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ISSN : 1225-8962(Print)
ISSN : 2287-982X(Online)
Physical Therapy Korea Vol.25 No.2 pp.62-70
DOI : https://doi.org/10.12674/ptk.2018.25.2.062

Comparison of the Cross-Sectional Area of Longus Colli and Muscle Activity of Sternocleidomastoid in Subjects With Forward Head Posture on the Two Craniocervical Flexion Methods

Min-chan Son1,2, Ui-jae Hwang1,2, Sung-hoon Jung1,2, Sun-hee Ahn1,2, Hyun-a Kim1,2, Oh-yun Kwon1,3,4
1Kinetic Ergocise Based on Movement Analysis Laboratory
2Dept. of Physical Therapy, The Graduate School, Yonsei University
3Dept. of Physical Therapy, College of Health Science, Yonsei University
4Dept. of Ergonomic Therapy, The Graduate School of Health and Environment, Yonsei University
Corresponding author: Oh-yun Kwon kwonoy@yonsei.ac.kr
April 3, 2018 April 3, 2018 May 6, 2018

Abstract

Background:

The craniocervical flexion (CCF) exercise is one of the effective exercise in correcting forward head posture (FHP). However, some people with FHP achieve CCF with compensatory movements, for example, low cervical flexion using superficial neck flexors such as the sternocleidomastoid (SCM) muscle. No study has yet investigated whether a dualpressure biofeedback unit (D-PBU) method to prevent low cervical flexion would be helpful in performing pure CCF movement.


Objects:

The purpose of this study was to compare the effects of the CCF using D-PBU method and the traditional CCF method on the cross-sectional area (CSA) of the longus colli muscle (LCM) and the activity of SCM muscle in subjects with FHP.


Methods:

Twentyfour FHP subjects (male: 16, female: 8) were recruited for this study. All subjects performed CCF using two different methods: The traditional CCF method and the CCF using D-PBU method. The CSA of the LCM was measured via ultrasound, and surface electromyography was used to measure SCM muscle activity.


Results:

The change in CSA of the LCM was significantly larger during the CCF using D-PBU method (1.28±.09) compared with the traditional CCF method (1.19±.08) (p<.05). The SCM muscle activity using the CCF using D-PBU method (2.01±1.97 %MVIC) was significantly lower than when using the traditional CCF method (2.79±2.32 %MVIC) (p<.05).


Conclusion:

The CCF using D-PBU method can be recommended for increasing LCM activation and decreasing SCM muscle activity during CCF movement in subjects with FHP.



초록


    Introduction

    Forward head posture (FHP) is defined as a protraction of the head anterior to the trunk in the sagittal plane (Silva et al, 2009). FHP usually involve shortened cervical spine extensors (suboccipital extensors, rectus capitis, superior obliques, and inferior obliques) and lengthened intrinsic cervical flexors [the longus colli muscle (LCM) and the longus capitis muscle] (Sahrmann, 2010; Jung et al, 2015). FHP also involves an extended middle cervical spine, and a flexed lower cervical spine (Harman et al, 2005). It is related to deep cervical flexor weakness (Griegel-Moris et al, 1992).

    Craniocervical flexion (CCF) exercise is one of the effective training methods to strengthen the deep cervical flexor muscles such as the LCM and longus capitis muscle in the upper cervical region, giving support to the cervical segments, and curve, rather than the superficial cervical flexor muscles like the sternocleidomastoid (SCM) muscle and anterior scalene muscle (Jull et al, 2004; Jull et al, 2009). However, poor activation of the LCM can affect the increased activation of the SCM during CCF exercise (Jull et al, 2004). Sahrmann (2010) showed that subjects with FHP using an extrinsic muscles such as the SCM cause excessive cervical vertebrae anterior translation rather than sagittal rotation, which occurs via intrinsic cervical muscles such as the LCM. Therefore, many studies (Falla et al, 2004; Jull et al, 2004; Jull et al, 2008) have used CCF, encouraging the action of the LCM and monitoring SCM activities.

