. 2.1k Downloads.AbstractThe first aim of this study was to translate the Neck Pain and Disability Scale (NPAD) from English into Dutch producing the NPAD–Dutch Language Version (DLV). The second aim was to analyze test–retest reliability and agreement of the NPAD–DLV and the Neck Disability Index (NDI)–DLV.
The NPAD was translated according to established guidelines. Thirty-four patients (mean age 37.5 years, 68% female) with chronic neck pain (CNP), within an outpatient rehabilitation setting, participated in this study. The NPAD–DLV and the NDI–DLV were filled out twice with a mean test–retest interval of 18 days.
Published in 1991, the Neck Disability Index (NDI) was the first instrument designed to assess self-rated disability in patients with neck pain. Structure / Content. The patients choose the statement that best describes their situation in each of ten sections. The sections concern impairments like pain (including headaches), and abilities like. The primary purpose of this study is to adapt the Neck Disability Index (NDI)and the Cervical Core Set 6 (CCS6) to the Spanish population. Other objectives are to determine the correlation between intensity of cervical pain, degree of disability, and quality of life; to determine the correlation.
The intraclass correlation coefficient of the NPAD–DLV was 0.76 (95% confidence interval (CI) 0.57–0.87) and of the NDI–DLV 0.84 (95% CI 0.69–0.92). The limits of agreement of the NPAD–DLV and the NDI–DLV were, respectively, ±20.9 (scale 0–100) and ±6.5 (scale 0–50). The reliability of the NPAD–DLV and the NDI–DLV was acceptable for patients with CNP. The variation (‘instability’) in the NPAD–DLV total scores was relatively large and larger than the variation of the NDI–DLV. Neck pain is a common musculoskeletal complaint in western societies. In the large majority of cases, the pathological basis for the neck pain is unclear and the complaints are labeled as ‘non-specific’ or ‘mechanical’.
Disability, limitations in activities and restrictions in participation in daily living and work, may be the result ,. The majority of the total costs of neck pain in the Netherlands were costs due to sick leave and disability payment.Self-reported disability in patients with neck pain is often measured by means of region-specific questionnaires. These questionnaires may measure disability or the functional status with greater responsiveness than generic health questionnaires. Questionnaires should have good psychometric qualities, among which is reproducibility. Reproducibility is the extent to which the same results are obtained on repeated tests when no real change in health status has occurred ,. Reproducibility may be influenced by random measurement errors and within patient variance ,. Both sources of variance may lead to score instability (natural variation) on repeated tests ,.
If a patient with neck pain fills out the same questionnaire on two occasions, it is relevant to know what score instability can be expected in a predefined retest interval or in a waiting period. Reproducibility does have two aspects: reliability and agreement, representing test–retest score stability over time on group level and on individual level, respectively. A measure for reliability is the intra-class correlation coefficient (ICC). It assesses not only the strength of the correlation between two repeated measures, but also if all measures on each subject are identical and do not differ systematically. To quantify the agreement, the test–retest score stability over time on individual level, the limits of agreement (LOA) can be calculated according to the method of Bland and Altman ,. The LOA lies two standard deviations (SD difference) above and under the mean total score difference of all patients between the first and second test. This means that, due to score instability, approximately 95% of all differences within patients will lie between these LOA on repeated tests ,.
In an individual patient, the change due to treatment should exceed these LOA before one can state that real change has occurred.The most used Neck Disability Questionnaires are the Neck Pain and Disability Scale (NPAD) and the neck disability index (NDI) , which are both translated into several languages ,. To be able to use the NPAD and NDI in different countries and social environments these questionnaires must not only be translated properly, but also culturally adapted and validated ,. These translations allow comparison of results of clinical research trials between countries. To investigate which questionnaire is most appropriate, psychometric studies are needed where questionnaires are applied simultaneously to the same sample of patients. The advantage of the NPAD over the NDI may be the simple wording and the unitary structure of the questions; moreover, the questionnaire is easy to complete with its visual analog scale structure ,. The NPAD has not been formally translated into Dutch and, consequently, psychometric qualities of the Dutch Language Version (NPAD–DLV) are unknown. The reliability of the NDI–DLV has been studied in patients with acute neck pain, but not in patients with chronic neck pain (CNP) other than patients with Whiplash associated disorder (WAD) ,.
