Head Posture and Neck Pain of Chronic Nontraumatic Origin: A Comparison Between Patients and Pain-Free Persons
Presented to the World Congress of Pain, International Association for the Study of Pain, August 17–22, 2008, Glasgow, UK.
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Abstract
Silva AG, Punt TD, Sharples P, Vilas-Boas JP, Johnson MI. Head posture and neck pain of chronic nontraumatic origin: a comparison between patients and pain-free persons.
Objective
To compare standing head posture measurements between patients with nontraumatic neck pain (NP) and pain-free individuals.
Design
Single-blind (assessor) cross-sectional study.
Setting
Hospital and general community.
Participants
Consecutive patients (n=40) with chronic nontraumatic NP and age- and sex-matched pain-free participants (n=40).
Interventions
Not applicable.
Main Outcome Measures
Three angular measurements: the angle between C7, the tragus of the ear, and the horizontal; the angle between the tragus of the ear, the eye, and the horizontal; and the angle between the inferior margins of the right and the left ear and the horizontal were calculated through the digitization of video images.
Results
NP patients were found to have a significantly smaller angle between C7, the tragus, and the horizontal, resulting in a more forward head posture than pain-free participants (NP, mean ± SD, 45.4°±6.8°; pain-free, mean ± SD, 48.6°±7.1°;P<.05; confidence interval [CI] for the difference between groups, 0.9°–6.3°). Dividing the population according to age into younger (≤50y) and older (>50y) revealed an interaction, with a statistically significant difference in head posture for younger participants with NP compared with younger pain-free participants (NP, mean ± SD, 46.1°±6.7°; pain-free, mean ± SD, 51.8°±5.9°; P<.01; CI for the difference between groups, 1.8°–9.7°) but no difference for the older group (NP, mean ± SD, 44.8°±7.1°; pain-free, mean ± SD, 45.1°±6.7°; P>.05; CI for the difference between groups, –4.9°–4.2°). No other differences were found between patients and pain-free participants.
Conclusions
Younger patients with chronic nontraumatic NP were shown to have a more forward head posture in standing than matched pain-free participants. However, the difference, although statistically significant, was perhaps too small to be clinically meaningful.
List of Abbreviations:
APAS (Ariel Performance Analysing System), CI (confidence interval), ICC (intraclass correlation coefficient), MANOVA(multivariate analysis of variance), NP (neck pain)
NECK PAIN IS A COMMON symptom in the general population1 and a frequent source of disability that carries important health and economic costs.2 Abnormalities in head posture are often considered to be associated with the development and persistence of NP, and some clinicians emphasize its importance during examination.3, 4, 5, 6, 7, 8 A forward head posture (or chin poking) is perhaps the most common abnormality associated with NP and is commonly defined as the protrusion of the head in the sagittal plane so that the head is placed anterior to the trunk.9, 10 Forward head posture can occur because of an anterior translation of the head, lower cervical flexion, or both,11 and it is claimed to be associated with an increase in upper-cervical extension.8, 10, 12 It is suggested that forward head posture leads to an increase in the compressive forces on the cervical apophyseal joints and posterior part of the vertebra5, 10, 12, 13 and to changes in connective tissue length and strength (because of stretching of the anterior structures of the neck and shortening of the posterior muscles) resulting in pain.5, 7, 10, 14 In addition, evidence suggests that the degree of forward head posture increases with age in asymptomatic people,15, 16 which may be related to changes that occur in the musculoskeletal system with age.17 Furthermore, the degree of forward head posture reported by Dalton,15 Raine,16 and colleagues for pain-free individuals over the age of 55 years was higher than that reported by Braun18 for patients with NP with a mean age of 38 years old. This highlights the relevance of controlling for age when comparing forward head posture between patients with NP and pain-free individuals and may suggest that the potential relationship between forward head posture and NP varies with age.
