The Effect of Ergonomic Latex Pillow on Head and Neck Posture and Muscle Endurance in Patients With Cervical Spondylosis: A Randomized Controlled Trial

Abstract

Objectives

Cervical pillows have frequently been reported to attenuate the symptoms of pain and disability. Although the main role of pillows is to optimize head and neck posture and relax the neck muscles, limited studies have examined the effectiveness of pillows from aspects beyond subjective outcome measures, especially their effect on head and neck posture and muscle performance. This study examines the effect of ergonomic latex pillow on the craniovertebral (CV) angle and cervical flexor and extensor muscle endurance in patients with cervical spondylosis.

Methods

This parallel-group, randomized, controlled trial was conducted from January to June 2017. The patients with cervical spondylosis were randomly allocated to the experimental and control groups, who both received identical standard physiotherapy 3 × a week for 4 weeks. The experimental group received an ergonomic latex pillow, but the control group was asked to continue sleeping on their usual pillow. The CV angle and flexor and extensor muscle endurance were measured before and after the intervention. The independent-sample t test was used to compare changes in the CV angle, whereas the Mann-Whitney test was used to compare changes in flexor and extensor muscle endurance between the groups, respectively.

Results

The experimental group showed significant changes in the CV angle and extensor muscle endurance. A significant increase was observed in extensor muscle endurance in the experimental group compared with the control group.

Conclusion

The ergonomic latex pillow may affect neck extensor muscle endurance and CV angle in patients with cervical spondylosis, although further studies are needed before any recommendations.

Introduction

Background and Objectives

Many health care practitioners prescribe cervical support pillows as an adjunctive therapy for the conservative management of patients with neck pain and cervical disc disease.¹ Various pillows with different shapes and materials are available in the market, and their effectiveness has been clinically examined by many researchers.^2,3 A significant amount of research supports the ability of cervical pillows to attenuate the symptoms of pain and disability and improve sleep quality.^4,5

The mechanism of effect of these pillows in reducing waking symptoms and neck pain is that they contribute to the relaxation of the neck muscles by supporting the neck and maintaining normal cervical lordosis and thus relieve the pain caused by unconscious muscle tension.⁶ They also prevent excessive biomechanical stress on anatomic structures and help unload and rehydrate the intervertebral discs.^4,7

Although the main role of pillows is reportedly to optimize the head and neck posture,⁸ limited studies can be found on its effectiveness from aspects beyond subjective outcome measures, especially its effect on head and neck posture, and this lack should be addressed because human beings spend one-third of their life in sleep and are unable to actively control their spine during sleep.⁷ Pillows therefore play an important role in maintaining ideal head and neck posture and can modify the muscle activity pattern, and their effectiveness should not be overlooked simply in this regard.

Scientific evidence suggests that head postural deviations affect the development and persistence of neck pain,⁹ which may be why the assessment of head posture has been emphasized as an important part of the physical examination of patients with cervical disorder and as a main factor involved in evaluating the health condition.^10,11 Moreover, the cervical muscles play a key role in controlling neck posture.¹² The reduced ability of these muscles to maintain the upright posture of the cervical spine may indicate their impaired endurance and inability to maintain cervical lordosis. Because various studies have frequently reported a significant association among weak neck muscles, poor posture, and neck pain experience,^13,14 and considering that pillows can alleviate pain and disability, it is crucial to examine whether pillows are capable of affecting head posture and muscle performance. The effectiveness of a modality such as pillows should not be solely judged based on the changes it causes in symptoms of pain and disability; it is also necessary to consider the impact of such an intervention on the factors that are likely to be effective in the persistence and exacerbation of neck pain and the patient's movement toward a faulty cycle.

Evaluating head and neck posture and muscle endurance is especially important in patients with cervical spondylosis. In this regard, patients with cervical spine spondylosis have shown increased fatigue in both their anterior and posterior neck muscles.¹⁵ In addition, by increasing muscle tension in the muscles responsible for raising the head, the forward head posture (FHP) causes an elevated load on the intervertebral discs of the cervical spine and leads to early degenerative changes in the discs that exacerbate spondylosis.¹⁶ This study was therefore conducted to investigate the effect of ergonomic latex pillows on the craniovertebral (CV) angle (a criterion for evaluating FHP) and also on cervical flexor and extensor muscle endurance in patients with cervical spondylosis. Our hypothesis was that the use of ergonomic latex pillows in conjunction with standard physical therapy would be more effective than standard physical therapy alone in increasing the CV angle and cervical muscle endurance in patients with cervical spondylosis.