The first aim of this study was to translate the NPAD from English into Dutch. The second aim was to analyze test–retest reliability and agreement of the NPAD–DLV and the NDI–DLV in patients with CNP in an outpatient rehabilitation setting. Translation and cross-cultural adaptation of the NPADThe NDAP was translated using a forward and backward translation procedure. Two native Dutch speakers (a clinician, aware of the concepts behind the questionnaire and a staff member of the pain rehabilitation team) independently translated and culturally adapted the original version. The translated versions were critically reviewed reciprocally, compared with one another and with the original English version. Disagreements were discussed and a consensus version was produced.
A backward translation (from Dutch into English) of this consensus version was made by a bilingual physiotherapist involved in spine research. The translators examined translation, backward translation and notes about the discussions made during the translation process.
A concept version of the NPAD–DLV was developed and pilot-tested on a heterogeneous group of ten patients and employees of the rehabilitation center, who were asked to comment critically on understandability of the questions and instructions, responses, wording and layout. Finally, a final NPAD–DLV was produced. Study sampleCNP patients were recruited from referrals by general practitioners or medical specialists for rehabilitation treatment in the Center for Rehabilitation at the University Medical Center Groningen, The Netherlands. Inclusion criteria for this study were: non-specific chronic neck pain (3 months duration), admitted for rehabilitation, age between 18 and 65 years, less than 2 years out of work due to CNP or still at work with frequent sick leave due to neck pain, and sufficient knowledge of the Dutch language to complete questionnaires. Exclusion criteria were: specific neck pain, status post surgery in the cervical region, cardiovascular or pulmonary diseases significantly diminishing physical capacity, pregnancy, addiction to drugs, extensive psychological or behavioral problems. ProceduresPrior to the first visit at the University Medical Center patients filled out a baseline questionnaire assessing demographics and clinical characteristics. During the first visit a review of the medical history and a physical examination was performed.
Immediately afterwards patients filled out the NPAD–DLV and the NDI–DLV. A second visit was scheduled, depending on subject availability, 1–5 weeks after the first visit, but prior to the start of the outpatient rehabilitation program. During the second visit the patients filled out the NPAD–DLV and the NDI–DLV for the second time.
All patients signed informed consent prior to entering the study. MeasurementsThe NPAD is a questionnaire whose development used the Million Visual Analogue Scale (VAS) as a template. The NPAD consists of 20 items. Each item has a VAS of 100 mm with numeric anchors at 0, 1, 2, 3, 4 and 5 (each 20 mm apart). Item scores range from 0 (no pain or limitation in activities) to 5 (as much pain as possible or maximal limitation).
The total NPAD score can vary from 0 to 100 points. Test–retest reliability, expressed as intraclass correlation coefficient (ICC), of different language versions of the NPAD ranged from 0.81 to 0.98 with retest intervals from 1 day to 1–2 weeks. ,.The NDI is a questionnaire based on the Oswestry low back pain disability questionnaire and consists of 10 items. Each item has six different assertions expressing progressive levels of pain or limitation in activities with a score between 0 (no pain or limitation) and 5 (as much pain as possible or maximal limitation). The total NDI scores can vary from 0 to 50 points. Test–retest reliability, expressed as ICC, of different language versions of the NDI ranged from 0.50 to 0.97 with retest intervals from 1 day to 3 weeks ,.
The ICC of the NDI–DLV was 0.90 in patients with acute neck pain in general practice over a retest interval of 7 days. For patients with WAD the test–retest reliability of the NDI–DLV was r = 0.81 over a retest interval of 3 months. Data analysesDescriptive statistics were calculated for the total scores of the two test sessions for both questionnaires.
Reliability of the NDAP–DLV and the NDI–DLV was expressed as ICCs for the total scores. ICCs of 0.75 or higher were interpreted as acceptable reliability. To quantify agreement (the test–retest score stability on individual level) of the NPAD–DLV and the NDI–DLV the limits of agreement were calculated as described by Bland and Altman ,. Statistical analyses were performed with SPSS 14.0.
A total of 181 neck patients were referred to the Center for Rehabilitation between November 2006 and December 2007. From this group 72 (40%) were admitted for rehabilitation. A total of 39 patients were eligible for inclusion in this study.