    A CCF test can be used as an indirect measurement of LCM contraction ability and be used to evaluate an individual’s ability to perform and maintain precise upper cervical flexion without mid or lower cervical spine flexion (Chiu et al, 2005; Mayoux-Benhamou, 1997). CCF is associated with the interrelated action of the LCM and longus capitis muscle to support and stabilize the lordosis of the cervical spine (Jull et al, 1999). However, some subjects with neck disorders perform CCF by retracting the cervical spine, using superficial neck flexors such as the SCM instead of pure CCF movement through deep neck flexors contraction (Chiu et al, 2005: Jull et al, 2000). This usage is related to uncontrolled movement such as upper cervical flexion with excessive low cervical flexion during the CCF movement (Comerford and Mottram, 2012).

    Many studies have shown the importance of identifying control impairments such as excessive low cervical flexion during cervical flexion and of diagnosis based on the impairment of movement in the cervical spine (Caldwell et al, 2007; Comerford and Mottram, 2012; Sahrmann, 2002). Comerford, and Mottram (2012) suggested that the upper cervical area can flex without low cervical flexion for the correction of the cervical flexion. In previous studies, a pressure biofeedback unit (PBU) was used to control craniocervical movement at the upper cervical region during CCF (Jung et al, 2015). During CCF, compensatory movements like retracting the cervical spine, performed by superficial muscles, were controlled just by the researcher (Falla et al, 2004; Jull et al, 2009). However, there are no studies using the objective apparatus that have investigated cervical movement during CCF both in the upper cervical region and lower cervical region by restricting low cervical flexion. So, this study suggests adding one more PBU under the lower cervical region to restrain low cervical flexion during CCF.

    The purpose of this study was to confirm the effects in subjects with FHP of using CCF using dual- PBU (CCF using D-PBU) method compared with the traditional CCF method using one PBU on a crosssectional area (CSA) of the LCM and the activity of the SCM muscle. We hypothesized that the CSA of the LCM would be larger and that the activity of the SCM muscle would be lower when using the CCF using D-PBU method than when using the traditional CCF method.

    Methods

    Subjects

    Twenty-four volunteers (16 males, 8 females) aged 20∼30 years at Yonsei University in Wonju participated in this study. The characteristics of the subjects are shown in Table 1. The inclusion criteria included ⑴ a young age (20∼30 years) and ⑵ the presence of FHP, where FHP was defined as having a craniovertebral angle less than 50˚ (Ruvio et al, 2017). The craniovertebral angle is a crossed angle between the line from the tragus of the ear to spinous process of the C7 vertebra and a horizontal line of the C7 spinous process in the sagittal plane (Yip et al, 2008). The reflective markers were an attached C7 spinous process and the tragus of the ear. Subjects were asked to flex and extend their necks three times until the head was in a comfortable position (Yip et al, 2008). The head and neck posture were recorded using a digital camera (Samsung, Seoul, Korea). To confirm subjects with FHP, Image J imaging software (U.S. National Institutes of Health, Maryland, USA) was used to measure the craniovertebral angle. Exclusion criteria included ⑴ being unable to achieve 30 ㎜Hg in upper cervical region through CCF ⑵ having a previous history of shoulder and neck surgery. All participants signed informed consent forms, and this study was approved by the Yonsei University Wonju Institutional Review Board (approval number: 1041849-201710-BM-123-01).

    Instrumentations and data processing

    The Myson U6 (Medison, Seoul, Korea) was used to record the image of the LCM. To measure the size of the LCM, a linear transducer (5-12 ㎒) was placed 2 ㎝ below the thyroid cartilage, perpendicular to the neck. To increase reliability, the examiner marked the location of the transducer with a marker. In this position, the outlines of the LCM can be visualized by the vertebrae body (inferiorly and medially), retropharyngeal space (superiorly), and carotid artery (laterally). The CSA of the LCM was calculated from the outlines linking the vertebrae body, the retropharyngeal space, and the carotid artery (Janvanshir K, 2011). The change in the LCM CSA during each CCF methods were shown as a proportion of the LCM CSA at starting position (ending position/starting position) (Jung et al, 2015).

