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Validation of the Spanish Version of the WOMAC Questionnaire for

Validation of the Spanish Version of the WOMAC Questionnaire for
Patients with Hip or Knee Osteoarthritis

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    • Clin Rheumatol (2002) 21:466–471ß 2002 Clinical Rheumatology Clinical RheumatologyOriginal ArticleValidation of the Spanish Version of the WOMAC Questionnaire forPatients with Hip or Knee OsteoarthritisA. Escobar1, J. M. Quintana2, A. Bilbao2, J. Azkarate3 and J. I. Guenaga4 ´ ¨1 Hospital of Basurto, Bilbao; 2Hospital of Galdakao, Vizcaya; 3Hospital of Mendaro, Mendaro; and 4Hospital of Santiago, Vitoria-Gasteiz, SpainAbstract: The aim of this study was to validate a OA ranged from 0.8 to 1.5. The Spanish version oftranslated version of the Western Ontario and McMaster WOMAC is a valid, reliable and responsive instrumentUniversities Osteoarthritis Index (WOMAC) question- in patients with hip or knee OA.naire in Spanish patients with hip or knee osteoarthritis(OA). The WOMAC questionnaire and the SF-36 were Keywords: Hip replacement; Knee replacement; Osteo-administered to a sample of 269 patients on the waiting arthritis; Quality of life; WOMAC validationlist for hip or knee replacement. We studied theconvergent validity and the item-scale correlation usingPearson’s correlation coefficient and Spearman’s p. Forthe reliability study we used another sample of 58 Introductionpatients who received the WOMAC twice within 15days. The Pearson’s, Spearman’s p, and intraclass Despite the fact that health-related quality of lifecorrelation coefficients were calculated. Internal con- (HRQoL) has long been the concern of healthcaresistency was measured by Cronbach’s a. The respon- clinicians and managers, over the last 30 years moresiveness study was carried out by resending the twoquestionnaires to all patients 6 months after surgical publications have begun to appear on the subject in the medical literature [1].intervention; responsiveness was measured by means of Although different types of outcome measures havethe paired t-test, the effect size I and the standardisedresponse mean. The Pearson’s coefficients for the been used to evaluate the effectiveness of both medical and surgical interventions, the patient’s point of view isconvergent validity ranged from 70.52 to 70.63. The now increasingly being considered. This is particularlycoefficients obtained for the item–scale correlation of thepain area were 0.74 or higher, 0.91 or higher for true with regard to chronic pathologies that are basically directed at improving or relieving symptoms. Instru-stiffness, and 0.61 or higher for function. When ments for measuring the HRQoL are one means tomeasuring the test–retest reliability, the coefficients evaluate the outcome based on patients’ opinions.ranged from 0.66 to 0.81. Internal consistency yieldeda Cronbach’s a ranging from 0.81 to 0.93. The Various instruments have been created and validated [2–5] to evaluate both the symptomatology and functionresponsiveness showed an effect size I ranging from on osteoarthritis (OA) of the hip or knee. However, the1.5 to 2.2 in patients who underwent hip replacement;for those who underwent knee replacement the range disease-specific questionnaire Western Ontario and McMaster Universities (WOMAC) is the most widelywas 1 to 1.8. The standardised response mean ranged used instrument for this purpose [6,7], and it has provedfrom 1.3 to 1.9 for patients with hip OA; those with knee to be the best for studies evaluating HRQoL after knee replacement [8,9].Correspondence and offprint requests to: Dr Antonio EscobarMartınez, Unidad de Investigacion, Hospital de Basurto, Avenida de ´ ´ Considerable effort has been made to standardise theMontevideo, 18, 48013 Bilbao, Spain. Tel: +34 944006000 ext. 5307; evaluation of the psychometric properties (validity,Fax: +34 944006180; E-mail: aescobar@hbas.osakidetza.net reliability and responsiveness) of quality-of-life ques-
