Using the patient s perspective to develop function short forms specific to total hip and knee replacement based on WOMAC function items

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1 T. R. Liebs, W. Herzberg, J. Gluth, W. Rüther, J. Haasters, M. Russlies, J. Hassenpflug From University of Schleswig-Holstein Medical Centre, Kiel, Germany ARTHROPLASTY Using the patient s perspective to develop function short forms specific to total hip and knee replacement based on WOMAC function items Although the Western Ontario and McMaster Universities (WOMAC) osteoarthritis index was originally developed for the assessment of non-operative treatment, it is commonly used to evaluate patients undergoing either total hip (THR) or total knee replacement (TKR). We assessed the importance of the 17 WOMAC function items from the perspective of 1198 patients who underwent either THR (n = 704) or TKR (n = 494) in order to develop jointspecific short forms. After these patients were administered the WOMAC pre-operatively and at three, six, 12 and 24 months follow-up, they were asked to nominate an item of the function scale that was most important to them. The items chosen were significantly different between patients undergoing THR and those undergoing TKR (p < 0.001), and there was a shift in the priorities after surgery in both groups. Setting a threshold for prioritised items of 5% across all follow-up, eight items were selected for THR and seven for TKR, of which six items were common to both. The items comprising specific WOMAC-THR and TKR function short forms were found to be equally responsive compared with the original WOMAC function form. Cite this article: Bone Joint J 2013;95-B: T. R. Liebs, Dr.med., Attending Orthopaedic Surgeon J. Hassenpflug, Prof. Dr.med., Professor and Chairman University of Schleswig-Holstein Medical Centre, Kiel Campus, Surgery, Michaelisstr. 1, Kiel, Germany. W. Herzberg, Dr.med., Chief Orthopaedic Surgeon Asklepios Westklinikum Hamburg, Department of Orthopaedic Surgery, Suurheid 20, Hamburg, Germany. J. Gluth, Attending Anesthesiologist Regio Klinikum Wedel, Department of Anesthesiology, Holmer Str. 155, Wedel, Germany. W. Rüther, Prof. Dr.med., Professor and Chairman Rheumaklinik Bad Bramstedt, Surgery, Oskar-Alexander-Str. 26, Bad Bramstedt, Germany. J. Haasters, Prof. Dr.med., Professor Konsul-Lorentzen-Str. 11, Kappeln, Germany. M. Russlies, Prof. Dr.med., Professor University of Schleswig-Holstein Medical Centre, Lübeck Campus, Surgery, Ratzeburger Allee 160, Lübeck, Germany. Correspondence should be sent to Dr T. R. Liebs; liebs@liebs.eu 2013 The British Editorial Society of Bone & Joint Surgery doi: / x.95b $2.00 Bone Joint J 2013;95-B: Received 7 August 2012; Accepted after revision 13 November 2012 The Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) questionnaire was developed in the 1980s to assess the impact of osteoarthritis (OA) of the hip and knee. 1 Although it was not designed initially to evaluate outcomes from total hip replacement (THR) and total knee replacement TKR, 2 it is commonly used for that purpose, because of its sensitivity to change and its construct validity. The index comprises 17 functional activities, five pain-related activities and two stiffness items. The function subscale of the WOMAC is a valid, reliable and responsive measure of functional impairment. 3 However, a subscale consisting of 17 items limits its usability, especially for larger trials and registries using patient-reported outcome measures (PROMs). All 17 items of the WOMAC function scale have the same weight on the final score. Several authors have shown that there is redundancy within the WOMAC function scale and that redundant items could be omitted from the scale. 4-6 Short questionnaires are known to be less of a burden in clinical trials 7 and to result in improved patient compliance. 8 If the WOMAC function score items are reduced from 17 to eight, this has been found to lead to a reduction of incomplete data from 24% to 6%. 9 Some of the individual WOMAC items, such as doing heavy domestic duties or getting in/out of a car, are affected by problems other than osteoarthritis, such as low back pain, fatigue and depression, and are therefore commonly confounded. 10 Competing short forms of the WOMAC questionnaire have been developed based on input from clinical and statistical experts, but still not differentiating between OA of the hip and knee. 11 Others include patient input, but have been validated only for a conservatively treated population. 4 The various short forms also differ in item selection from within WOMAC, and so are not strictly comparable. It is crucial for a reduced score to be at least as responsive as the full score. The incorporation of an individual patient s priorities improves the responsiveness of the index, but the inevitable lack of standardisation makes subsequent analysis exceptionally difficult. 12 This study assessed patients priorities with the WOMAC function items, both before and after undergoing THR or TKR. These priorities were used to develop knee- or hip-specific short versions of the WOMAC function questionnaire. Patients and Methods We analysed prospectively collected data from three multicentre randomised controlled trials evaluating different rehabilitation measures VOL. 95-B, No. 2, FEBRUARY