In clinical practice, subjective methods of head posture assessment seem to prevail.8 It is believed that the majority of clinicians and particularly physiotherapists make a simple examination of head posture based on their own visual determination of the alignment of the head and describe abnormal head posture with subjective descriptions such as “mild” or “significant.”19 Nevertheless, clinicians seem to use head posture assessment to inform treatment strategies in managing NP and monitoring treatment outcome.4, 5, 8 Furthermore, several influential textbooks on musculoskeletal assessment recommend the assessment of head posture when examining patients with NP.3, 6, 7, 20, 21
The recommendation for head posture assessment appears to be based on the assumption that patients with NP have poorer posture than pain-free individuals.6 However, studies investigating differences in head posture measurements between patients with NP and pain-free participants show conflicting results; some claim a difference in head posture measurements,18, 22, 23 whereas others do not.24, 25 To date, studies have failed to match groups accurately in terms of age, have not blinded assessment optimally, and have not reported sample size calculations.18, 22, 23, 25 The reliability of the procedures used is either not reported,23 authors failed to use the appropriate statistics,24 or it may be argued that their procedures lacked reliability.18, 25 Our study took these shortcomings into account in a number of ways. First, patients and controls were matched for age and sex. Second, a sample size calculation was performed, informed by a previous study.23Finally, we examined the reliability of the digitization process to facilitate the interpretation of our findings. The main aim of this study was to determine whether participants with chronic nontraumatic NP had a more forward head posture than pain-free participants. The secondary objectives were (1) to determine whether participants with chronic nontraumatic NP had a more extended head than pain-free participants, (2) to determine whether participants with chronic nontraumatic NP had a more side-flexed head than pain-free participants, and (3) to explore the effect of age on head posture across the sample of patients with NP and pain-free participants. Head posture was characterized by measuring angles between anatomic landmarks, and the study used a single-blind (assessor) cross-sectional design.
Methods
Participants
A total of 96 patients and 50 pain-free participants were assessed for eligibility. From them, 56 patients and 10 pain-free participants were excluded. Patients were excluded because they did not meet the inclusion criteria (n=47), refused to participate (n=2), or presented other reasons (n=7). Pain-free participants were excluded because they did not meet the inclusion criteria (n=10). A total of 80 participants entered the study: 40 patients with chronic NP of nontraumatic origin as their main presenting complaint and 40 pain-free participants matched for age (within 1 year) and sex. Patients were consecutively recruited from those referred by a physician for physiotherapy because of NP at the Hospital da Prelada, Portugal. Control participants were recruited from the general population.
The sample size was determined according to the findings of a previous study.23 The present study was powered to detect a difference of 2.7° (the difference found to be statistically significant by Shiau and Chai23) for the angle between C7, the tragus, and the horizontal between the groups when variance was 12.3° for pain-free individuals and 24.0° for NP patients (α=.05 and power=80%). The sample size was determined by using an equation from Kirkwood and Sterne26 to calculate the sample size for comparing 2 means from 2 independent samples.
Inclusion and Exclusion Criteria
Patients included in the study were required to have NP as their main current complaint and to have had NP for more than 6 months. NP was defined as pain felt dorsally between the inferior margin of the occiput and T1.27 Pain-free participants had no current NP and reported they had never had NP for more than 3 consecutive days.
It has been suggested that head posture could be influenced by conditions affecting the respiratory,28 the auditory, the visual,29 the neurologic,30 and the musculoskeletal systems.29 Thus, participants were excluded if they reported any of the following conditions: (1) a history of cervical or facial trauma or surgery; (2) congenital anomalies involving the spine (cervical, thoracic, lumbar); (3) bony abnormalities such as scoliosis; (4) any systemic arthritis; (5) recurrent middle ear infections over the last 5 years or any hearing impairment requiring the use of a hearing aid; (6) persistent respiratory difficulties over the last 5 years that had necessitated absence from work, required long-term medication, or interfered with daily activities; (7) any visual impairment not corrected by glasses; (8) any disorder of the central nervous system; or (9) pregnancy or breast-feeding. Inclusion and exclusion criteria were established by self-report.
