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Clinical measurement of craniovertebral angle by electronic head posture instrument: A test of reliability and validity
Manual Therapy 14 (2009) 363–368
Contents lists available at ScienceDirect
Manual Therapy journal homepage: www.elsevier.com/math
Original Article
Clinical measurement of craniovertebral angle by electronic head posture instrument: A test of reliability and validityq Herman Mun Cheung Lau a, Thomas Tai Wing Chiu a, *, Tai-Hing Lam b a b
Department of Rehabilitation Sciences, The Hong Kong Polytechnic University, Hung Hom, Hong Kong Department of Community Medicine, The University of Hong Kong, Hong Kong
a r t i c l e i n f o
a b s t r a c t
Article history: Received 13 August 2007 Received in revised form 6 May 2008 Accepted 19 May 2008
The study was a cross-sectional reliability study with the objective of assessing the reliability and validity of the Electronic Head Posture Instrument (EHPI) in measuring the craniovertebral (CV) angle for subjects with or without neck pain. Twenty-six subjects (mean age ¼ 36.88, SD 9.95) with chronic neck pain and 27 subjects (mean age ¼ 31.85, SD 7.63) without neck pain were recruited. The CV angle was measured by the EHPI which consists of an electronic angle finder, a transparent plastic base and a camera stand. Two therapists were recruited to assess the intra- and inter-rater reliability of the EHPI in two separate sessions of measurement. The difference in CV angle between the two groups was determined. The CV angle of the patient group (mean 43.94, SD 3.61) was significantly smaller (p < 0.001) than that of the normal group (mean 50.58, SD 2.09). Intra-rater (intra-class correlation coefficient (ICC) ranged from 0.86 to 0.94) and inter-rater (ICC ranged from 0.85 to 0.91) reliability of the EHPI in measuring CV angle for both groups of subjects were high. In conclusion the EHPI was found to be reliable and valid in measuring the CV angle for subjects with or without neck pain. Ó 2008 Elsevier Ltd. All rights reserved.
Keywords: Craniovertebral angle Reliability Validity
1. Introduction Neck pain is a common musculoskeletal disorder in the general population. A systematic review of neck pain over the world showed that the one-year prevalence ranged from 16.7% to 75.1% for the entire adult population with a mean of 37.2% (Fejer et al., 2006). In a recent telephone survey done in Hong Kong, Chiu and Leung (2006) reported that the 12 month prevalence was 53.6%. Posture of the head and neck has long been recognized as a factor contributing to the onset and perpetuation of cervical pain and dysfunction (Harrison et al., 2005; Persson et al., 2007). Forward head posture is one of the common poor head postures seen in patients with neck disorders (Hickey et al., 2000). A number of studies suggested that forward head posture predisposes individuals towards pathological conditions such as thoracic outlet syndrome and cervical spondylogenic changes (Rocabado, 1983; Ayub et al., 1984). There are many instruments used for assessing the head posture, such as the Rocabado Posture Gauge
q The various parts of the EHPI are readily available in the commercial market and we had no financial support from the manufacturers. No conflict of financial interest was involved in this measurement tool. * Corresponding author. Tel.: þ852 27666709; fax: þ852 23308656. E-mail address: [email protected] (T.T. Wing Chiu). 1356-689X/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.math.2008.05.004
designed by Mariano Rocabado which is a T-shaped instrument. It measures the horizontal distance from the tangent of the most posterior thoracic spinous process to the most anterior cervical spinous process in standing position. The distance measured is the amount of the forward head posture of the subject (Willford et al., 1996). Moreover head posture can be measured by the plumb line and photographic imaging (Wilmarth and Hilliard, 2003). The use of plumb line is, however, limited to the subjective nature of determining the degree of forward head posture and discrepancies can be caused by the viewing angulation of the examiner in relation to the patient. Problems of photographic imaging are related to the time expenditure required for accurate assessment and it does not allow for immediate results (Wilmarth and Hilliard, 2003). One of the objective methods of assessing head posture is through measuring the craniovertebral (CV) angle. This is the angle between a horizontal line through the spinous process of C7 and a line from spinous process of C7 through the tragus of the ear (Raines and Twomey, 1994; Joe et al., 2003). Joe et al. (2003) studied the reliability of measuring the CV angle with Coutts overlay sheet (a transparent grid sheet for mapping) and a protractor in a lateral photograph in 29 female students, and the intra-rater reliability was very high. They also suggested that smaller CV angles indicate greater protraction of the head and larger angles are more representative of ‘ideal’ sagittal plane head/neck alignment. However, the result was limited to young female students only. In many
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previous studies, investigators suggested that there were associations between the forward head posture and neck pain and disability (Griegel-Morris et al., 1992; Szeto et al., 2002). They found that those subjects with head, neck and shoulder discomfort or pain are more likely to have a smaller CV angle. In a recent study Yip et al. (2008) concluded that patients with small CV angle had a greater forward head posture and the greater the forward head posture, the greater the disability. Yip et al. (2008) also recommended that the CV angle could provide clinicians with further objective information on the disability and severity of patients with neck pain. An instrument, the Head Posture Spinal Curvature Instrument (HPSCI) was developed to measure both the CV angle and cervical curvature (Willford et al., 1996; Wilmarth and Hilliard, 2003). It was designed to provide more efficient assessment tool with immediate feedback. The HPSCI is a non-invasive, inexpensive measurement method which has been demonstrated to produce consistent and stable intra-rater results (intra-class correlation coefficient, ICC ¼ 0.9) across days and trials in 27 healthy subjects (Willford et al., 1996). However, its measuring scale was accurate to the whole number only; there is potential error in attempting to choose which way to read the scale when the indicator falls between two whole numbers. Despite the good intra-rater reliability, Wilmarth and Hilliard (2003) did not investigate the validity of the instrument which is essential for a clinical measuring tool, because strong reliability does not suggest strong validity (Portney and Watkins, 2000). Moreover, the inter-rater reliability in assessment of patients with neck pain has not been elucidated. Manual therapists utilize different methods to achieve correction of forward head posture in patients with neck pain (Harrison et al., 1996). Assessment of posture is an important component of evaluation and affects the design of a treatment regimen. However, clinical evaluation of head posture is generally based on the clinician’s subjective visual impression. Besides, it is difficult to compare patients with each other and to quantify the improvements. Clinicians are continually looking for easier, safer, more objective and reliable devices to measure the head posture which is not yet available in the literature. Hence, the Electronic Head Posture Instrument (EHPI) was developed. The measuring scale of this instrument is accurate to one decimal place and the reading can be taken automatically by the electronic sensor. The objective of this study was to examine the reliability and validity of the EHPI in subjects with and without neck pain.
