Abstract
Background Cervicogenic headache (CGH) is defined as headache symptoms originating from the cervical spine. Cervical dysfunction from abnormal posture has been proposed to aggravate or cause CGH, but there are conflicting reports as to whether there is an association between posture and CGH.
Objective The purpose of this study was to evaluate differences in cervical spinal posture, measured on radiographs, between patients with probable CGH and asymptomatic control participants.
Design A single-blinded comparative measurement design was used.
Methods Differences in postural variables from radiographs between participants with CGH (n=30) and age- and sex-matched asymptomatic control participants (n=30) were determined using paired t tests or the nonparametric equivalent. Postural variables were general cervical lordosis (GCL, Cobb angle C2–C7), upper cervical lordosis (UCL, sagittal alignment C2 compared with C3–C4), and C2 spinous process horizontal deviation. Logistic regression determined postural variables, increasing the likelihood of CGH.
Results There were no significant differences in posture between the CGH and control groups. The mean GCL was 10.97 degrees (SD=7.50) for the CGH group and 7.17 degrees (SD=5.69) for the control group. The mean UCL was 11.86 degrees (SD=6.46) for the CGH group and 9.44 degrees (SD=4.28) for the control group. The mean C2 spinous process horizontal deviation was 3.00 mm (SD=1.66) for the CGH group and 2.86 mm (SD=2.04) for the control group. However, there was a significant association between greater GCL and an increased likelihood of having CGH (odds ratio=1.08; 95% confidence interval=1.001, 1.191).
Limitations The findings are limited to an association between GCL and posture, as cause and effect cannot be determined.
Conclusions The association between greater GCL and increased likelihood of having CGH suggests that GCL might be considered in the treatment of patients with CGH. However, as the data do not support posture as a cause of CGH, it is unknown whether addressing posture would reduce CGH.
Assessment and treatment of abnormal posture is common despite there being very little evidence that altered posture is associated with symptoms or that treatment strategies can improve posture-related symptoms.1,2 The assessment of posture assumes that identifying postures that are different to the “ideal” posture may provide a meaningful clinical sign that may be related to dysfunction or symptoms.3 If abnormal posture is not related to dysfunction or symptoms, the justification of clinical postural assessment is limited. Therefore, research to establish associations between postural variables and symptoms in patients is important for justifying current clinical practices. There are very few postural abnormalities that have been directly related to symptoms.2
Cervicogenic headache (CGH) is a type of secondary headache where the symptoms originate from a dysfunction in the cervical spine.4,5 Cervical dysfunction from abnormal posture is one factor that has been proposed to aggravate or cause CGH.6,7 The proposed association between abnormal cervical posture and headache has been demonstrated in migraine and tension-type headaches,8–10 but there are conflicting results in CGH.1,11–13 Despite this lack of agreement, clinicians routinely assess and treat altered posture for CGH1,2; therefore, it is important to examine possible associations in order to guide treatment.
The craniovertebral angle (between the horizontal line passing through C7 and a line extending from the tragus of the ear to the tip of the C7 spinous process10) as measured from photographs has been used to investigate associations between cervical posture and CGH, with conflicting results. Two studies in adults showed no association11,13 and one study in children aged 6 to 12 years showed an association between a smaller craniovertebral angle (ie, increased forward head posture) and the presence of CGH.14 This conflicting evidence suggests that craniovertebral angle measurements may not isolate the specific postural factors that may be associated with CGH symptoms.15 Therefore, to determine potential posture variations in patients with CGH, radiographic measurements are needed. Only one identified study used radiographs to assess static cervical lordosis posture in patients with headache and showed that decreased cervical lordosis was associated with tension headaches.16 Tension headache is considered a different headache type than CGH; therefore, postural presentations may differ in CGH, requiring investigation.
The C2 is proposed as the most common cervical level for CGH genesis, with both the C1–2 and C2–3 joints suggested as the dominant motion segment.15,16 The C2–3 motion segment has been reported by some groups to be the most common source of CGH symptoms,5,17,18 with diagnostic blocks suggesting the third occipital nerve located at C2–3 was implicated as the pain source in approximately 53% of 15 patients with CGH.19 Alternatively, C1–2 was reliably palpated by 2 examiners as the symptomatic cervical level in 63% of 60 patients with CGH.20 Two investigations of “unilateral”21 and migraine22 headaches that assessed the position and symmetry of the C2 spinous process using imaging (computed tomography and radiography, respectively) demonstrated that altered C2 spinous process horizontal plane alignment is associated with headaches. However, due to the use of descriptive rather than standardized headache criteria, the participant samples potentially included a mix of headache types, so conclusions about the relationship of C2 spinous process horizontal alignment and CGH cannot be determined.