Experimental Procedures
Ethical approval to conduct the research was requested and obtained from the Leeds Metropolitan University Faculty of Health Research Ethics Sub-Committee (UK), the Ethical Committee of Hospital da Prelada (Portugal), and the Service of Bioethics and Medical Ethics (Portugal). Participants were assessed on 1 occasion when measures of head posture and NP were taken. Three anatomic head angles were measured (fig 1): (1) the angle formed by the line connecting C7 to the tragus of the ear and the horizontal, which gives the position of the head relative to the trunk when the gaze is in horizontal or in natural head posture, with decreasing values indicative of a more forward head posture; (2) the angle formed by the line connecting the tragus of the ear to the canthus of the eye and the horizontal, which gives the position of the upper cervical spine with increasing values indicative of a more extended head; and (3) the angle formed by the line connecting the inferior margins of both ears and the horizontal, which provides information relating to side flexion.31 These angles were chosen because they had been used in previous studies enabling the comparison of results and were found to be reliable (ICC≥.71).31
Fig 1
The anatomic angles: (A) the angle between C7, the tragus, and the horizontal; (B) the angle between the tragus, the eye, and the horizontal; and (C) the angle between the inferior margins of the right and the left ear and the horizontal.
Participants stood in their stocking feet in a position they felt was natural for them. The standing position was chosen because it was found to be the most commonly used by clinicians when assessing head posture for patients with NP32; our intention was to mimic this situation as much as possible. Participants were instructed to have a similar distribution of body weight through each foot, to place their feet slightly apart, and to have their arms by their sides. The spinous process of C7 was identified by palpation according to Hickey et al33 and marked with a cylindrical adhesive marker made of foam. To facilitate the natural head posture that was sought, participants were asked to tilt their head forwards and backwards with decreasing amplitude until they felt that a natural head posture was reached.34 Once settled, measurements were taken.
The video cameras recorded participants' sagittal and frontal standing head posture at a distance from the participant's right side of 200cm and at 160cm from the frontal view. They were fixed on tripods and connected to a laptop computer running customized software (APAS).a One second (25 images) of data was collected via the “Capture Module” of the APAS software. Bubble levels on the tripods maintained camera alignment, and a 30-cm wide cube fixed to an adjustable tripod of iron was used to calibrate the system.35
After recording a sequence of 25 frames (corresponding to 1s), individual frames were manually digitized by an investigator blind to the type of participants and to the aims of the study. To monitor the reliability of the digitization process, 3 participants were randomly selected and their data digitized 3 times at 3 different sessions: t0, t1 (a week after t0), and t2 (1 month after t0). The order of the sequences was randomized within each session to minimize any learning or order effect. The 2-dimensional (x and y) coordinates of C7, the tragus of the ear, the canthus of the eye, and the inferior margins of both ears were calculated. These coordinates were used in the trigonometric formula of the tangent used to calculate the head angles.
Patients' NP history during the preceding week was taken including average NP intensity, frequency, duration, and localization by using a questionnaire developed by the authors. Patients were asked to rate their average NP intensity by using a 10-cm visual analog scale. The extremes of the scale were labelled “no pain” and “worst possible pain.”
The order that participants (patients or pain-free participants) entered the data-collection stage of the study was randomized by using software named Research Randomizerb to minimize any order effects that may have emerged.
Data Analysis
Statistical analysis was performed by using SPSS version 15.c The mean anatomic angles in degrees from the 25 frames were calculated for each participant and entered for statistical analysis. Anatomic angles and participants' weight and height comprised the continuous data and passed the Kolmogorov-Smirnov test for normality. Thus, an unpaired t test was used to detect any difference in the height and weight between the pain-free control participants and the participants with NP. To explore the differences between groups and the effect of age, a MANOVA was performed with group (NP vs pain-free) and age (participant's age > study sample mean age vs participant's age ≤ study sample mean age) entered as the factors. The variability of head posture during 1 second was interpreted by using frequency distributions, and a t test was used to detect any difference between participants with NP and pain-free participants. ICC3,1 was used to evaluate the intraobserver reliability of the digitization procedures on the same day and across days.