months and without any treatment were recruited in the patient group. Any person who had history of fracture injury at the cervical and shoulder region or vertebral column, scoliosis, severe thoracic kyphosis, spasmodic torticollis, rheumatic disease, temporomandibular joint dysfunction, neurological motion disorder or back pain, or loss of standing balance were excluded. Explanation and informed consent were obtained from each subject. The project was approved by the University’s Review Board for Health Science Research involving Human Subjects. 2.2. Apparatus The CV angle was measured by the EHPI which consists of an electronic angle finder, a transparent plastic base and a camera stand. The electronic angle finder ‘SmartTool Angle Finder’ made by M-D Building Products (United States) was fixed on a transparent plastic base. The combined Angle Finder and the plastic base (now named as Angle Finder) were mounted on a tripod camera or video camera stand – HAMA ‘Gamma 74’ which was made in Germany (Fig. 1). The Angle Finder could be used to identify and digitally display degrees/percent slope quickly and pitch to 1/10 degree accuracy. Two parallel lines were marked on the opposite sides of the transparent base. The targeted markers were aligned with the two parallel lines of the plastic base simultaneously, in order to measure the CV angle (Fig. 1). The camera stand was used to adjust the height and the tilting angle of the Angle Finder to measure the CV angle. Measurement validity defines the extent to which an instrument measures what it is intended to measure (Portney and Watkins, 2000). It is therefore necessary to establish the validity of the EPHI to detect different angles of rotation from the horizontal. An ‘index table’, validated in angle measurement was used as a criterion to test the measurement validity of the Angle Finder and the steps were as follows. The Angle Finder was reset to ‘0 ’ and mounted to the index table as shown in Fig. 2. The index table was rotated counter-clockwise and then clockwise again such that the readout from Angle Finder was 0.0 . The pointer of the index table was set to 0 . After that, the index table was rotated clockwise manually by hand to 90 with stops over each 5 rotation. The readings from the index table and the Angle Finder were recorded at each step. The index table was then rotated counter-clockwise back to 0 with stops over on each 15 rotation with the reading recorded. 2.3. Procedure of measuring the CV angle
2. Materials and methods 2.1. Subjects This study was a cross-sectional reliability study with a convenient sampling from the out-patient clinic of the Physiotherapy Department in the Prince of Wales Hospital, Shatin, Hong Kong. In order to carry out a contrast-group comparison to investigate the validity of the EHPI, the present authors adopted the following approach for calculation of the sample size. Using a software package from Number Cruncher Statistical System (NCSS) – power analysis and sample size for Windows (1996), it was estimated that a total of 52 subjects, i.e. 26 subjects in each of the patient group and normal group, would be required (Hintze, 1996). The following parameters were used as inputs to the program: (1) 0.05 alpha; (2) 90% power; (3) two-sided alternative; (4) an effect size of 0.5 (this was chosen because an effect size of 0.5–0.7 was considered moderate by Cohen (1977)). Twenty-seven volunteers aged 19–53 years (mean 31.85 years, SD 7.63) and without neck pain during the past 6 months were recruited in the normal group (Ylinen et al., 2004). Twenty-six subjects aged 20–55 years (mean 36.88 years, SD 9.95) with diagnosis of more than one episode of neck pain during the past 3
The EPHI was put on the standardized marking on the floor and the HAMA stand was adjusted into the position until the bubble of the horizontal indicator and the central marking overlapped. The distance from the subject to the centre of the HAMA stand was standardized to 0.3 m while the distance between the operator and the HAMA stand was 0.5 m because this was the longest distance that the testers can reach. The subjects were asked to put on sportswear in order to expose their neck and the upper thoracic spine. They were also required to remove their socks and shoes. The seventh cervical (C7) spinous process was palpated and identified and an adhesive pin marker (Fig. 1) was attached over its midpoint of the most prominent part. The subject was then asked to stand with his/her left shoulder in front of the EPHI. Another pin marker was fixed at tragus of his/her left ear. The subject was instructed to stand comfortably with their weight distribution evenly on both feet and to keep their eyes looking straight ahead. He/she was then instructed to flex and extend the head for three times and then rest it in a comfortable position. A virtual line was drawn between the two pin makers from midpoints of the tragus to C7. The therapist adjusted the EHPI until the two indicator lines were aligned with the markers. The reading from the Angle Finder represented the CV angle, as seen in Fig. 1.