The aim of this study was to determine if cervical spine posture is altered in patients with CGH compared with age- and sex-matched asymptomatic individuals. This is a first step in determining whether posture is worth considering in larger studies that assess the possible factors contributing to CGH symptoms. Determining whether there is a relationship between CGH and cervical posture may potentially provide clinicians with evidence supporting the assessment and treatment of abnormal posture in this patient group.
Method
A single-blind, age- and sex-matched comparative measurement design was used to evaluate differences in cervical spinal posture, as measured on cervical radiographs, between asymptomatic participants (control group) and participants with CGH. Participants were recruited using flyers placed on noticeboards on the university campus where the study was conducted. Interested participants were first screened by telephone for inclusion. All participants provided written informed consent.
Participants
Participants were healthy adults aged between 18 and 50 years with a primary complaint of headache and no history of significant medical conditions that might be potential contraindications to physical examination of the cervical spine, including known cancer, osteoporosis, nerve root symptoms, inflammatory or infectious diseases affecting the neck, instability of the cervical spine, or reported potential vertebrobasilar insufficiency symptoms.23 This age range was used so that altered upper neck posture associated with different age groups15 was not a confounding factor in the analysis of posture in the symptomatic and asymptomatic groups. Potential participants who were possibly pregnant were excluded, as radiography was to be used in the study. Asymptomatic participants were matched by age and sex with participants with CGH. Participants with a diagnosis of CGH were included if their pattern of symptoms was consistent with the diagnostic criteria of the Cervicogenic Headache International Study Group (CHISG, Appendix).24 These diagnostic criteria have been used widely as the basis for inclusion in CGH studies.13,25,26 The potential participants with CGH were screened by telephone for a pattern of symptoms consistent with the CHISG diagnostic criteria.
To be included in the study, participants had to have: (1) a unilateral headache at least once per week over the previous 2 months (unilaterality consistent on one side, not a headache that swapped sides); (2) neck pain before, during, or following the headache; and (3) pain aggravated by movement or specific postures of the neck. This description of neck pain is consistent with criterion Ia(1) of the CHISG criteria. Individuals who experienced an aura with their headache or who were involved in claiming workers' or third-party compensation or litigation were excluded. Those individuals reporting the required pattern of headache symptoms progressed to a physical assessment to determine study eligibility as long as they also had not received any manual therapy treatment for the previous 2 months, as the potential effect of manual therapy on posture is unknown.
The physical assessment consisted of an experienced physical therapist (with professional qualifications in manual therapy and 16 years of clinical experience) applying pressure over the spinous and articular processes of the cervical spine with the participant in a prone position. The techniques used for this palpation assessment were common cervical spine posteroanterior passive accessory intervertebral movement assessment techniques.25 A potential participant with headache was eligible if he or she met the CHISG criteria for the reproduction of “head pain, similar to the usually occurring one” with palpation.24 The identification of patients with CGH thus required potential participants to meet criteria Ia(1) and Ia(2) and criterion III of the CHISG criteria (Appendix). Participants also may have met criteria Ib and Ic, but potential participants were not excluded if they did not meet these criteria (Appendix). As diagnostic blocks were not used (criterion II, Appendix), participants with CGH were considered to have “probable” CGH, based on the best available diagnostic criteria without the use of invasive techniques. Asymptomatic participants also underwent the physical palpation assessment to maintain consistency between study groups, as the possible effects of this palpation assessment on posture are unknown. The therapist performing the physical assessment was blinded as to the headache status of the potential participant. Asymptomatic participants were eligible as long as they did not report any head pain during the physical assessment.
