Effect of the craniocervical brace on craniocervical angle,thoracic kyphosis angle,and trunk extensor muscle activity during typing in subjects with forward head posture

Abstract

BACKGROUND: The relationship between forward head posture (FHP) and thoracic kyphosis has been a subject of interest in the rehabilitation field for visual display terminal workers.

OBJECTIVE: The aim of this study was to investigate the immediate effects of the craniocervical brace use on craniocervical angle (CCA), thoracic kyphosis angle (TKA), and trunk extensor muscle activity.

METHODS: Twelve young male subjects with forward head posture (21.6±1.9 years) participated in this study. We compared CCA & TKA and trunk extensor muscle activity between with and without application of the craniocervical brace during visual display terminal work.

RESULTS: When wearing the craniocervical brace, the subjects demonstrated significantly greater CCA at the start and the end of the task and less change in CCA during the task (p < 0.05). While non-significantly less TKA was seen at the start of the task, significantly less TKA was observed at the end of the task when using the craniocervical brace (p < 0.05). The craniocervical brace use also led to significantly less change in TKA (p < 0.05). There was no significant difference in the trunk extensor muscle activity.

CONCLUSIONS: Use of the craniocervical brace decreased FHP immediately, lessened thoracic kyphosis over time, and prevented the worsening of FHP and thoracic kyphosis during visual display terminal work.

Keywords

Cervical alignment cervical spine computer work forward head posture habitual posture thoracic kyphosis

1 Introduction

Remaining in a poor posture for a long time, such as during visual display terminal (VDT) work, can cause musculoskeletal disorders [1 –4]. Several studies have found that individuals suffer increased neck pain, forward head posture (FHP), thoracic kyphosis, and low back pain during VDT work [4 –7]. FHP is the protrusion of the head in the sagittal plane, with an enlargement in upper-cervical extension [8 –10]. One study defined FHP as a craniocervical angle (CCA) of less than 42.5°; that is the angle between the true horizontal and a line drawn from the tip of the spinous process of C7 to the mid-point of the tragus of the ear [9]. A less CCA indicates a greater FHP which causes various musculoskeletal disorders, such as chronic neck pain, decreased balancing ability, and changes in postural control [11, 12]. In addition, greater FHP tend to increase thoracic kyphosis angle (TKA) which is an exaggeration of the normal thoracic curve that ranges from 20° to 45°, in terms of the Cobb measurement [13]. (Fig. 1) Thoracic kyphosis and co-contraction of trunk flexor and extensor muscles tend to increase compression loading through the spine, resulting in increased intervertebral disc loads [14 –16]. Therefore, thoracic erector spinae(TES) and lumbar erector spinae(LES) has a role in thoracic kyphosis [17].

The relationship between FHP and thoracic kyphosis has been a subject of interest in the rehabilitation field. Several studies have reported that FHP is frequently coupled with thoracic kyphosis and that the two have a moderate to high correlation [18 –20]. One study insisted that mobility of the thoracic spine plays a major role in patients with cervical impairments [18]. The study reported that patients with cervical impairments had significantly greater thoracic kyphosis than healthy controls, and that thoracic kyphosis was significantly related to neck pain-related disability [18]. However, manipulation and mobilization of the thoracic spine in patients with cervical dysfunction may result in positive clinical outcomes[21 –23].

Any change in cervical lordosis may influence postural changes in the thoracic and lumbar spine because these areas of the spine are interrelated biomechanically [18]. Although there is increasing evidence to suggest that improved thoracic kyphosis may lead to improved clinical outcomes in patients with cervical dysfunction, little is known about how improving FHP may improve thoracic kyphosis. A previous study reported that reduced FHP with cervical spinal manipulative therapy led to reduce recurrent severe mid-thoracic pain [24]. However, that study used multimodal treatments; including bracing the thoracic vertebrae directly, so how isolated interventions that improve FHP may influence thoracic vertebral alignment remain unknown.

