Translation, cross-cultural adaptation and validation of the Danish version of the Oxford hip score

OHS

The OHS is a short, 12-item questionnaire for patients undergoing THR.⁸ It was designed as an intervention- and site-specific outcome measure to assess functional ability, daily activities and pain from the patient’s perspective. Items are answered by ticking a box on a five-point Likert scale. Originally, the raw scores were added to obtain a sum score between 12 and 60, with higher scores being better. Due to modifications, the sum score is now described as ranging from 0 (worst) to 48 (best).^9,10 The OHS has been translated into different languages and used in several clinical studies and registry settings. It has been shown to be consistent, reliable, valid and sensitive to clinical change following THR.^11-18 Thresholds in the OHS associated with patient satisfaction with post-surgical outcomes have been estimated.¹⁹ A license for the study and translation was obtained from Isis Innovation (Oxford, United Kingdom).

Procedure for translation and cross-cultural adaptation

The translation and cross-cultural adaptation process for the OHS was carried out in accordance with a recommended best-practice methodology,²⁰ and involved the following steps:

1. An uninformed forward-translation from English to Danish (by translator T1, Associate Professor in English Language in Denmark (mother tongue Danish, fluent in English).

2. An uninformed back-translation from Danish to English (by translator T2, Associate Professor in English Language in Denmark (mother tongue English, fluent in Danish).

3. An expert panel consensus meeting, during which the original and back-translated English versions were compared, and clinical/linguistic issues in the Danish forward-translated version were resolved.

4. Five new individually uninformed back-translations from Danish to English (by five members of a multidisciplinary group that included professional translators and experienced health professionals; two with English as their mother tongue, three with Danish as their mother tongue, and all bilingual).

5. A new expert panel consensus meeting with translators and coordinators, where the versions were reviewed, reconciled and harmonised, and the back-translations compared with the original English version and prior translations. This resulted in consensus on the Danish version of the OHS.

6. The final Danish language version was tested for understanding on 24 patients (ten men and 14 women) with a mean age of 65 years (24 to 86), with hip dysfunction, hip osteoarthritis or THR, by experienced health professionals. After completing the OHS, the respondents were systematically interviewed and debriefed on their thoughts concerning the relevance of the questions, the specific wording of each item, any difficulties in understanding the questions, the readability, and their experience in answering the questionnaire. The interviewing health professionals also assessed the patient’s ability to complete the PROM, using the same criteria.

7. We used the PROMs in theirstandard lay-out, and based on the testing, we made minimal adjustments to optimise readability for elderly patients, and to facilitate automated forms processing. Written instructions for the PROM were added, layout, font, text size and points in correspondences were adjusted after consulting typographers and educationalists, and these final modifications were incorporated after examination of the outcomes from the debriefing. The Danish language version of the OHS was proofread by a key in-country consultant and project manager, and a report prepared of the translation process.

Data collection

We used a cross-sectional design. Our study was a secondary analysis of data from a previous study of a cohort of 5777 patients from the Danish Hip Registry.²¹ The patients had received a primary THR either one to two, five to six, or ten to 11 years before dispatch of the PROMs. Patients who had revision surgery, or received contralateral THR following the index operation, were not excluded from the study. For the current study, we included the subgroup of all patients between the ages of 30 and 80 years who had answered the OHS. These patients, as part of the original cohort, had received one generic PROM, either the EuroQol 5D-3L (EQ-5D)²² or Short-Form 12 (SF-12),²³ and one disease-specific PROM, either the Hip dysfunction and Osteoarthritis Outcome Score (HOOS)²⁴ or the OHS.⁸ We also included 215 patients who had previously answered the HOOS. These patients were asked to also complete the OHS to enable comparison of disease-specific PROMs. They were randomly selected from the original cohort, and received the OHS at two years after completing the HOOS. This gave us a total of 2278 patients for the current study. For test-retest validation, 212 patients received the OHS twice within two weeks, at a median of 7.1 years (3.1 to 12.8) after their index operation (Fig. 1). We assumed the patients to be in the same state regarding their hip when answering the questionnaires.

Fig. 1

Flow chart showing participation (OHS, Oxford hip score; HOOS, Hip dysfunction and Osteoarthritis Outcome Score; SF-12, Short-Form 12; EQ-5D, EuroQol 5D-3L).

We included between 187 and 907 patients for each combination of PROMs to calculate construct validity and internal consistency, and 166 patients completed the test-retest. These numbers are all higher than the recommended minimum proposed by Terwee et al.²⁵ All PROMs were posted to the patients with a return-addressed and stamped envelope. Paper questionnaire formats were used, and up to two reminder letters were sent.²⁶ All returned PROMs were scanned electronically, using a validated automated forms processing technique.²⁷ The study was conducted in accordance with the STROBE statement.²⁸

Other PROMs

As a part of the validation, the Danish OHS was compared with two generic outcome measures (EQ-5D and SF-12) and a disease-specific outcome measure (HOOS).