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Fig. 1. Measuring CV angle by the EHPI. When two indicator lines were aligned with the markers (C7 spinous process and tragus), the reading from the Angle Finder would represent the CV angle.
Two physiotherapists with five years of clinical experience in treating patients with neck pain were involved in this experiment to test the intra- and inter-rater reliability of the EHPI. They were trained by one of the authors (HL) to operate the EHPI for measuring CV angles. Two sessions were arranged to measure the CV angle. The reading of each session was taken by two therapists, respectively. In each session, the subject was asked to stand up for the first therapist to take the measurement. He/she was then required to walk around the room and then resume standing for the second therapist, who was blinded to the results of the first measurement, to repeat the measuring procedure. The second session was arranged 7 days later, in order to minimize the memory effect of the therapists. This amounted to four trials in two sessions [i.e. 2(1 þ1)]. Each subject was informed to avoid any unusual activities within the 7 days between the two sessions in order to minimize the changes in his/her neck pain conditions. They were also required to report any change of the neck condition before the second session.
2.4. Statistical analysis 2.4.1. Validity Paired t-test and Pearson’s correlation test were used to examine if there was any significant difference and the correlation between the readings of the index table and the Angle Finder as a test of validity. 2.4.2. Inter/intra-tester reliability ICC Model 1, Form 1 was used to determine the intra-rater and Model 2, Form 1 for the inter-rater reliability of using the EHPI. It has been suggested that ICCs below 0.50 represent poor reliability, ICCs from 0.50 to 0.75 represent moderate reliability and ICCs above 0.75 indicate good reliability (Portney and Watkins, 2000).
Fig. 2. Validity test of smart tool with the index table. The Angle Finder was put on top of the arm of the index table. In the lower figure, the Angle Finder was moved along with the arm of the index table to 30.0 in order to check the measurement validity of the Angle Finder.
2.4.3. Descriptive analysis on normal group and patient group Independent sample t-tests were used to determine if there was any difference in the demographic characteristics and the CV angle between the normal group and the patient group. The minimal level of detectable change (MDC) was calculated according to the formula: standard error of measurement (SEM) z-score at the
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showed that the intra-rater (ICC ranged from 0.86 to 0.94) and inter-rater (ICC ranged from 0.85 to 0.91) reliability of the EHPI in measuring the CV angle for both groups of subjects were high. The SEM was 1.193 and the MDC was 3.31.
Table 1 Demographic characteristics of normal group and patient group. Study part
Normal group (n ¼ 27)
Patient group (n ¼ 26)
Age Mean (standard deviation) (years) Range (years)
31.9 (7.6) 19–53
36.5 (9.7) 20–55
3.4. CV angle of normal group vs patient group
Gender Male Female
n 12 15
n 11 15
The CV angle of the patient group (group mean 43.9, SD 3.6) was significantly smaller (p < 0.001) than that of the patient group (group mean 50.6, SD 2.1) (Table 3)
% 22.6 28.3
% 20.8 28.3
two-sided 95% confidence intervals (z ¼ 1.96) O2, where SEM ¼ SD O1 ICC (Beaton, 2000). The level of significance was set to be 0.05. SPSS version 14.0 program was used for statistical analysis.
4. Discussion 4.1. Validity The validity of the EPHI to detect different angles of rotation from the horizontal was demonstrated by the non-significant difference and the high correlation between the readings from the index table which acted as a standard for measurement. Also, the validity of a clinical measuring tool depends on its ability to differentiate the symptomatic subjects from non-symptomatic ones. The EHPI is also valid in this aspect which can be demonstrated by the contrast-group comparison as discussed in the later section.
3. Results 3.1. Descriptive analysis A total of 26 subjects (11 males, 15 females) were recruited in the patient group and 27 subjects (12 males, 15 females) in the normal group. The demographic characteristics of the subjects are shown in Table 1. It was found that there was no significant difference in the age (p ¼ 0.061) or gender (p ¼ 0.88) between the two groups.
4.2. Reliability 3.2. Validity Result of the paired t-test demonstrated that there was no significant difference (p ¼ 1.000) between the readings of the index table and the Angle Finder at different angles of rotation. They are highly correlated with each other as indicated by the result of Pearson’s correlation test (p ¼ 0.000, r ¼ 1.000) and the X–Y plot as shown in Fig. 3.
It was found that the intra- and inter-rater reliability of using the EHPI to measure the CV angle were high, which demonstrated that this CV angle measurement method was highly repeatable for both the normal group and the patient group. The inter-tester reliability results for trial 2 were better than that of trial 1; this may be due to the practice effect which can help to decrease the random errors of measurement (Portney and Watkins, 2000).
3.3. Reliability
4.3. Normal group vs patient group
Reliability of the EHPI was analyzed separately in the normal group and the patient group as shown in Table 2. The results
The contrast-group comparison of the present study confirmed that the CV angle of the non-symptomatic subjects as measured by
100.00
Smart Tool
80.00
60.00
40.00
20.00 R Sq Linear =1
0.00 0.00
20.00
40.00
60.00
80.00
100.00
Index Table Fig. 3. X–Y plot of index table and Angle Finder. Validity of the Angle Finder in correlation to the index table is shown where the linear line represented that these two tools were highly correlated with each other.