    • Validation of Spanish WOMAC 467tionnaires to ensure that the versions of the questionnaire Statistical Analysisthat have been adapted for use in another language areequivalent to the original questionnaire [10]. Descriptive data are expressed as percentages and The goal of the present study was to evaluate the means, with a standard deviation for the populationvalidity, reliability and responsiveness of the Spanish studied.version of the WOMAC questionnaire. Psychometric PropertiesPatients and Methods Validity To evaluate differences in mean scores between the different groups of clinical severity (slight, moderate,The sample consisted of 269 patients who underwent hip and severe), a one-way analysis of variance was carriedreplacement (142) or knee replacement (127) surgery at out in the three WOMAC dimensions. We usedthe Department of Orthopedics, Hospital of Basurto, Scheffe’s test for multiple comparisons. ´between March 1999 and February 2000. This is a To determine the convergent and divergent validitiestertiary hospital covering a population of approximately we calculated Pearson’s correlated coefficient and350.000 inhabitants of the Bilbao area. All patients Spearman’s p between the WOMAC dimensions andfulfilled clinical and radiographic criteria for the the SF-36 scales, when the questionnaire was adminis-diagnosis of primary OA, with just one joint affected. tered before surgery. Likewise, we evaluated theWe excluded patients who were unable to complete the WOMAC item–scale correlation using Pearson’s corre-questionnaires either because of languge difficulties, a lation coefficient and Spearman’s p.psychiatric disorder or sensory impairment. All patientsreceived a disease-specific questionnaire, WOMAC, and Reliability The reliability of the internal consistency ofa generic one, SF-36, as well as another series of the dimensions was assessed using Cronbach’s ademographic and clinical questions by mail. Patients had coefficient.to complete both questionnaires while they were on the To study test–retest reliability, we enrolled a differentwaiting list for surgery and 6 months after surgery. sample of 92 patients who received the WOMAC The classification into groups of severity (slight, questionnaire while they were on the waiting list formoderate and severe) was established through questions surgery, and then again 15 days later while they werenot included in the WOMAC questionnaire, concerning still on the waiting list. They were explicitly askedpain and the type of daily activities the person could whether they had experienced any change in their healthcarry out. status since completing the previous questionnaire, with The WOMAC is a disease-specific self-administered no change being detected. We calculated Pearson’squestionnaire developed to study patients with hip or correlation coefficient, Spearman’s p coefficient and theknee OA and requires about 5 min to complete. It has a intraclass correlation coefficient.multidimensional scale made up of 24 items groupedinto three dimensions: pain (five items), stiffness (two Responsiveness To evaluate the changes produced afteritems) and physical function (17 items). We used the surgery, the WOMAC questionnaire was sent again 6Likert version with five response levels for each item, months [18,19] after discharge to the patients whorepresenting different degrees of intensity (none, mild, underwent hip or knee replacement surgery. The changesmoderate, severe or extreme) that were scored from 0 to were evaluated by three methods: the paired t-test; the4. The final score for the WOMAC was determined by effect size I, or standardised effect size, defined as theadding the aggregate scores for pain, stiffness and difference between the mean baseline scores and follow-function. up scores on the measure, divided by the standard The higher the score, the worse the patient’s deviation of the baseline scores; and the effect size II orcondition; therefore, an improvement was achieved by the standardised response mean, defined as the meanreducing the overall score. The data were standardised to score change divided by the standard deviation of thata range of values from 0 to 100, where 0 represents the score change [20]. According to the literature [21,22],best health status and 100 the worst possible status. The values higher than 0.8 are proposed to represent highoriginal questionnaire is reliable, valid and sensitive to responsiveness.the changes in the health status of patients with hip orknee OA [2,11]. Moreover, several internationalorganisations have recommended this questionnaire for Resultsevaluating OA [12,13], and it has been translated intoSpanish and adapted for the population of Spain [14]. Of the 269 patients who received both questionnaire, 203 The SF-36 is a generic questionnaire on HRQoL that (75.5%) were included in the study because theyhas been translated into Spanish and validated [15]. The completed both the WOMAC disease-specific ques-questionnaire evaluates eight dimensions regarding both tionnaire and the generic SF-36 questionnaire (Table 1)physical and mental health and is widely used in HRQoL and underwent knee replacement surgery (n = 103) orstudies [16,17]. hip replacement (n = 100). The reliability study was
