Rasch analysis of the Oxford Knee Score

A comprehensive analysis of the pre- and postoperative responses to each of the 12 Oxford knee score questions one year following knee arthroplasty

AIMS

To assess the pre- and postoperative responses to each of the 12 individual Oxford Knee Score (OKS) questions and percentages of those that were better, same or worse after primary knee arthroplasty (KA).

METHODS

A single centre retrospective cohort study conducted over a 24-month period which included 3259 patients with completed OKS preoperatively and 1-year after KA. There were 1286 males and 1973 females, with an overall mean age of 70.0 (range 34-94). The mean scores for each question of the OKS were compared between baseline and 1-year. The percentage of patients who reported better, the same or worse postoperative symptoms for each question were calculated and represented on a heatmap.

RESULTS

There were significant (p < 0.001) improvements in all 12 questions, all of which demonstrated moderate (Q2, Q7) or large effect sizes. Improvements in individual question responses varied. Symptoms of pain and limping demonstrated the greatest improvement, with 86% of patients enjoying a positive change in their symptoms. Despite this improvement 1067 (41.4%) continued to have mild to severe pain in their knee, and 442 (17.3%) patients limped often to all the time when walking postoperatively. Whereas other questions that did not improve to the same extent for example washing and drying only improved in 53% of patients but only 347 (13.5%) had moderate/extreme trouble or found it impossible to do this postoperatively. Preoperatively four questions (Q1, Q6, Q7, Q8) demonstrated floor effects, postoperatively all questions apart from question 7 (kneeling) demonstrated ceiling effects.

CONCLUSION

The mean improvement and outcome at 1-year for each of the 12 questions varied according to the patient's preoperative response. As a clinical tool, the heatmap (improvement, same and worse) will enable communication to patients about their potential change in their knee specific symptoms according to their preoperative responses.

LEVEL OF EVIDENCE

Retrospective study, Level III.

Minimal important change thresholds change over time after knee and hip arthroplasty

OBJECTIVES

The minimal important change (MIC) reflects what patients, on average, consider the smallest improvement in a score that is important to them. MIC thresholds may vary across patient populations, interventions used, posttreatment time points and derivation methods. We determine and compare MIC thresholds for the Oxford Knee Score and Oxford Hip Score (OKS/OHS) at 3 months postoperatively to 12- and 24-month thresholds in patients undergoing knee or hip arthroplasty.

STUDY DESIGN AND SETTING

This cohort study used data from patients undergoing total knee arthroplasty (TKA), unicompartmental knee arthroplasty (UKA), or total hip arthroplasty (THA) at a public hospital between February 2016 and February 2023. At 3, 12, and 24 months postoperatively, patients responded to the OKS/OHS and a 7-point anchor question determining experienced changes in knee or hip pain and functional limitations. We used the adjusted predictive modeling method that accounts for the proportion improved and the reliability of the anchor question to determine MIC thresholds and their mean differences between time points.

RESULTS

Complete data were obtained from 695/957 (73%), 1179/1703 (69%), and 1080/1607 (67%) patients undergoing TKA, 474/610 (78%), 438/603 (73%), and 355/507 (70%) patients undergoing UKA, and 965/1315 (73%), 978/1409 (69%), and 1059/1536 (69%) patients undergoing THA at 3, 12, and 24 months, respectively. The median age ranged from 68 to 70 years and 55% to 60% were females. The proportions improved ranged between 83% and 95%. The OKS/OHS MIC thresholds were 0.1, 4.2, and 5.1 for TKA, 1.8, 5.6, and 3.4 for UKA, and 1.3, 6.1, and 6.0 for THA at 3, 12, and 24 months postoperatively, respectively. The reliability ranged between 0.64 and 0.82, and the MIC values increased between three and 12 months but not between 12 and 24 months.

CONCLUSION

Any absence of deterioration in pain and function is considered important at 3 months after knee or hip arthroplasty. Increasing thresholds over time suggest patients raise their standards for what constitutes a minimal important improvement over the first postoperative year. Besides improving our understanding of patients' views on postoperative outcomes, these clinical thresholds may aid in interpreting registry-based treatment outcome evaluations.

Item response theory assumptions were adequately met by the Oxford hip and knee scores

OBJECTIVES

To develop item response theory (IRT) models for the Oxford hip and knee scores which convert patient responses into continuous scores with quantifiable precision and provide these as web applications for efficient score conversion.

