AUTHOR COPY. Carol McFarland a,, Sharon Wang-Price b and Shanan Richard c

Transcription

1 Journal of Back and Musculoskeletal Rehabilitation 28 (2015) DOI /BMR IOS Press Clinical measurements of cervical lordosis using flexirule and inclinometer methods in individuals with and without cervical spine dysfunction: A reliability and validity study Carol McFarland a,, Sharon Wang-Price b and Shanan Richard c a Texas Spine and Joint Hospital, Tyler, TX, USA b School of Physical Therapy, Texas Woman s University, Dallas, TX, USA c Parkland Health & Hospital System, Dallas, TX, USA Abstract. OBJECTIVE: The purposes of this study were to determine the reliability and validity of two clinical measurements of cervical lordosis and to compare these measurements of individuals with cervical spine symptoms to those of asymptomatic individuals. METHODS: Fifty-seven participants were recruited for the study: 18 following cervical fusion, 20 with neck pain and no surgery, and 19 with no neck pain. Cervical lordosis was measured using a flexible ruler (flexirule) and a modified bubble inclinometer. Intertester and intratester reliability were calculated for both methods. Validity was assessed by correlating measurements taken using both methods to Cobb angles between C2 and C7 on lateral view radiography of the participants in the cervical fusion and the neck pain groups. RESULTS: Intraclass correlation coefficients (ICCs) revealed good intratester reliability for both methods. Intertester reliability was fair for the flexirule method but good for the inclinometer method. Pearson correlations with radiographic angles were poor for both methods. ANOVAs showed no significant difference in cervical lordosis measurements between asymptomatic and symptomatic groups. CONCLUSION: Although both the flexirule and inclinometer methods are reliable, neither method correlated with the Cobb angle on the radiography, suggesting these methods may measure different aspects of cervical spine alignment. Keywords: Cervical spine, sagittal alignment, inclinometer, Cobb angle, posture 1. Introduction Cervical spine posture and specifically cervical lordosis has been shown to be an important factor in evaluation and intervention selection for patients with cervical pathology. Significant correlations have been found between cervical spine postural deviations and chronic neck pain [1 4], headache [5], degenerative Corresponding author: Carol M. McFarland, 777 S. Broadway, Tyler, TX 75701, USA. Tel.: ; cmcfarland@ nctv.com. disc disease [1,6], and peripheral problems such as carpal tunnel syndrome [7]. Poor cervical spine posture has also been related to decreased cervical muscle performance, restricted cervical motion, and maximal voluntary ventilation due to poor positioning of respiratory musculature in individuals with chronic neck pain [2,3,8,9]. Adequate, but not excessive cervical lordosis is considered an important component of cervical spine posture [1,4,10]. Many spine specialists use radiography for spinal curvature assessments to identify spinal pathologies and to make decisions about spinal surgery. Radiogra- ISSN /15/$35.00 c 2015 IOS Press and the authors. All rights reserved

2 296 C. McFarland et al. / Clinical measurements of cervical lordosis using flexirule and inclinometer methods phy is expensive, is time-consuming and exposes patients to radiation [10,13,14,23]. However, a feasible clincial method to assess cervical lordosis from surface measures has not been validated [10,11,23]. Visual estimates of spinal posture, such as increased or decreased kyphosis or lordosis, are commonly used in the clinic, but these visual methods have been shown to have poor reliability and validity [12]. Cobb angles from C2 to C7 on lateral view radiography are used to estimate the extent of cervical spine lordosis. A clinically normal cervical lordosis from C2 to C7 has been described as a Cobb angle of degrees, with subjects in standing and eyes focused straight ahead [4,13,14]. A cervical lordosis of less than 20 from C2 to C7 has been shown to be related to cervical dysfunction and pain [4]. Decreased cervical lordosis, especially involving a kyphotic deformity from trauma or degeneration, may cause narrowing or impingement of the spinal canal [13]. Neurosurgical studies often use normal cervical spine lordosis as an outcome to determine optimal space in the spinal canal as well as the intervertebral foramen. Often, the primary aim of cervical surgery is to lessen or correct the deformities [13 17]. Following cervical fusion, patients have been shown to have areas of either increased or decreased cervical lordosis, therefore assessing cervical posture has been advocated for a standard pre- and post-surgical assessment [13 15]. The flexirule and inclinometer are two commonly used clinical instruments in postural assessments of the spine. Both have been shown to be reliable for measurements of the thoracic and lumbar spine curvatures [18 22]. Previous studies have addressed the use of the flexirule for measuring cervical lordosis, but did not find the flexirule method valid or reliable [11, 23]. However, these studies took measurements from occiput to C7 [11,23], whereas most of the researchers have considered C2 to C7 to be more representative of the overall cervical lordotic curve [1,4,13]. We speculate