Using a brace to correct CCA would be beneficial for individuals with FHP, as using a brace may improve posture, muscle activity, instability of joints, and proprioceptive capability, and prevent the worsening of symptoms [25 –29]. Although an inventor suggested a craniocervical brace to correct FHP, there was no investigation of the effects of such a brace [30]. Thus, the present study is the first reported trial to investigate the immediate effects of the craniocervical brace use on CCA, TKA, and trunk extensor muscle (TEM) activity. We hypothesized that using the craniocervical brace would modify CCA, TKA, and TES and LES activity while subjects performed VDT work for 10 min.

2 Methods

2.1 Subjects

Twelve young male subjects with FHP participated in this study. To be included, the subjects had to present with a CCA of 42.5° or less [9]. Exclusion criteria were previous cervical spine surgery, history of neurological disorders, and participation in any neck exercise program in the past 12 months [31]. The 12 men had a mean age of 21.6±1.9 years, height of 177.3±4.2 cm, weight of 69.9±5.0 kg, body mass index of 22.2±1.4 kg/m², CCA of 39±2.2°, and neck disability index of 4.8±7.6%.

We used the G-power software for a power analysis [32]. A sample size of eight was calculated to achieve a power of 0.95 and an effect size of 1.52 with an α level of 0.05, based on differences in the change in CCA and TKA between the conditions of wearing and not wearing the craniocervical brace in a pilot study with four subjects.

All subjects provided written informed consent. The protocol for this study was approved by theYonsei University Wonju Institutional Review Board.in agreement with the guidelines of the Yonsei University Wonju Institutional Review Board.

2.1.1 Electromyography

Surface electromyography (EMG) was used to evaluate the activities of the TES and LES. After shaving, roughening, and swabbing the subject’s skin with alcohol-soaked cotton, disposable Ag/AgCl surface electrodes were positioned parallel to the muscle fibers of the dominant leg (TES at T4 level, 5 cm lateral from the spinous process at T4; LES, approximately 2 cm from the L3 spine over the muscle mass with a center-to-center spacing of 2 cm) [33]. EMG data were collected at a sampling rate of 1000 Hz using the Tele-Myo 2400T EMG instrument with a wireless telemetry system (Noraxon, Scottsdale, AZ, USA) and analyzed using Myo-Research Master Edition 1.06 XP software (Noraxon). The EMG signals were amplified, band-pass filtered (10 and 450 Hz), notch-filtered (60 Hz), and processed into root mean square data with a moving window of 50 ms. Reference isometric voluntary contractions (RVCs) were used to normalize the EMG data. RVCs were used instead of maximum voluntary contractions to decrease the risk of injury or residual muscle soreness. For TES and LES, holding a three-point stance with a dominant leg raise was performed for 5 s without moving the center of mass to the non-tested side. We used the middle 3 s of the 5 s contraction for data analysis. A 1 min rest was provided for all subjects between trials to prevent muscle fatigue. EMG data are presented as the mean percentageRVC.

2.1.2 CCA, TKA, and Changes in CCA, TKA between the start and end of task

CCA and TKA at the start and end of task were measured using a digitized, sagittal-view photograph of the subject in a sitting posture. Six light-reflective markers, 3.5 cm in diameter, were placed over the tragus of the subject’s ear (the center of the flexible ear hook of a headphone piece), C7 (while flexing the head and neck, the spinous process of C6 was felt to move forward while that of C7 remained stationary), T1 (spinous process of the first thoracic vertebra), T3 (3 cm below the T1 marker), T11 (3 cm proximal to the L1 marker), and L1 vertebra (spinous process of first lumbar vertebra) [34, 35]. To minimize image distortion, we mounted the camera on a tripod to ensure that the camera was perpendicular to the horizontal. ImageJ software (National Institutes of Health, Bethesda, available at http://www.rsb.info.nih.gov/ij) was used to measure CCA and TKA from the captured images. CCA and TKA were captured at the start and end of the 10 min VDT task which was a typing of Korean national anthem. Changes in CCA and TKA were calculated between the differences in CCA and TKA at the start and end of the continuous VDT work [4]. CCA measurements (quantified by the angle between the true horizontal and a line drawn from the tip of the spinous process of C7 to the mid-point of the tragus of the ear) showed good intra-rater reliability in previous studies (intraclass correlation coefficients of 0.88–0.98) [9, 36], as did TKA measurements, quantified by the relative angle between the straight lines defined by T1-T3 and T11-L1 (intraclass correlation coefficients of 0.83–0.92) [34, 35].