2 240 T. R. LIEBS, W. HERZBERG, J. GLUTH, W. RÜTHER, J. HAASTERS, M. RUSSLIES, J. HASSENPFLUG Table I. Pre-operative characteristics of the surgical population Characteristic Total hip replacement (n = 704) Total knee replacement (n = 494) p-value Mean (SD) age (yrs) 68.2 (9.7) 70.0 (8.4) Mean (SD) body mass index (kg/m 2 ) 27.0 (4.3) 29.2 (4.7) < Male (n, %) 271 (38.5) 141 (28.5) < Mean (SD) WOMAC * Physical function 55.5 (23.2) 52.6 (24.3) Pain 53.9 (24.7) 52.2 (23.5) Stiffness 54.7 (27.6) 51.8 (29.9) Mean (SD) Short-Form 36 Physical component summary 27.6 (7.4) 28.2 (7.4) Mental component summary 49.0 (12.2) 49.1 (12.2) Mean (SD) Lequesne hip/knee score 11.7 (3.1) 11.1 (3.0) * WOMAC, Western Ontario and McMaster Universities osteoarthritis index. Each subscore ranges from 0 (best) to 100 (worst) Mann-Whitney U test chi-squared test Table II. Follow-up attendance and rates for total hip (THR) and knee replacement (TKR) patients Pre-operative 3 months 6 months 12 months 24 months Total (n, %) (92) 1069 (89) 1013 (85) 944 (79) THR (93) 632 (90) 612 (87) 569 (81) TKR (90) 437 (88) 401 (81) 375 (76) after primary THR and TKR that have been published The study protocol was approved by the local ethics committee and all participants gave written informed consent. A data and safety monitoring board monitored the study. All patients who were scheduled to receive THR or TKR for OA at participating centres between 1 January 2003 and 30 April 2006 were included in the study. Exclusion criteria included: 1) a history of septic arthritis; 2) hip or knee fracture; 3) intra-operative complications; 4) revision arthroplasty; 5) rheumatoid arthritis; 6) lower extremity amputations; 7) malignancy; and 8) inability to complete the questionnaires because of cognitive or language difficulties. The WOMAC, Short-Form (SF)-36 16,17 and the Lequesne scores 18 were recorded pre-operatively and at three, six, 12 and 24 months post-operatively (Table I). The SF-36 is a 36-item questionnaire that measures eight multi-item dimensions of health, in which higher scores represent a better quality of life. The Lequesne score comprises five questions pertaining to pain or discomfort, four questions about activities of daily living, one question dealing with maximum distance walked, and one question asking if walking aids are required. The score ranges from 0 to 24, with higher scores representing a lower quality of life. All other aspects of the trial have previously been published A total of 1425 patients were available; of these, 227 were excluded or refused to participate, leaving a total of 1198 patients (704 THR and 494 TKR). The follow-up rate at three months was 92%, at six months 89%, at 12 months 85% and at 24 months 79% (Table II). There was no clear relationship between WOMAC scores at baseline and loss to follow-up. We administered the standard version 19,20 of the WOMAC index. Upon completion of the WOMAC index, patients were asked to think about all the questions they had just completed and to mark one question from the function domain that they felt was most important to them. For the WOMAC scales, responses were recorded on a visual analogue scale with terminal descriptors. Scores were calculated for each category and standardised to a score of 0 to 100, with higher scores indicating more pain, stiffness or dysfunction. Statistical analysis. We calculated the frequencies of patient priorities on the WOMAC items pre-operatively and at all follow-up periods, separately for THR and TKR. Items that were deemed to be important by 5% of the patients across the follow-up intervals were identified and used to calculate a WOMAC THR function short form and a WOMAC TKR function short form, with no item having any weighting. We compared the results of these newly defined shortened forms alongside the original 2 and other published WOMAC function short forms. 4,11 Responsiveness was assessed through the standardised response mean (SRM), calculated as the mean change between the pre-operative and the 12-month scores divided by the standard deviation of the change in score. 21 The construct validity of the short forms was assessed using Spearman s correlation coefficient between scores of the different forms. Internal consistency was assessed using Cronbach s α. THE BONE & JOINT JOURNAL