    The activation of the SCM muscle was measured by EMG (Noraxon Telemyo 2400T, Noraxon, Scottsdale, AZ, USA). The electrodes for the SCM were placed 2 ㎝ from each electrode, parallel to the SCM muscle fibers, and were attached around the middle part between the clavicle and the mastoid process (Criswell, 2010). A Myoresearcher XP Master Edition (Noraxon Inc., Scottsdale, USA) was used to collect signals. A band-pass filter applied between 20 ㎐ and 450 ㎐ to filter the raw signals. Root mean squares were calculated using 50 ㎳. The data were recorded at a 1000 ㎐ sampling rate.

    To normalize the EMG signals of the SCM, maximum voluntary isometric contraction (MVIC) was used. To obtain the SCM MVIC data, the standard manual muscletest position was used. Each subject was asked to lie supine, and turn their face toward the nontested side, with lateral flexion against resistance in the opposite direction above the temporal region, applied by the examiner (Kendall et al, 2005). The MVIC data was collected three times for five seconds, with a three minutes rest between muscle contractions. To calculate the mean value, the data from the middle three seconds of each trial were used. The EMG data of SCM was expressed as a percentage of the MVIC. The data of SCM activity was collected when PBU pressure of upper cervical region achieved 30 ㎜Hg.

    A PBU (Pressure biofeedback unit, Healience, Seoul, Korea) is a sensitive apparatus showing pressure increases in cervical nodding. Visible feedback on the pressure is provided by a manometer (Jung et al, 2015). In this study, PBUs were used to control the movement and measure the pressure of the upper cervical region and the lower cervical region when performing traditional CCF method and CCF using D-PBU method. The data of PBU in the lower cervical region was collected when PBU pressure of upper cervical region achieved 30 ㎜Hg.

    Procedure

    Prior to the measurement, the order of the trials was randomized to remove any order effects, based on a random number generating process using Microsoft Excel ver. 2010 (Microsoft Corporation, Washington, US). The traditional CCF and CCF using D-PBU methods were used for the intervention. Before the intervention, subjects were given ten minutes of practice time to acclimatize to the traditional CCF method and the CCF using D-PBU method. Each method was performed two times, with a resting time of 30 seconds. There was also a five minutes resting time between interventions to prevent carryover effects. The average value of two trials was used to analyze the data. The other researcher was blinded to the experimental circumstances during variables analysis.

    The starting position of the traditional CCF method is a supine crook lying, with the subject lying with neutral neck position where towels are used to make the line of face horizontal with the surface. One pressure sensor is located in the upper cervical region, with a pressure of 20 ㎜Hg (Jull et al, 2008). The other pressure is placed in the lower cervical region, with a pressure of 40 ㎜Hg. The ultrasound image was recorded in starting position. The subjects performed CCF until the upper cervical region pressure was 30 ㎜Hg (Jung et al, 2015), ignoring lower cervical region pressure. The subjects maintained both the starting and ending positions for five seconds. The examiner recorded the EMG data, the ultrasound image, and the PBU data of lower cervical region both for the starting position and when the PBU pressure of upper cervical region achieved 30 ㎜Hg.

    The process of the CCF using D-PBU method is similar to the traditional CCF method, except that one more PBU controlling low cervical flexion movement is added in the lower cervical region. The starting position for the CCF using D-PBU method is the same as for the traditional CCF method. However, subjects are asked to maintain a lower cervical region pressure of 40 ㎜Hg as much as possible to prevent low cervical flexion, until they achieve 30 ㎜Hg pressure in the upper cervical region with the PBU during CCF. The problem with CCF is excessive low cervical flexion rather than upper cervical flexion (Comerford and Mottram, 2012). For the pure CCF, PBU at the lower cervical region was used to control the low cervical flexion during CCF. The data were recorded both in the starting position and when the upper cervical region pressure achieved 30 ㎜Hg, in the same way as for the traditional CCF method (Figure 1).

