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

Abstract

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 origin. This study examined the neck flexor synergy during performance of the cranio-cervical flexion test, a test targeting the action of the deep neck flexors.

Seventy-five volunteer subjects participated in this study and were equally divided between Group 1, asymptomatic control subjects, Group 2, subjects with insidious onset neck pain and Group 3, subjects with neck pain following a whiplash injury. The cranio-cervical flexion test was performed in five progressive stages of increasing cranio-cervical flexion range. Subjects’ performance was guided by feedback from a pressure sensor inserted behind the neck which monitored the slight flattening of the cervical lordosis which occurs with the contraction of longus colli. Myoelectric signals (EMG) were detected from the muscles during performance of the test.

The results indicated that both the insidious onset neck pain and whiplash groups had higher measures of EMG signal amplitude (normalized root mean square) in the sternocleidomastoid during each stage of the test compared to the control subjects (all P<0.05) and had significantly greater shortfalls from the pressure targets in the test stages (P<0.05). No significant differences were evident between the neck pain groups in either parameter indicating that this physical impairment in the neck flexor synergy is common to neck pain of both whiplash and insidious origin.

Introduction

Neck pain is a common condition causing substantial personal and financial costs (Côté et al., 1998; Holmstrom et al., 1992). 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 (WAD) 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 (Côté et al., 2001; Radanov and Sturzenegger, 1996). 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 WAD.

Changes in cervical flexor muscle function have been investigated in neck disorders of both whiplash and insidious origins. Vernon et al. (1992) in an initial comparative study of neck isometric strength and flexor/extensor strength ratios, found that subjects with both WAD 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 WAD, 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 (C-CFT) (Jull, 2000). The cranio-cervical movement aims to assess the anatomical action of longus capitis in synergy with longus colli, rather than that of the superficial flexors, sternocleidomastoid (SCM) 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 (Mayoux-Benhamou et al., 1994). In the C-CFT, the subject performs five increments of increasingly inner range cranio-cervical flexion in a supine lying position (Falla et al., 2003a; Jull, 2000). Patients are guided to the test level by feedback from a pressure unit (Stabilizer, Chattanooga, USA) which is placed behind the neck to monitor the progressive flattening of the cervical lordosis which results from the contraction of longus colli (Mayoux-Benhamou et al. (1994), Mayoux-Benhamou et al. (1997)). Performance in the test has been examined in subjects with WAD (Jull, 2000) and cervicogenic headache (Jull et al., 1999). 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 WAD (Jull, 2000) and in a study of patients with chronic neck pain (Sterling et al., 2001), amplitudes of muscle signals (electromyography, EMG) were measured in the sternocleidomastoid (SCM) during the test, following Cholewicki et al.'s (1997) hypothesis that increased activity of the superficial muscles could be a measurable compensation for poor segmental stability, or in this case of the C-CFT, poorer activation of the longus colli. It was shown that both neck pain patient groups had higher amplitudes of muscle signals in the SCM.

There has not been a direct comparison of performance in the C-CFT between patients with neck pain from whiplash and insidious origin. This study was undertaken to make this comparison. A clinically applicable version of the C-CFT was used.