During the waiting period after the first visit, 5 patients decided not to start with the rehabilitation program, 33 completed the NPAD–DLV and 32 the NDI–DLV twice. Characteristics of the study sample are presented in Table. In the translation and cross-cultural adaptation of the NPAD, minor changes were made in item 13 and item 18. In item 13 (outlook in life and the future), the given examples ‘depression and hopelessness’ were deleted because the respondents of the pre-final version found this superfluous. In item 18 (trouble with looking up or down) the text was changed into: bending the head forwards or backwards, because looking up and down can be done with the eyes only and without flexion–extension of the cervical spine.
Details were added in the general instruction to emphasize that all items should be answered regarding the intensity of the neck pain or neck pain related disability. The mean retest interval was 18.2 days (SD 6.2, range 6–34). Test and retest results are presented in Table.
Item 20 of the NPAD–DLV, concerning pain pills, was left blank by 2 (6%) patients. This item presumes the patient is taking medication. Item 7 of the NDI–DLV concerning driving was left blank by 2 (6%) patients; for these patients the score was adjusted using the mean of the answers on the rest of the questionnaire. The ICC of the NPAD–DLV was 0.76 (95% confidence interval (CI) 0.57–0.87) and of the NDI–DLV 0.84 (95% CI 0.69–0.92). The LOAs of the NPAD–DLV and the NDI–DLV were, respectively, ±20.9 (scale 0–100) and ±6.5 (scale 0–50) (Table ). The cross-cultural adaptation of the NPAD followed the forward and backward translation procedure. This procedure warranted on the one hand the meaning of the original items and on the other hand capturing of contents and meanings of the questions in the translation into the Dutch language.
Other than the production of a more detailed general instruction, only minor modifications were made in items 13 and 18. The adaptation of item 18 is supported by the fact that the developers of the NPAD questionnaire have explicitly related this item to ‘neck problems’ and other authors to ‘neck dysfunction related to activities of the cervical spine’ ,. The new NPAD–DLV was easy to comprehend. To complete both the NPAD–DLV and the NDI–DLV required maximally 15 min. The number of missing responses was negligible, which was in agreement with other non-English versions of the questionnaires ,.The NPAD–DLV and the NDI–DLV demonstrated acceptable reliability in a sample of patients with CNP.
The retest interval depended on the availability of the patient. In our rehabilitation setting it is normal to have a waiting period (1–2 months) between intake and start of the program. Therefore, it is interesting to know the extent of changes in questionnaire outcome occurring in absence of treatment. The sample sizes in our study were similar to other reproducibility studies except for four other studies where the sample sizes were 23, 17, 102 and 101, respectively. The female to male ratio in the current study is similar to that in most former reproducibility studies.
,.In our study, the mean total score of the NPAD–DLV was 50.7 and of the NDI–DLV 22.6. In other studies, the mean total scores of the NPAD ranged from 38.2 to 60.5 and of the NDI from 11.0 to 23.0 ,. In general, studies carried out in tertiary referral centers have higher total scores than those in primary care settings.
In all studies, where both questionnaires were used, including ours, the NPAD scores were approximately 10% higher than the NDI scores when presented in% of a 0–100 scale ,.The reliability of the NPAD–DLV in our study (ICC = 0.76) was lower than in reliability studies with shorter retest intervals (less than 2 weeks ICC = 0.81–0.98 , ). The reliability of the NDI–DLV in our study (ICC = 0.84) was somewhat lower than in most former NDI studies with generally shorter retest intervals (less than 2 weeks ICC = 0.50–0.97 , ; 2 weeks, ICC = 0.88 ; 3 weeks ICC = 0.68 ). Perceived recovery (change) in the retest interval, to include the ‘stable’ patients in the reliability studies, was assessed in only the half of above mentioned NPAD and NDI studies ,. Apart from that it seems not to have resulted in differences in the extent of ICCs ,. A trend may be seen that studies with a shorter retest interval do have higher ICCs.
When looking at another region-specific questionnaire, the same trend was reported. To test for the bias caused by differences in retest interval duration we assessed a partialled retest correlation; this means that we assessed the test–retest correlation for the NPAD–DLV and NDI–DLV while ‘controlling’ the effect of retest interval duration. The Pearson correlations for the test–retest reliability while ‘controlling’ or ‘not controlling’ for retest interval duration were r = 0.70 and r = 0.72 for the NPAD and r = 0.87 and r = 0.87 for the NDI. These results indicate that the influence of the effect of retest interval duration is minimal or negligible.The NPAD is claimed to be a questionnaire with four underlying dimensions.