    Statistical analysis

    For determine relative reliability in two trials, 95% confidence intervals (CIs) intra-class correlation coefficients (ICCs) was used. Standard errors of the measurement (SEM) was calculated to confirm the precision of measurement in the same unit (Kim et al, 2017a).

    To analyze the data, the Statistical Package for Social Science version 23 (SPSS Inc., Chicago, IL, USA) was used. The KolmogorovSmirnov test was used to identify the normal distribution of the data. The data from this study are shown as a mean±standard deviation. The difference in muscle activity, muscle CSA, and PBU data between the two methods was compared by a paired ttest. The significance level (α) was set at .05 to confirm statistical significance.

    Results

    The intra-rater reliability of measurements for 24 participants is reported in Table 2. The results of ICC were very high in all measurements (ICC>.92). The SCM muscle activity was 2.79±2.32 %MVIC and 2.01±1.97 %MVIC, respectively, for the traditional CCF method and the CCF using D-PBU method. The SCM muscle activity using the CCF using D-PBU method was significantly lower than that for the traditional CCF method (t=3.988, p=.001) (Figure 2). The change in the LCM CSA (ending position/ starting position) was 1.19±.08 and 1.28±.09, respectively, for the traditional CCF method and the CCF using D-PBU method. The change of LCM CSA in the CCF using D-PBU method was significantly larger than that for the traditional CCF method (t=-6.849, p<.001) (Figure 3). The pressure of the PBU in the lower cervical region was 44.15±6.59 ㎜Hg, and 40.25±.78 ㎜Hg, respectively, for the traditional CCF method and the CCF using D-PBU method. The pressure for the traditional CCF method using the PBU under the lower cervical region was significantly increased compared with that for the CCF using D-PBU method (t=2.987, p=.007) (figure 4).

    Discussion

    Previous studies showed that accurate CCF can be performed with the LCM and longus capitis rather than superficial neck flexors such as SCM (Falla et al, 2004; Jull et al, 2008; Jung et al, 2015). Therefore, this study compared the CSA of the LCM, the muscle activity of the SCM, and the PBU pressure between the traditional CCF method and the CCF using D-PBU method in subjects with FHP. The results showed that the CSA of the LCM was significantly larger and the muscle activity of SCM was significantly lower using the CCF using D-PBU method compared with the traditional CCF method. The traditional CCF method also had a significantly increased pressure of the PBU under the lower cervical region compared with that of the CCF using D-PBU method.

    The LCM plays an important role in stabilizing the cervical spine and controlling neck posture (MayouxBenhamou et al, 1994). FHP is associated with a weakness of the deep cervical flexor muscles, such as the LCM (GriegelMoris et al, 1992). It is important to correct FHP through exercise (Harman et al, 2005). Jull et al (2009) showed that performing CCF exercise using one PBU in the upper cervical region is an effective method of activating deep cervical muscles such as the LCM. In this study, CCF using one PBU and D-PBU was compared, to detect which methods would be most effective in activating the LCM. The results showed that the CSAs proportion of LCM were 1.19±.08 and 1.28±.09, respectively, when using the traditional CCF method and CCF using D-PBU method. This means that it is more effective to use the CCF using D-PBU method than to use the traditional CCF method to activate the LCM.

