German translation and external validation of the Radboud Skills Questionnaire in patients suffering from Complex Regional Pain Syndrome 1

We recruited patients from the outpatient clinic of Balgrist University Hospital, Zurich, Switzerland and through advertisements posted on two self-help homepages for patients afflicted with CRPS 1 (http://​www.​morbus-sudeck.​ch, http://​sudeck.​foren-city.​de). We included all eligible and consenting adult patients suffering from CRPS 1 of the upper extremity with fulfilled International Association for the Study of Pain (IASP) criteria [13], more than 18 years of age, illness duration of more than three months and the ability to complete the questionnaires. The study protocol was approved by the local Ethics Committee (Spezialisierte Unterkomission für Orthopädie der Kantonalen Ethikkommission, Zurich, Switzerland) and informed consent was obtained from all participants.

In 1999, Oerlemans et al. constructed and validated the RASQ to measure the level of disability in activities of daily living in patients with CRPS 1 of the upper extremity [12].

The questionnaire construction was based on the Dutch elaboration of the International Classification of Impairments, Disabilities and Handicaps (ICIDH), an earlier version of the International Classification of Functioning, Disability and Health (ICF) model [14]. The questionnaire contains items of 'disabilities due to hand disease' domain of the ICF model. In order to be applied to both hands, the questionnaire includes items referring to two-handed activities in daily living or social activities. The constructed questionnaire was judged for its merit in Delphi rounds with experts and then readjusted. The original version of the RASQ questionnaire consists of 11 categories, with the first four addressing personal care (15 questions), the next three addressing domestic activities (17 questions) and the latter four addressing other activities (13 questions). The RASQ was reliable in terms of response stability (median coefficients of variation 2.2 to 6.6%) and the correlations between categories of items were fair to good [12]. A numeric score (1-5, with an extra score of '9' for 'not applicable' for patients who never perform the involved activity) is assigned to each question of the RASQ. In order to avoid implications on the scores, we scored every missing or not applicable response with the mean score of the specific question. The Disabilities of the Arm, Shoulder and Hand Questionnaire (DASH) questionnaire is a standardized patient-completed upper extremity outcome measure [9]. Using a self-reporting system, patients choose scores of on to five to 30 items relating to impairments and activity limitations, as well as participation restrictions in leisure activities and work. The DASH questionnaire was translated in many languages. The German questionnaire was obtained from http://​www.​dash.​iwh.​on.​ca

We followed a sequential forward and backward translation approach (see figure 1) [15]. Two professional translators translated the original Dutch version of the RASQ into German. In a consensus meeting a rheumatologist, a specialist in physical medicine and rehabilitation, a physical therapist and an epidemiologist assessed the consistency of the translation and judged its face validity. They then agreed on the first German version for these formats. The questionnaire was pilot tested in five CRPS 1 patients to identify difficulties in comprehension and interpretation of the questions. In addition, we tested various possible wordings of items, answer choices and instructions if the translation team considered more than one possible version. A Dutch translator with experience in biomedical sciences but unaware of the original versions performed a back translation of the German version into the source language (Dutch). A team of experts (a rehabilitation specialist, a rheumatologist, an epidemiologist and a physical therapist) compared the back translation with the Dutch versions to check for conceptual discrepancies. After a second pilot test (n = 5 CRPS 1 patients), the translation team discussed the comments from these patients and decided by consensus on modifications. Finally, the experts approved the final German version of the RASQ (RASQ_G).

Both questionnaires were offered to CRPS 1 patients meeting the inclusion criteria. Based on formal sample size calculations for regression analysis the required number of patients for the validity assessment was established at 50. Patients received both questionnaires either during a visit to our outpatient clinic or by mail. Participants were asked to complete both questionnaires on the same day and to mail them back to our institution.

Values are reported as mean ± SD, medians and interquartile ranges (IQR) or as absolute number and percentage. Linear regression analysis and individual prediction intervals were used to assess the relationship between the RASQ_G and the German DASH questionnaire (DASH_G). Data storage and statistical analyses were performed with the SPSS 12 statistical software package (SPSS Inc. Headquarters, 233 S. Wacker Drive, 11th floor Chicago, Illinois 60606).

The wording of the questions and response options correspond to the original version. We did not add or remove items nor changed the response categories.

The demographic and clinical characteristics of the participants are shown in table 1. We enrolled 57 patients suffering from CRPS 1 of the upper extremity in this study (female/male 37/20). Surgery was the most common initiating event (54.4%). Median disease duration was 1.9 years (IQR 0.9 to 4.3). Average score for the RASQ_G was 140.1 ± 39.2 and for the DASH_G 55.4 ± 22.0.

We found a high correlation between the RASQ_G and the DASH_G (R² = 0.83). The regression function showed an intercept of -15.2 and a slope of 0.50. Figure 2 shows the 95% prediction intervals and the regression line.