2.2 Procedures

Before data collection, a height-adjustable table and chair were used to establish the sitting posture. The workstation for typing included a desktop computer and 17-inch LCD monitor, inclined backwards by 20° and with the top of the display positioned 20° below eye level. The subjects positioned their feet at shoulder width. The height of the chair was adjusted for the starting position of 90° flexion of hip, knee, and arms [6]. The starting calibration posture was achieved by locating the line from the tragus to the acromion, parallel to the vertical line with the chin-in posture. The subjects adopted a comfortable and natural working posture, and performed the computer work in Microsoft Word. To select the most comfortable workstation configuration (such as keyboard position), a familiarization session (less than 10 min) was allowed. We collected the data of CCA, TKA, and EMG activities at start and end of the 10 min VDT work with and without wearing the newly designed a craniocervical brace and compared the data between the conditions of wearing and not wearing the craniocervical brace (Fig. 2). A 5 min rest was provided between trials to avoid muscle fatigue [7, 37]. The craniocervical brace was made of very light breathable foam, covered with a soft knit material, and was easy to open and close for suitable adjustment (length = 38 cm, width = 7.6 cm, weight = 70 g). It was placed at the chin (front upper part) and the atlanto-occipital joint (back upper part) snuggly, but not tightly to provide low-level retraction force at the subject’s chin [38]. We asked subjects to report the comfort level of the wearing the craniocervical brace in a 5-point Likert scale (‘much more’ and ‘more comfortable’, ‘unchanged’, and ‘more’ and ‘much more’ uncomfortable), and the comfort level was within comfort level [38]. The test orders (wearing vs. not wearing the craniocervical brace) were selected randomly by drawing a card from a box to reduce any order effect. The data collection were repeated three times and averaged to reduce measurement errors. After finished using the craniocervical brace for 10 min, the comfort level of the brace was scored again.

2.2.1 Statistical analysis

Kolmogorov-Smirnov Z-tests were performed to evaluate the normality of data distribution. A within-subjects, paired t-test analysis was used to examine the immediate effects of using the craniocervical brace on CCA and TKA at the start and end of the task, and changes in CCA and TKA and TES and LES activity during the task. Statistical significance was set at 0.05. Statistical analyses were performed using the SPSS software (ver. 18.0 for Windows; SPSS, Inc., Chicago, IL).

3 Results

Kinematic changes are described in Table 1. When wearing the craniocervical brace, the subjects demonstrated significantly greater CCA at the start (t = –3.94, P = 0.002) and the end (t = –4.931, P = 0.001) of the task and less change in CCA (t = –3.298, P = 0.007) during the task. While non-significantly less TKA (t = –1.911, P = 0.082) was seen at the start of the task, significantly less TKA (t = 4.661, P = 0.001) was observed at the end of the task when using thecraniocervical brace. The craniocervical brace use also led to significantly less change in TKA (t = 4.056, P = 0.002).

There was no significant difference in the activity of TES (without brace = 172.6±104.1% RVC vs. with brace = 154.5±81.5% RVC) or LES (withoutbrace = 32.7±19.5% RVC vs. with brace = 29.6±17.2% RVC) muscles (Fig. 3). Seven subjects reported the comfort level as ‘unchanged’ while 5 subjects reported ‘more uncomfortable’ at the end of using the craniocervical brace.