Results
In each group of participants (patients and pain-free), there were 6 men and 34 women, and the mean ± SD age was 50.2±7.9 (range, 33–69) for patients and 50.2±7.9 (range, 34–68) for pain-free participants. The dominance of women in the sample is typical of the population of people with NP. Fejer et al1 conducted a systematic review on NP and found that women reported more NP than men in 83% of the studies included in the systematic review. Patients' anthropometric characteristics were (mean ± SD) height, 159.0±7.0cm, and weight, 69.0±11.0kg. Pain-free participants' anthropometric characteristics were (mean ± SD) height, 160.0±8.2cm, and weight, 65.5±12.7kg. An unpaired t test found no difference between the pain-free participants and the participants with NP for height (t=−.20, P>.05) and weight (t=1.3, P>.05). The characteristics of NP are summarized in table 1.
| NP Characteristics | Results |
|---|---|
| Intensity | Minimum=2 |
| Maximum=10 | |
| Mean ± SD, 5.6±2.1 | |
| Frequency during the week before data collection | Always (everyday and all day) (n=15) |
| Several times (more than 3 times per week) (n=10) | |
| Occasionally (2 or 3 times per week) (n=11) | |
| Rarely (1 time per week) (n=4) | |
| Duration | >6mo<5y (n=13) |
| ≥5y<10y (n=13) | |
| ≥10y<15y (n=9) | |
| ≥20y<30y (n=1) | |
| ≥30y (n=4) | |
| Pain location | Central part of the neck (n=10) |
| Left side of the neck (n=3) | |
| Right side of the neck (n=6) | |
| Bilateral (n=21) |
Concerning the variability of head posture during 1 second of video recording, results show that the SD from the 25 digitizations of each angle for each participant varied from 0° to 1° for a great majority of participants (≥75%) for all the angles. There was no statistically significant difference between patients and pain-free participants (angle C7, tragus, horizontal, t=.35, P>.05; angle tragus, eye, horizontal, t=.76, P>.05; angle right ear, left ear, horizontal, t=.65, P>.05).
The digitization procedure was found to be highly reliable as shown by the ICC values when comparing measurements on the same day and across days for the 3 angles (ICCs varied between .98 and .99).
Angular Measurements
A MANOVA conducted on the data from the 3 angular measurements revealed a significant main effect of pain (F3,73=2.76,P<0.05) and age (F3,73=4.35, P<0.05). The group × age interaction between the 2 factors failed to reach statistical significance (F3,73≤1.19, P>.05). The results of individual analysis of variances performed on the data from each angle to further explore the differences found are presented later.
Angle Between C7, the Tragus, and the Horizontal
Values for this angle are indicative of the position of the head relative to the trunk. and decreasing values are indicative of a more forward head posture. NP participants were found to have a statistically significant smaller angle than age-matched pain-free participants, indicating a more forward head posture (NP, mean ± SD, 45.4°±6.8°; pain-free, mean ± SD, 48.6°±7.1°; F1,76=4.3, P<.05) (table 2).
Abbreviation: PF, pain-free participants.
Statistically significant for P<.05.
†Statistically significant for P<.01.
The cut point for age was 50 years (the study sample mean age). Twenty-one participants from each group were categorized as young (ie, ≤50y) and 19 from each group as older (ie, >50y). There was a significant main effect for age, with older participants having a more forward head posture than the younger participants (mean age >50 ± SD, 44.9°±6.8°; mean age ≤50 ± SD, 48.9°±6.9°; F1,76=7.4, P<.05). Planned comparisons revealed no statistically significant differences in values for the C7, tragus, horizontal angle between NP and pain-free participants for the older participants (NP, mean ± SD, 44.8°±7.1°; pain-free, mean ± SD, 45.1°±6.7°; F1,36<1.0, P>.05). However, younger NP participants had a statistically significant more forward head posture than younger pain-free participants (NP, 46.1°±6.7°; pain-free, 51.8°±5.9°; F1,40=8.9, P<.01).