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Table 2 Intra-rater and inter-rater reliability of therapists A and B in measuring CV angle for subjects of patient group and normal group. Patient group ICC (95% CI) n ¼ 26
Normal group ICC (95% CI) n ¼ 27
Intra-rater reliability
Therapist A Therapist B
0.87 (0.73–0.94) 0.94 (0.86–0.97)
0.87 (0.74–0.94) 0.86 (0.72–0.93)
Inter-rater reliability
First trial Second trial
0.86 (0.71–0.94) 0.91 (0.83–0.96)
0.85 (0.71–0.93) 0.88 (0.76–0.95)
the EHPI was significantly smaller than that of the patients with neck pain. This concurred with the previous findings that patients with neck pain have a forward head posture [bad posture] (Edmondston et al., 2007; Cho, 2008; Yip et al., 2008) as compared to non-symptomatic subjects (Haughie et al., 1995; Hickey et al., 2000). It is well accepted that forward head posture predisposed individual towards pathological condition over the cervical and cranial region. Johnson (1998) suggested that persisted forward head posture might increase loading of the cervical joints and abnormal stress on the posterior cervical structures and cause myofascial pain. However, the exact mechanism is still unknown, further study in this aspect is warranted. As there was no statistically significant difference in terms of the age and gender between the two groups, these two factors should not contribute to the difference in the CV angle between the two groups. Raines and Twomey (1994) reported that, regardless of the difference in population samples, the CV angle is a reliable indicator of variation in the head and neck posture. To be clinically useful and valid an instrument should be able to distinguish normal subjects from the patients. The present study has demonstrated significant difference in the CV angle between the patient group and the normal group. This helps strengthen the validity of the EHPI in clinical measurement. The MDC for the measurement of CV angle by the EHPI was 3.31. This implies that when the CV angle measured by the EHPI demonstrated a difference of 3.31 or more, the therapist can be confident that there is a real change of the CV angle and not just a measurement error. In comparison with previous studies (Joe et al., 2003; Wilmarth and Hilliard, 2003; Yip et al., 2008) the present study achieved the following improvements: the automatic display of all the measurement data in the Angle Finder helped reduce the possibility of transcription and calculation errors. In addition, all the measurement data were digitalized to one decimal place. This helped minimize the inaccuracies caused when reading an analogue scale where the indicator falls between two whole numbers. Moreover, the Angle Finder can quickly identify any angle with good accuracy within 0.1. 4.4. Clinical implications Clinicians always try to correct their patients’ forward head postures by various treatment approaches. In order to assess the
effectiveness of these approaches, it is vital to develop an objective method to measure the posture of the patients. The device involved should be practical, user-friendly, reliable and objective in its quantification. The EHPI serves the above purpose as it is an inexpensive, portable and convenient apparatus that allows clinicians to collect an accurate, reliable and objective reading. The instrument provides clinicians with additional useful and reliable information to monitor patients’ condition and progression. 4.5. Limitations of the study The sagittal plane position of the cervical, thoracic or lumbar spine was not measured. This was one of the limitations of this study because the CV angle depends on the relative position of the entire spine. It must be borne in mind that the CV angle is an index reflective of only one part of the total picture of the cervical and head posture. Accurate assessment of complete head and neck posture requires a cephalometric radiographic analysis which was not available in this study. Moreover, further study may be required to elucidate if there are any differences when the subject is in a standing vs a sitting position for analysis of head posture. Due to the limited number of subjects who participated in the study, and the possibility of selection bias in the recruitment of normal subjects, the CV angle measurement results cannot be regarded as a baseline reference for the particular group. In addition, the age group of this study was limited to 19–55 years; therefore further investigation with larger sample size involving different age groups is indicated. Also, responsiveness of the CV angle as measured by the EHPI should be tested in a longitudinal study for subjects with neck pain. 5. Conclusion We have demonstrated that the EHPI was valid in measuring the CV angle. There was a high degree of test–retest reliability in measuring the CV angle for both the normal subjects and those with neck pain. The CV angle of subjects with neck pain was significantly smaller than that of the normal subjects. With increasing demand being placed on evidence-based practice, a valid and reliable outcome measuring tool should contribute to better clinical service and evaluation.
Table 3 CV angle of subjects in normal group and patient group measured by therapists A and B. Minimum CV angle
Maximum CV angle
Individual mean SD
Group mean SDa
Normal (n ¼ 27)
First session therapist A Second session therapist A First session therapist B Second session therapist B
47.4 46.3 47.1 46.5
56.7 57.0 55.4 55.5
51.02.4 51.22.3 50.12.1 50.02.1
50.62.1
Patient (n ¼ 26)
First session therapist A Second session therapist A First session therapist B Second session therapist B
33.7 35.3 35.6 33.7
49.5 48.2 49.5 50.1
43.83.4 44.13.6 44.03.7 43.93.8
43.93.6
Normal/patient
a
Group mean is the mean CV angle measured by both therapists in two sessions of each group.