    • 468 A. Escobar et al.Table 1. Baseline characteristics of the study population Table 2. Quality-of-life measure (mean + SD) using the WOMAC scale, ordered by anatomic location and severity Hip replacement Knee replacement (n = 100) (n = 103) Pain Function Stiffness nMean age (yr) (SD) 68.6 (10.3) 70.9 (6) Hip*Gender (%) Severity Men 44 (44) 30 (29.1) Slight 32.9 (17.2) 44.2 (18.8) 34.4 (20) 12 Women 56 (56) 73 (70.9) Moderate 36.7 (9.4) 53.6 (12) 40.6 (17) 12Severity (%) Severe 60.1 (16.9) 70.7 (14.6) 64.8 (22.7) 76 Slight 12 (12) 8 (7.8) Knee Moderate 12 (12) 25 (24.3) Severity Severe 76 (76) 70 (67.9) Slight 29.4 (15.4){ 35.8 (15.1){ 34.4 (21.9){ 8WOMAC* Moderate 50.2 (17.3){ 54.8 (17){ 49.5 (18.6) 25 Pain 53.9 (19.4) 57 (18) Severe 62.6 (14.7){ 5.3 (15.4){ 61.8 (23.2){ 70 Function 65.4 (17.5) 60.5 (17.7) Stiffness 58.3 (24.5) 56.7 (23.4) *.P<0.05 for differences between the severe–slight and severe– moderate groups. {*.Standardised data from 0 to 100. Mean score + standard deviation. .P<0.0001 for differences between the three groups, except forA higher score indicates a worse state. stiffness, where the difference is between slight and severe (P<0.05).conducted based on a different sample of 58 patients out The WOMAC pain dimension correlated best with theof 92 to whom were sent the WOMAC questionnaire SF-36 bodily pain scale (r = 70.6, p = 70.55)while on the waiting list (63%). compared with the rest of the scales (Tables 3). The function dimension of the WOMAC questionnaire achieved the highest Pearson correlation coefficient ofValidity 70.63 (p = 70.59) with the SF-36 pain scale, whereas this coefficient was 70.52 (p = 70.59) with theThe descriptive data for the mean score, as well as the physical function scale of the same questionnaire. Thestandard deviation for each of the WOMAC dimensions stiffness dimension obtained coefficients of r = 70.5ordered by anatomic location of the illness and its (p = 70.48) with the bodily pain scale of the SF-36. Theseverity, are shown in Table 2. The results showed an coefficients are negative, given the fact that for theincrease in the score for each domain as the severity of the WOMAC questionnaire, compared with the SF-36, theillness increased for both anatomic locations. For patients scores decrease with improvements in the HRQoL. Allwith knee OA, the differences were statistically sig- correlations were significant (P<0.0001).nificant between all levels of severity, except for the Regarding the item–domain correlation, the five itemsgroup classified as moderate on the stiffness dimension. in the pain dimension obtained coefficients of more thanIn patients with hip OA, statistically significant differ- 0.74 (P<0.0001) with their dimension, which was lowerences were observed between the severe and slight groups with the other two dimensions (stiffness and function).and the severe and moderate groups; no differences were The two items on stiffness obtained coefficients of moreseen between the moderate and slight groups. than 0.91 (P<0.0001) with their own dimension, whichTable 3. Convergent and divergent validities: Pearson’s correlation coefficient (Spearman’s p) WOMAC SF-36 Pain Function Stiffness BP PF RP GH VT SF RE MHWOMACPain 71Function 70.79 71Stiffness 70.57 70.71 71SF-36BP 70.6 (70.55) 70.63 (70.59) 70.5 1PF 70.4 70.52 (70.59) 70.38 0.39 1RP 70.35 70.43 70.33 0.45 0.27 1GH 70.33 70.34 70.22 0.35 0.28 0.26 1VT 70.47 70.5 70.37 0.61 0.37 0.38 0.5 1SF 70.45 70.52 70.4 0.54 0.34 0.41 0.37 0.57 1RE 70.31 70.31 70.27 0.28 0.12 0.25 0.37 0.37 0.43 1MH 70.41 70.43 70.33 0.43 0.3 0.4 0.5 0.64 0.57 0.57 1All the correlations were significant (P<0.0001).BP, bodily pain; PF, physical functioning; RP, role-physical; GH, general health; VT, vitality; SF, social functioning; RE, role-emotional; MH,mental health.