Radiographic Methods
The study used radiographic measurements to quantify posture, as these methods have been demonstrated to allow specific segmental measurements of cervical spine posture.15,27 Two standard views of the cervical spine (one anterior-posterior [AP] open-mouth view and one lateral view, both in a standing position) were used to facilitate generalization to clinical practice. Radiographic examinations were performed by a registered radiographer with 35 years of experience using standardized positioning techniques and participant instructions.28 The radiographic views and instructions were consistent with a standard cervical radiographic series as performed in clinical radiography practice. Participants were asked to stand in a normal comfortable posture with their arms relaxed and to look straight ahead. The images were taken in suspended respiration during normal shallow breathing at rest, with the instruction to “stop breathing now.” Participants were not given any instructions for the timing of inspiration or expiration, as forced voluntary breathing causes thoracic cavity movement and body sway, whereas normal involuntary breathing does not result in excessive movement or blurring of the image.28
Radiographs were performed using a Philips Diagnostic Vertical Bucky Stand attached to a Philips Optimus 50 Medium Frequency Generator and Philips R0 1648 Hi-Speed Rotating Anode X-Ray tube in a Philips ROT 360 X-ray Tube Housing (Philips Healthcare, Best, Holland). Two Fuji Computed Radiography (model DS, Fujifilm Holdings Corp, Tokyo, Japan) imaging cassettes were used: one 18- × 24-cm cassette (for AP open-mouth view) and one 24- × 30-cm cassette (for lateral view). The cassettes contained a standard definition Fuji Digital Image Receptor Plate, Model CR ST-VI (Fujifilm Holdings Corp). All images were obtained using a grid technique (105 lines/inch 12:1 grid). A focal film distance of 178 cm was used for the lateral view radiographic projection, and a focal film distance of 110 cm was used for the AP open-mouth view.
Radiographic Measurements
The radiographic images were obtained digitally and then transferred to Centricity Webpacs V2.1 (GE Medical Systems, Milwaukee, Wisconsin), a software system used to perform measurements. A qualified radiographer experienced in the use of this measurement tool performed all measurements using the same computer and monitor for each participant. A second experienced radiographer repeated the measurements on a subset of 20 randomly selected participants to determine interrater reliability of the on-screen measurement techniques. Both radiographers were blinded to the headache status of each participant and the measurements of the other radiographer. Good reliability has been demonstrated for these methods when they were performed by drawing on hard copies of radiographs15,29–31 but is unknown for digitized images using the Centricity Webpacs software.
The posture measurements performed on the lateral radiographic view were general cervical lordosis (GCL) and upper cervical lordosis (UCL). The GCL measurement was based on the Cobb method.29 It was obtained by drawing lines parallel to the inferior end plates of C2 and C7, and then the software package generated perpendicular lines to those drawn. The acute angle formed between these lines was calculated by the software package and recorded as GCL (Fig. 1A). A higher value for GCL indicated a participant had greater cervical lordosis between C2 and C7. The UCL radiographic measurement, based on the technique described by Johnson,15 involved drawing a line between the most superior-posterior point on the odontoid process of C2 and the most inferior-posterior point on the body of C2. A second line was then drawn connecting the most inferior-posterior point on the body of C3 with the most inferior-posterior point on the body of C4. The angle for UCL was determined by measuring the acute angle formed between these 2 lines (Fig. 1B). A higher value for UCL indicated a participant had greater cervical lordosis between C2 and C4. The AP open-mouth radiograph view was used to measure the position of the C2 spinous process relative to the midline (Fig. 2). This procedure involved a measurement of the distance that the C2 spinous process deviated from the midline at the level of the atlas.27 This measurement was determined by drawing 2 vertical lines: one passing through the midpoint of the tip of the odontoid process and one passing through the midpoint of the spinous process of C2. The distance (in millimeters) between these 2 lines determined the C2 spinous process deviation, with greater values for increased deviation.
(A) Example of a general cervical lordosis measurement (Cobb C2–C7 measurement). Single asterisk represents the angle (in degrees) used in analysis, with a higher value indicating increased lordosis between C2 and C7. (B) Example of an upper cervical lordosis measurement on a radiograph. Double asterisk represents the angle (in degrees) used in analysis, with a higher value indicating increased lordosis between C2 and C4.
Example of a C2 spinous process horizontal deviation measurement on a radiograph. The perpendicular distance (in millimeters) between the 2 lines represents the value used in analysis, with a higher value indicating increased C2 spinous process horizontal deviation.
Data Analysis
Sample size estimations suggested that potentially meaningful differences of 10 and 5 degrees in GCL29 and UCL,15 respectively, between groups could be detected with 80% power with 22 to 24 participants per group. As the variability of C2 spinous process horizontal deviation was unknown, 30 participants per group were recruited. Intraclass correlation coefficients (ICC [2,1]) and 95% confidence intervals (95% CIs) determined the intertester reliability of the radiographic measurements. Data were checked for normality, and nonparametric methods were used where appropriate. Differences in C2 spinous process horizontal deviation and UCL between the CGH group and control group were determined using t tests. The difference in GCL between groups was determined using the Wilcoxon rank sum test.