STUDY DESIGN AND SETTING

Data from the National Health Service patient-reported outcome measures program were used to test the assumptions of IRT (unidimensionality, monotonicity, local independence, and measurement invariance) before fitting models to preoperative response patterns obtained from patients undergoing primary elective hip or knee arthroplasty. The hip and knee datasets contained 321,147 and 355,249 patients, respectively.

RESULTS

Scree plots, Kaiser criterion analyses, and confirmatory factor analyses confirmed unidimensionality and Mokken analysis confirmed monotonicity of both scales. In each scale, all item pairs shared a residual correlation of ≤ 0.20. At the test level, both scales showed measurement invariance by age and gender. Both scales provide precise measurement in preoperative settings but demonstrate poorer precision and ceiling effects in postoperative settings.

CONCLUSION

We provide IRT parameters and web applications that can convert Oxford Hip Score or Oxford Knee Score response sets into continuous measurements and quantify individual measurement error. These can be used in sensitivity analyses or to administer truncated and individualized computerized adaptive tests.

Validation and interval scale transformation of the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) in patients undergoing knee arthroplasty, using the Rasch model

Objectives

Interval scale reduce measurement bias compared to ordinal scale. We aimed to evaluate the fit of Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) to the Rasch model and derive the transformation table for interval scale measurement.

Methods

Data from osteoarthritis patients listed for knee arthroplasty (KA) pre-operatively, and at 6- and 12- months post-operative was used. WOMAC was calibrated for fit to the Rasch model for monotonicity, homogeneity, local item independence and absence of differential item functioning (DIF) in a randomly selected 900 patients, 300 from each time point; parameter estimates were then imported into the full data set. Responsiveness was reported through Standard Error of Measurement (SEM); Smallest Detectable Difference (SDD), %SDD and effect sizes (ES) between baseline and 6-months. WOMAC was transformed from ordinal to interval values.

Results

1136 patients (mean age 65.9 years, 69.9% female) were included. WOMAC pain (0-20), function (0-68) and total scores (0-96) had adequate fit to Rasch model with good reliability (Person Separation Index: 0.76, 0.80 and 0.79). No item deletion was required. The SEM, SDD, %SDD and ES of WOMAC total were 4.4, 6.9, 10.1, and 1.97. No significant DIF was seen for age, sex, body mass index, type of KA, languages, and education level. WOMAC pain, function and total scores were transformed to interval scales.

Conclusion

WOMAC total, pain and function scales had adequate fit to the Rasch model, providing unidimensional measure with good reliability and responsiveness. Transformation of WOMAC to interval scale measurement is applicable to other studies.

Cost-Effective Healthcare in Rehabilitation: Physiotherapy for Total Endoprosthesis Surgeries from Prehabilitation to Function Restoration

Knee and hip joint replacements for the elderly are increasingly placing a burden on healthcare. Our aim was to verify the efficiency of the prehabilitation program among patients with knee arthroplasty (TKA) and hip arthroplasty (THA), taking into account the length and cost of postoperative rehabilitation and the restoration of function. We introduced a two-week preoperative physiotherapy program for patients awaiting knee and hip replacement surgery. We measured the duration and costs of the hospital stays, the active and passive range of motion of the hip and knee joints, and the quality of life. In the study, 99 patients participated (31 male, 68 female), with a mean age of 69.44 ± 9.69 years. We showed that, as a result of the prehabilitation program, the length of postoperative hospital stay decreased (THA: median 31.5 (IQR 26.5-32.5) vs. median 28 (IQR 21-28.5), TKA: median 36.5 (IQR 28-42) vs. median 29 (IQR 26-32.5)), and the patients' quality of life showed a significant improvement (TKA: median 30.5 (IQR 30-35) vs. median 35 (IQR 33-35), THA: median 25 (IQR 25-30) vs. median 33 (IQR 31.5-35)). The flexion movements were significantly improved through prehabilitation in both groups. Based on our positive results, we recommend the introduction of prehabilitation into TKA- and THA-related care.

Use of computerised adaptive testing to reduce the number of items in patient-reported hip and knee outcome scores: an analysis of the NHS England National Patient-Reported Outcome Measures programme

OBJECTIVE

Over 160 000 participants per year complete the 12-item Oxford Hip and Knee Scores (OHS/OKS) as part of the NHS England Patient-Reported Outcome Measures (PROMs) programme. We used a modern computational approach, known as computerised adaptive testing (CAT), to simulate individually tailored OHS and OKS assessment, with the goal of reducing the number of questions a patient must complete without compromising measurement accuracy.

