes inserted via the nose and fixed to the oropharynx with suction have demonstrated increasing deep cervical flexor muscle EMG activity with progressive stages of the craniocervical flexion test in asymptomatic patients. [17] The purpose of the present study was to compare deep and superficial cervical flexor muscle activity and craniocervical flexion range of motion (ROM) across the five stages of the craniocervical flexion test between patients with chronic neck pain and asymptomatic controls.

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Discussion

The present study supports the proposal that decreased performance of the craniocervical flexion test is related to impaired performance of the deep cervical flexor muscles. These data confirm that activity of the deep cervical flexor muscles is modified in the present sample of individuals with chronic neck pain and argue that this may be associated with increased activity of the superficial neck muscles.

      Methodologic Considerations

The craniocervical flexion test was designed to assess the activation capacity of the deep cervical flexor muscles. [3, 4] Data from the present study are consistent with previous findings that indicate an incremental increase in deep cervical flexor EMG amplitude across the five stages of the craniocervical flexion test [17] and the concomitant increase in craniocervical flexion. [22]

The reference voluntary contraction of combined craniocervical and cervical flexion selected for normalization of EMG amplitude was not a true maximum voluntary contraction. As such, comparisons between the amplitude of deep and superficial cervical flexor muscle activation must be made with caution. Recording of deep cervical flexor muscle activation involved a novel EMG technique for the assessment of the deep cervical flexor muscles. In a previous study that evaluated this technique, [17] EMG amplitude from the deep cervical flexor muscles increased in the absence of superficial cervical flexor muscle activation. This observation provided greater confidence that cross talk from the superficial cervical flexor muscles was of minimal concern and helped to verify the accuracy of this technique. However, further research remains necessary to ensure cross talk from other nearby muscles, such as the submandibular muscles, do not bias the results. Given the location of the electrode and the small interelectrode distance incorporated in the electrode design, there is confidence that the majority of signals detected are from the longus colli and longus capitis muscles. The low impedance associated with detection over a mucosal surface and fixation of the electrodes with suction further assured the quality of the myoelectric signals obtained. Other techniques have been used to record EMG via mucosa, such as recordings made from the crural fibers of diaphragm through the esophageal wall. [23] Problems associated with movement of the electrode that have been reported with that technique are avoided in the present setup by fixation of the electrode with suction. The authors’ new EMG recording technique has now been applied successfully in multiple investigations. The procedure was well tolerated by all patients, and no side effects associated with the technique or anesthetic were reported.

      Impairment of the Craniocervical Flexion Test

The methods used in the present study were laboratorybased measures and were therefore limited to a small sample of patients. However, previous clinical research has demonstrated significantly inferior performance on the craniocervical flexion test in patients with idiopathic neck pain and with neck pain after a whiplash injury. [2-4] Furthermore, impaired performance on the craniocervical flexion test has been identified in both the acute [24] and chronic phases [3, 4] of neck pain and is not associated with fear avoidance. [24] In general, neck pain patients had reduced ability to reach and maintain the targets of pressure in the cuff under the cervical spine. Furthermore, surface EMG recordings of the superficial flexors indicated that this was associated with significantly higher EMG amplitude in the superficial neck flexors compared with asymptomatic controls. [4] This was hypothesized to be related to impaired performance of the deep cervical flexor muscles and even represent a strategy to compensate for dysfunction of the deep cervical flexor muscles. [4] The direct recordings from the deep cervical flexor muscles in the present study support this hypothesis, as there was a trend for deep cervical flexor EMG activity to be reduced at all stages of the craniocervical flexion test, with a significant between-group difference at the higher stages of the test (28–30 mm Hg).

A trend was present to suggest greater normalized 1-second RMS values from the sternocleidomastoid and anterior scalene muscles bilaterally in the patients with neck pain compared with control group patients, although the difference was not significant. The smaller sample size used in the present initial investigation compared with the study by Jull [4] may account for the lack of statistical significance, in consideration of the large variation of normalized 1-second RMS values for the sternocleidomastoid and anterior scalene muscles within the neck pain group.

The conflicting changes in deep and superficial muscles of the neck are consistent with findings for other regions of the body. For instance, there is increasing data to indicate that activity of the deep muscles of the lumbar spine, such as transversus abdominis [25, 26] and lumbar multifidus, [27] is impaired in individuals with low back pain. Numerous studies suggest that individuals with low back pain have increased activity of superficial muscles, such as the erector spinae, during gait [28] and at the end of range of trunk flexion. [29, 30] Furthermore, when load is removed from the trunk, coactivation of the superficial trunk muscles is increased. [31] In line with the pain-adaptation model, [32] this has been argued to represent a strategy to restrict motion of the spine. Consistent with the variability identified in the present study, previous data indicate that there may be considerable variation in the specific muscles that have increased activity. [33]

Neck pain patients also performed less craniocervical flexion ROM to reach each pressure target of the craniocervical flexion test. This finding suggests that the pressure increase in the cuff under the cervical spine of neck pain patients was induced by a different movement strategy. For example, this may be because of efforts to push the head and neck back into the pressure sensor by neck retraction. This raises several important questions. First, is the change in strategy due to impaired performance of the deep muscles (either weakness or reduced activation) or is it due to increased activity of the superficial muscles? Second, what is the mechanism for the change in muscle activity? Third, does the change precede or follow the onset of neck pain? Further studies are required to clarify these issues. However, the data can be used clinically in that they support the clinical guideline to observe the quality of the movement and note any excess activity of the superficial muscles in their analysis of patient performance.

      Clinical Implications

Testing and retraining the cervical flexor synergy as a component of a specific active stabilization program for the cervicobrachial region is now used widely in clinical practice in the treatment of patients with various neck pain syndromes. To date, the efficacy of this specific exercise approach has been established in a recent clinical trial in patients with cervicogenic headache. [2] In that study, the specific muscle retraining led to a reduction in the frequency and intensity of headaches and a reduction in the scores on the Northwick Park Neck Pain Questionnaire, which was associated with improved performance on the craniocervical flexion test. The present data indicate that the changes in performance of craniocervical flexion test and clinical improvement may be because of changes in the deep cervical flexor muscles. Further investigation of changes in deep cervical flexor function with this specific exercise training is warranted in a variety of neck pain conditions.

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Conclusion

Differences in the contributions (normalized 1-second RMS values) of the deep and superficial neck flexors were demonstrated between patients with neck pain and control group patients when the staged craniocervical flexion test was performed, although with the limited sample size, differences were not consistently statistically significant for the superficial muscles. Nevertheless, lower EMG amplitudes in the deep cervical flexor muscles were associated with higher values in the superficial muscles, which suggests that patients with neck pain use an altered muscle

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Key Points

• Research indicates individuals with neck pain have an inferior ability to increase
  and hold progressively inner range positions of craniocervical flexion. This has
  been hypothesized to reflect dysfunction of the deep cervical flexor muscles.

• This study provides data to support the proposal that decreased performance of the
  craniocervical flexion test is related to impaired performance of the deep cervical
  flexor muscles.

• The present data indicate that the changes in performance of craniocervical flexion
  test and clinical improvement in individuals with neck pain may be due to changes in
  the deep cervical flexor muscles.

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