that inclusion of segments from the occiput to C2 may affect measurements of cervical lordosis. No studies have investigated reliability or validity for the use of the flexirule or the inclinometer in assessing cervical spine posture for individuals who have undergone cervical spine surgery or those with neck pain. The purposes of this study were (1) to determine the reliability of measurements of cervical lordosis using both the flexirule and inclinometer methods on individuals following cervical spine surgery, individuals with neck pain and no surgery, and individuals with no neck pain, (2) to determine the criterion validity of the flexirule and inclinometer methods by correlating them with the Cobb angles obtained from radiography on individuals following cervical spine surgery and individuals with neck pain and no surgery, (3) to compare the flexirule and inclinometer measurements of cervical lordosis of individuals following cervical spine surgery and individuals with neck pain respectively to those of individuals without neck pain, and (4) to identify relationships between disability, pain, and posture measurements. 2. Methods 2.1. Participants Fifty-seven men and women (mean age 48.1 ± SD 13.1) were recruited for the study and classified into one of the three groups based on their existing symptoms and/or a history of surgery. Group 1 included individuals who had anterior cervical fusion (ACF) surgery within the past year (n = 18); Group 2 consisted of individuals with neck pain but no history of cervical spine surgery (n = 20); Group 3 included adults with no existing neck pain (n = 19). ACF is the most common surgical procedure for neck pain. To minimize the effect of various surgical procedures on the posture alignment, only those who received ACF were eligible for the study. Participants in Group 3 were matched by age to those in Group 2 because the angle from C2 to C7 and the incidence of forward head posture have both been shown to increase with age [15,24]. After being informed of the procedures and risks, participants signed a written consent form that was approved by the Institutional Review Board at the primary investigator s affiliated institution. The study was conducted according to the Declaration of Helsinki. The participants with congenital musculoskeletal disorders that caused postural deviations of their own were excluded from the study. Individuals with intractable pain, severe motor loss, extensive myelopathy or could not tolerate testing positioning or procedures were also excluded from the study Instrumentation Cervical lordosis was determined using two clinical instruments: A flexirule (Staedtler Mars Co., Nuremberg, Germany) and an inclinometer (Baseline,Fabrication Enterprises Inc., Irvington, New York). The flexirule is a narrow (5 mm by 8 mm) flexible 75 cm

3 C. McFarland et al. / Clinical measurements of cervical lordosis using flexirule and inclinometer methods 297 ruler that can conform to the contour of the spine and maintain its shape while the contour is traced onto a paper grid for measurement [11,23]. The inclinometer has an indicator and a 360 movable scale. The 0 point of the scale is aligned with the indicator at the first measurement, allowing easy reading of the change in angle at a second measurement. The base of a traditional inclinometer is too wide for the cervical spine; therefore, the base of the inclinometer was cut down to 3 cm in length so that it had a better fit over a cervical spinous process. The Neck Disability Index (NDI) is a self-report questionnaire (10 items) to determine the patient s perception of function and disability associated with cervical disorders. The NDI questionnaire was chosen because it has been reported to be reliable and valid for determining the level of function and disability due to neck pain [25 28]. The minimal detectable change of NDI was reported as 5/50 for uncomplicated neck pain and 10/50 for cervical radiculopathy [27,28]. The Numeric Pain Rating Scale (NPRS) of 0 10 was used to assess participant s pain level. The NPRS was selected because it is easy to administer and has good reliability with the minimal clinically important difference reported to be 1.3 [27,28]. Both the NDI and NPRS scores were collected to identify relationships between disability, pain, and posture measurements Procedure All participants completed a brief medical intake form which included demographics, pain descriptions, and a history of neck pain and surgery. This information was used for group assignment (i.e., whether the participants had spine surgery, neck pain without surgery, or were symptom free). Only those participants with cervical dysfunction (Group 1 and 2) were asked to rate their pain level using the NPRS, and their disability level due to neck dysfunction using the NDI questionnaire. Three testing sessions were conducted on the same day within which cervical lordosis measurements were taken using both the flexirule and the inclinometer methods. One measurement per method was taken during each session. The first investigator took measurements in the first and third session, and the second investigator took measurements during the second session. A rest period of at least five minutes was given between sessions. The measurements taken by the first investigator during the first and third