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References Ayub E, Glasheen-Wray M, Kraus S. Head posture: a case study of the effects on the rest position of the mandible. Journal of Orthopaedic and Sports Physical Therapy 1984;5:179–83. Beaton DE. Understanding the relevance of measured change through studies of responsiveness. Spine 2000;25:3192–9. Chiu TW, Leung SL. Neck pain in Hong Kong: a telephone survey on prevalence, consequences and risk groups. Spine 2006;31(16):E540–4. Cho CY. Survey of faulty postures and associated factors among Chinese adolescents. Journal of Manipulative and Physiological Therapeutics 2008;31(3):224–9. Cohen J. Statistical power analysis for the behavioural sciences. New York: Academic Press; 1977. Edmondston SJ, Chan HY, Chi Wing Ngai G, Warren MLR, Williams JM, Glennon S, et al. Postural neck pain: an investigation of habitual sitting posture, perception of good posture and cervicothoracic kinaesthesia. Manual Therapy 2007;12(4):363–71. Fejer R, Kyvik K, Hartvigsen J. The prevalence of neck pain in the world population: a systemic critical review of the literature. European Spine Journal 2006;15: 834–48. Griegel-Morris P, Larson K, Mueller-Klaus K, Oatis CA. Incidence of common postural abnormalities in the cervical, shoulder, and thoracic region and their association with pain in two age groups of healthy subjects. Physical Therapy 1992;72:425–31. Harrison AL, Barry-Greb T, Wojtowicz GW. Clinical measurement of head and shoulder posture variables. The Journal of Orthopaedic and Sports Physical Therapy 1996;23(6):353–61. Harrison DE, Haas JW, Cailliet R, Harrison DD, Holland B, Janik TJ. Concurrent validity of flexicurve instrument measurements: sagittal skin contour of the cervical spine compared with lateral cervical radiographic measurements. Journal of Manipulative and Physiological Therapeutics 2005;28: 597–603. Haughie L, Fiebert IM, Roach KE. Relationship of forward head posture and cervical backward bending to neck pain. Journal of Manual and Manipulative Therapy 1995;3:91–7.
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Contents lists available at ScienceDirect
Manual Therapy journal homepage: www.elsevier.com/math
Original Article
Clinical measurement of craniovertebral angle by electronic head posture instrument: A test of reliability and validityq Herman Mun Cheung Lau a, Thomas Tai Wing Chiu a, *, Tai-Hing Lam b a b
Department of Rehabilitation Sciences, The Hong Kong Polytechnic University, Hung Hom, Hong Kong Department of Community Medicine, The University of Hong Kong, Hong Kong
a r t i c l e i n f o
a b s t r a c t
Article history: Received 13 August 2007 Received in revised form 6 May 2008 Accepted 19 May 2008
The study was a cross-sectional reliability study with the objective of assessing the reliability and validity of the Electronic Head Posture Instrument (EHPI) in measuring the craniovertebral (CV) angle for subjects with or without neck pain. Twenty-six subjects (mean age ¼ 36.88, SD 9.95) with chronic neck pain and 27 subjects (mean age ¼ 31.85, SD 7.63) without neck pain were recruited. The CV angle was measured by the EHPI which consists of an electronic angle finder, a transparent plastic base and a camera stand. Two therapists were recruited to assess the intra- and inter-rater reliability of the EHPI in two separate sessions of measurement. The difference in CV angle between the two groups was determined. The CV angle of the patient group (mean 43.94, SD 3.61) was significantly smaller (p < 0.001) than that of the normal group (mean 50.58, SD 2.09). Intra-rater (intra-class correlation coefficient (ICC) ranged from 0.86 to 0.94) and inter-rater (ICC ranged from 0.85 to 0.91) reliability of the EHPI in measuring CV angle for both groups of subjects were high. In conclusion the EHPI was found to be reliable and valid in measuring the CV angle for subjects with or without neck pain. Ó 2008 Elsevier Ltd. All rights reserved.
Keywords: Craniovertebral angle Reliability Validity
1. Introduction Neck pain is a common musculoskeletal disorder in the general population. A systematic review of neck pain over the world showed that the one-year prevalence ranged from 16.7% to 75.1% for the entire adult population with a mean of 37.2% (Fejer et al., 2006). In a recent telephone survey done in Hong Kong, Chiu and Leung (2006) reported that the 12 month prevalence was 53.6%. Posture of the head and neck has long been recognized as a factor contributing to the onset and perpetuation of cervical pain and dysfunction (Harrison et al., 2005; Persson et al., 2007). Forward head posture is one of the common poor head postures seen in patients with neck disorders (Hickey et al., 2000). A number of studies suggested that forward head posture predisposes individuals towards pathological conditions such as thoracic outlet syndrome and cervical spondylogenic changes (Rocabado, 1983; Ayub et al., 1984). There are many instruments used for assessing the head posture, such as the Rocabado Posture Gauge
q The various parts of the EHPI are readily available in the commercial market and we had no financial support from the manufacturers. No conflict of financial interest was involved in this measurement tool. * Corresponding author. Tel.: þ852 27666709; fax: þ852 23308656. E-mail address: [email protected] (T.T. Wing Chiu). 1356-689X/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.math.2008.05.004
designed by Mariano Rocabado which is a T-shaped instrument. It measures the horizontal distance from the tangent of the most posterior thoracic spinous process to the most anterior cervical spinous process in standing position. The distance measured is the amount of the forward head posture of the subject (Willford et al., 1996). Moreover head posture can be measured by the plumb line and photographic imaging (Wilmarth and Hilliard, 2003). The use of plumb line is, however, limited to the subjective nature of determining the degree of forward head posture and discrepancies can be caused by the viewing angulation of the examiner in relation to the patient. Problems of photographic imaging are related to the time expenditure required for accurate assessment and it does not allow for immediate results (Wilmarth and Hilliard, 2003). One of the objective methods of assessing head posture is through measuring the craniovertebral (CV) angle. This is the angle between a horizontal line through the spinous process of C7 and a line from spinous process of C7 through the tragus of the ear (Raines and Twomey, 1994; Joe et al., 2003). Joe et al. (2003) studied the reliability of measuring the CV angle with Coutts overlay sheet (a transparent grid sheet for mapping) and a protractor in a lateral photograph in 29 female students, and the intra-rater reliability was very high. They also suggested that smaller CV angles indicate greater protraction of the head and larger angles are more representative of ‘ideal’ sagittal plane head/neck alignment. However, the result was limited to young female students only. In many