The EQ-5D is a standardised generic measure of health outcome.^22,29 The EQ-5D gives a summary index (EQ-5D Index) and a VAS score (EQ-VAS). Its psychometric properties have been validated for THR³⁰ and for patients with rheumatoid arthritis.³¹ A license for the study was obtained from The EuroQol Group.³²

The SF-12 is a short form of the SF-36 with 12 items,^23,33 a generic measure of health status. The SF-12 gives a physical component summary score (PCS) and a mental component summary score (MCS). Its psychometric properties have been validated for osteoarthritis patients.³⁴ A license for the study was obtained from The Medical Outcomes Trust Health Assessment Lab and Quality Metric Incorporated.³⁵

The HOOS includes five subscales: pain, other symptoms, function in daily living, function in sport and recreation, and hip-related quality of life.²⁴ The HOOS-Physical Function Short form (HOOS PS) is a five-item short form of the two HOOS subscales: function in daily living and sport and recreation function. The HOOS PS has been validated for THR.³⁶ We used the HOOS subscales Pain (HOOS Pain), HOOS PS and Hip-related Quality of Life (HOOS QoL).³⁷

Psychometric properties

The Danish OHS was examined for response rate, floor and ceiling effects, skew of the distribution, missing items, construct validity, reliability (intraclass correlation, limits of agreement and inter item correlation reliability), and internal consistency. We defined response rate as the percentage of patients who agreed to participate and answer the questionnaire, missing items as the percentage of all questionnaires with too many items missing to calculate a sum score, as recommended,¹⁰ floor and ceiling effects as the percentage of patients at the extreme ends of the PRO (no possibility to measure a meaningful deterioration of, or improvement in, their condition), calculated as the percentages of patients with the lowest (0) or highest (48) possible sum score out of the total number of patients. Construct validity was tested by comparing the Spearman’s correlation coefficients of the OHS scores with the domains of the HOOS, EQ-5D, and SF-12. We hypothesised that the OHS should have moderate to high (0.50 to 0.80) correlations with HOOS Pain, HOOS PS and HOOS QoL; the pain/ discomfort domain, mobility, current state of health and the usual activities domain from the EQ-5D; and the general health, physical component score and body pain domains from the SF-12, since these domains are similar to those of the OHS. We also hypothesised that the OHS should show lower (< 0.50) correlations with the anxiety/depression and self-care domains of the EQ-5D, and the mental component score, vitality and social functioning domains from the SF-12, since these domains are not directly a part of the OHS. Reliability was measured as the intraclass correlation coefficients (ICC), and the limits of agreement (LOA). The time period between the repeated administrations was 2 weeks. Internal consistency was determined by calculating Cronbach’s Alpha³⁸ for the OHS. A value for Cronbach’s Alpha > 0.8 was considered “good” while a value ≥ 0.9 was considered “excellent”.³⁹ We used COSMIN definitions and taxonomy to describe psychometric properties.⁴⁰

Statistical analysis

Descriptive statistics were used to describe patient characteristics. Response rate, floor and ceiling effects, and missing items were calculated as proportions with 95% confidence intervals (CI). We used a chi-squared test to compare proportions. A p-value < 0.05 was considered significant. For test-retest, we used the STATA ‘sample’ command to draw random samples of the original cohort from the Danish Hip Registry. Construct validity was tested by comparing the Spearman’s correlation coefficients. Internal consistency was determined by calculating Cronbach’s Alpha. Intraclass correlation (ICC) was calculated as ICC[2,1] with STATA ‘icc23’ command (two-way random effects model). Bland and Altman’s limits of agreement were calculated by STATA ‘concord’ command. The STATA software Version 11.0 (StataCorp LP, College Station, Texas) was used for all statistical analyses.

Ethics

The study was approved by the Danish Data Protection Agency (number 2008-41-2593), the Danish National Board of Health, and DHR. The study was presented for the Science Ethics Committee of the Region of Southern Denmark. They declared that the study did not require acceptance from the committee due to no intervention or human material were included. All patients gave informed written consent and the study was carried out in accordance with the Declaration of Helsinki.

Patients

Patient characteristics are listed in Table I, and their mean scores for PROMs are listed in Table II. Non-responders were predominantly younger patients and had the diagnoses ‘low impact fractures’ and ‘other arthritis’ more often than responders. The mean OHS score was 40. Post-operative follow-up was a median of 4.9 years (0.9 to 10.5).

Translation and cross-cultural adaptation

The translation process revealed minor discrepancies in wording and comprehension for items 1 (Usual level of hip pain), 8 (Pain on standing up from sitting), 9 (Limping when walking), 11 (Work interference due to pain), 12 (Pain in bed at night) and option 4 in item 6 (Walking time before severe pain), so these were rephrased in the translation process. Some patients had problems with item 3 (Trouble with transport), which was resolved by adding a written instruction for the questionnaire.

Psychometric properties

The OHS had a response rate of 87.4%, no floor effect and 19.9% ceiling effect in our post-operative patients. The frequency distribution of the scores was negatively skewed (Fig. 2), with a skew value of -1.39. Only 1% of patients had too many items missing to calculate a sum score (Table III). Regarding construct validity, OHS showed the highest correlations with the HOOS Pain, HOOS PS and HOOS QoL; the pain/discomfort domain, mobility, current state of health and the usual activities domain from the EQ-5D; and the body pain domain from the SF-12 (rho = ±0.51 to 0.62) (Tables IV to VI). The OHS showed the lowest correlations with the anxiety/depression and self-care domains of the EQ-5D; and the mental component score, vitality and social functioning domains from SF-12 (rho = ±0.32 to 0.46). SF-12 general health, body pain domain and physical component score had a correlation of 0.38 to 0.49. Thus 12 of the 15 predefined hypotheses about the strength of correlation were confirmed. The test-retest reliability of the OHS sum score was established with an ICC of 0.96 (95% CI 0.94 to 0.97), and limits of agreement was -0.05 (95% CI -4.67 to 4.58) (Table VII). For internal consistency, the overall Cronbach’s alpha was 0.99, and the average inter-item correlation was 0.88 (Table VIII).

Fig. 2

Bar chart showing the skew of distribution of the Oxford hip score (OHS).

Supplementary material

The Danish version of the Oxford hip score with instructions is available alongside this article at www.bjr.boneandjoint.org.uk