Angle Between the Tragus, the Eye, and the Horizontal
Values for this angle relate to the position of the upper cervical spine, and increasing values are indicative of a more extended head. Values were comparable for the pain patients and pain-free participants (NP, mean ± SD, 21.0°±6.4°; pain-free, mean ± SD, 18.8°±7.7°; F1,76=1.9, P>.05). There were no differences in this angle between the older group and the younger group (mean age >50 ± SD, 19.6°±7.4°; mean age ≤50 ± SD, 20.1°±6.9°, F1,76<1.0, P>.05).
Angle Between the Inferior Margins of the Right and the Left Ear and the Horizontal
Values for this angle are indicative of cervical side flexion, with 0° indicating perfect symmetry. Rather than entering directional values for the analysis (ie, negative values=left side flexion, positive values=right side flexion), absolute values were entered to provide an indication of overall deviation from symmetry. Measurements revealed higher values for NP participants (mean ± SD, 2.3°±1.8°) compared with pain-free participants (mean ± SD, 1.8°±1.5°), but the difference failed to reach statistical significance (F1,74=2.6, P>.05). The older group of participants showed a greater deviation from symmetry (mean ± SD, 2.6°±2.0°) compared with the younger group (mean ± SD, 1.6°±1.2°), leading to a significant main effect for age (F1,74=7.1, P<.05). We had intended to analyze directional errors in relation to the location of pain in the NP group, but very few participants (n=9) complained of unilateral NP (see table 2).
Discussion
The results partially support our hypothesis that patients with NP have a more forward head posture in standing than age-matched pain-free participants. However, the clinical significance of this finding may be questionable. First, the ability of a clinician to detect 3.2° through typical clinical observation is unlikely, although it has not been tested to date. Second, it is possible that intraindividual variation for the angle between C7, the tragus, and the horizontal is higher than the intergroup difference found. The only study that can inform this was undertaken by Wilmarth and Hilliard36 who found the variation within subjects over a 3-day period to be around 1°. It may also be worth considering the clinical significance of the finding in terms of a change in head posture relating to a change in NP. A study from Falla et al37 suggests that a decrease in NP intensity may be independent of an improvement in forward head posture. In this study, the change in the angle between C7, the tragus, and the horizontal was measured during a 10-minute computer task before and after an exercise program in 2 groups of patients with NP. A statistically significant decrease in NP intensity was reported for both groups, but only 1 group showed a statistically significant improvement in forward head posture. However, it is unknown whether a change in head posture of a higher magnitude than that reported by Falla et al37 is related to a decrease in NP intensity or whether the group that showed a change in head posture will have any sustained benefits (eg, decrease in the frequency of relapses). Further studies are needed to clarify the clinical significance of our findings.
Our results suggest that age may be critical to the relationship between head posture and NP. For participants over 50 years of age, there was no association between head posture and NP. However, for younger participants, NP seems far more clearly associated with forward head posture where the mean difference (5.7°; CI, 1.8°–9.7°) was almost twice that for the overall sample (3.2°; CI, 0.9°–6.3°). To our knowledge, this is the first time that this age-related finding has been reported. It has implications for previous and future studies and may be of potential clinical relevance. It also raises questions about the relationship between the etiology and natural history of NP and head posture; does NP lead to the development of a more forward head posture? Does a more forward head posture predispose people to suffer NP? The results from the older group do not suggest that forward head posture is indicative of NP and, perhaps, therefore, suggest limitations in the value of measuring head posture in older patients presenting with chronic NP. Further research should help clarify this. The absence of a difference in forward head posture found for older participants with and without NP may be related to changes in the mechanisms involved in the maintenance of head posture with age. Age-related degenerative changes have an impact on the structure of tissues and the subsequent mechanics of the cervical spine.3, 38Studies have shown a reduction in proprioception for neck movements of persons over the age of 45 years, regardless of NP.39 Therefore, age-related changes may well contribute to a more forward head posture even in the absence of pain.
For the younger group, the more marked forward head posture for NP participants may be sufficient to be of relevance to the examining clinician, although the ability to recognize a mean difference of 5.7° may still be problematic if assessed by observation alone. A more reliable and accurate procedure may be needed to measure forward head posture in clinical practice so that it can be monitored and used to inform decisions regarding treatment.