Methods

Participants and Trial Design

This parallel-group, randomized, controlled trial is part of a large data collection on the effects of ergonomic latex pillows that was carried out from January to June 2017 at the outpatient physical therapy clinic of Hazrat-e Rasoul Hospital (Tehran, Iran). The data assessor was also blinded.

Patients with cervical spondylosis were referred by a spine specialist, and those who met the eligibility criteria were included in the study. The inclusion criteria consisted of age 30 to 60, chronic pain in the cervical region with or without pain radiating to the upper limbs, grade II or III cervical spondylosis based on radiographic changes in the cervical spine (grade II presented as obvious anterior osteophytosis with minimal disk-space narrowing and mild sclerosis of the vertebral plates, grade III presented as moderate disk-space narrowing with sclerosis of the vertebral plates and osteophytosis), a score ≥2 on the Numerical Pain Rating Scale, and a score ≥20% on the Neck Disability Index.

The exclusion criteria consisted of having other nonspecific neck pain injuries such as acute neck strain; postural neck ache; whiplash; fibromyalgia; psychogenic neck pain; inflammatory diseases such as rheumatoid arthritis, ankylosing spondylitis, or polymyalgia rheumatica; metabolic diseases such as Paget's disease, osteoporosis, gout, or pseudo-gout; infections such as osteomyelitis or tuberculosis; tumor; spinal canal stenosis; scoliosis and congenital anomalies of the cervical, thoracic, or lumbar spine; temporomandibular joint disorder or surgery; recurrent middle ear infections in the last 5 years; hearing impairment requiring a hearing aid; chronic respiratory disorders leading to absenteeism from work or requiring long-term treatment over the last 5 years; pregnancy or breastfeeding; history of trauma or fracture or surgery of the cervical or cervicothoracic spine; and history of using cervical pillows (any pillow except the regular feather, cotton, or sponge pillows commonly used in the authors’ country). The patients who had received physical therapy or training for neck pain during the last 3 months or wore a cervical collar were excluded from the study. The eligibility criteria were monitored through clinical examinations before entering the trial.

Sample Size

The sample size was estimated as 38 (19 per group) using G*Power 3.0.1 (Franz Faul, University of Kiel, Kiel, Germany) with α = 0.05, power = 0.8, and effect size = 0.83 (based on the means and standard deviations from the pilot study). Anticipating a conservative dropout rate, the sample size was increased to 44.

Randomization and Allocation

Before beginning the trial, the random allocation sequence was generated via a computerized random number by a person not involved in any stage of the study. For the allocation concealment, the randomization codes were kept in sealed opaque envelopes numbered sequentially. The responsible researcher was unaware of the patient's group allocation until the envelopes were opened at the beginning of the intervention. Before this stage, the experimental and control groups both signed a written informed consent form. The research project was approved by the ethics committee of Iran University of Medical Sciences (9311502004) and was registered at the Iranian Registry of Clinical Trials (ID: IRCT2014021916643N1).

Intervention

Both groups received identical standard physical therapy 3 × /wk for 4 weeks. Each physical therapy session consisted of a 5-minute ultrasound with a 1-MHz frequency and 1.5 W/cm²,¹⁷ followed by 20 minutes of conventional transcutaneous electrical nerve stimulation to the pain region,¹⁸ 20 minutes of superficial moist heat via a hot pack¹⁹ and isometric and stretching exercises of the cervical muscles.²⁰ All the participants were asked to follow their routine daily activities. The experimental group received an ergonomic latex pillow (WB001 Latex Pillow CE1674) with the size of 50 × 30 × 10 cm. The pillow's brand was removed, and it was covered with a white pillowcase. The ergonomic latex pillow supported the participants in the supine and side-sleeping positions. The participants received instructions on how to sleep on the pillow in the correct position. They were instructed to put only their head and neck on the pillow and not their shoulders and chin in the hollow of the shoulder. The patients in the control group were asked to continue sleeping on their usual pillow. In addition, all the participants were given ergonomic instructions on their routine daily activities.