    The CCF movement involves the action of the LCM and longus capitis, not the action of the SCM and scalenes (Falla et al, 2003). The purpose of CCF tests has been to assess synergistic anatomical action of deep cervical muscles such as the LCM and the longus capitis muscle, rather than SCM and the anterior scalene muscles (Jull et al, 2004). These tests have shown that pure CCF does not involve the retraction of the cervical spine by superficial muscles (Chiu et al, 2005). Therefore, many studies have supervised the muscle activity of SCM by observation or palpation during CCF (Fernández-de-las-Peñas et al, 2007; Falla et al, 2003; Jull et al, 2008). To more precisely control the compensation motion by superficial muscles such as the SCM, in this study, we added one more PBU under the lower cervical region, unlike the configuration in the traditional CCF method. The resulting data (traditional CCF method: 2.79±2.32 %MVIC; CCF using D-PBU method: 2.01±1.97 %MVIC) demonstrated that the CCF using D-PBU method activated SCM less than the traditional CCF method. This means that the activity of the SCM would be restricted using the CCF using D-PBU method through obstructing low cervical region flexion or retraction by maintaining a lower cervical region pressure of PBU 40 ㎜Hg.

    In this study, the new CCF using D-PBU method, using one more PBU at the lower cervical region, showed more ideal results in terms of performing pure CCF movement than did the traditional CCF method. The pressure of the PBU was significantly increased in the traditional CCF method compared to that with the CCF using D-PBU method (traditional CCF method: 44.15±6.59 ㎜Hg; CCF using D-PBU method: 40.25±.78 ㎜Hg). Some studies used biofeedback for controlling muscles, strengthening the target muscles, and decreasing compensation (Koh et al, 2016; Roy et al, 2010). For example, Kim et al (2017b) used a PBU to decrease compensation movement. Noh et al (2014) also used CCF using D-PBU to control the pelvic rotation angle during an active straight leg raise and confirmed that the pelvic rotation angle was significantly lower with DPBU than with a single PBU. In this study, using the CCF using D-PBU method not only maintained lower cervical stabilization through restricting SCM activation during CCF, but it also allowed unsupervised training by selfmonitoring through the lower cervical region pressure of the PBU.

    There are some limitations in this study to be considered. First, this study investigated the immediate effects of the CCF using D-PBU method and not the longterm effects. Therefore, the longterm effects of the CCF using D-PBU method will also need to be studied. Second, the subjects of this study were only young adults with FHP, so it is difficult to generalize these results to the overall population. Third, this study investigated only FHP subjects. Further studies are necessary to investigate the effects of the CCF using D-PBU method in subjects with other neck disorders.

    Conclusion

    In this study, we compared the effects of the CCF using D-PBU method and the tradtional CCF method on the CSA of the LCM and the muscle activity of SCM in subjects with FHP. The results showed that CCF using D-PBU method produced more increased LCM activation and lower SCM muscle activity than traditional CCF method. These results suggest that the CCF using D-PBU method can provide more benefits than the traditional CCF method in subjects with FHP.

    Figure

    PTK-25-62_F1.gif

    Craniocervical flexion using dual-pressure biofeedback unit (CCF using D-PBU) method (A: starting position, B: ending position).

    PTK-25-62_F2.gif

    A comparison of SCM activity using two different methods. *p<.05, (SCM: sternocleidomastoid, MVIC: maximum voluntary contraction, CCF: craniocervical flexion, DPBU: dual-pressure biofeedback unit).

    PTK-25-62_F3.gif

    A comparison of LCM CSA (ending position/starting position) using two different methods. *p<.05, (LCM: longus colli muscle, CSA: cross-sectional area, CCF: craniocervical flexion, DPBU: dual-pressure biofeedback unit).

    PTK-25-62_F4.gif

    A comparison of PBU pressure in the lower cervical region using two different method. *p<.05, (PBU: pressure biofeedback unit, CCF: craniocervical flexion, DPBU: dual-pressure biofeedback unit).

    Table

    Characteristics of the subjects (N=24)

    amean±standard deviation.

    Intra-rater reliability of measurements (N=24)

    aintraclass correlation coefficient
    bconfidence interval
    cstandard error of the mean
    dsternocleidomastoid
    etraditional craniocervical flexion
    fcraniocervical flexion using dual-pressure biofeedback unit
    glongus colli muscle
    hcross-sectional area.

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