    • Validation of Spanish WOMAC 469were lower with the other two dimensions. Finally, for Internal consistency, evaluating using Cronbach’s athe 17 items in the function dimension, all but two coefficient, gave values of 0.82 for pain, 0.93 forobtained coefficients of more than 0.61 (P<0.0001). The function, and 0.81 for stiffness.two items were: What degree of difficulty do you havedescending stairs? and What degree of difficulty do youhave standing? and obtained 0.54 and 0.55, respectively,although they correlated better with the pain dimension Responsiveness(r = 0.59 and r = 0.63, respectively). The data forSpearman’s correlation coefficient gave the same results. All patients underwent either hip or knee replacement surgery. Six months after surgery they again receivedReliability both the WOMAC and SF-36. A significant statistical improvement was observed (P<0.001) in the threeTo assess the test–retest reliability of the WOMAC WOMAC dimensions and in the SF-36 in patients whoquestionnaire in the sample of 58 patients, we used underwent hip replacement (Table 5) and those whoPearson’s correlation coefficient, Spearman’s p coeffi- underwent knee replacement (Table 6). The effect size Icient and the intraclass correlation coefficient. The values for patients with a hip replacement were 1.9 fordescriptive data for the pre and post scores, as well as pain, 2.2 for function and 1.5 for stiffness. For those whothe corresponding coefficients, are given in Table 4. The underwent knee replacement surgery, the values werecoefficients ranged from 0.66 to 0.81, with the lower 1.8, 1.5 and 1, respectively. The effect size II values, orones corresponding to stiffness and the higher ones to the standardised response means, for patients whofunction. All coefficients were statistically significant underwent hip replacement were 1.8 for pain, 1.9 for(P<0.0001). function and 1.3 for stiffness. For patients who under-Table 4. Analysis of WOMAC’s test–retest reliabilityWOMAC Test Retest Correlation coefficient ¯ X (D.E.) ¯ X (D.E.) Pearson p Intraclass Cronbach’s aPain 53 (18.4) 51.7 (20) 0.78 0.79 0.78 0.82Function 62.1 (16.4) 62.6 (17.6) 0.81 0.81 0.81 0.93Stiffness 63.4 (24) 62.1 (21.2) 0.67 0.66 0.67 0.81All coefficients were statistically significant (P<0.0001).Table 5. Changes in the HRQoL measured by WOMAC in patients who underwent hip replacementVariable Pre intervention Post intervention Difference P SRM* Effect size I ¯ X (D.E.) ¯ X (D.E.) ¯ X (D.E.)WOMACPain 53.9 (19.4) 16.2 (16) 37.7 (20.5) <0.0001 1.8 1.9Function 65.3 (17.5) 27.4 (17.7) 37.9 (19.9) <0.0001 1.9 2.2Stiffness 58.3 (24.5) 22.4 (18.4) 35.9 (26.8) <0.0001 1.3 1.5SE-36Bodily pain 30.7 (27.1) 58.4 (28.4) 27.3 (30.3) <0.0001 0.9 1Physical functioning 19.8 (19.1) 48.7 (22.4) 28.9 (25.7) <0.0001 1.1 1.5Table 6. Changes in HRQoL measured by WOMAC in patients who underwent knee replacementVariable Pre intervention Post intervention Difference P SRM* Effect size I ¯ X (D.E.) ¯ X (D.E.) ¯ X (D.E.)WOMACPain 53.0 (18.0) 24.4 (17.6) 32.6 (21.9) <0.0001 1.5 1.8Function 60.3 (17.7) 32.7 (18.7) 27.6 (21.8) <0.0001 1.3 1.5Stiffness 56.7 (23.4) 33.0 (22.2) 23.7 (31.1) <0.0001 0.8 1SE-36Bodily pain 34.7 (28.2) 51.1 (28.9) 15.6 (34.1) <0.0001 0.5 0.5Physical functioning 25.0 (21.6) 50.2 (24.5) 25.2 (27.1) <0.0001 0.9 1.2*.Standardised response mean or effect size II.