3 USING THE PATIENT S PERSPECTIVE TO DEVELOP FUNCTION SHORT FORMS SPECIFIC TO TOTAL HIP AND KNEE REPLACEMENT 241 Table III. Frequency distribution of patient priorities of Western Ontario and McMaster University Osteoarthritis Index (WOMAC) function items pre-operatively and at three, six, 12 and 24 months after total hip replacement (THR) or total knee replacement (TKR) THR TKR Item Pre-op 3-mth 6-mth 12-mth 24-mth Mean Retained Pre-op 3-mth 6-mth 12-mth 24-mth Mean Retained 1. Descending stairs x 2. Ascending stairs x x 3. Rising from sitting x x 4. Standing x x 5. Bending to floor x x 6. Walking on flat x x 7. Getting in/out of car x x 8. Going shopping Putting on socks x Rising from bed Taking off socks Lying in bed Getting in/out of bath Sitting Getting on/off toilet Heavy domestic duties x Light domestic duties Total Categorical data were compared using chi-squared tests. All p-values were two-tailed; no corrections were made for multiple comparisons, and a p value < 0.05 was selected to indicate statistical significance. Statistical analysis was performed using SPSS software (SPSS Inc., Chicago, Illinois). Results Patients who underwent TKR were older than those undergoing THR (70.0 years (SD 8.4) versus 68.2 years (SD 9.7), p = 0.005), but they scored significantly better on the baseline WOMAC function scale (52.6 (SD 24.3) versus 55.5 (SD 23.2), p = 0.045) and on the baseline Lequesne score (Table I). Of the 704 THR patients assessed pre-operatively, 554 marked the item on the WOMAC function scale most important to them: the five most commonly selected items were walking on flat (25.5%, n = 141), standing (13.5%, n = 75), bending to floor (13.4%, n = 74), ascending stairs (10.1%, n = 56), and rising from sitting (7.9%, n = 44). Of the 494 pre-operative TKR patients, 380 marked an item: the five most commonly selected were standing (23.2%, n = 88), walking on flat (21.6%, n = 82), descending stairs (12.4%, n = 47), bending to floor (8.4%, n = 32), and rising from sitting (7.4%, n = 28) (Table III). These differences between the hip and knee selections were significant (p < 0.001, Pearson chi-squared test). The following items were selected by fewer than 2% of patients before either THR or TKR: rising from bed, taking off socks, lying in bed, getting out/in of bath, sitting, getting on/off toilet and light domestic duties (Table III). There was a shift in priorities after both TKR and THR. At one year post-operatively, THR patients most commonly selected bending to floor as the most important item (23.2%, compared with 13.4% pre-operatively), Proportion of patients who selected item to be most important (%) Standing Bending on floor Walking on flat Heavy domestic Baseline Follow-up (mths) Fig. 1 Graph showing the importance of selected Western Ontario and McMaster Universities osteoarthritis index (WOMAC) items in patients undergoing total hip replacement. whereas walking on flat lost importance and dropped from 25.5% pre-operatively to 12.7% post-operatively (Table III and Fig. 1). One year after TKR both standing and walking on flat lost their importance (from 23.2% to 15.7% and from 21.6% to 9.9%, respectively), while other items, e.g. bending to floor (increased by 5.9%), descending stairs (increased by 5.1%) and getting in/out of car (increased by 4.7%) were selected more often as being important (Table III). The mean pre-operative WOMAC long-form function scores are shown in Table IV. When the items identified were used to calculate a WOMAC-THR function short form and a WOMAC-TKR function short form, the forms resulted in slightly higher values for the improvement after both THR (mean change 43.2 (SD 24.2) vs 40.0 (SD 23.2)) and TKR (mean change 38.4 (SD 27.5) vs 33.2 (SD 25.4)) compared with the original full WOMAC function scale. VOL. 95-B, No. 2, FEBRUARY 2013