Outcomes

Primary outcome measures were CV angle and flexor and extensor muscle endurance. Before the first assessment, baseline characteristics including age, body mass index, average hours of sleep, and severity and duration of the disease were recorded, and the CV angle and flexor and extensor muscle endurance of all participants were measured. Also, pain intensity and disability were evaluated by Numeric Pain Rating Scale and Neck Disability Index, respectively, at baseline. The privacy of all participants was respected, and their photographs were protected from publishing anywhere. The assessor was blinded to group allocation. After 4 weeks of intervention, all the objective measurements were evaluated again.

CV Angle

To assess the forward head posture, the participants’ CV angles were measured. A smaller CV angle indicates a more severe forward head posture. The CV angle is the intersection between the horizontal line and the line that passes through the tragus of the ear and the C7 spinous process.

The evaluation was carried out by taking 3 photographs from the right sagittal view of each participant. A digital camera (Canon IXY, 12MP, Japan) was located on a fixed base and adjusted without tilt or rotation at a distance of 1.5 m from the participant.²¹ The camera was leveled at the height of the participant's shoulder, and to choose a standard head and neck posture for all the participants, a self-balanced maneuver was applied. The participants had to flex and extend their head and neck in a full range and gradually decrease the range of motion until reaching their natural position and then maintain that posture.²² They were asked to take their natural standing position and not change it while taking photographs. Two markers were attached to the ear tragus and the seventh cervical (C7) spinous process. To find the C7 spinous process, each participant flexed their neck and the more prominent process was then chosen as the C7 landmark. A plumb rope was hanged from the ceiling so that it passed the anterior external malleolus of the participant. The plumb line was used for recognizing the true vertical line on digital images. All the participants had to look at a point directly in their front to fix their eye level. The photographs were transferred to the computer, and the best photo taken was chosen for the assessment.²³ The CV angle was measured using Adobe Acrobat software.

Extensor Muscle Endurance

The participants were asked to lie prone on a plinth, with their head over the plinth and supported by a pillow and the arms kept on the sides. A band was fastened across the T6 level to prevent thoracic extension. An inclinometer was placed around the head by a 5-cm strap, and a 2-kg weight was suspended from the participant's head above the ear. The head and cervical region of the participant was placed in a neutral position. After support of the participant's head and weight were removed, the participants held this position until they felt pain in their neck or could not maintain the position anymore, and if their head position reached beyond 5°, an inclinometer was used to measure the exact number. The duration of maintaining the position was calculated in seconds using a stopwatch.¹²

Flexor Muscle Endurance

The participants lay in the supine position and were asked to flex their upper neck and lift their head about 2.5 cm off the bed. During the test, the examiner's hand was lying under the participant's head. The participants had to hold this position until they could no longer maintain it or until the examiner touched the participant's head or perceived a reduced neck flexion upon witnessing the loss of skin folds posterior to the jaw during the test position. The duration of maintaining the position was calculated in seconds using a stopwatch.²⁴

Statistical Analysis

Data were analyzed in SPSS 16.00. To reduce the risk of bias, the data were coded and the statistician was blinded to the group allocations. Shapiro-Wilk's test was used for testing the normality of the variables. The independent-sample t test was used for comparing the baseline characteristics between the groups, except for flexor muscle endurance, which was compared using Mann-Whitney test, and the χ² test was used to compare the grade of cervical spondylosis and sex at baseline between the groups. The paired t test was used to compare changes in the CV angle within each group, and the independent-sample t test was used to compare these changes between the 2 groups. The Wilcoxon and Mann-Whitney tests were used to compare changes in flexor and extensor muscle endurance within and between the groups, respectively. P < 0.05 was taken as the level of statistical significance in all the analyses. Because our participants were not selected by random sampling, it was assumed that the parametric tests were not appropriate; therefore, this study carried out a statistical analysis based upon nonparametric tests. However, there were no differences between this analysis and the data analysis based upon parametric tests.

Results

Between January and June 2017, 85 patients with cervical spondylosis were screened, and 44 of them met the eligibility criteria and entered the study and were randomly allocated to the experimental (21) and control (23) groups. Two of the patients from the control group were excluded because they could not complete the physical therapy sessions for personal or job-related reasons. The data from these 2 patients were therefore not included in the analysis (Fig 1). Table 1 shows the distribution of the participants based on the severity of cervical spondylosis and similarity between the groups regarding the baseline demographic and clinical characteristics (Table 1). Statistically significant changes were observed in the CV angle and extensor muscle endurance within the experimental group; however, flexor muscle endurance did not differ significantly before and after the intervention in the experimental group (Table 2). None of the mentioned variables showed significant changes within the control group. A significant increase was observed in extensor muscle endurance in the experimental group compared with the control group, but no significant differences were observed between the groups in the CV angle and flexor muscle endurance (Table 2).

