Neck Solutions

Impairment in the cervical flexors: a comparison of whiplash and insidious onset neck pain patients

From: Man Ther. 2004 May;9(2):89-94

Neck pain is a common condition causing substantial personal and financial costs. Broadly, onset may be insidious or may follow trauma. Pain is often persistent or recurrent in nature. Neck pain of traumatic origin following a motor vehicle crash (whiplash) often poses a particular challenge in management. There are several influences that may impact on the perception of neck pain and disability in persons with whiplash associated disorders compared to those with an insidious onset of neck pain. These include the magnitude of the injury, psychological responses to injury and pain, social factors and litigation. There has been little investigation into whether or not differences exist in the nature of physical impairment associated with neck pain of whiplash and insidious origins which may contribute to the greater difficulty often encountered in the rehabilitation of patients with whiplash associated disorders.

Changes in cervical flexor muscle function have been investigated in neck disorders of both whiplash and insidious origins. Vernon et al. in an initial comparative study of neck isometric strength and flexor/extensor strength ratios, found that subjects with both whiplash associated disorders and insidious onset neck pain had lesser strength than asymptomatic subjects. There was a progressive anterior-to-posterior muscle imbalance in the neck pain subjects, with the cervical flexors becoming relatively weaker as compared to the extensors. This was more apparent in subjects with whiplash associated disorders, suggesting that there could be a difference in the degree of impairment between these subject groups.

Cervical flexor muscle function has also been examined using the cranio cervical flexion test. The cranio cervical movement aims to assess the anatomical action of longus capitis in synergy withlongus colli, rather than that of the superficial flexors, sternocleidomastoid and anterior scalene muscles,which flex the neck but not the head. The longus colli muscle has a unique role in the support of the cervical segments and curve. In the cranio cervical neck flexion test, the subject performs five incrementsof increasingly inner range cranio cervical flexion in a supine lying position. Patients are guided to the test level by feedback from apressure unit which isplaced behind the neck to monitor the progressive flattening of the cervical lordosis which results from the contraction of longus colli. Performance in the test has been examined in subjects with whiplash associated disorders and cervicogenic headache. The results of these studies indicated that patients were less able to achieve and hold the progressive positions of the test as compared to the respective control subjects. These results inferred dysfunction in the deep neck flexors, as no direct measure of these muscles could be made. In the study of subjects with whiplash associated disorders and in a study ofpatients with chronic neck pain, amplitudes of muscle signals (electromyography, EMG) were measured in the sternocleidomastoid during the test, following Cholewicki et al.’s hypothesis that increased activity of the superficial muscles could be a measurable compensation for poor segmental stability,or in this case of the cranio cervical neck flexion test, poorer activation of the longus colli. It was shown that both neck pain patient groups had higher amplitudes of muscle signals in the sternocleidomastoid.

There has not been a direct comparison of performance in the cranio cervical neck flexion test between patients with neck pain from whiplash and insidious origin. This study was undertaken to make this comparison. A clinically applicable version of the cranio cervical neck flexion test was used. Dysfunction in the neck flexor muscles has been found to be associated with neck pain of both whiplash and insidious origins. However there has been little investigation into whether or not differences exist between the groups which might impact on the rehabilitation process.

The results of this study revealed a strong linear relationship between the magnitude of the sternocleidomastoid normalized RMS values and each progressive stage of the test for all groups but there were higher levels of sternocleidomastoid normalized RMS values in the neck pain and whiplash groups in all stages of the cranio cervical neck flexion test compared to the asymptomatic control group. This is in accord with the findings of previous studies of subjects with whiplash associated disorders and insidious onset neck pain. No significant differences were evident between the neck pain and whiplash associated disorders groups indicating that this physical impairment or altered pattern of muscle coordination is common to neck pain of both whiplash and insidious origin and would not seem to be a reason why patients with chronic whiplash associated disorders often are more challenging to treat than patients with insidious origin neck pain.

