1. INTRODUCTION:

The forward head posture is known as the cause of abnormal neck pain in students carrying around heavy weight or remaining seated for elongated time^1-3. Forward head posture is defined as a posture in which the cervical vertebrae projects forward, and when the imbalance, pain, fatigue, and limited movement of the muscles are observed⁴. The Forward head posture not only causes the musculoskeletal changes of the neck as the shortening of the extensor at the back of the neck and the neck muscles of the front, but causes the pressure of the cervical vertebrae structures as zygapophysial joints and ligaments^5-7.

The forward head posture is also related to the pain of the relatively stretched upper cervical vertebrae, bent lower cervical vertebrae and the pain of the shoulders and the neck⁸. For these reasons, the forward head posture not only causes the pain of the neck but changes the movement pattern of the neck as well^9,10.

A backpack is a form used by hikers, travellers, soldiers and students to carry around things¹¹. Backpacks are appropriate methods to carry loads by maintaining stability and closely and proportionately to the spine ^11,12. However, carrying around backpacks every day causes physical pressure, and causes the head or the soma to lean forward¹³, causing problems as pain, discomfort, misalignments of postures^5,14, and changes of gait ^4,15.

The craniovertebral angle is defined as the angle of the horizontal line crossing the spinous process of C7 and the line connecting the tragus of the ear with C7. In prior research, there were changes of the craniovertebral angle in carrying backpacks, and the angle of the head and neck increased the forward head posture¹⁶. In prior research stated that those with small craniovertebral angles had tension headaches¹⁷, and another research reported that it led to the forward head posture and increase of neck pain ¹⁸. Such pain from decrease of the craniovertebral angle and the forward head posture is a general problem experienced by 70% of the population ⁹, with 30% of the adults complaining neck pain and 5-10% complaining discomfort in using their necks¹¹.

The sternocleidomastoid is attached across the diagonal line to attach to the apical protrusions and stomach line of the bones of the eye from the lateral fork attached to the appendage bone and the lateral fork attached to the barb bone. The muscles contracting to one side are the bending muscles of the head and neck of the head, and the contraction muscles of the opposite sides are able to bend or extend the head and neck. The longus colli muscle is located at the each side of the neck bone that it leads to the region of the neck bone through many attachments between the vertebrae bodies, the anterior nodules of the transverse process, and the anterior ring of the ring. The tissues located at the front of the longus colli muscle bend the neck bone area, and the lateral tissues provide the vertical stability of the neck bone with the scalene muscles. The muscles as longus colli muscle guarantee the vertical stability of the frontal plane and the sagittal plane¹⁴.

In prior research used electromyogram (EMG) to measure the changes of the upper trapezius and the serratus anterior in subjects with the forward head posture¹⁹ and another research measured the muscular activity of the sternocleidomastoid muscle, upper trapezius and mid cervical paraspinal muscle when carrying the backpack of the same weight (15% of the weight) on the back, back and front (the weights of the backpacks in front and back are each 7.5%) and carrying them in changed weights (the backpack in the front is 5% and the backpack in the back is 10%) with EMG, and the EMG muscle activity of the sternocleidomastoid muscle when carrying the backpack of the same weight (15% of the same weight) on the back and back and front had statistically significant differences compared to not carrying the backpack²⁰.

The prior research stated that the longus colli muscle and the neck muscles toward the back stabilize the cervical vertebrae against gravity²¹. However, there was no research measuring the changes of the muscles. Most of the ultrasonic researches were research measuring the relationship between the muscle’s cross sectional and lateral pain in patients with headaches from the neck²² and viewing only the muscles through ultrasonic waves ²³, and yet there were no research viewing the changes of the muscle thickness from the load. In other words, this research has its purpose in measuring the changes of the forward head posture, longus colli muscle and sternocleidomastoid muscle from backpacks.

Table 1: General characteristics of the subjects(n = 30)

Characteristic	Value
Age(yr)	21.3 ± 2.05
Hight(cm)	173.43 ± 7.37
Weight(kg)	67.43 ± 11.1

^aAll values are mean value ± standard deviation (SD)

2. MATERIALS AND METHODS:

The subjects of this research were 30 students of Chungcheongnamdo’s S University that had not suffered from neck pain. The selection criteria were those without the medical history of surgical treatments from neck pain and disorder and those without neurologic problems. Before the experiment, through writing clarifying the purpose and method of research, sufficient information was provided, agreement in research participation was gained, and a total of 30 subjects was selected, and the general characteristic of the participants is as [Table 1]. This research received the approval of Sunmoon University’s Institutional Review Board.

2.1. Measurement:

While the subject is standing, the subject faces forward and has a comfortable position. The subjects measured without backpacks (0%) and backpacks of 5%, 10% and 15% of their own weights, and the subject was measured of craniovertebral angle, longus colli muscle and sternocleidomastoid muscle respectively three times

The position of the backpack was located between 12th thoracic vertebrae and the 3rd lumbar vertebrae in which the higher weight of the middle part of the backpack causes minimum position changes⁶. Generally, the standard backpack without internalframe or backsupport, with two pads and adjustable shoulder straps(21inch) generally used by students was used in the experiment.