sessions were used to examine intratester reliability and the measurements collected by the two different investigators were used to determine intertester reliability. Further, radiographs related to the current episodes of the participants of Groups 1 and 2 were obtained Cervical lordosis measurement using the flexirule method The flexirule method was applied with a similar protocol used in the previous studies for measuring sagittal alignment of the thoracic and lumbar spine [18,19]. During the measurement, the participants were in a standing position with their arms relaxed at sides and eyes looking straight ahead. The C2 and the C7 segments were identified and marked using removable adhesive skin markers. The first palpable spinous process below the occiput was identified as C2. A small nod increases the prominence of C2 and confirms its location on some individuals [24,29]. Next, the vertebrae were counted to identify C7. The C7 segment location was confirmed by performing a neck extension. During neck extension, anterior movement of the C6 makes it less palpable, whereas the C7 tends to remain in the same position [24,29]. The flexirule was then molded to the cervical lordosis between these two markers. Marks were then made on the flexirule with small stickers indicating the location of the C2 and the C7 spinous processes. The flexirule was then transferred to the paper grid and the curve was traced on the paper with the C2 and the C7 markers as the ends of the curve. Two linear measurements were made from the transposed curve tracing. The linear distance (in cm) from the C2 to the C7 was drawn and labeled L. Then the greatest perpendicular distance from the L to the curve was measured, drawn, and labeled Dmax, the term used to represent the greatest depth of the curve. Ratios of Dmax/L were calculated as an index for cervical lordosis, with larger values indicating a greater cervical lordosis. The Dmax/L ratio reportedly describes the dimensions of the curve [18,19] Cervical lordosis measurement using the inclinometer method To measure cervical lordosis, the base of the C2 and C7 spinous processes were identified with the skin markers described for the flexirule method. The inclinometer was positioned in the sagittal plane with the center of the base over the C2 spinous process and the two feet of the inclinometer base placed in the interspinous spaces above and below the C2. The inclinometer was set to zero in the C2 position and was then moved over the C7 spinous process. The number of de-

4 298 C. McFarland et al. / Clinical measurements of cervical lordosis using flexirule and inclinometer methods Table 1 Characteristics and cervical lordosis measurements of participants in three groups (post-surgery, neck pain and asymptomatic participants) Group 1 Post-Surgery (n = 18) Group 2 Neck Pain (n = 20) Group 3 Asymptomatic (n = 19) Gender (# female, # male) 12 F, 6 M 16 F, 4 M 13 F, 6 M Demographic Data Mean (SD) Mean (SD) Mean (SD) Age (years) 55.1 (9.9) 45.7 (12.4) 44.2 (13.9) Numeric Pain Rating Scale 3.1 (2.9) 4.3 (1.9) NA** Neck Disability Index (%) 17.9 (8.6) 19.9 (8.0) NA** Cervical Lordosis Measurements Mean (SD) Mean (SD) Mean (SD) Flexirule method (%) 7.5 (2.9) 7.3 (2.8) 9.1 (2.0) Inclinometer method ( ) 41.9 (9.0) 41.8 (10.6) 43.9 (5.1) Cobb angle on radiography ( ) 11.3 (11.3) 13.7 (10.9)* NA** Cobb angle data on Group 2 was based on 15 available radiographs; Numeric Pain Rating Scale, Neck Disability Index scores, and Cobb angles were not available for the asymptomatic participants because they did not have existing neck pain and the radiography was not justified. grees were read and recorded in the C7 position, for the cervical lordosis angle. The inclinometer method is designed to estimate the angle of lordosis by using tangents to the end of the curve [30] Radiographic postural measurement Cervical spine lateral radiography was imaged while the participants were standing with their arms relaxed at their sides and with their eyes focused straight ahead, following the guidelines set by the radiology department of the affiliated hospital. We used the participant position from the imaging method as the participant position for the flexirule and inclinometer methods. Participants in Group 1 had their radiographs taken on the day of posture measurements, but radiographs of Group 2 were obtained from earlier dates because participants in Group 2 often had radiographbefore they were referred to physical therapy. On lateralview radiograph of the cervical spine, the angle of lordosis was measured from C2 to C7 and estimated by the Cobb angle. The angle formed between lines along the superior endplate of the C7 and the inferior endplate of the C2 vertebral bodies defines the Cobb angle of cervical lordosis [13,16] Data analysis Descriptive data was reported for demographics of all participants, cervical lordosis measurements of the inclinometer and flexirule methods, the NDI scores and the NPRS scores. Intraclass correlation coefficients (ICC) were used to determine the interrater (ICC 2,1 ) and intrarater (ICC 3,1 ) reliability. Criterion validity was determined by examining the association between the radiographic Cobb angles and the flexirule cervical lordosis measurements, and between the radiographic Cobb angles and the inclinometer cervical postural