A matched-pairs binary logistic regression determined whether measurements taken of cervical spinal posture on radiographs (GCL, UCL, and C2 spinous process horizontal deviation) demonstrated an association with the likelihood of experiencing CGH. Analyses were completed using JMP 10 and SAS 9.2 (SAS Institute Inc, Cary, North Carolina).
Results
Approximately 300 potential participants were screened by telephone using the CHISG criteria (Fig. 3). The most common reasons for exclusion were the presence of bilateral headache or an aura. Control participants were only recruited when a participant of the same sex and similar age had already been recruited in the CGH group, so exclusions occurred if matching was not possible. Thirty participants with probable CGH (mean age=31.4 years, SD=10.0; 4 male, 26 female) and 30 age- and sex-matched controls (mean age=29.8 years, SD=9.4; 4 male, 26 female) were recruited. Participants with CGH reported a mean frequency of 1.2 headaches per week (SD=1.8, range=1–7) and a mean duration of 152.4 weeks (SD=311.7, range=2 months–30 years). All potential CGH group participants who met the telephone screening criteria reported reproduction of their familiar headache on palpation and were included in the study. Digital radiographs were technically compromised for 2 participants (one from the CGH group and one from the control group); therefore, radiographic data analyses are from 58 participants. The intertester reliability of the radiographic measurements was good to excellent: UCL (ICC=.75; 95% CI=.47, .89), C2 spinous process horizontal deviation (ICC=.88; 95% CI=.73, .95), and GCL (ICC=.90; 95% CI=.77, .96).
Flow diagram of study participants. CGH=cervicogenic headache, CHISG=Cervicogenic Headache International Study Group.
There were no significant differences between the control and CGH groups for the 3 radiographic postural measurements (Tab. 1). Logistic regression demonstrated that as the GCL increased, there was a statistically significant increased likelihood of having CGH (P=.042). The odds ratio of 1.08 (95% CI=1.00, 1.19) suggests that with each degree increase of GCL, there was an approximate 8% increased likelihood of having CGH in this sample. There were no associations between CGH and UCL or C2 spinous process deviation (Tab. 2).
Comparisons of Radiographic Postural Variables Between Participants With Cervicogenic Headache (CGH) and Age- and Sex-Matched Asymptomatic Individuals
Associations Between the Radiological Measurements of the Cervical Spinal Postural Variables and the Likelihood of Experiencing Cervicogenic Headache
Discussion
This study is the first to investigate the association between posture and CGH using a radiographic analysis of the cervical spine. The results indicate that cervical spine posture, as defined by the radiographic methods used in this study, cannot be used to differentiate between individuals with probable CGH and those who are asymptomatic. However, an increase in GCL was found to be associated with an increased likelihood of experiencing CGH, although UCL and C2 spinous process horizontal deviation were not associated with CGH. The significant variability in cervical spinal posture in the absence of symptoms has been reported to contribute to difficulties in distinguishing postural types between asymptomatic and symptomatic individuals.15,32 This result also is consistent with a previous study in CGH that indicated isolated clinical signs were not sufficient to differentiate individuals with CGH from those who were asymptomatic.33 Although the posture variables measured in this study did not differentiate individuals with CGH from those who were asymptomatic, the association between increased GCL and an increased likelihood of having CGH suggests that GCL may be worth considering in assessment of patients with CGH.
Interpreting the odds ratio for the association between GCL and CGH (1.08), each degree of increased lordosis increases the odds of having CGH by 8% (compared with the control group in this study). However, the 95% CI for the odds ratio (1.0, 1.19) suggests that there is either no association or the odds of having CGH may be as high as 19% per degree increase in GCL. As the 95% CI value for the odds ratio suggests that there may not be an association, the routine assessment of GCL as an isolated clinical sign is not justified. The inability of any single clinical sign or injection procedure to discriminate CGH is consistent with the description of CGH as a syndrome34–36 characterized by a combination of movement, joint, and muscle dysfunction.37,38 However, a combination of clinical signs (restricted cervical movement, impairment in the craniocervical flexion test, and palpable upper cervical joint dysfunction) has been demonstrated to reliably identify CGH.33 The results of the current study suggest that further investigation may be warranted to determine if increased GCL may improve the identification of CGH when considered in combination with other clinical signs.