2.2. Experiment Equipment and Parts of Measurement:

2.2.1. Craniovertebral angle measurement equipment (electrogoniometer):

The measurement of the craniovertebral angle was measured at a comfortable posture in standing position. The measurements was made by using an electrogoniometer (Digital absolute + axis, 12-1027, USA, 2012). The spinous process of the 7th cervical vertebrae was marked, and the electrogoniometer was positioned on the left shoulder. The fixed arm with the axis of the C7 spinous process was aligned horizontally on the floor, and the moving arm was aligned on the external auditory meatus of the left ear. The angle formed by the two angles was recorded as craniovertebral angle ²⁰.[Figure 1].

[Figure 1] Measurement of craniovertebral angle

2.2.2. Ultrasonic video recording equipment:

With the subjects standing, the measurement was conducted by using an ultrasonography diagnosis equipment (Ultrasonography, ezono 3000, Germany, 2011). The head and neck were positioned in neutral positions. The measurement of ultrasonography was conducted 2cm away from thyroid cartilage laterally ²⁴. Prove was located vertically from the longitudinally of the neck to gain a cross-sectional image. The border of the muscles was located above and below the retropharyngeal space, the lower vertebral body, the carotid artery, and the posterior pharyngeal space. The cross-sectional area and thickness of the longus colli muscle or the anteroposterior dimension and width or lateral dimension were measured from the border of the longus colli muscle to the greatest distance (the facial contour was not included in the measurement) ²⁵. The shape ratio was calculated as a value dividing the width by the thickness (Lateral dimension / Anterior-posterior dimension).

Each muscle was measured a total of three times. For intra-day reliability, two measurements. Study process were conducted with a minimum of 1 hour interval, and for inter-day reliability, the third Measurement was measured after a week [Figure 2][Figure 3].

[Figure 2] Ultrasonographic equipment using the cross-sectional area and the sternocleidomastoid muscle

SCM: Sternocleidomastoid, CA: Carotid artery RPS: Retropharyingeal space, LC: Longus colli, VB: Vertebral body

[Figure 3] Measurement of longus colli muscle and Sternocleidomastoid muscle by ultrasonography

2.3. Analysis method:

All measurement values were statistically analyzed by using SPSS/PC ver18.0 for Windows program(SPSS INC. Chicago. IL). The test of normality utilized Shapiro-Wilk, and all satisfied the normal distribution. The general characteristics of the subjects used percentage and frequency analysis, and to explore the differences in thicknesses of sternocleidomastoid muscle and longus colli muscle when the weight of the backpack is 0%, 5%, 10% and 15% of the weight, one-way repeated ANOVA was used. For the differences between each factor, paired comparison was conducted with Bonferroni test and all statistic significance was set as p<0.05 as shown in table 2.

The study was designed in a single-blind, randomized control and the study process is shown in Figure 4.

[figure 4] Study process

[Table 2] Changes in CVA, APD, LD, CSA, and SCM according to backpack weight (n = 30)

	Load				F
	0%	5%	10%	15%	F
CVA	50.09 ± 3.86^a	49.69 ± 3.70	49.54 ± 3.66	48.47 ± 3.63	16.336^*
APD	7.22 ± 1.17	7.16 ± 1.28	7.21 ± 1.34	7.08 ± 1.47	.329
LD	7.50 ± 1.13	7.36 ± 1.13	7.41 ± 1.31	7.24 ± 1.03	1.085
CSA	54.82 ± 14.51	53.43 ± 15.13	54.31 ± 16.58	51.83 ± 15.49	1.346
SCM	6.90 ± .96	6.91 ± .88	6.96 ± .92	7.09 ± 1.03	1.452
shape ratio	1.05 ± .17	1.05 ± .17	1.05 ± .18	1.019 ± .22	.047

^*p<.05, ^aAll values are mean value ± standard deviation(SD), CVA: Craniovertebral angle, APD: Anterior posterior dimension, LD: Lateral dimension, CSA: Cross sectional area, APD: Anterior posterior dimension, SCM: Sternocleidomastoid

3. RESULTS AND DISCUSSION:

3.1. RESULT:

3.1.1. Goniometer:

[Figure 5] Comparison of craniovertebral angle according to backpack weight

3.1.2. Ultrasonic Inspections:

The 30 subjects were applied weights of 5%, 10% and 15% in standing posture carrying backpacks. The thicknesses of longus colli muscle and sternocleidomastoid muscle according to the weights of the backpack showed no statistically significant differences[Figure 6][Figure 7][Figure 8](p>.05).

[Figure 6] Comparison of the vertical thickness of longus colli muscle according to backpack weight

[Figure 7] Comparison of Thickness of sternocleidomastoid muscle According to backpack weight

[Figure 8] Comparison of the horizontal thickness of longus colli muscle according to backpack weight

3.2. DISCUSSION:

This research gave loads according to the weights of the backpack in standing position (0%, 5%, 10% and 15%) and hoped to study the influences on craniovertebral angle, longus colli muscle, and sternocleidomastoid muscle through ultra-sonographic diagnosis equipment and electronic goniometer.

