Original ArticleReliability of ultrasonography for the cervical multifidus muscle in asymptomatic and symptomatic subjects☆
Introduction
Research has shown that ultrasonography can be used to precisely evaluate muscle dimensions both on the appendicular (Stokes and Young, 1986; Kelly and Stokes, 1993) and the axial skeleton ([19], [20]; Emshoff et al., 1999). Among the imaging modalities it is the most cost-effective and feasible method for measurements of the muscular tissue. The muscles are visualized in real-time and measurements can be obtained in a relaxed state and in different states of contraction as well as during movements (Harcke et al., 1988; Rezasoltani et al., 2002). Ultrasonography has been used as a diagnostic tool for the lumbar multifidus (Hides et al., 1995) and is now also used as a biofeedback method for recruiting the deep muscles in the lumbo-pelvic region (Richardson et al., 1999). Due to the load differences between the cervical and lumbar spine, the cervical multifidus is a much smaller muscle than its counterpart in the lumbo-sacral region. It may therefore be more difficult to identify the cervical multifidus muscle.
Recent research into the passive integrity of the cervical spine has demonstrated that women with chronic whiplash associated disorders (WAD), grade II, have a different configuration of the cervical lordosis from asymptomatic women (Kristjansson and Jónsson, 2002). The relatively increased lordosis in the upper cervical spine and diminished lordosis in the lower cervical spine observed in this patient group are of great clinical importance (Kristjansson and Jónsson, 2002). Interestingly, the same pattern was found in the whole study sample of 100 young asymptomatic subjects when a heavy experimental load was imposed on the cervical spine (Ingelmark, 1942). The altered configuration of the cervical lordosis in this experimental study, conducted 60 years ago, strongly indicates that this pattern was due to increased muscle activity of the superficial torque-producing muscles and the incapability of the tonic deep segmental cervical muscles to maintain the cervical alignment under such great load conditions. One explanation for the altered configuration of the cervical lordosis in patients with WAD may therefore be muscle imbalance due to overactive superficial muscle and/or the diminished holding capacity of the deep cervical muscles.
Another recent study exploring sagittal plane segmental motion, conducted on the very same study sample as the above study on the configuration of the lordosis, (Kristjansson and Jónsson, 2002) found a subgroup of WAD patients who exhibited increased sagittal plane segmental motion of the mid-cervical segments (Kristjansson et al., 2003). The compromise on the passive integrity of the mid-cervical segments and kyphotic alignment at the C4-level in some WAD patients, grade II, indicates that the passive load-bearing capacity of the mid-cervical spine may be reduced (Kristjansson and Jónsson, 2002; Kristjansson et al., 2003). The relatively increased lordosis in the upper cervical spine in WAD patients, grades II, may therefore be a compensatory mechanism reflecting an attempt by the body to bear the weight of the head under these circumstances (Kristjansson and Jónsson, 2002). The compromises to the passive integrity of the cervical spine may be the primary source of dysfunction in these patients, and the aforementioned muscle imbalance in the cervical spine may develop secondarily to pain, further increasing the dysfunctional state of these patients.
Cumulative evidence suggests that the deeper muscles are better suited to producing fine graded reflex mediated muscle stiffness than the more superficial muscles (Sjölander et al., 2002). It has recently been suggested that scaling muscle spindle counts to a motor unit number may better represent the sensitivity of the γ muscle spindle system (Boyd-Clark et al., 2002). Moreover, the distribution of the spindles seems to be strategically arranged for a particular function. New evidence shows that the longus colli muscle has significantly greater spindle density than the multifidus in the same cervical region, but the multifidus comprises a greater proportion of Type I fibres. The muscle spindles of this muscle pair are also arranged differently ([3], [4]). This might reflect the different functional requirements of these muscles i.e. the longus colli may act more as a balancer of the cervical lordosis (Mayoux-Benhamou et al., 1994) while the cervical multifidus acts as a segmental adjuster (Conley et al., 1995).
A measure of cervical multifidus size is an important indicator for whether the muscle is capable of performing its important segmental stabilizing functions. The purpose of this study was to assess whether ultrasonography can be used to reliably depict the size of the cervical multifidus in asymptomatic and symptomatic subjects. The shape ratio was also measured to be able to, in future research, to compare the geometry of the multifidus muscle with the geometry obtained of the cervical multifidus muscle by other imaging modalities.
Section snippets
Subjects
The participants included 10 asymptomatic women and 10 women with chronic WAD, grade II, according to the Quebec task force classification of WAD (Spitzer et al., 1995). The women were matched according to age, weight and height to minimize the effect of these factors may have on actual muscle size in different individuals (Table 1). The asymptomatic women were a sample of convenience from university students who had no previous history of neck pain or injury. The women in the chronic WAD group
Results
The subjects’ characteristics are presented in Table 1. The descriptive results of the measurements of the cervical multifidus muscle at the C4-level are summarized in Table 2. The mean difference between groups was 0.23 cm2 (95% confidence interval, 0.13 – 0.33). The Mann–Whitney U-test revealed that this difference was significant (P=0.03). The shape ratio was similar between groups and sides (Table 2). The plots of the CSA trials performed within days and between the left and the right sides
Discussion
The results of this study indicate that the ultrasonography protocol used in this study is reliable in detecting the size of the cervical multifidus muscle at the C4-level in asymptomatic subjects (Table 3). For the symptomatic group, the intra-tester agreement was acceptable (Table 3) but the inter-tester agreement was questionable (Table 3). This is apparent when the limit of agreement (Table 3) is compared to the standard deviations of the measurements (Table 2) and the 95% confidence
Conclusion
Therapists can use ultrasonography to depict the size of the cervical multifidus muscle at the C4-level by following a strict measurement protocol. The lack of agreement for the symptomatic group in this study was due to loss of clarity of the fascial layer between the semispinalis cervicis and the multifidus muscles. This is probably a diagnostic sign of muscle atrophy that can be used as an indicator of whether treatment interventions are successful in building up the size of the cervical
Acknowledgements
The author would like to thank radiologist Pálmar Hallgrı́msson for his participation in this study and Sandra Eaton M.A., M.Ed. for grammatical corrections to the manuscript.
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This study was conducted at an outpatient physiotherapy research clinic.