Previous studies have demonstrated an association between decreased cervical lordosis and tension-type headache14 or neck pain.39,40 In contrast, the present study demonstrated an association between CGH and increased cervical lordosis. This finding is consistent with the results of a previous study in children that demonstrated increased forward head posture as measured by craniovertebral angle (which might be expected to be associated with increased cervical lordosis) was associated with having CGH. These results together suggest that increased cervical lordosis may well be unique to CGH and could be associated with the upper cervical muscle dysfunction that is a feature of CGH.33,41 One possible theory explaining the relationship between CGL and CGH may be related to muscle dysfunction,42 as upper cervical flexor muscle dysfunction has been established as a feature of CGH33,41 and treatments to improve muscle function and control have been demonstrated to be effective in patients with CGH.41,43–45 However, the effects of improved muscle function on posture in patients with CGH are unknown, as relationships between improved muscle function and posture have been demonstrated only in patients with neck pain46,47 and not CGH.
The interpretation of the results of the present study should be made in the light of the results of previous studies investigating cervical lordosis. No previous studies were identified assessing general GCL in patients with CGH using the radiographic C2–C7 Cobb angle measurement, and few studies in patients with cervical dysfunction were identified. C2–C7 Cobb angles have been reported for patients with neck pain39 and asymptomatic individuals.48 Using measurement methods similar to those of the current study, Harrison et al39 found greater lordosis in people with neck pain compared with asymptomatic controls. Harrison et al reported Cobb angles (X̅=12.7°, SD=12.5°) in their chronic pain group (neck pain symptoms >12 weeks) that were comparable to those of the current study (X̅=11.0°, SD=7.5°). Conversely, Matsumoto et al49 found no difference in the prevalence of lordotic curvature versus nonlordotic curvature in patients with acute whiplash compared with asymptomatic controls; however, these findings were based on observation rather than measurements. The GCL values in asymptomatic participants in the current study (X̅=7.1, SD=5.7) are consistent with C2–C7 Cobb angles reported by Park et al48 for their asymptomatic younger group (mean age=9.0 years, SD=11.0, range=20–29) but much lower than values reported for asymptomatic participants in the study by Harrison et al (X̅=26.8, SD=9.7). Harrison et al excluded participants with excessive head protrusion (perpendicular distance from C2 to C7 >25.4 mm for their pain groups and >10 mm for their control group), partially explaining the differences. Harrison et al also had a lower proportion of female participants (50%) compared with the current study (86%), and women have been shown to have greater cervical lordosis than men (demonstrated using different radiographic assessment methods).16,50 These findings suggest that increased GCL may be a factor in both neck pain and headache, but further research is needed to confirm this conclusion.
The lack of statistically significant associations between the 2 investigated upper cervical spinal postural variables and CGH suggests that despite the upper cervical region being considered the predominant region for the generation of CGH,51–53 symptoms may not be associated with upper cervical postural variations. As increased UCL is one of the components of forward head posture, these results support the findings of previous investigations that concluded there is no association between forward head posture and CGH.11,13 However, these results contrast with the findings of a study by Budelmann et al14 showing forward head posture was greater in children with CGH. The current study findings of no association between CGH and C2 spinous process horizontal deviation concur with a previous study reporting that deviation of the C2 spinous process in patients with headache may be coincidental.54 These findings potentially mean that other impairments in the upper cervical region (eg, muscular dysfunction) may instead be contributing to symptoms, rather than localized postural characteristics. Furthermore, the association of GCL with CGH despite expectations that the UCL would more likely be involved is consistent with a previous case study that showed improvements in CGH following treatment to improve general posture.55 One hypothesis may be that altered general posture contributes to the likelihood of CGH due to the effects on larger muscle groups (eg, levator scapulae) that attach to the upper cervical levels.