Previous studies measuring the angle between C7, the tragus, and the horizontal in patients with NP and pain-free participants show conflicting results. Shiau,23 Braun,18 and colleagues found a statistically significant difference between patients and controls, whereas Harrison,25 Visscher,40 and colleagues did not. Shiau and Chai23 used photographs and a sample of 51 patients with NP aged between 19 and 66 years old and 28 pain-free participants aged 20 to 34 years old. A mean angle of 54.0°±4.9° for patients and 56.7°±3.5° for pain-free participants was reported. Braun18 used a personal analysis digitizing system and a sample of 9 patients with a mean age of 38 years old and 40 pain-free participants with a mean age of 28 years old and reported values of 48.2°±3.2° and 55.4°±4.6° for patients and controls, respectively. Harrison et al25 used a goniometer and a sample of 10 patients (age 23–43y) and 41 pain-free participants (age 20–45y). Patients were found to have mean angular values of 49.4°±4.2°, and pain-free participants had mean angular values of 49.3°±7.0°. Visscher et al40 used photographs and a sample of 10 patients and 45 pain-free participants (age was not specified) and reported mean angular values of 51.1°±6.5° for patients and of 52.3°±4.5° for pain-free participants. The results reported in these studies for the angle between C7, the tragus, and the horizontal tend to show higher means and smaller SDs than those reported in our study. However, it is difficult to compare the results because of the different procedures, age groups, and NP definitions used.
With regards to the other 2 angles measured, the results contribute to the relatively minimal data previously reported. The results for the angle between the tragus, the eye, and the horizontal (patients, 21.0°±6.4°; controls, 18.8°± 7.7°) show that NP and pain-free participants in our sample showed comparable results to those reported by Harrison et al25 (patients, 21.6°±6.4°; controls, 18.8°± 4.2°). It is claimed that a more forward head posture is associated with an increase in head extension,8, 10, 12 but our results do not support this. To our knowledge, there are no studies comparing side flexion in participants who have NP and those who are pain-free, but studies conducted in healthy participants16, 31 confirm that this angle approaches 0, indicating a symmetrical head posture with regards to this measurement. Additionally, Shiau and Chai23 measured the angle between the line that joins both pupils and the horizontal, which also gives an indication of side flexion, and they too found values approaching 0 (patients, 1.7°±1.7°; controls, –1.7°±1.6°). Our results suggest that age may be indicative of asymmetry for this angle with participants in the older group showing a statistically significant asymmetry for this angle compared with the younger group. No difference was found between NP and pain-free participants.
The sample size was informed by the findings of a previous study and powered to detect a difference of 2.7° for the angle between C7, the tragus, and the horizontal between patients and pain-free participants. Thus, the study had sufficient power to detect a difference between both groups for the angle between C7, the tragus, and the horizontal, but the angles between the tragus, the eye, and the horizontal and between the inferior margins of the right and the left ear and the horizontal were not taken into account when calculating sample size.
The study aimed to minimize errors and bias by recruiting a sample matched for age and sex, setting careful selection criteria, having randomized order to avoid any serial effects in the data collection, and blinding the digitization procedure. However, the self-report of exclusion and inclusion criteria may not be the most appropriate, and we did not screen participants for balance disorders that may have affected head posture. This needs to be considered in future studies.
Conclusions
Patients with chronic nontraumatic neck pain aged 50 years or below had a more forward standing head posture than pain-free individuals, whereas there was no difference between these groups for older participants. No difference was found between patients and pain-free participants for head extension and side flexion. Further research is needed to clarify whether the statistically significant difference found is clinically meaningful. Future studies comparing head posture for patients and controls should take age into account in their design.
Suppliers
aAriel Dynamics Inc, 4885 Ronson Ct, Ste A, San Diego, CA 92111.
bResearch Randomizer, www.randomizer.org.
cSPSS Inc, 233 S Wacker Dr, 11th Fl, Chicago, IL 60606.
Acknowledgments
We thank the Hospital da Prelada, Portugal, for supporting the study. We also thank the anonymous reviewers for their valuable comments in an earlier version of the article.
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