Cranio cervical flexion is the action of longus capitis in synergy with longus colli. The presence of progressively increasing sternocleidomastoid normalized RMS values in each test stage in all subject groups suggests that these muscles were recruited to further stabilize the neck as the contractile demand of the longus capitis increased inthe inner ranges of cranio cervical flexion. The presence of higher sternocleidomastoid normalized RMS values in the neck pain groups infers that altered patterns of co-ordination maybe present between the deep and superficial flexor muscles in patients with neck pain, and this higher activity may be a measurable compensation for poorer active contractile capacity of the longus colli and capitis muscles. The clinical version of the cranio cervical neck flexion test used in this study has the deficit of no direct measure of the activity of longus capitis and colli. The muscles are deep and not accessible for use of conventional surface EMG.

Falla et al. used a novel surface EMG electrode in a laboratory version ofthe cranio cervical neck flexion test. A bipolar surface electrode was inbuilt intoa nasopharageal suction catheter and the electrode was inserted via the nasal passage and suctioned onto theback of the throat adjacent to the uvula, over the longuscapitis and colli. In their study on asymptomatic subjects, they demonstrated a stronger linear relationship between the amplitude of the deep neck flexor muscle signal and the increasing incremental stages of the test, which confirms anatomical predictions for the test. In a further study of 10 neck pain and 10 controlsubjects, Falla et al. again demonstrated a strong linear relationship between the EMG amplitude of the deep neck flexor muscles and the incremental stages of the cranio cervical neck flexion test for both control and neck pain subjects. However, the amplitude of deep neck flexor EMG was less in the neck pain group than for the control group and the difference was significant for the higher levels of the test. Although not significant, there was a strong trend for greater EMG activity in the sternocleidomastoid and anterior scalene muscles in the neck pain group. These findings lend support to the contention that the higher levels of sternocleidomastoid normalized RMS values measured in all stages of the cranio cervical neck flexion test in our study of neck pain patients as compared to the control subjects may reflect a compensation strategy for poorer contractile capacity of the deep cervical flexors. Further study on larger sample sizes to better understand the compensation strategies in the cranio cervical neck flexion test as well as their sensitivity and specificity to neck pain patients is warranted.

The pressure unit, which is inserted behind the neck inthe cranio cervical neck flexion test, monitors the slight flattening of the cervicalspine accompanying the contraction of the longus colli. The results of the differences between the pressure target and that attainedby the subjects in this study revealed that the controlgroup could quite accurately perform and control the cranio cervical flexion action to the designated pressuresof each task. In contrast, both neck pain groups demonstrated larger pressure shortfalls at all stages ofthe cranio cervical neck flexion test. This again would infer poorer active contractile capacity of the longus colli to flatten thecervical curve, particularly in the latter three stages ofthe test. At the 30mmHg stage of the test, the whiplash associated disorders group had a particularly large shortfall indicating that many of the subjects could not perform this stage of the test. This was associated with a levelling off of the EMG normalized RMS values in the whiplash associated disorders group at the test stage. Thus the results of the study show that the neck pain groups of both insidious and whiplash origin have difficulty attaining the pressure targets of the test and in association they both exhibit higher normalized RMS values in the sternocleidomastoid, indicating similar impairment in the neck flexor synergy.

The neck pain groups were of similar age and gender and reported similar levels of pain associated with their condition, although the insidious onset neck pain grouphad a longer history of their condition than the whiplash group. These differences in length of history did not impact on results. Similar findings of the lack of effect of length of history were reported by Nederhand et al. in their study of muscle activation patterns of upper trapezius in patients with whiplash associated disorders and patients with chronic nonspecific neck pain. These authors concluded that cervical muscle dysfunction was apparently not related to a specific traumatic injury as was also found in this study. Thus these changes in musclefunction appear not to be time dependent beyond acertain point and the common factor may be the presence of pain.