Factor analyses in other language NPADs identified two to four factors on which different items were loading ,. The factorial structure presented in the original publication was based on a relatively small sample ( n = 95); therefore, the stability of the observed factor solution may be questioned and too sample specific to be reproducible in different samples. Therefore, comparison of the ICCs for subscales in different (language) NPAD studies is challenging.
However, a principal component analysis in a German study with a sample size of 448 indicated a one-factor solution for the NPAD, and it was concluded that the NPAD is a multidimensional assessment instrument measuring different dimensions of one construct neck pain, in a stable manner. Because above mentioned reasons and because factor analysis was not an aim of the current study only total scores were used to analyze the reliability of the NPAD–DLV.If a patient with neck pain fills out the same questionnaire on two occasions, in a waiting period prior to the start of a rehabilitation program, a (very) short time interval increases the probability of carryover or recall effects due to memory, mood or practice, whereas a larger interval increases the probability the clinical status has changed and that the score of the first session has been forgotten. There are several explanations for possible changes of the clinical status during the waiting period: the effect of the clinic consultation, the anticipation of the patient on the program, the effect of a period of waiting before the real rehabilitation program starts, the chronic neck pain itself with its fluctuations and the questionnaires itself.To quantify the agreement, the test–retest score stability over time on individual level, the ‘limits of agreement’ (LOA) were calculated. No criteria are available for interpretation of the LOA. Smaller LOA means more stability and indicate that the natural variation is smaller. The SD difference (the standard deviation of the mean total score difference off all patients between the first and second test) and the LOA of the NPAD–DLV in the present study (10.4 and ±20.9) were somewhat higher than in one other study (9.0 and ±17.9) with a retest interval of 1 day.
In this French study, a 5 point ordinal transition scale was used to include clinically stable patients. Despite a clear difference in retest intervals, the differences in SD difference were small. The SD difference and the LOA of the NDI–DLV in the present study (3.2 and ±6.5) was similar to most other NDI studies with shorter retest intervals (1 day, SD difference 3.4, LOA ±6.7 ; 1 week, SD difference 3.9, LOA ±7.8 ; 1 week SD difference 1.5, LOA ±3.0 ; 1–2 weeks, SD difference 4.4, LOA ±8.9 ). In three of these four studies, a transition scale was used to include clinically stable patients ,. Proportionally, the SD difference of the Greek study was similar to the SD difference of the present study (SD difference/mean total score was 0.12 and 0.14, respectively).
The NDI reliability studies have shown smaller SD difference and smaller natural variations compared to the NPAD reliability studies ,. Larger instability of the NPAD may be explained by differences in operationalizations of ‘neck disability’ between items of the NPAD and the NDI ,. Post hoc analysis showed that the amount of natural variation of the NPAD–DLV could not be attributed to individual items of the questionnaire. Clinical effects of therapy in an individual patient should exceed the limits of agreement before one can state that real change has occurred. The minimal clinically important difference (MCID) is suggested to be 11 points on the NPAD and 2 to 10 points on the NDI ,.
Based on the variation in the current study, patients have to change at least 21 points on the NPAD–DLV (scale 0–100) and at least 7 points on the NDI–DLV (scale 0–50), will these patients be judged as having ‘really’ changed.There are limitations to consider in evaluating our research. First, the sample size is relatively small ( n.
MethodsThe translation was carried out according to the International Quality of Life Association (IQOLA) Project. Sixty patients were treated due to degenerative and discopathic disorders in the cervical spine filled out the NDI-PL and the CDS-PL. The pain level was evaluated using the Visual Analog Scale. The mean age of the assessed group was 47.1 years (SD 8.9). We used Cronbach's alpha to assess internal consistency. We assessed the test-retest reliability using the Intraclass Correlation Coefficients (ICCs). The Spearman's rank correlation coefficient (rS) was used to determine dependency between quantitative characteristics.
The Mann-Whitney test was applied to determine dependency between quantitative and qualitative characteristics. ResultsThe Cronbach's alpha values were excellent for the NDI-PL in the test and in the retest (0.84, 0.85, respectively), and for the CDS-PL (0.90 in the test and in the retest). Intraclass Correlation Coefficients were excellent for the CDS-PL and NDI-PL and equalled 0.93 (95% CI from 0.89 to 0.95) and 0.87 (95% CI from 0.80 to 0.92), respectively The concurrent validity was good in the test and in the retest (rs = 0.42 p. ConclusionsThe present versions of the NDI-PL and CDS-PL, the first to be published in Polish, have proven to be reliable and valid for patients with degenerative changes in the cervical spine.