    • 470 A. Escobar et al.went knee replacement, the values were 1.5, 1.3 and 0.8, both cases. This could be a result of the fact that the datarespectively. The results for the SF-36 were lower for all do not have a normal distribution and are similar to thoseindicators. described [24]. The divergent validity was studied according to levels of severity. Regarding the patients who underwent hip replacement surgery, no statistically significant differ-Discussion ences were found between slight and moderate severity, which could be the result of the small number of patients in both groups.Hip and knee OA is a chronic illness that, despite being Reliability is another psychometric characteristic to benon-life-threatening, does cause morbidity: it has an evaluated in a questionnaire. A reliable measurement isimportant social impact, and in many cases it leads to a one that produces the same results when it iship or knee replacement to improve the patient’s quality administered two or more times under the sameof life [23]. conditions. In the present study the questionnaire was Various instruments have been used to measure sent to the patients a second time, 15 days after they hadHRQoL in these orthopaedic patients [22,24]; however,the WOMAC questionnaire is the disease-specific replied to the first one. They were asked whether theyinstrument most widely used in clinical practice for had experienced any change that could affect theiroutcome measurement [6,7]. health; a negative response was obtained from all The advantages of disease-specific questionnaires patients. The values of all the reliability coefficientssuch as the WOMAC are derived from the fact that indicate that the dimensions are coherent, they arethey are more closely focused on the illness or similar to those obtained for the Swedish version of theimpairment under study (in this case OA) and should questionnaire [28], and are slightly lower than thosebe better at detecting the changes resulting from obtained for the Hebrew version with regard to internaltreatment than questionnaires that are not disease consistency [29].specific. The disadvantge is that they cannot detect The instrument’s responsiveness presents more diffi-other types of impairment or complications in areas or culties regarding both its concept and the way in whichorgans that are not specifically related to the illness to measure or quantify it. In our study we measured theunder study [24] that could be important to the patient. so-called internal responsiveness, defined as the ability To adequately compare the studies carried out in of a measure to change over a specific period [20]. Alldifferent countries, the versions of the questionnaires the results of the WOMAC questionnaire showed goodshould be adapted and validated. Although the WOMAC responsiveness and therefore a significant improvementquestionnaire has been translated and adapted for a in the patients’ health states after knee or hipSpanish population [14] its psychometric properties have replacement surgery, with values higher than thosenot been studied, and this was the goal of this present shown by other authors [27]. As observed in Tables 5study. and 6, these changes were greater than those for the SF- The psychometric properties of the questionnaires 36. This confirms that the disease-specific instrument ismeasuring the HRQoL are established by studying their more sensitive to changes experienced by patients thanvalidity, reliability and responsiveness. the generic questionnaire for the corresponding scales. There are various ways of determining the validity of These data confirm the data obtained in other studies thata questionnaire, one of which is convergent and have used the same questionnaires to make a comparisondivergent validity. This is generally done by comparing [9,24].the instrument under study with other instruments that A possible limitation in the use of the WOMAChave already been validated. The SF-36 is a widely used questionnaire is the age of the population to which it wasinstrument [25,26] and has been validated in Spanish directed, particularly in the case of patients who[14]. Our data on validity present moderate correlations underwent hip or knee replacement, as age does notwhen the dimensions of both questionnaires werecompared, with correlation coefficients ranging from limit the indication for surgery [6,30], and for older70.4 to 70.6, which agrees with other studies [27,28]. people it is possible to limit both the number ofAs expected, for both Pearson’s coefficient and responses as well as the interpretation of some items.Spearman’s p the WOMAC pain dimension obtained A further limitation is that the responses may bethe best correlation with the SF-36 bodily pain scale influenced by another type of problem, such as backcompared with the rest of the scales. For the stiffness pain [31], which is common in our practice.dimension, the highest coefficient values were found in In conclusion, the Spanish version of the WOMACthe bodily pain scale with both coefficients. When disease-specific questionnaire offers psychometric prop-analysing the data for the function dimension, we erties that make it a valid, reliable and responsiveoberved that it correlated best with the bodily pain and instrument for patients with hip or knee OA who havefunction scales of the SF-36 (r = 70.63 and r = 70.52, undergone a hip or knee replacement. A genericrespectively), although with Spearman’s coefficient this instrument that measures different but complementaryrelation changed slightly, with coefficients of 70.59 in health areas should accompany it.
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