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previous studies, investigators suggested that there were associations between the forward head posture and neck pain and disability (Griegel-Morris et al., 1992; Szeto et al., 2002). They found that those subjects with head, neck and shoulder discomfort or pain are more likely to have a smaller CV angle. In a recent study Yip et al. (2008) concluded that patients with small CV angle had a greater forward head posture and the greater the forward head posture, the greater the disability. Yip et al. (2008) also recommended that the CV angle could provide clinicians with further objective information on the disability and severity of patients with neck pain. An instrument, the Head Posture Spinal Curvature Instrument (HPSCI) was developed to measure both the CV angle and cervical curvature (Willford et al., 1996; Wilmarth and Hilliard, 2003). It was designed to provide more efficient assessment tool with immediate feedback. The HPSCI is a non-invasive, inexpensive measurement method which has been demonstrated to produce consistent and stable intra-rater results (intra-class correlation coefficient, ICC ¼ 0.9) across days and trials in 27 healthy subjects (Willford et al., 1996). However, its measuring scale was accurate to the whole number only; there is potential error in attempting to choose which way to read the scale when the indicator falls between two whole numbers. Despite the good intra-rater reliability, Wilmarth and Hilliard (2003) did not investigate the validity of the instrument which is essential for a clinical measuring tool, because strong reliability does not suggest strong validity (Portney and Watkins, 2000). Moreover, the inter-rater reliability in assessment of patients with neck pain has not been elucidated. Manual therapists utilize different methods to achieve correction of forward head posture in patients with neck pain (Harrison et al., 1996). Assessment of posture is an important component of evaluation and affects the design of a treatment regimen. However, clinical evaluation of head posture is generally based on the clinician’s subjective visual impression. Besides, it is difficult to compare patients with each other and to quantify the improvements. Clinicians are continually looking for easier, safer, more objective and reliable devices to measure the head posture which is not yet available in the literature. Hence, the Electronic Head Posture Instrument (EHPI) was developed. The measuring scale of this instrument is accurate to one decimal place and the reading can be taken automatically by the electronic sensor. The objective of this study was to examine the reliability and validity of the EHPI in subjects with and without neck pain.
months and without any treatment were recruited in the patient group. Any person who had history of fracture injury at the cervical and shoulder region or vertebral column, scoliosis, severe thoracic kyphosis, spasmodic torticollis, rheumatic disease, temporomandibular joint dysfunction, neurological motion disorder or back pain, or loss of standing balance were excluded. Explanation and informed consent were obtained from each subject. The project was approved by the University’s Review Board for Health Science Research involving Human Subjects. 2.2. Apparatus The CV angle was measured by the EHPI which consists of an electronic angle finder, a transparent plastic base and a camera stand. The electronic angle finder ‘SmartTool Angle Finder’ made by M-D Building Products (United States) was fixed on a transparent plastic base. The combined Angle Finder and the plastic base (now named as Angle Finder) were mounted on a tripod camera or video camera stand – HAMA ‘Gamma 74’ which was made in Germany (Fig. 1). The Angle Finder could be used to identify and digitally display degrees/percent slope quickly and pitch to 1/10 degree accuracy. Two parallel lines were marked on the opposite sides of the transparent base. The targeted markers were aligned with the two parallel lines of the plastic base simultaneously, in order to measure the CV angle (Fig. 1). The camera stand was used to adjust the height and the tilting angle of the Angle Finder to measure the CV angle. Measurement validity defines the extent to which an instrument measures what it is intended to measure (Portney and Watkins, 2000). It is therefore necessary to establish the validity of the EPHI to detect different angles of rotation from the horizontal. An ‘index table’, validated in angle measurement was used as a criterion to test the measurement validity of the Angle Finder and the steps were as follows. The Angle Finder was reset to ‘0 ’ and mounted to the index table as shown in Fig. 2. The index table was rotated counter-clockwise and then clockwise again such that the readout from Angle Finder was 0.0 . The pointer of the index table was set to 0 . After that, the index table was rotated clockwise manually by hand to 90 with stops over each 5 rotation. The readings from the index table and the Angle Finder were recorded at each step. The index table was then rotated counter-clockwise back to 0 with stops over on each 15 rotation with the reading recorded. 2.3. Procedure of measuring the CV angle
2. Materials and methods 2.1. Subjects This study was a cross-sectional reliability study with a convenient sampling from the out-patient clinic of the Physiotherapy Department in the Prince of Wales Hospital, Shatin, Hong Kong. In order to carry out a contrast-group comparison to investigate the validity of the EHPI, the present authors adopted the following approach for calculation of the sample size. Using a software package from Number Cruncher Statistical System (NCSS) – power analysis and sample size for Windows (1996), it was estimated that a total of 52 subjects, i.e. 26 subjects in each of the patient group and normal group, would be required (Hintze, 1996). The following parameters were used as inputs to the program: (1) 0.05 alpha; (2) 90% power; (3) two-sided alternative; (4) an effect size of 0.5 (this was chosen because an effect size of 0.5–0.7 was considered moderate by Cohen (1977)). Twenty-seven volunteers aged 19–53 years (mean 31.85 years, SD 7.63) and without neck pain during the past 6 months were recruited in the normal group (Ylinen et al., 2004). Twenty-six subjects aged 20–55 years (mean 36.88 years, SD 9.95) with diagnosis of more than one episode of neck pain during the past 3
The EPHI was put on the standardized marking on the floor and the HAMA stand was adjusted into the position until the bubble of the horizontal indicator and the central marking overlapped. The distance from the subject to the centre of the HAMA stand was standardized to 0.3 m while the distance between the operator and the HAMA stand was 0.5 m because this was the longest distance that the testers can reach. The subjects were asked to put on sportswear in order to expose their neck and the upper thoracic spine. They were also required to remove their socks and shoes. The seventh cervical (C7) spinous process was palpated and identified and an adhesive pin marker (Fig. 1) was attached over its midpoint of the most prominent part. The subject was then asked to stand with his/her left shoulder in front of the EPHI. Another pin marker was fixed at tragus of his/her left ear. The subject was instructed to stand comfortably with their weight distribution evenly on both feet and to keep their eyes looking straight ahead. He/she was then instructed to flex and extend the head for three times and then rest it in a comfortable position. A virtual line was drawn between the two pin makers from midpoints of the tragus to C7. The therapist adjusted the EHPI until the two indicator lines were aligned with the markers. The reading from the Angle Finder represented the CV angle, as seen in Fig. 1.