The NDI-PL and CDS-PL have excellent internal consistency and test-retest reliability, and good concurrent validity. The adapted questionnaires showed a strong inter-correlation both in the test and in the retest. No ceiling or floor effects were detected in the NDI-PL and CDS-PL.
The NDI-PL and CDS-PL are comparable with other versions and can be recommended and used in international comparative studies. BackgroundAnnually about 30% of the population experience neck pain (NP), 14% of whom report complaints lasting longer than 6 months ,. MethodsThe NDI questionnaire was designed by Vernon and Mior in 1992 to assess pain intensity and the related limitations of cervical spine function during the execution of everyday activities. The NDI is based on the Oswestry Disability Index and is composed of 10 questions: pain intensity, personal care, lifting, reading, headaches, concentration, work, driving, sleeping, and recreation. Each item is scored from 0 (no disability) to 5 (total disability). The maximum possible score is 50. However, the sum of the scores obtained is often doubled to give a percentage score out of 100.
The interpretation is as follows: 0-20 normal, 21-40 mild disability, 41-60 moderate, 61-80 severe and 80 or over (complete or exaggerated disability). Since the questionnaire is straightforward, the average patient needs approximately 5 minutes to complete it ,.The CDS consists of 15 items that evaluate the impact of neck pain. Three items evaluate pain severity directly, including the patient's perception of the future impact of neck pain, eight items evaluate disability during everyday activities and four items focus on social interaction and recreation ,. There are three possible answers to select from each item; 'yes' (2 points), 'occasionally' (1 point), and 'no' (0 points). For items 1 - 5 however the scoring is reversed and here 'yes' carries a score of 0, 'occasionally' 1 and 'no' 2. The highest score attainable is 30, indicating worst possible impact, the lowest is 0 where no impact of neck pain can be identified.
90 seconds is invariably sufficient in order to complete the questionnaire. Translation procedureThe translation was carried out in accordance with the recommendations proposed by Beaton et al.
In the first stage two independent translators, of whom one had a medical background, translated the original versions of the NDI and CDS into Polish. In the second stage, a team comprised of the project authors and both translators compared and synthesised the translations. In the third phase, two bilingual translators performed the back-translation where the Polish versions of the questionnaires were translated into the original language. In the fourth stage, the expert committee reviewed all translations and created a prefinal version of the questionnaires. In order to evaluate the psychometric properties of the questionnaire, 60 patients who fulfilled the inclusion criteria for the study completed the NDI-PL, CDS-PL and 100-mm Visual Analogue Scale twice. (See additional file: Copenhagen Neck Functional Disability ScalePolish version and additional file: Neck Disability IndexPolish version).
Evaluation of the psychometric properties of the NDI-PL and CDS-PL1. We analyzed means, minimal and maximal values, standard deviations and 95% confidence intervals for the general results, for the CDS-PL dimensions and for the NDI-PL questions.2. We analyzed floor and ceiling effects (% of patients with the minimal score and% of patients with the maximum score). Ceiling and floor effects are considered to be present if more than 15% of respondents achieved the lowest or highest possible total score.3.
We used Cronbach's alpha to assess internal consistency. Additionally, we performed analyses of the item-total correlation for the NDI-PL and CDS-PL.4. We analyzed the correlations between the NDI-PL and CDS-PL.5. We performed an assessment of the test-retest reliability using the Intraclass Correlation Coefficients (ICCs), type 2.1. The NDI-PL and CDS-PL were completed twice at a 24-hour interval.6. For construct-related validity, the concurrent validity method was used.
To examine the concurrent validity, the relation between the NDI-PL and CDS-PL and 100-mm Visual Analogue Scale was examined by the Spearman's rank correlation coefficient.Statistical analysis was carried out using the Statistica program. In the quality field we supplied the number of units for specific categories of a given characteristic and their relative percentage values.
The Spearman's rank correlation coefficient (rS) was used to determine dependency between quantitative characteristics. The Mann-Whitney test was applied to determine dependency between quantitative and qualitative characteristics.The borderline value of statistical significance was set at p = 0.05. Test results with a greater value than this were deemed to be statistically irrelevant.
Cronbach's alpha values were accepted as follows: ≥0.80 as excellent, 0.70-0.79 as adequate. ParticipantsPatients eligible for the study were consecutively recruited from June 2009 to September 2010. Eligibility criteria were the following: written consent of the patient, neck pain lasting more than 3 months; ability to read and speak Polish fluently; age 18-60 years.