METHODS

We fit the 2018/2019 PROMs data to an item response theory (IRT) model. We assessed IRT model assumptions alongside reliability. We used parameters from the IRT model with data from 2017/2018 to simulate CAT assessments. Two simulations were run until a prespecified SE of measurement was met (SE=0.32 and SE=0.45). We compared the number of questions required to meet each cut-off and assessed the correlation between the full-length and CAT administration.

RESULTS

We conducted IRT analysis using 40 432 OHS and 44 714 OKS observations. The OHS and OKS were both unidimensional (root mean square error of approximation 0.08 and 0.07, respectively) and marginal reliability 0.91 and 0.90. The CAT, with a precision limit of SE=0.32 and SE=0.45, required a median of four items (IQR 1) and two items (IQR 1), respectively, for the OHS, and median of four items (IQR 2) and two items (IQR 0) for the OKS. This represents a potential 82% reduction in PROM length. In the context of 160 000 yearly assessments, these methodologies could result in the omission of some 1 280 000 redundant questions per year, which equates to 40 000 hours of patient time.

CONCLUSION

The application of IRT to the OHS and OKS produces an efficient and substantially reduced CAT. We have demonstrated a path to reduce the burden and potentially increase the compliance for these ubiquitous outcome measures without compromising measurement accuracy.

Application of the Rasch measurement framework to mammography positioning data

The purpose of this article is to provide raw data and measure-validation data pertaining to a co-submission published in European Journal of Radiology and entitled: Development and validation of a novel measure of adverse patient positioning in mammography. This Data in Brief article serves not only to provide greater detail than its companion article but also as an educational worked example of the Rasch measurement framework. Rasch measurement is a form of modern psychometric technique and our articles provide the first known example of its use in the evaluation of clinical radiological image quality. The data consist of observations of mammographic images, plus limited participant parameters relevant to the measure validation process. Also provided are validation indices produced by subjecting the primary data to Rasch analysis. An expert observer generated the primary data by reviewing mammographic images to judge the presence or absence of a set of features developed through theory and consultation with other experts. The validation data were generated through Rasch analysis, performed using Winsteps® software, which mathematically models the probability of having a correct response (or a present feature in this dataset) to an item in a given measurement instrument (e.g. questionnaire), as a function of the participant's ability/position on the underlying construct under study. The data can be reused by anyone wishing to learn and practice psychometric validation techniques. They can also form a basis for researchers wishing to build on our preliminary measure for the assessment of mammographic clinical image quality.

Machine Learning and Primary Total Knee Arthroplasty: Patient Forecasting for a Patient-Specific Payment Model

BACKGROUND

Value-based and patient-specific care represent 2 critical areas of focus that have yet to be fully reconciled by today's bundled care model. Using a predictive naïve Bayesian model, the objectives of this study were (1) to develop a machine-learning algorithm using preoperative big data to predict length of stay (LOS) and inpatient costs after primary total knee arthroplasty (TKA) and (2) to propose a tiered patient-specific payment model that reflects patient complexity for reimbursement.

METHODS

Using 141,446 patients undergoing primary TKA from an administrative database from 2009 to 2016, a Bayesian model was created and trained to forecast LOS and cost. Algorithm performance was determined using the area under the receiver operating characteristic curve and the percent accuracy. A proposed risk-based patient-specific payment model was derived based on outputs.

RESULTS

The machine-learning algorithm required age, race, gender, and comorbidity scores ("risk of illness" and "risk of morbidity") to demonstrate a high degree of validity with an area under the receiver operating characteristic curve of 0.7822 and 0.7382 for LOS and cost. As patient complexity increased, cost add-ons increased in tiers of 3%, 10%, and 15% for moderate, major, and extreme mortality risks, respectively.

CONCLUSION

Our machine-learning algorithm derived from an administrative database demonstrated excellent validity in predicting LOS and costs before primary TKA and has broad value-based applications, including a risk-based patient-specific payment model.

DEMQOL and DEMQOL-Proxy: a Rasch analysis

Background

DEMQOL and DEMQOL-Proxy are widely used patient reported outcome measures (PROMs) of health related quality of life in people with dementia (PWD). Growing interest in routine use of PROMs in health care calls for more robust instruments that are potentially fit for reliable and valid comparisons at the micro-level (patients) and meso-level (clinics, hospitals, care homes).

