Bilateral Asymmetry of Semispinalis Capitis Muscle Thickness and Neck Motion During Prone Neck Extension in Subjects with Unilateral Posterior Neck Pain

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J. Phys. Ther. Sci. 25: 37–40, 2013 Bilateral Asymmetry of Semispinalis Capitis Muscle Thickness and Neck Motion during Prone Neck Extension in Subjects with Unilateral Posterior Neck Pain

Kyue-nam Park, MS, PT1), Oh-yun Kwon, PhD, PT2), Sung-dae Choung, MS, PT1), Si-hyun Kim, MS, PT1)

1) Department of Rehabilitation Therapy, Graduate School, Yonsei University 2) Department of Physical Therapy, Kinetic Ergocise Based on Movement Analysis Laboratory, College of Health Science, Yonsei University: 234 Maiji-ri, Heungup-myon, Wonju-si, Kangwon-do, 220-710, Republic of Korea. TEL: +82 33-760-2721, FAX: +82 33-760-2496, E-mail: [email protected]

Abstract. [Purpose] This study compared the bilateral thicknesses of the semispinalis capitis muscle and neck motions between subjects with and without unilateral posterior neck pain (UPNP). [Subjects] The study recruited 20 young subjects with UPNP at the end-range of neck extension and 20 age- and sex-matched subjects without neck pain as a control group. [Methods] The bilateral thicknesses of the semispinalis capitis in a relaxed prone position were measured bilaterally using ultrasonography. A three-dimensional motion-analysis system was used to measure the asymmetry of neck motions at 45° of prone neck extension. [Results] We found that the asymmetry of the semispinalis capitis muscle was greater in the UPNP group than in the controls. Neck rotation to the painful side and lateral bending to the non-painful side were greater in the UPNP group at 45° of prone neck extension than in the controls. [Conclusion] Asymmetric thickness of the semispinalis capitis muscles might be the cause of asymmetric neck motions in subjects with UPNP. Key words: Asymmetry, Muscle thickness, Neck motion (This article was submitted Aug. 9, 2012, and was accepted Sep. 14, 2012)