measurements respectively, using the Pearson- Table 2 Reliability (intraclass correlation coefficient, ICC) and criterion validity (Pearson correlation coefficient, r) of the inclinometer and flexirule methods for cervical lordosis measurements Statistics 95% CI Reliability of flexirule method Intrarater ICC = Interrater ICC = Reliability of inclinometer method Intrarater ICC = Interrater ICC = Criterion validity (correlated to Cobb angles) Inclinometer r = 0.07 Flexirule r = 0.25 product moment correlation coefficient with the alpha set at 0.05 for a test of significance. Two separate oneway ANOVAs were used to examine the difference in cervical lordosis measurements between the three groups for each measurement method: flexirule and inclinometer. The alpha was set at 0.05 for a significance of the ANOVA tests. The Pearson correlation coefficients were also calculated and scatter plots were created to examine relationships between the NDI and the NPRS scores and two cervical lordosis measurements for participants in Group 1 and Results Table 1 lists characteristics of the participants for each group, including their age, sex, NDI scores, NPRS scores, cervical lordosis measurements of both the flexirule and inclinometer methods, and the Cobb angles of radiograph. Chi-square tests showed no significant difference in gender distribution between groups. The ICCs (Table 2) demonstrated that both clinical methods of cervical lordosis measurement had good intrarater reliability, with an ICC of 0.84 for the flexirule method and an ICC of 0.94 for the inclinometer method. However, the interrater reliability was fair

5 C. McFarland et al. / Clinical measurements of cervical lordosis using flexirule and inclinometer methods 299 NDI NDI Flexirule Measurements (%) NPRS Flexirule Measurements (%) Inclinometer Measurements ( ) Inclinometer Measurements ( ) Fig. 1. Scatter plots illustrating the lack of a relationship between the Neck Disability Index (NDI) and the Numerical Pain Rating Scale (NPRS) scores and the cervical lordosis measurements of the flexirule and inclinometer methods for participants post cervical surgery (Group 1) and participants with neck pain (Group 2) combined. NPRS for the flexirule method (ICC = 0.53) and good for the inclinometer method (ICC = 0.84). Pearson correlation coefficients are summarized in Table 2 and revealed a poor association between the Cobb angles and the cervical lordosis measurements of the flexirule method as well as a poor association between the Cobb angles and the cervical lordosis measurements of the inclinometer method. Given that the Cobb angle was the reference criterion for determining cervical lordosis alignment, the poor associations do not support criterion validity for these two clinical measurementsfor cervicallordosis. In addition, the ANOVA results showed no differences in cervical lordosis measurement between the three groups, p = 0.08 (η 2 = 0.09) for the flexirule and p = 0.70 (η 2 = 0.02) for the inclinometer methods. Lastly, Pearson correlation coefficients (Table 2) and scatter plots (Fig. 1) showed poor association between both the NDI and NPRS scores and the flexirule and inclinometer measurements in participants with cervical spine surgery (Group 1) and in participants with neck pain (Group 2). These results indicate that there was no relationship between surface measures of cervical spine lordosis and neck pain symptoms or disability. 4. Discussion The results of the study showed that both flexirule and inclinometer had good-to-excellent intrarater reliability. The results also showed good interrater reliability for the inclinometer method but fair reliability for the flexirule method to determine cervical lordosis. One possible source of error may have occurred during palpation used to identify spinous process. Another potential source of variation may have been the smaller inclinometer base, which could have decreased the likelihood that the inclinometer was aligned appropriately. Also, because the flexirule method involves additional steps of moving the flexirule to paper, tracing the curve, and measuring the tracing, there are additional sources of error which can occur during the transfer. Our reliability findings in the cervical spine are similar to those in the lumbar spine. Previous studies showed good reliability (ICC = 0.97) in the lumbar

6 300 C. McFarland et al. / Clinical measurements of cervical lordosis using flexirule and inclinometer methods and thoracic curves measured with a flexirule [18], and excellent reliability (ICC = 0.96) when using an inclinometer to measure lumbar lordosis [20]. The lower ICC values in the cervical spine could be attributed to smaller cervical spinal curves and segments, making segment identification difficult, therefore increasing errors. Although the intrarater reliability was good for both the flexirule and the inclinometer methods, this study did not find these two clinical methods to be valid when correlated to the radiographic Cobb angles. We speculate that the shape of the cervical vertebral bodies and the ligament nuchae may contribute to the lack of correlation finding. In addition, the surface measurements used a tangent method of assessing the curve or a calculation of an angular representation of the curve depth versus length measurements. Both of these estimations