MRI of cervical segments of the spine was carried out in all cases. The analysis did not include pregnant woman and patients suffering from spinal tumors, vertebral traumatic fractures, neurological and psychiatric disorders causing difficulty in speech communications. All physical examinations were performed by the same physician, a neurosurgeon. All patients were operated on due to discopathy and vertebral degenerative changes in the cervical spine.
Surgery was carried out via anterior vertebral approach and consisted of the decompression of the spinal cord and subsequent arthrodesis. Clinical state was determined before surgery in our study.All examined persons were guaranteed anonymity and written consent was required. Demographic variables and the previous history of disease were taken from all of the patients. Disability was evaluated with the NDI-PL and the CDS-PL.
The pain level was evaluated using 100 mm Visual Analogue Scale. Table summarizes the demographic and clinical characteristics of the patients.
![Index Index](/uploads/1/2/5/3/125390644/983439022.png)
TestRetestMinMaxMeanvalue95%ConfidenceintervalSDMinMaxMeanvalue95%ConfidenceintervalSDfromtofromtoNDI-PLTotal score33621.619.620.618.522.68.0Pain intensity052.11.01.72.21.0Personal care041.31.21.01.40.9Lifting052.62.62.22.91.4Reading042.42.42.12.71.2Headaches052.42.11.82.51.4Concentration041.51.41.11.71.0Work052.62.42.12.71.2Driving052.82.72.33.11.3Sleeping052.21.11.72.51.4Recreation052.52.42.02.71.3CDS-PLTotal score03017.715.517.715.619.98.3Pain severity063.93.43.44.52.1Disability0169.07.97.67.69.94.3Social interaction084.84.34.35.72.7. Floor and ceiling effectWe have analyzed floor and ceiling effects for the general results of the CDS-PL and NDI-PL. In the case of CDS-PL, in both the test and retest, 3.3% of patients received the minimum score (2 participants), and the 1.7% of patients received the maximum score (1 participant). Patients with the minimum and maximum score were not identified in the test nor in the retest of the general result of the NDI-PL. Both in the CDS-PL and NDI-PL floor or ceiling effects were not detected as less than 15% achieved the minimum or maximum possible scores. Internal consistencyTable presents the Cronbach's alpha values, concurrent validity in the test and in the retest and test-retest reliability measured by the Pearson correlation coefficient.
The Cronbach's alpha values are excellent for the NDI-PL in the test (0.84) and in the retest (0.85). Cronbach's alpha values for the CDS-PL are excellent, and equalled 0.90 in the test and in the retest (Table ). Moreover, the analyses of item-total correlation confirmed that both scales are internally consistent (Table and Table ). Questions of CDSTestRetestrsp valuersp value1. Can you sleep at night without neck pain interfering?0.61. The correlation between selected patient clinical characteristics and the results of the NDI-PL and CDS-PLWe have also assessed the correlation between selected patient clinical characteristics and the results of the adapted assessment tools. The only statistically significant correlations were identified between CDS-PL and changes in signal intensity in spinal cord in MRI (p = 0.29) and between NDI-PL and changes in signal intensity in spinal cord in MRI (p = 0.44) and the sagittal dimension of the vertebral canal on the discopathy level (p = 0.23), in the first completion of the questionnaires (Table ).The present results confirmed our hypothesis.
We have proved that the NDI-PL and CDS-PL have excellent internal consistency and test-retest reliability, good concurrent validity and showed a strong inter-correlation both in the test and in the retest. Moreover, no ceiling or floor effects were detected in the NDI-PL and CDS-PL. DiscussionTo our knowledge, this is the first study of a Polish version of a questionnaire assessing disability in everyday activities in patients with neck pain.
Even though there are several region-specific functional outcome questionnaires measuring neck disorders available, no Polish version has ever been validated. Our study indicated that NDI-PL and CDS-PL are valid and reliable methods for measuring disability in Polish patients with neck pain.There have been numerous studies on the reliability and validity of the Neck Disability Index for patients with neck pain ,. Vernon and Mior obtained a high degree of test-retest reliability in patients with post-traumatic neck pain, using the Pearson correlation coefficient.The internal consistency of each questionnaire was assessed using Cronbach's alpha. We also assessed the item-total correlations. Our study indicated that NDI-PL and CDS-PL are internally consistent.