4 Discussion

We investigated the immediate effects of using the craniocervical brace on CCA, TKA, and the activity of the TES and LES muscles in subjects performing VDT work for 10 min. These results can be explained by the fact that craniocervical braces provide a retraction force directly on the cervical vertebrae and thus correct FHP during VDT work. In addition, they decrease FHP immediately and maintain the correct posture, helping to prevent exaggerated FHP during such work. Several researchers have introduced various methods to correct FHP using spinal manipulation, anterior head weighting, traction, a form board, devices such as the Occivator, a neck retraction assistant device, and correction exercises [27 , 40]. Nevertheless, the most common non-surgical treatment for posture correction is bracing, either alone or in combination with exercise [28, 41]. Also, bracing may have more potential for preventing the progression of musculoskeletal disorders and may have no negative impact on musculoskeletal disorders [28]. Consequently, craniocervical braces should be recommended for individuals withFHP.

The effects of the craniocervical brace on TKA may also be delayed. Although the craniocervical brace did not have an immediate effect on TKA, it led to a significantly less TKA at the end of the task. This result indicates that correction of FHP using a craniocervical brace may decrease thoracic kyphosis indirectly and with a slight delay, and prevent exaggerated thoracic kyphosis during such work. Thus, a physical therapist should note that excessive TKA would be related with the presence of FHP and correcting the FHP would be a treatment for lessening excessive TKA.

There was no significant difference in TES or LES muscle activity between the groups, although TKA changed significantly. O’Sullivan et al. [42] reported that there was no difference in superficial lumbar multifidus or TES activity between lumbo-pelvic upright and slump sitting [42]. Also, two previous studies reported no significant difference in the activity of thoracic paraspinal muscles in long lordosis and kyphosis sitting [43, 44]. Our results are consistent with these studies. However, another previous study reported significantly higher activities of the lumbar paraspinal and multifidus in upright sitting (about 5° thoraco-lumbar angle in T10) than kyphosis sitting (about 15° thoraco-lumbar angle in T10) for 45 s and a unique role of the lumbar paraspinal muscles for subtle adjustment and/or support of lumbar lordosis during changes in sitting posture [43]. In contrast, there was no significant difference in LES in our study. We assumed that use of the craniocervical brace would change the kinematics (CCA and TKA), but that relatively small changes in TKA (about 5°) would likely not alter LES activity.

Our study has several limitations. First, a cause-and-effect relationship between FHP and thoracic kyphosis cannot be assumed, given that our study has a cross-sectional design. Therefore, interpretation of the observed results should be considered with caution. Second, generalizability is limited because only young and healthy male subjects were participated. The results could have been different if the study had included female participants and/or subjects with symptoms. Third, measurements of CCA and TKA were done via photographic analysis using anatomical markers. Although such analyses are reliable for quantifying CCA and TKA, the anatomical alignment of the spine could have some errors due to variation in surface measurements. Fourth, even though this study showed favorable findings of wearing the craniocervical brace for 10 min, 5 subjects reported “uncomfortable” at the end of the task. Thus, longitudinal studies are recommended to determine the long term effects of wearing a craniocervical brace during VDT work in subjects with FHP.

5 Conclusion

This study provides evidence of an immediate effect of using the craniocervical brace on CCA, TKA, and trunk extensor muscle activity during VDT work in subjects with FHP. Use of the craniocervical brace decreased FHP immediately, lessened thoracic kyphosis over time, and prevented the worsening of FHP and thoracic kyphosis during the task. However, the significant differences in kinematics were not associated with differences in trunk extensor muscle activity between groups. Therefore, the craniocervical brace can be recommended for patients with FHP to correct and prevent excessive FHP and thoracic kyphosis.

Conflict of interest

The authors have no conflict of interest to report.

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