of cervical lordosis are different mathematically than the direct Cobb angle measurement. Further, the Cobb angle is highly influenced by the shape of the vertebral body but the flexirule and the inclinometer method are not. The superficial cervical curvature could be affected by the tightening of the thick ligament nuchae which attaches directly to the spinous process of the cervical spine. The presence of the ligament nuchae may limit surface measurement of the cervical lordosis. Therefore, the Cobb angle may not be the most appropriate reference criterion for comparison to these two skin measures. Another possible criterion reference could have been surface measurements along the cervical spinous processes made on the radiographs using flexicurve. However, the skin surface and some spinous processes were not fully visible on radiographs provided for this study. Thus, the surface measurements derived from the the radiographs would be too variable for valid comparisons between the radiograph and the flexirule methods. Unlike the cervical spine, the lumbar and thoracic curves do not have a thick ligament to occupy the curvature space. The validity of the flexirule method has been established by comparing the flexirule curvature to the radiographic Cobb angles of thoracic and lumbar curves with correlation coefficients of 0.87 by Lundon et al. [18]. Lack of association could be due to the differences in timing when the flexirule measurements were taken. The flexirule measurements were taken immediately after the imaging in Lundon et al. study, but a significant time lapsed after the participants had their radiography images in our study. However, the validity of inclinometer measures for lumbar lordosis also has been reported with varying results, so the conclusions about its validity cannot be made [20]. Therefore, inclinometers are used more often for measuring lumbar range of motion, rather than a measure for static posture such as lumbar lordosis [20,22]. We also found no significant differences in cervical lordosis measurements between the three groups for both the flexirule (p = 0.08) and the inclinometer (p = 0.70) methods. Lack of differences between the groups with neck disorders and the group without neck pain may indicate that these two clinical cervical lordosis methods were not able to distinguish between participants with and without neck pathology. Although cervical lordosis measurements of the flexirule method were lower in the patient groups (Group 1 and 2) as compared to the asymptomatic group (Group 3), the effect size (η 2 = 0.09) was very small, indicating a considerably larger sample size may be needed to find a significant difference. Cervical lordosis has been used as a primary outcome measurement to determine if patients restore optimal sagittal alignment and capability for normal biomechanical and neurological function of the cervical spine after surgery [13,15]. In this study, we did not find a relationship between the cervical lordosis measurements and the participants disability (NDI scores) and pain level (NPRS scores). Our findings are consistent with Grob et al. s study in which no relationship was found between cervical spine curvature and patient s neck pain [17]. Okada et al. also found no relationship between cervical spine curvature and symptoms, but did identify increased likelihood of disc degeneration in patients with decreased cervical lordosis at the 10-year follow-up [6]. Lack of association may indicate that the cervical lordosis curve reflects different aspects of impairment than the NDI and the NPRS do in the cervical spine patient population. However, caution should be made not to generalize the abovementioned statement because we did not collect NDI and NPRS scores from the asymptomatic participants (Group 3). If there was a difference in the NDI and NPRS scores between the asymptomatic group and the other two patient groups, the result could provide further support of this statement. Although the two methods are reliable and have been used as a clinical tool to assess the cervical posture, lack of difference in the cervical lordosis measurements between the patient populations and the participants without neck symptom indicates that neither method could differentiate the patient population from the asymptomatic individuals. Therefore, although they are easy to apply, neither method can be

7 C. McFarland et al. / Clinical measurements of cervical lordosis using flexirule and inclinometer methods 301 recommended as a clinical method for assessing cervical spine curvature. Development and validation of another clinical tool for cervical lordosis assessment may be warranted. Forward head carriage (i.e., alignment of the C0 to the C2) has been suggested to assess cervical posture because researchers have found correlation between the C0-C2 angle measures and neck pain [5, 24,29]. The C0-C2 angle may be better used to predict radiographic lordosis [15]. 5. Conclusion The results demonstrated good reliability for the inclinometer method, but fair for the flexirule method to determine cervical lordosis. Neither method correlated with measures taken from the radiographs, suggesting that these two methods and the Cobb angle may measure different aspects of cervical lordosis. 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