Methods

We used modern psychometric methods (based on the Rasch model) to re-evaluate DEMQOL (1428 PWDs) and DEMQOL-Proxy (1022 carers) to ensure they are fit for purpose. We evaluated scale to sample targeting, ordering of item thresholds, item fit to the model, and differential item functioning (sex, age, relationship), local independence, unidimensionality and reliability on the full set of items and a smaller item set.

Results

For both DEMQOL and DEMQOL-Proxy the smaller item set performed better than the original item set. We developed revised scores using the items from the smaller set.

Conclusions

We have improved the scoring of DEMQOL and DEMQOL-Proxy using the Rasch measurement model. Future work should focus on the problems identified with content and response options.

A Systematic Review of Measurement Properties of Patient-Reported Outcome Measures Used in Patients Undergoing Total Knee Arthroplasty

BACKGROUND

While clinical research on total knee arthroplasty (TKA) outcomes is prevalent in the literature, studies often have poor methodological and reporting quality. A high-quality patient-reported outcome instrument is reliable, valid, and responsive. Many studies evaluate these properties, but none have done so with a systematic and accepted method. The objectives of this study were to identify patient-reported outcome measures (PROMs) for TKA, and to critically appraise, compare, and summarize their psychometric properties using accepted methods.

METHODS

MEDLINE, EMBASE, SCOPUS, Web of Science, PsycINFO, and SPORTDiscus were systematically searched for articles with the following inclusion criteria: publication before December 2014, English language, non-generic PRO, and evaluation in the TKA population. Methodological quality and evidence of psychometric properties were assessed with the COnsensus-based standards for the selection of health Status Measurement INstruments (COSMIN) checklist and criteria for psychometric evidence proposed by the COSMIN group and Terwee et al.

RESULTS

One-hundred fifteen studies on 32 PROMs were included in this review. Only the Work, Osteoarthritis or joint-Replacement Questionnaire, the Oxford Knee Score, and the Western Ontario and McMaster Universities Arthritis Index had 4 or more properties with positive evidence.

CONCLUSION

Most TKA PROMs have limited evidence for their psychometric properties. Although not all the properties were studied, the Work, Osteoarthritis or joint-Replacement Questionnaire, with the highest overall ratings, could be a useful PROM for evaluating patients undergoing TKA. The methods and reporting of this literature can improve by following accepted guidelines.

Histopathological subgroups in knee osteoarthritis

OBJECTIVE

Osteoarthritis (OA) is a heterogeneous, multi-tissue disease. We hypothesised that different histopathological features characterise different stages during knee OA progression, and that discrete subgroups can be defined based on validated measures of OA histopathological features.

DESIGN

Medial tibial plateaux and synovium were from 343 post-mortem (PM) and 143 OA arthroplasty donations. A 'chondropathy/osteophyte' group (n = 217) was classified as PM cases with osteophytes or macroscopic medial tibiofemoral chondropathy lesions ≥grade 3 to represent pre-surgical (early) OA. 'Non-arthritic' controls (n = 48) were identified from the remaining PM cases. Mankin histopathological scores were subjected to Rasch analysis and supplemented with histopathological scores for subchondral bone marrow replacement and synovitis. Item weightings were derived by principle components analysis (PCA). Histopathological subgroups were sought using latent class analysis (LCA).

RESULTS

Chondropathy, synovitis and osteochondral pathology were each associated with OA at arthroplasty, but each was also identified in some 'non-arthritic' controls. Tidemark breaching in the chondropathy/osteophyte group was greater than in non-arthritic controls. Three histopathological subgroups were identified, characterised as 'mild OA', or 'severe OA' with mild or moderate/severe synovitis.

CONCLUSIONS

Presence and severity of synovitis helps define distinct histopathological OA subgroups. The absence of a discrete 'normal' subgroup indicates a pathological continuum between normality and OA status. Identifying specific pathological processes and their clinical correlates in OA subgroups has potential to accelerate the development of more effective therapies.

Rasch analysis of the Western Ontario Osteoarthritis of the Shoulder index - the Danish version

Purpose

The Western Ontario Osteoarthritis of the Shoulder (WOOS) index is a disease-specific, patient-reported, 19-question survey that measures the quality of life among patients with osteoarthritis (OA). The purpose of this study was to validate the Danish version of WOOS for OA and fractures (FRs) using modern test theory.