INTRODUCTION muscle is ambiguous. Therefore, ultrasonography is valid for measuring the thickness, but not the width or cross- The cervical paraspinal muscles play an important role in sectional area, of the cervical multifidus and semispinalis neck extension, maintaining the lordotic curve of the cervical capitis muscles12, 13). Previous studies have demonstrated spine1). The cervical paraspinal muscles also contribute to that bilateral symmetry is seen in ultrasound images of the proprioception of head and neck movements2), and postural posterior neck muscles of healthy subjects and patients with balance while standing3). To improve the performance of bilateral neck pain7, 11). the cervical paraspinal muscles, neck extension exercises Asymmetry of the paraspinal muscles has been reported in the sitting or prone position are often advocated in the in unilateral spinal pain14). In patients with unilateral back management of patients with mechanical neck pain4). Neck pain, a reduction in muscle cross-sectional area, i.e., atrophy extension exercises are effective at increasing the size of the of the multifidus or psoas major, ipsilateral to the side of cervical paraspinal muscles in patients with mechanical neck pain has been demonstrated15–17). Unless the atrophic pain5). multifidus muscle is worked with specific exercises, the The size of the cervical paraspinal muscles is measured decreased muscle size will not recover in patients with when evaluating muscle function and provides a basis for unilateral back pain18). In addition to the lumbar paraspinal therapeutic interventions in patients with chronic neck muscles, asymmetry of the cervical paraspinal muscles has pain6–8). Measuring the size of the cervical paraspinal been demonstrated in patients with unilateral posterior neck muscles is considered an objective method of estimating pain (UPNP)19). The semispinalis capitis muscle was smaller indirect strength9–11). Ultrasonography is commonly used on the painful side than on the non-painful side in ultrasono- to assess muscle size, including the atrophy and symmetry graphic images of patients with UPNP or migraine13, 19, 20). of the cervical paraspinal muscles11, 12). A previous study Although a previous study found that semispinalis capitis suggested that an obscure outline of the fascial layer in ultra- thickness was asymmetrical in patients with UPNP19), no sound images was a diagnostic feature of muscle atrophy8). study has determined whether the asymmetric thickness However, the cervical muscle is smaller than the lumbar of the semispinalis capitis influences neck motion during spine, and the lateral boundary of the deep posterior neck prone neck extension in subjects with UPNP. Therefore, we 38 J. Phys. Ther. Sci. Vol. 25, No. 1, 2013 compared the bilateral thicknesses of the cervical paraspinal used to measure concurrent neck rotation and lateral bending muscles in the relaxed prone position, and neck motions during prone neck extension24). A triple-active marker was while performing prone neck extension between a UPNP fixed to the back of the subject’s head with a specially and control groups. We hypothesized that there would be designed headband. The transducer sensor was placed above greater asymmetry of muscle thickness and neck motions in the back of the head to measure the concurrent neck motions subjects with UPNP than in the control group subjects. during prone neck extension. Before recording the concurrent neck motions, the head and neck in the prone position were SUBJECTS AND METHODS calibrated to zero as reference positions relative to a neutral head position. The neutral head position was defined as the This study recruited 20 subjects with UPNP from among position without rotation, lateral flexion, or exaggerated graduate students of Yonsei University, Korea (Table 1). cervical lordosis4). The sampling rate was 20 Hz. A belt The inclusion criteria for selecting subjects with UPNP was fastened around the upper thoracic region to prevent were that the subjects had UPNP at the end-range of active thoracic extension while performing prone neck extension. neck extension and passive neck extension with rotation The subjects were asked to perform prone neck extension to one side in the sitting position21, 22). The peak intensity comfortably to 45° with their eyes open and to maintain of the UPNP in this study exceeded 50 mm on a 100-mm this position for 5 seconds. A fixed target bar was placed at visual analogue scale (VAS) when performing active neck the level of 45° of prone neck extension. The subjects were extension and passive neck extension with rotation in the instructed to perform prone neck extension while viewing sitting position. The average pain intensity of the neck the bar in front of their face until their head touched the target exceeded 30 mm VAS during the past 6 weeks23). Subjects bar. Neck motion data were recorded while the subjects held with bilateral posterior neck pain or those who were unable 45° of prone neck extension. Data of the middle 3 seconds to perform prone neck extension to 45° due to UPNP, of the 5-second measurement were used in the analysis25). migraine, or dizziness were excluded. The mean value of three trials was calculated to determine Twenty age-, sex-, and weight-matched healthy subjects the range of concurrent neck motions at the targeted angle of were recruited as a control group from among graduate active prone neck extension. students of Yonsei University. Inclusion criteria for The independent t-tests was performed to compare the selecting control subjects were the ability to perform prone difference in the bilateral thicknesses of the semispinalis neck extension to 45° and no history of past or present neck capitis muscles in the relaxed prone position, and neck pain, migraine, neurological, or orthopedic problems. Before motions during prone neck extension between the UPNP this study, the principal investigator explained all of the and control groups. The paired t-test was used to compare procedures to the subjects in detail. All subjects signed an the thicknesses of the painful and non-painful sides of the informed consent form approved by the Yonsei University semispinalis capitis muscles within the subjects with UPNP. Faculty of Health Sciences Human Ethics Committee. Statistical significance was accepted for values of p < 0.05. To measure the bilateral thicknesses of the semispinalis Data are expressed as the mean and standard deviation (SD). capitis muscles, each subject was scanned by a SonoAce Statistical analyses were performed using SPSS 12.0.1 X4 ultrasound scanner with a 7.5-MHz linear array trans- software (SPSS, Chicago, IL). ducer. The subjects were asked to assume a relaxed prone position with a pillow under their chest and abdomen to RESULTS maintain a straight lumbar and thoracic spine. To enable them to breathe during the ultrasonographic measurement, The mean difference in the bilateral muscle thicknesses we placed a doughnut-shaped air cushion with a hole for the of the semispinalis capitis muscle was significantly greater nose and mouth under the subject’s head. The head and neck in subjects with UPNP (p<0.05) (Table 2). Within the UPNP were positioned neutrally when viewing the subject from the group, the muscle thickness on the painful side was signifi- side13). The subject’s arms were placed symmetrically on cantly smaller than that on the non-painful side (0.46 ± 0.12 the table at 90° of shoulder abduction. After applying warm vs. 0.58 ± 0.12 cm; p<0.05). gel to both sides of C3, the ultrasound probe was positioned The range of neck rotation toward the painful side and with its long axis in the transverse plane. The spinous lateral bending toward the non-painful side at 45° of prone process of the C3 vertebra was identified as the midline and neck extension were significantly greater in the UPNP group the probe was moved laterally so that the vertebral lamina than in the control group (p<0.05) (Table 3). and separating fascia were clearly visible. The image was then frozen on the monitor. The thicknesses of both semispi- DISCUSSION nalis capitis muscles were analyzed at the greatest depth from the dorsal to the ventral boundary of the muscle1). The This study investigated whether asymmetric thickness of intra-rater reliability of the ultrasound measurement of the the semispinalis capitis influences neck motion during prone posterior neck muscles was previously shown to be high; the neck extension in subjects with UPNP. We demonstrated intraclass correlation coefficient for the semispinalis capitis that subjects with UPNP had asymmetric thicknesses of was 0.98–0.9911). the semispinalis capitis and performed asymmetrical neck A three-dimensional ultrasonic motion-analysis system motions, including neck lateral bending and rotation during (CMS-HS) (Zebris Medizintechnik, Isny, Germany) was prone neck extension. To our knowledge, this is the first 39