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Fig. 1. Measuring CV angle by the EHPI. When two indicator lines were aligned with the markers (C7 spinous process and tragus), the reading from the Angle Finder would represent the CV angle.
Two physiotherapists with five years of clinical experience in treating patients with neck pain were involved in this experiment to test the intra- and inter-rater reliability of the EHPI. They were trained by one of the authors (HL) to operate the EHPI for measuring CV angles. Two sessions were arranged to measure the CV angle. The reading of each session was taken by two therapists, respectively. In each session, the subject was asked to stand up for the first therapist to take the measurement. He/she was then required to walk around the room and then resume standing for the second therapist, who was blinded to the results of the first measurement, to repeat the measuring procedure. The second session was arranged 7 days later, in order to minimize the memory effect of the therapists. This amounted to four trials in two sessions [i.e. 2(1 þ1)]. Each subject was informed to avoid any unusual activities within the 7 days between the two sessions in order to minimize the changes in his/her neck pain conditions. They were also required to report any change of the neck condition before the second session.
2.4. Statistical analysis 2.4.1. Validity Paired t-test and Pearson’s correlation test were used to examine if there was any significant difference and the correlation between the readings of the index table and the Angle Finder as a test of validity. 2.4.2. Inter/intra-tester reliability ICC Model 1, Form 1 was used to determine the intra-rater and Model 2, Form 1 for the inter-rater reliability of using the EHPI. It has been suggested that ICCs below 0.50 represent poor reliability, ICCs from 0.50 to 0.75 represent moderate reliability and ICCs above 0.75 indicate good reliability (Portney and Watkins, 2000).
Fig. 2. Validity test of smart tool with the index table. The Angle Finder was put on top of the arm of the index table. In the lower figure, the Angle Finder was moved along with the arm of the index table to 30.0 in order to check the measurement validity of the Angle Finder.
2.4.3. Descriptive analysis on normal group and patient group Independent sample t-tests were used to determine if there was any difference in the demographic characteristics and the CV angle between the normal group and the patient group. The minimal level of detectable change (MDC) was calculated according to the formula: standard error of measurement (SEM) z-score at the
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showed that the intra-rater (ICC ranged from 0.86 to 0.94) and inter-rater (ICC ranged from 0.85 to 0.91) reliability of the EHPI in measuring the CV angle for both groups of subjects were high. The SEM was 1.193 and the MDC was 3.31.
Table 1 Demographic characteristics of normal group and patient group. Study part
Normal group (n ¼ 27)
Patient group (n ¼ 26)
Age Mean (standard deviation) (years) Range (years)
31.9 (7.6) 19–53
36.5 (9.7) 20–55
3.4. CV angle of normal group vs patient group
Gender Male Female
n 12 15
n 11 15
The CV angle of the patient group (group mean 43.9, SD 3.6) was significantly smaller (p < 0.001) than that of the patient group (group mean 50.6, SD 2.1) (Table 3)
% 22.6 28.3
% 20.8 28.3
two-sided 95% confidence intervals (z ¼ 1.96) O2, where SEM ¼ SD O1 ICC (Beaton, 2000). The level of significance was set to be 0.05. SPSS version 14.0 program was used for statistical analysis.
4. Discussion 4.1. Validity The validity of the EPHI to detect different angles of rotation from the horizontal was demonstrated by the non-significant difference and the high correlation between the readings from the index table which acted as a standard for measurement. Also, the validity of a clinical measuring tool depends on its ability to differentiate the symptomatic subjects from non-symptomatic ones. The EHPI is also valid in this aspect which can be demonstrated by the contrast-group comparison as discussed in the later section.
3. Results 3.1. Descriptive analysis A total of 26 subjects (11 males, 15 females) were recruited in the patient group and 27 subjects (12 males, 15 females) in the normal group. The demographic characteristics of the subjects are shown in Table 1. It was found that there was no significant difference in the age (p ¼ 0.061) or gender (p ¼ 0.88) between the two groups.
4.2. Reliability 3.2. Validity Result of the paired t-test demonstrated that there was no significant difference (p ¼ 1.000) between the readings of the index table and the Angle Finder at different angles of rotation. They are highly correlated with each other as indicated by the result of Pearson’s correlation test (p ¼ 0.000, r ¼ 1.000) and the X–Y plot as shown in Fig. 3.
It was found that the intra- and inter-rater reliability of using the EHPI to measure the CV angle were high, which demonstrated that this CV angle measurement method was highly repeatable for both the normal group and the patient group. The inter-tester reliability results for trial 2 were better than that of trial 1; this may be due to the practice effect which can help to decrease the random errors of measurement (Portney and Watkins, 2000).