In comparison to the French version of CDS , where all items had good or fair correlations with the total score, almost all items of CDS-PL had very good correlations with the general result. The Cronbach's alpha coefficient of the total score of CDS-PL was excellent and higher, compared to the French version of CDS. However, the Cronbach's alpha in our study was exactly the same as in the original version of the CDS (0.90).Excellent internal consistency of the NDI-PL (0.90) is comparable with the results from other studies - Spanish, Finnish, Iranian or Brazilian versions of NDI ,. It is higher than the value obtained by Vernon and Mior (0.8) in the original NDI. Pearson correlation coefficients between individual NDI-PL item scores and the total ranged from 0.43 to 0.77 (test) and from 0.56 to 0.81 (retest) and, as in the original version of the NDI , no item dominated with an especially high correlation and no item appeared to be redundant.We assessed the test-retest reliability of NDI-PL and CNFDS-PL using the Intraclass Correlation Coefficients (ICCs). We decided to choose a retest interval of 2 days, similarly to the authors of the Spanish or Iranian version of NDI, in order to avoid variations in the clinical status of the patients and to avoid the patients remembering their previous answers.
As suggested by Holt et al. , a long interval period may be inappropriate for a test-retest study of health measures because too many changes in the patient's health status can occur. Opinions regarding the appropriate interval have varied from 1 hour to 1 year, but a retest interval of 2 to 14 days is generally accepted. The very good test-retest reliability of NDI-PL is comparable with the results of the Iranian (0.90) and Greek (0.93) versions of the NDI ,. Our findings are also similar to the original version of NDI (0.90). Furthermore, the NDI-PL test-retest reliability values were found to be slightly higher than those achieved during the initial trials for the original version when study participants completed the questionnaires with an interval of 2 days between the first and second test as occurred in our study (0.80).For the NDI-PL and CDS-PL the expected good concurrent validity was observed. As in the Spanish version of the NDI, a good correlation with the VAS score is evident, which may signify, as highlighted by Andrade et al , that the NDI is designed to assess not pain levels as such but rather disability due to pain experienced.
The results of our study showed that the correlation between NDI-PL and CDS-PL is very high, showing a clear association between these two measures, which seem to measure similar constructs.What is more, our examinations proved that the degree of spinal cord compression and spinal cord ischemic changes, expressed as changes of MRI signal intensity, correlate with the disability scales NDI-PL and CDS-PL. Intervertebral cervical disc herniation and degenerative changes are associated with narrowing of the sagital diameter of the spinal canal.
Progressive compression may lead to spinal cord ischemia, leading to histopathological changes of the spinal cord. Nonetheless, these changes may or may not be symptomatic ,. LimitationsOur population was limited to patients with degenerative and discopathic disorders in the cervical spine, which may limit the generalizability of the findings to other populations. Fifteen (25%) of the patients participating in our study omitted the section concerned with driving (section 8).
This is consistent with both the Dutch and Turkish versions of the NDI, where 21% and 23.87% of participants did not answer this section ,. It was not necessary to modify this section as the number of patients who omitted it was low. The study evaluating the Greek version of the NDI recorded that 44.6% of patients decided not to answer the questions on 'driving'. Future researchDespite the fact that we confirmed that both adapted assessment tools have excellent internal consistency, test-retest reliability, and good concurrent validity, further investigation is required to provide additional data for the evaluation of the psychometric properties of the NDI-PL and CDS-PL. In future studies responsiveness, which is a useful property required for determining if the measures are sensitive to detect changes over time, should be tested. Likewise, the item-level analyses of the NDI-PL and CDS-PL would be helpful in future research to provide a more detailed analysis of the functioning of the items for the population.
ConclusionOur study presents an analysis of the psychometric properties of two region-specific functional disability scales for patients with degenerative changes in the cervical spine. As far as we know, this article describes the first attempt at translation and validation of questionnaires appropriate for Polish-speaking patients with neck pain.
We have indicated, that the present versions of the NDI-PL and CDS-PL, the first to be published in Polish, have proven to be reliable and valid.The NDI-PL and CDS-PL have excellent internal consistency and test-retest reliability, and good concurrent validity. The adapted questionnaires showed a strong inter-correlation both in the test and in the retest. No ceiling or floor effects were detected in the NDI-PL and CDS-PL. The NDI-PL and CDS-PL are comparable with other versions and can be recommended and used in international comparative studies.