Table 1. Descriptive data of the participants Table 2. Comparison of mean percentage difference of thickness between bilateral semispinalis capitis in each group UPNP group Control group Parameter (N=20) (N=20) UPNP group Control group Mean ± SD Mean ± SD Muscle (N=20) (N=20) Gender (male/female) 10/10 10/10 Mean ± SD (%) Mean ± SD (%) Age (years) 23.4 ± 1.9 23.4 ± 2.1 Semispinalis capitis 26.78 ± 15.18 a 2.57 ± 2.97 a Body mass (kg) 66.8 ± 8.4 65.5 ± 9.4 a p<0.05 Height (cm) 173.4 ± 5.8 172.8 ± 6.9 Visual analog scale (mm) 60.5 ± 7.7 None

Table 3. Comparison of range of neck motion between the two groups during prone neck extension

UPNP group (N=20) Control group (N=20) Motion Mean ± SD Mean ± SD End range (degrees) End range (degrees) Neck rotation 3.95 ± 4.13 a (Non-painful side) 1.51 ± 2.95 a Neck lateral bending –4.36 ± 5.61 a (Painful side) –1.22 ± 2.67 a a p<0.05

study to show that subjects with UPNP have an asymmet- However, unilateral contraction of the semispinalis capitis rical movement pattern during active prone neck extension, induces neck extension with ipsilateral lateral bending1). as well as asymmetrical thickness of the semispinalis capitis. In addition to unilateral contraction of the semispinalis Consistent with previous results, the bilateral asymmetry capitis muscle, concurrent lateral bending during prone of the semispinalis capitis thickness was greater in the UPNP neck extension occurred toward the hypertrophic semispi- group than in the control group19). The marked bilateral nalis capitis (non-painful) side of subjects with UPNP. It is asymmetry of the posterior neck muscle thickness may possible that the semispinalis capitis on the hypertrophic side indicate pathology in the neck11). Pain-related fear of neck is more likely to be activated than the atrophic side via reflex movement is a possible reason for the asymmetry of the inhibition14, 30), resulting in lateral neck bending toward the muscle thickness2). Hodges26) demonstrated that pain due to hypertrophic side during prone neck extension in the UPNP lumbar injury in a porcine model induced a rapid reduction group. The concurrent neck rotation toward the side opposite in the muscle size and atrophy of the lumbar multifidus. that of lateral bending may be induced by the biomechanical Danneels14) suggested that low back pain inhibits the trunk properties of the neck. According to Feipel31), the direction stabilizing muscles via both reflex inhibition and changes of coupled rotation and lateral bending is ipsilateral in the in the coordination of the stabilizing muscles. Prolonged lower cervical spine and contralateral in the upper cervical or repetitive disuse due to pain or reflex inhibition induces spine. Contralateral coupling in the upper cervical levels is muscle atrophy as muscular adaptation27, 28). UPNP may lead necessary to maintain the head in an erect position31). In our to disuse of the semispinalis capitis muscle on the painful side study, subjects with UPNP carefully performed prone neck due to neck pain-related fear during prone neck extension2). extension with an erect head along the straight line in front In contrast, the muscle on the non-painful side is likely to of their face. Maintaining the head in an erect position may become hypertrophic relative to the painful side. Dangaria result in contralateral coupling between neck rotation and and Naesh15) suggested that unilateral hypertrophy on the lateral bending in the upper cervical spine during prone neck non-painful side of the psoas major muscle is due to overuse extension. in patients with lower back pain, resulting in compensatory It remains to be determined whether the asymmetry hypertrophy. Repeated and sustained contraction of the of muscle thicknesses while resting and neck motion non-painful side might induce hypertrophy compared to the during prone neck extension causes UPNP or if the UPNP thickness of the painful side in subjects with UPNP28). triggers the asymmetry. Due to the cross-sectional design Repeated asymmetric movements of the neck can give of the current study, causation could not be determined. A rise to asymmetric stress on the unilateral facet joints29). longitudinal study is needed to clarify the cause and effect Our present study demonstrated there was greater neck relationship between UPNP and the asymmetry of muscle motion asymmetry, including a greater range of concurrent thicknesses and neck motions. However, it is clear that prone neck lateral bending toward the non-painful side and neck neck extension exercises should be performed symmetrically rotation toward the painful side, during prone neck extension with minimal motion in both the transverse and frontal planes in the UPNP group than in the controls. The actions of the with the symmetrical use of the bilateral semispinalis capitis semispinalis capitis muscle include neck extension, in muscles in patients with UPNP. The results of this study can which the semispinalis capitis muscles contract bilaterally1). be applied to the management of patients with UPNP for the 40 J. Phys. Ther. Sci. Vol. 25, No. 1, 2013 selective activation of the atrophied semispinalis capitis and 83–88. [Medline] [CrossRef] 9) Mayoux-Benhamou MA, Wybier M, Revel M: Strength and crosssectional to minimize asymmetric neck motions during prone neck area of the dorsal neck muscles. Ergonomics, 1989, 32: 513–518. [Medline] extension exercise. 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