Patients and methods

The study included 1,987 arthroplasties in 1,943 patients that were reported to the Danish Shoulder Arthroplasty Register between 2006 and 2011. These included 847 OA and 1,140 FR cases.

Results

Principal component analysis indicated the unidimensionality of WOOS. The person reliabilities showed a floor-ceiling effect, indicating that a dichotomy was the best fit for the WOOS scale. For OA, WOOS showed good reliability (item and person reliability of 0.98 and 0.76) and good targeting, with a person mean of −0.56 logits. FR also showed good targeting (person mean of −0.08) and good reliability (item and person reliabilities of 1.00 and 0.86, respectively). All WOOS items fit well with the OA sample except items 5 and 6 (pertaining to grinding and the influence of weather). In addition, item 6 showed signs of degrading the scale with an outfit mean square of 2.46. Only item 6 showed a misfit for FR with no sign of scale degradation. The residual principal component analysis confirmed the unidimensionality of FR but not OA. Six items displayed clinically significant differential item functioning between OA and FR.

Conclusion

Rasch analysis showed that WOOS had a good fit with the Rasch model when used as a dichotomous scale for OA and FR. However, the results were valid only when WOOS was divided into two categories with a threshold of 950 (50% of the maximum score). For the use of WOOS in future clinical research, we recommend that a dichotomous score be reported as a measure of clinical failure in OA and FR.

High correlation of the Oxford Knee Score with postoperative pain, but not with performance-based functioning

PURPOSE

The Oxford Knee Score (OKS) is a widely known patient-related outcome measure (PROM) to determine pain and knee functioning before and after total knee arthroplasty (TKA). Self-reported function is mainly influenced by change in pain; therefore, it was hypothesized that the OKS correlates more with pain than with performance-based functioning.

METHODS

In a prospective cohort of 88 patients, who had a cementless mobile-bearing TKA, included in a randomized clinical trial, the correlation between the overall OKS, and its subscales for pain (PCS) and function (FCS), with performance-based functioning using the DynaPort^® Knee Score (DKS), visual analogue scale score for pain (VAS) and the Knee Society Score (KSS) was evaluated. All scores were measured preoperatively, 6 months and 1 year after surgery. Overall change in outcome over time was analysed until 5 years after surgery.

RESULTS

All scores improved over time. The DKS was influenced by sex, preoperative BMI and age. The internal consistency of the OKS PCS increased over time, whereas the OKS FCS remained the same. The mean postoperative OKS FCS showed moderate correlation with the DKS (r = 0.65, p < 0.001), and the mean postoperative OKS and OKS PCS showed high correlation with the VAS (r = -0.79 and r = -0.82, respectively, p < 0.001). The mean postoperative KSS showed high correlations with the OKS (r = 0.80, p < 0.001), the OKS PCS (r = 0.72 p < 0.001) and OKS FCS (r = 0.74, p < 0.001).

CONCLUSION

The postoperative OKS and the OKS PCS showed high correlation with pain, but only the postoperative OKS FCS was well correlated with performance-based functioning. This suggests that the OKS is more related to pain and tells us less on postoperative functioning. This is important when the OKS as PROM is used to evaluate the quality of orthopaedic care of patients with TKA.

LEVEL OF EVIDENCE

III.

Patient-reported outcome measures after total knee arthroplasty: a systematic review

Objectives

A lack of connection between surgeons and patients in evaluating the outcome of total knee arthroplasty (TKA) has led to the search for the ideal patient-reported outcome measure (PROM) to evaluate these procedures. We hypothesised that the desired psychometric properties of the ideal outcome tool have not been uniformly addressed in studies describing TKA PROMS.

Methods

A systematic review was conducted investigating one or more facets of patient-reported scores for measuring primary TKA outcome. Studies were analysed by study design, subject demographics, surgical technique, and follow-up adequacy, with the ‘gold standard’ of psychometric properties being systematic development, validity, reliability, and responsiveness.

Results

A total of 38 articles reported outcomes from 47 different PROMS to 85 541 subjects at 26.3 months (standard deviation 30.8) post-operatively. Of the 38, eight developed new scores, 20 evaluated existing scores, and ten were cross-cultural adaptation of existing scores. Only six of 38 surveyed studies acknowledged all ‘gold standard’ psychometric properties. The most commonly studied PROMS were the Oxford Knee Score, New Knee Society Score, Osteoarthritis Outcome Score, and Western Ontario and McMaster Universities Osteoarthritis Index.