Fig 1.

Flowchart of participant screening, allocation, and assessment.

Table 1.

Baseline Demographic and Clinical Characteristics of Patients in the Experimental and Control Groups

Variables		Experimental Group (N = 21) Mean ± SD	Control Group (N = 21) Mean ± SD	P Value
Age (y)		46.38 ± 7.93	47.09 ± 8.19	.77
Grade of cervical spondylosisa	2	11	16	.10
	3	10	5
Sex	Male	0	3	.23
	Female	21	18
Body mass index (kg/m2)		27.82 ± 3.93	26.93 ± 4.06	.47
Pain intensity		4.61 ± 1.61	5.31 ± 1.53	1
Neck Disability Index		35.25 ± 13.10	32.89 ± 14.50	.11

SD, standard deviation.

^aAccording to radiography result.

Table 2.

Comparing the Groups Based on Primary Outcome Measures

Variables	Experimental Group (N = 21)			Control Group (N = 21)			P Value (within groups)
	Pretest Mean ± SD	Posttest Mean ± SD	Change of the Variables (95% CI)	Pretest Mean ± SD	Posttest Mean ± SD	Change of the Variables (95% CI)	Experimental Group	Control Group	P Value (between groups at baseline)	P Value (between groups after the intervention)
Craniovertebral angle (°)	46.50 ± 6.45	50.56 ± 4.90	4.06 (1.81-6.30)	46.68 ± 4.69	48.52 ± 7.06	1.84 (-0.44 to 4.14)	.001a	.10	.92	.15
Flexor muscles endurance (s)	25.12 ± 16.76	36.56 ± 21.31	11.43 (0.42-22.45)	22.08 ± 13.57	26.29 ± 13.84	4.20 (-1.93 to 10.34)	.07	.086	.73	.89
Extensor muscles endurance (s)	52.08 ± 28.02	143.39 ± 101.68	91.31 (45.52-137.10)	78.32 ± 54.97	93.28 ± 70.06	14.98 (-20.40 to 50.33)	.001a	.17	.06	.003a

SD, standard deviation.

^aThe difference is significant at the 0.05 level.

Discussion

Cervical pillows are commonly prescribed by health care practitioners as a therapeutic option.²⁵ Although part of the effectiveness of these pillows regarding subjective outcome measures is frequently investigated in studies,⁴ their effect on factors such as abnormal head posture and cervical muscle dysfunction, which appear to be closely related to the experience of neck pain, disability, and even restriction of cervical movements, has often been neglected.26, 27, 28

This randomized controlled trial was carried out to investigate the effect of a 4-week use of ergonomic latex pillows together with routine physical therapy compared with the administration of routine physical therapy alone in patients with cervical spondylosis. After 4 weeks of intervention, the results showed a significant increase in the CV angle, which indicates reduced FHP, and in extensor muscle endurance in the experimental group, but flexor muscle endurance showed no changes. In the control group, no significant changes were observed in any of the outcome measures. Extensor muscle endurance was the only variable that demonstrated a significant difference between the groups.

Forward head posture is one of the most common postural abnormalities appearing as increased lordosis in the upper cervical spine and decreased lordosis in the lower cervical spine.29, 30, 31 The significant increase in the CV angle in the experimental group confirms the hypothesis about the mechanism of action of the pillow and its role in maintaining normal neck lordosis. This finding also highlights the results of a previous study extracted from the same data, which suggest that the ergonomic latex pillow is more successful in reducing pain compared to routine physical therapy. Since, in the FHP, head deviation from a normal alignment exerts an abnormal compressive load on the posterior neck structures, it develops and exacerbates neck pain. This pillow may be said to protect the normal cervical lordosis during sleep by relaxing the muscles and unloading the discs and subsequently improving the posture and eventually reducing symptoms.²⁹

The association of FHP with pain and disability frequently reported in previous studies also confirms this claim.²⁶ Studies conducted on the effectiveness of these pillows with longer follow-ups, compared with ones with a shorter period of exposure, have reported more significant results in favor of this effectiveness perhaps because they have managed to correct the head and neck alignment in the long term.⁵ Lee et al³² observed no significant differences in FHP between their experimental and control groups. Karim³³ compared 3 types of pillows, namely polyester, latex, and Beautyrest pillows, with no pillows at all and found no differences among their outcomes, although the participants were healthy people aged 20 to 30 captured in the supine and recumbent positions, whereas the present study evaluated this posture in the standing position.