The craniovertebral angle was measured to be respectively 50.09°, 49.69°, 49.54°, and 48.87° with the backpack weights of 0%, 5%, 10% and 15%. The thickness of longus colli muscle was measured to be 7.22mm, 7.16mm, 7.21mm and 7.08mm and the thickness of sternocleidomastoid muscle and 6.90mm, 91mm, 6.96mm, and 7.09mm that significant differences were only shown in craniovertebral angle, and there were no differences in muscles. As a result, there were only significant differences in craniovertebral angle when the weight of the backpack was 15%. As mentioned in prior research the result that craniovertebral angle only showed significant differences at 15% were deducted¹⁶. If load is given to back of the human body like backpack extension torque torque occurs on the trunk of the body, and the trunk and the head leans forward¹². This means that the backpack lessens the craniovertebral angle and causes the forward head posture. Also, theoretically, if the head moves forward from the weight center of gravity, the head and neck reflexes as vestibular neck reflex (the neck posture stabilization reaction from the cervical nerve and the labyrinth of the ears)³. Therefore, such movement of the COG not only causes the ankles, hip joints or the head to face forward but cause musculoskeletal changes as the shortening of the extensor muscles at the back of the neck and the tightening of the neck muscles at the front.

However, there were only differences in angle in this research, and had no statistically significant changes in muscles. However, in case of the craniovertebral angle, as the weight of the backpack increased, the angle decreased, and in comparing the 15% group with other groups, significant differences were observed. Unlike the measurement of longus colli muscle and sternocleidomastoid muscle, significant differences were observed even after carrying the backpack for a short time that imbalance of the posture was more notable than fatigue of the muscle.

The thickness of longus colli muscle showed tendency of becoming thinner with the load of the backpack yet showed no significant difference. It seems that there were no significant differences as the backpack weight limitation of this experiment was 15%, and the time carrying the backpack was short. However, the thickness of longus colli muscle tended to lessen with the increase of load that carrying the backpack for elongated time would have led to significant differences. Therefore, if the load of the backpack increased or if the backpack was carried for elongated time, the thickness of longus colli muscle may become thinner, causing weakness of the muscles.

In case of sternocleidomastoid muscle, the thickness increased with weight that the increase of the thickness could be observed. Yet statistically significant differences were not observed. However, as the graph model showed tendencies of increasing gradually with increase of weight, if the load of the backpack increased or if the backpack was carried for elongated time, significant differences are anticipated. This seems as the thickening of the sternocleidomastoid muscle, and shows that the muscle contracts to lead to the extension of the upper cervical vertebrae and the bending of the lower cervical vertebrae among neck bending effects, an effect of sternocleidomastoid muscle²⁶.

However, without the deep workings of the deep neck flexor, the increase of the activities of the sternocleidomastoid muscle cannot lead to the appropriate stabilization of the cervical vertebrae that forward head posture is caused.

Abnormal posture changes from the usage of backpacks may cause round shoulders, turtle neck, changes in neck muscle activity and muscle fatigue. Also, factors as load of the backpack, abnormal neck posture (forward head posture) and fatigue(weakening) of the neck muscle are reported to cause headaches^8,16,27. Also, those complaining from neck pain reported to have smaller deep cervical flexor compared to that of normal people ^13,15.

However, though the length of the muscle did not show significant differences, the thickness of the muscle showed tendency of becoming thinner. Based on such results and conclusions from prior researches, when backpacks are applied for longer time as the usage of general backpacks, or if heavier backpacks, the usage of such backpacks may cause pain, and even changes of the backpack may be caused. Therefore, it could be said that the proper weight of the backpack without the change of the craniovertebral angle is ideal at the scope of 10% or less of the weight without changes in body balance or change of muscles.

The limitations of this research is that most of the study subjects were men that the changes of women’s craniovertebral angle and muscles could not be observed, and as groups had small number of subjects because the total number of subjects was 30, the results could not be generalized. Also, the remaining muscles other than longus colli muscle and sternocleidomastoid muscle were not measured that the changes of these muscles were unknown, and weights beyond 15% were not measured, causing difficulty in verifying changes arising from heavier loads, and variables of time after carrying the backpacks were excluded. Therefore, in future research, researches complementing these limitations to add variables on time regarding loads beyond 15% with more female subjects and more subjects are needed.

4. CONCLUSION:

This research explored the changes of craniovertebral angle, longus colli muscle and sternocleidomastoid muscle were examined according to the backpack weights of 5%, 10% and 15% of body weight. Longus colli muscle and sternocleidomastoid muscle did not show change in any weight, yet craniovertebral angle showed significant changes in 15% weight, causing forward head posture. Therefore, we are able to conclude that weight of 15% or more causes forward head posture.

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Received on 11.12.2017 Modified on 10.02.2018

Research J. Pharm. and Tech 2018; 11(7): 2997-3002

DOI: 10.5958/0974-360X.2018.00552.8

Comparison of the thickness of Longus colli and Sternocleidomastoid according to weight of backpack and measurement of craniocervical angle