4 242 T. R. LIEBS, W. HERZBERG, J. GLUTH, W. RÜTHER, J. HAASTERS, M. RUSSLIES, J. HASSENPFLUG Table IV. Responsiveness to change of the Western Ontario and McMaster Universities (WOMAC) function original long form, the short forms by Whitehouse et al 11 and Tubach et al, 4 and the newly developed WOMAC total hip replacement (THR) and total knee replacement (TKR) function short-forms (SRM, standardised response mean) THR (mean with SD) TKR (mean with SD) Version of WOMAC function Pre-operative 12-month Change SRM Pre-operative 12-month Change SRM Original (long form) 55.5 (23.2) 15.5 (17.0) 40.0 (23.2) (24.3) 17.4 (19.3) 33.2 (25.4) 1.31 Tubach short form 57.4 (24.3) 14.4 (17.3) 42.9 (24.8) (24.8) 19.5 (19.9) 37.4 (27.2) 1.38 Whitehouse short form 56.1 (24.0) 14.3 (17.0) 41.7 (24.5) (25.1) 17.6 (19.1) 34.1 (26.7) 1.28 New THR function short form 58.4 (24.0) 15.2 (17.9) 43.2 (24.3) New TKR function short form (24.7) 21.4 (20.4) 38.4 (27.5) 1.39 The TKR function short form demonstrated slightly improved responsiveness compared with the original WOMAC function long form and the short forms produced by Whitehouse et al 11 and Tubach et al, 4 which can be assembled from the same data set (Table IV). The construct validity of the specific WOMAC-THR and TKR function short forms was excellent (r 0.95). Internal consistency for the WOMAC-THR and TKR function short forms was excellent pre-operatively (THR α = 0.915; TKR α = 0.909) and at 12 months follow-up (THR α = 0.924; TKR α = 0.922). Discussion The WOMAC score was designed for the evaluation of the non-operative treatment of OA and it does not differentiate between hip or knee osteoarthritis. Nevertheless, it is frequently used for the evaluation of outcome following THR and TKR. Our analysis clearly demonstrated that several items of the WOMAC function score were considered to be important by only a small minority of patients undergoing surgery and that their priorities change in the post-operative period. As symptoms improve, simple activities such as walking on the flat become easier for patients and they come to focus on more difficult challenges. Patients undergoing THR found different items of the WOMAC score to be important compared with those after TKR. Therefore, it is unlikely that the WOMAC function long form is sufficiently sensitive for both TKR and THR. The short forms for THR and TKR resulted in slightly improved responsiveness, as measured by the SRM, compared with the long form. Using 5% as a cut-off for the frequencies of functions reported as priorities by patients led to a set of six items that were considered to be important by both patients undergoing THR and those undergoing TKR. Of these items four are included in both versions of the published WOMAC short forms. 4,11 However, other items included were not considered important by our patients, with, for example, rising from bed, sitting and getting on/off toilet being important for < 1% in our population. Other items considered very important by our patients, e.g. standing (23.2%) before TKR or bending to floor (23.2%) one year after THR, are not included in the existing published WOMAC short forms. 4,11 An outcome measure must be both responsive and valid. Our short form has several advantages that, in theory, should result in a high validity: item selection is based solely on the patient s perspective and in particular we differentiate between those undergoing either TKR or THR both before and after surgery. Studies in which patients were randomised to different types of prosthesis have failed to demonstrate a significant effect of different surgical procedures on the health-related quality of life. 22 Therefore, it is a matter of debate whether the currently available PROMs are sufficiently sensitive to detect potential differences between different prostheses. Our forms appear to have greater responsiveness and are a step towards a WOMAC function short form with a suitable sensitivity to change. Selection of the items for the short version of WOMAC has been set somewhat arbitrarily to a priority of 5% frequency of items chosen by patients. However, this threshold appears to be used quite commonly and resulted in a comparable number of items to be selected compared with the published short forms. 4,11 It could be argued that selecting a specific weighting for each item, as in the SF-36, for example, might be more appropriate. However, as previous WOMAC short forms did not use weighting factors, we used the same approach. Further research is needed to assess whether responsiveness could be improved by using separate weighting factors for the hip and the knee. In our study patients were allowed to show preference for only one item of the WOMAC function scale and this could be regarded as open to bias. To our knowledge there are no studies analysing how many items should be selected by patients. Although the eligibility criteria were fairly broad, the analysis was restricted to patients undergoing unilateral primary THR or TKR. Therefore, these results cannot be transferred to patients undergoing conservative treatment, revision or bilateral total joint replacement. Because the specific WOMAC THR and TKR function short forms are subsets of the WOMAC long form, it is THE BONE & JOINT JOURNAL