The changes in the CV angle were only 4° in the experimental group in the present study, and although this degree of correction in the head posture is statistically significant, it cannot be considered clinically significant with certainty because previous studies have reported a minimal detectable change of 4° in the CV angle. Despite the significant increase in the CV angle in the experimental group, the changes in this variable were not clinically significant after a period of treatment between the 2 groups.

Studies also suggest that the cervical flexor muscles play a key role in maintaining the cervical spine posture.³⁴ Because flexor muscle endurance did not change significantly during the intervention in any of the groups or between the groups, this argument could explain the lack of significant differences in FHP between the 2 groups, as FHP causes weakness of the cervical flexor muscles.³⁵ It can thus be argued that the head posture correction was not clinically significant because flexor muscle endurance did not improve in this study.

Another importance of the cervical flexor muscles in maintaining the neutral posture is that these muscles have a high density of muscle spindles.³⁶ The changes that occur in the cervical muscle length as a result of FHP cause impaired afferent input from the mechanoreceptors that are present in the cervical muscles and a poor position sensation and the forward drift of the head.^37,38 This action may thus endanger the person by way of a defective cycle.

Another possible explanation for flexor muscle endurance is the effect of fear of movement/(re)injury with muscle activity, meaning that the patient refuses to maximize his efforts due to the anticipation of pain and to prevent the aggravation of pain during flexor muscle endurance testing.³⁹ It is also likely that the reduction in the activity of the cervical flexor muscles as a result of FHP could decrease the number of type-I muscle fibers and convert them into type-II fibers that are less resistant to fatigue.⁴⁰ Our treatment strategy, which was based on the correct positioning of the neck during sleep, was probably ineffective in recruiting these muscles and modifying their activity patterns, and the endurance of these muscles could therefore not be improved.

The findings of the present study showed that neck extensor muscle endurance was the only variable improved significantly by this multimodal intervention, including the ergonomic latex pillow and routine physical therapy. A possible explanation for this finding is that the ergonomic latex pillow prevents the placement of the cervical spine segments in an extreme posture by maintaining normal cervical lordosis and enabling the relaxation of the posterior neck muscles during sleep. In fact, the examined pillow may help prevent extensor muscle fatigue during daily activities by decreasing the muscle tension caused by poor posture, and this effect can be seen as increased endurance. The aforementioned mechanisms were not investigated in the present study, and this is merely a scientific speculation to justify the findings of this study. As a result, we cannot overlook the role of other unknown factors in achieving these findings.

Limitations and Generalizability

This study had some limitations. Given that most of our participants were women, the generalization of the results to men should be performed with caution. Also, whether the patients, according to the instructions of the researcher, used the pillow is questionable. However, similar studies have relied upon patient honesty. To address this concern in the present study, the patients were asked to record a daily log of the number of hours they rested and used the pillow.

Conclusion

It seems that the ergonomic latex pillow as a part of a multimodal rehabilitation program may effect changes in neck extensor muscle endurance and the CV angle in patients with cervical spondylosis, although further studies are needed before any recommendations.

Funding Sources and Conflicts of Interest

This research received no specific grants from any funding agency in the public, commercial, or not-for-profit sectors. Also the authors have no conflicts of interest to declare with respect to the research, authorship, or publication of this article.

Contributorship Information

Concept development (provided idea for the research): F.F.

Design (planned the methods to generate the results): F.A.

Supervision (provided oversight, responsible for organization and implementation, writing of the manuscript): B.F., F.A.

Data collection/processing (responsible for experiments, patient management, organization, or reporting data): F.F., A.A.

Analysis/interpretation (responsible for statistical analysis, evaluation, and presentation of the results): F.F., F.A.

Literature search (performed the literature search): F.F.

Writing (responsible for writing a substantive part of the manuscript): F.F.

Critical review (revised manuscript for intellectual content, this does not relate to spelling and grammar checking): F.A.

Practical Applications

• •Cervical support pillows are an adjunctive therapy for the conservative management of patients with cervical disk disease.
• •The main role of pillows is to optimize the head and neck posture and relax the neck muscles.
• •Ergonomic latex pillows increase extensor muscle endurance in patients with cervical spondylosis.

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