3.3. Reliability
4.3. Normal group vs patient group
Reliability of the EHPI was analyzed separately in the normal group and the patient group as shown in Table 2. The results
The contrast-group comparison of the present study confirmed that the CV angle of the non-symptomatic subjects as measured by
100.00
Smart Tool
80.00
60.00
40.00
20.00 R Sq Linear =1
0.00 0.00
20.00
40.00
60.00
80.00
100.00
Index Table Fig. 3. X–Y plot of index table and Angle Finder. Validity of the Angle Finder in correlation to the index table is shown where the linear line represented that these two tools were highly correlated with each other.
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Table 2 Intra-rater and inter-rater reliability of therapists A and B in measuring CV angle for subjects of patient group and normal group. Patient group ICC (95% CI) n ¼ 26
Normal group ICC (95% CI) n ¼ 27
Intra-rater reliability
Therapist A Therapist B
0.87 (0.73–0.94) 0.94 (0.86–0.97)
0.87 (0.74–0.94) 0.86 (0.72–0.93)
Inter-rater reliability
First trial Second trial
0.86 (0.71–0.94) 0.91 (0.83–0.96)
0.85 (0.71–0.93) 0.88 (0.76–0.95)
the EHPI was significantly smaller than that of the patients with neck pain. This concurred with the previous findings that patients with neck pain have a forward head posture [bad posture] (Edmondston et al., 2007; Cho, 2008; Yip et al., 2008) as compared to non-symptomatic subjects (Haughie et al., 1995; Hickey et al., 2000). It is well accepted that forward head posture predisposed individual towards pathological condition over the cervical and cranial region. Johnson (1998) suggested that persisted forward head posture might increase loading of the cervical joints and abnormal stress on the posterior cervical structures and cause myofascial pain. However, the exact mechanism is still unknown, further study in this aspect is warranted. As there was no statistically significant difference in terms of the age and gender between the two groups, these two factors should not contribute to the difference in the CV angle between the two groups. Raines and Twomey (1994) reported that, regardless of the difference in population samples, the CV angle is a reliable indicator of variation in the head and neck posture. To be clinically useful and valid an instrument should be able to distinguish normal subjects from the patients. The present study has demonstrated significant difference in the CV angle between the patient group and the normal group. This helps strengthen the validity of the EHPI in clinical measurement. The MDC for the measurement of CV angle by the EHPI was 3.31. This implies that when the CV angle measured by the EHPI demonstrated a difference of 3.31 or more, the therapist can be confident that there is a real change of the CV angle and not just a measurement error. In comparison with previous studies (Joe et al., 2003; Wilmarth and Hilliard, 2003; Yip et al., 2008) the present study achieved the following improvements: the automatic display of all the measurement data in the Angle Finder helped reduce the possibility of transcription and calculation errors. In addition, all the measurement data were digitalized to one decimal place. This helped minimize the inaccuracies caused when reading an analogue scale where the indicator falls between two whole numbers. Moreover, the Angle Finder can quickly identify any angle with good accuracy within 0.1. 4.4. Clinical implications Clinicians always try to correct their patients’ forward head postures by various treatment approaches. In order to assess the
effectiveness of these approaches, it is vital to develop an objective method to measure the posture of the patients. The device involved should be practical, user-friendly, reliable and objective in its quantification. The EHPI serves the above purpose as it is an inexpensive, portable and convenient apparatus that allows clinicians to collect an accurate, reliable and objective reading. The instrument provides clinicians with additional useful and reliable information to monitor patients’ condition and progression. 4.5. Limitations of the study The sagittal plane position of the cervical, thoracic or lumbar spine was not measured. This was one of the limitations of this study because the CV angle depends on the relative position of the entire spine. It must be borne in mind that the CV angle is an index reflective of only one part of the total picture of the cervical and head posture. Accurate assessment of complete head and neck posture requires a cephalometric radiographic analysis which was not available in this study. Moreover, further study may be required to elucidate if there are any differences when the subject is in a standing vs a sitting position for analysis of head posture. Due to the limited number of subjects who participated in the study, and the possibility of selection bias in the recruitment of normal subjects, the CV angle measurement results cannot be regarded as a baseline reference for the particular group. In addition, the age group of this study was limited to 19–55 years; therefore further investigation with larger sample size involving different age groups is indicated. Also, responsiveness of the CV angle as measured by the EHPI should be tested in a longitudinal study for subjects with neck pain. 5. Conclusion We have demonstrated that the EHPI was valid in measuring the CV angle. There was a high degree of test–retest reliability in measuring the CV angle for both the normal subjects and those with neck pain. The CV angle of subjects with neck pain was significantly smaller than that of the normal subjects. With increasing demand being placed on evidence-based practice, a valid and reliable outcome measuring tool should contribute to better clinical service and evaluation.
Table 3 CV angle of subjects in normal group and patient group measured by therapists A and B. Minimum CV angle
Maximum CV angle
Individual mean SD
Group mean SDa
Normal (n ¼ 27)
First session therapist A Second session therapist A First session therapist B Second session therapist B
47.4 46.3 47.1 46.5
56.7 57.0 55.4 55.5
51.02.4 51.22.3 50.12.1 50.02.1
50.62.1
Patient (n ¼ 26)
First session therapist A Second session therapist A First session therapist B Second session therapist B
33.7 35.3 35.6 33.7
49.5 48.2 49.5 50.1
43.83.4 44.13.6 44.03.7 43.93.8
43.93.6
Normal/patient
a
Group mean is the mean CV angle measured by both therapists in two sessions of each group.
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