5 USING THE PATIENT S PERSPECTIVE TO DEVELOP FUNCTION SHORT FORMS SPECIFIC TO TOTAL HIP AND KNEE REPLACEMENT 243 relatively simple to compare results across studies using either the long or the short version. Only the scoring algorithm needs to be changed, not the items of the WOMAC questionnaire itself. This could increase the scale s acceptability and usefulness and facilitate further work, which is necessary to further validate specific WOMAC THR and TKR function scales. No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. References 1. Bellamy N. Osteoarthritis: an evaluative index for clinical trials [MSc thesis]. McMaster University, Hamilton, Ontario, Canada; Bellamy N, Buchanan WW, Goldsmith CH, Campbell J, Stitt LW. Validation study of WOMAC: a health status instrument for measuring clinically important patient relevant outcomes to antirheumatic drug therapy in patients with osteoarthritis of the hip or knee. J Rheumatol 1988;15: McConnell S, Kolopack P, Davis AM. The Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC): a review of its utility and measurement properties. Arthritis Rheum 2001;45: Tubach F, Baron G, Falissard B, et al. Using patients and rheumatologists opinions to specify a short form of the WOMAC function subscale. Ann Rheum Dis 2005;64: Ryser L, Wright BD, Aeschlimann A, Mariacher-Gehler S, Stucki G. A new look at the Western Ontario and McMaster Universities Osteoarthritis Index using Rasch analysis. Arthritis Care Res 1999;12: Sun Y, Stürmer T, Günther KP, Brenner H. Reliability and validity of clinical outcome measurements of osteoarthritis of the hip and knee: a review of the literature. Clin Rheumatol 1997;16: Yang KG, Raijmakers NJ, Verbout AJ, Dhert WJ, Saris DB. Validation of the short-form WOMAC function scale for the evaluation of osteoarthritis of the knee. J Bone Joint Surg [Br] 2007;89-B: Kalantar JS, Talley NJ. The effects of lottery incentive and length of questionnaire on health survey response rates: a randomised study. J Clin Epidemiol 1999;52: Baron G, Tubach F, Ravaud P, Logeart I, Dougados M. Validation of a short form of the Western Ontario and McMaster Universities Osteoarthritis Index function subscale in hip and knee osteoarthritis. Arthritis Rheum 2007;57: Wolfe F. Determinants of WOMAC function, pain and stiffness scores: evidence for the role of low back pain, symptom counts, fatigue and depression in osteoarthritis, rheumatoid arthritis and fibromyalgia. Rheumatology (Oxford) 1999;38: Whitehouse SL, Lingard EA, Katz JN, Learmonth ID. Development and testing of a reduced WOMAC function scale. J Bone Joint Surg [Br] 2003;85-B: Seror R, Tubach F, Baron G, et al. Individualising the Western Ontario and McMaster Universities osteoarthritis index (WOMAC) function subscale: incorporating patient priorities for improvement to measure functional impairment in hip or knee osteoarthritis. Ann Rheum Dis 2008;67: Liebs TR, Herzberg W, Rüther W, et al. Ergometer cycling after hip or knee replacement surgery: a randomized controlled trial. J Bone Joint Surg [Am] 2010;92- A: Liebs TR, Herzberg W, Rüther W, et al. Multicenter randomized controlled trial comparing early versus late aquatic therapy after total hip or knee arthroplasty. Arch Phys Med Rehabil 2012;93: Liebs TR, Herzberg W, Roth-Kroeger AM, Rüther W, Hassenpflug J. Women recover faster than men after standard knee arthroplasty. Clin Orthop Relat Res 2011;469: Ware JE Jr, Kosinski M, Bayliss MS, et al. Comparison of methods for the scoring and statistical analysis of SF-36 health profile and summary measures: summary of results from the Medical Outcomes Study. Med Care 1995;33(Suppl):AS264 AS Bullinger M. German translation and psychometric testing of the SF-36 Health Survey: preliminary results from the IQOLA Project (International Quality of Life Assessment). Soc Sci Med 1995;41: Lequesne MG, Mery C, Samson M, Gerard P. Indexes of severity for osteoarthritis of the hip and knee: validation-value in comparison with other assessment tests. Scand J Rheumatol Suppl 1987;65: Bellamy N. The WOMAC Knee and Hip Osteoarthritis Indices: development, validation, globalization and influence on the development of the AUSCAN Hand Osteoarthritis Indices. Clin Exp Rheumatol 2005;23: Bellamy N. WOMAC osteoarthritis index: a user s guide. Ontario: London Health Science Centre, Liang MH, Fossel AH, Larson MG. Comparisons of five health status instruments for orthopedic evaluation. Med Care 1990;28: Ethgen O, Bruyère O, Richy F, Dardennes C, Reginster JY. Health-related quality of life in total hip and total knee arthroplasty: a qualitative and systematic review of the literature. J Bone Joint Surg [Am] 2004;86-A: VOL. 95-B, No. 2, FEBRUARY 2013