Limitations
The participants in this study were recruited via advertisements rather than patients presenting at a clinic, which may bias the results. However, strict selection criteria were used, based on the CHISG major criteria for CGH diagnosis.24 The CHISG recommends the use of diagnostic anesthetic blockades to provide a definitive CGH diagnosis,24 which this study did not utilize. Previous studies also did not use diagnostic anesthetic blockades, as they are considered invasive and associated with unjustifiable risk in the research setting with volunteer participants.13,43 Moreover, diagnostic anesthetic blockades abolish other types of headaches56 and, therefore, do not establish an unequivocal CGH diagnosis. They also rely on the participant presenting for assessment at the time he or she is experiencing symptoms. Participants were included in the current study if they regularly experienced CGH, rather than if they had a presenting headache, and the presence or absence of CGH symptoms at the time the radiograph was taken was not recorded. As CGH is typically an intermittent headache that does not occur in a predictable cycle and that patients often present in the clinical setting during symptom-free periods, it was considered important to investigate posture regardless of participants' symptoms at the time of assessment. Furthermore, although the reproduction of a participant's familiar headache was used as one assessment component to identify patients with CGH as recommended in the CHISG diagnostic criteria, it is acknowledged that pain on palpation of the cervical spine also may occur in patients with other types of headaches, suggesting this criterion is not specific to CGH.57 The reproduction of familiar headache by palpation was used in addition to the descriptors consistent with CGH as described in the CHISG criteria as an additional component supporting the likelihood of a participant's headache being cervical in origin, as in a previous study.58
In terms of the possible confounders of the posture measurements, the radiographs in this study were not assessed for pathology, so other possible contributors to the presenting postures cannot be determined. Furthermore, the palpation assessment may have been a confounding factor, as the effect of palpation on posture is unknown. To minimize the potential for confounding, the palpation assessment was performed on all participants using the same method and in the same sequence regardless of the participants' headache status. Lastly, as this study used a comparative study design, only an association between posture and CGH can be demonstrated, and it is unknown whether increased GCL posture causes CGH or having CGH leads to an increase in GCL. Additional factors that may contribute to symptoms, such as psychosocial variables, were not explored in this study; therefore, the interpretation of the results is limited to the possible association of posture to symptoms.
Future Research
Future investigations could aim to determine if the postural association identified in the current study is a causative factor for CGH or instead a response to symptoms and if changing the GCL has an effect on symptoms. Additionally, a larger multifactorial study may investigate posture with other possible factors (eg, psychosocial factors) influencing the development of symptoms. Further research into cervical posture using radiographs in other headache types may help determine whether posture could be useful for diagnostic differentiation of headache types. Research also may focus on the potential relationships between upper cervical muscle dysfunction and posture, which might direct future treatment strategies in CGH.
In conclusion, the present study showed that 3 components of static cervical spinal posture commonly used clinically cannot be used to discriminate participants with CGH from asymptomatic individuals. However, increased GCL was associated with an increased likelihood of having CGH. Therefore, clinicians may consider GCL when assessing or treating patients with CGH. It should be noted that the results of this study suggest the degree of GCL cannot identify a patient with CGH, so the routine assessment of GCL in all patients with CGH is not supported.
The Bottom Line
What do we already know about this topic?
Clinicians often consider abnormal cervical spine posture to be associated with cervicogenic headache (CGH); however, researchers have disagreed about whether altered posture is actually linked to CGH.
What new information does this study offer?
This study compared a population of patients with CGH with age- and sex-matched control participants. The researchers found that individuals with increased general cervical lordosis had an increased likelihood of experiencing CGH.
If you're a patient or a caregiver, what might these findings mean for you?
Your physical therapist may need to address general cervical lordotic posture to reduce your likelihood of experiencing CGH.
Appendix.
Major criteria for cervicogenic headache diagnosis recommended by the Cervicogenic Headache International Study Groupa
a Major criteria as described by Sjaastad et al.24 Criterion II was not used in the current study.
Footnotes
All authors provided concept/idea/research design, writing, and data collection. Mr Farmer, Dr Snodgrass, and Mr Buxton provided data analysis. Mr Farmer and Dr Rivett provided project management. Dr Snodgrass and Mr Buxton provided facilities/equipment. Dr Snodgrass, Mr Buxton, and Dr Rivett provided consultation (including review of the manuscript before submission). The authors acknowledge John Tessier for his assistance with data collection.
The study protocol was approved by the University of Newcastle's Human Research Ethics Committee.
An abstract of the study was presented at the Musculoskeletal Physiotherapy Australia 16th Biennial Conference; October 1–5, 2009; Sydney, Australia.
- Received February 24, 2014.
- Accepted October 2, 2014.
- © 2015 American Physical Therapy Association
References
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