Conclusions

A single, validated, reliable, and responsive PROM addressing TKA patients’ priorities has not yet been identified. Moreover, a clear definition of a successful procedure remains elusive.

Cite this article: Bone Joint Res 2015;4:120–127

Comparative demographics, ROM, and function after TKA in Chinese, Malays, and Indians

BACKGROUND

There is marked racial disparity in TKA use rates, demographics, and outcomes between white and Afro-Caribbean Americans. Comparative studies of ethnicity in patients undergoing TKAs have been mostly in American populations with an underrepresentation of Asian groups. It is unclear whether these disparities exist in Chinese, Malays, and Indians.

QUESTIONS/PURPOSES

We therefore determined whether (1) TKA use; (2) demographics and preoperative statuses; and (3) functional outcomes at 2 years after TKA differed among three ethnic groups, namely, Chinese, Malays, and Indians who underwent TKA.

METHODS

From our hospital joint registry we identified 5332 patients who had a primary TKA from 2004 to 2009. The cohort was stratified by race and subsequently compared for demographics, preoperative knee ROM, and deformity. At the second postoperative year we determined Knee Society scores, Oxford knee scores, and obtained SF-36 health questionnaires.

RESULTS

Six percent more Chinese patients underwent TKAs compared with Malays or Indians. Malays were operated on at a younger age with a higher body mass index. Chinese patients had more severe preoperative varus deformity. There were no major differences in joint ROM in all races. For Knee Society, Oxford knee, and SF-36 scores, Chinese patients had consistently higher preoperative and postoperative scores. Malays presented with the lowest preoperative scores but had the greatest improvement in scores at followup with postoperative scores similar to Chinese counterparts. Indians had the lowest postoperative scores and worst improvement of all

CONCLUSIONS

The variations in demographics, preoperative statuses, and subsequent postoperative outcomes between the races should be considered when comparing TKA outcome studies in Asian populations.

Comparison of the responsiveness of the SF-36, the Oxford Knee Score, and the Knee Society Clinical Rating System in patients undergoing total knee replacement

OBJECTIVES

To compare the responsiveness of the Knee Society (KS) Clinical Rating System, the general health status measure Short Form 36 (SF-36), and both the raw and Rasch-based scores of the condition-specific Oxford Knee Score (OKS) in patients undergoing total knee replacement (TKR) METHODS: Data were prospectively collected as part of routine care from adult patients who underwent TKR between 2001 and 2006. OKS data fit the Rasch partial credit model after removing items regarding limping and kneeling. Responsiveness was assessed using effect size (ES), standardised response mean (SRM), and relative validity (RV).

RESULTS

Among 702 patients with complete data at baseline and two follow-ups, the pain subscale of the KS (KS-P), raw-OKS, and Rasch-OKS consistently had higher levels of responsiveness than all eight SF-36 and the other KS subscales. At 6-month follow-up, Rasch-OKS had the largest ES and KS-P had the largest SRM (2.7 and 2.0, respectively). When compared to raw-OKS, the RVs of KS-P, Rasch-OKS, SF-36 bodily pain, and SF-36 physical functioning were 1.1, 0.66, 0.49, and 0.36, respectively. A similar ordering of responsiveness was observed at 24-month follow-up.

CONCLUSION

The OKS and KS-P are more responsive than most SF-36 subscales in TKR patients. Raw-OKS and Rasch-OKS have comparable responsiveness. Different responsiveness indices may give different results.

Modern psychometrics applied in rheumatology--a systematic review

BACKGROUND

Although item response theory (IRT) appears to be increasingly used within health care research in general, a comprehensive overview of the frequency and characteristics of IRT analyses within the rheumatic field is lacking. An overview of the use and application of IRT in rheumatology to date may give insight into future research directions and highlight new possibilities for the improvement of outcome assessment in rheumatic conditions. Therefore, this study systematically reviewed the application of IRT to patient-reported and clinical outcome measures in rheumatology.

METHODS

Literature searches in PubMed, Scopus and Web of Science resulted in 99 original English-language articles which used some form of IRT-based analysis of patient-reported or clinical outcome data in patients with a rheumatic condition. Both general study information and IRT-specific information were assessed.

RESULTS

Most studies used Rasch modeling for developing or evaluating new or existing patient-reported outcomes in rheumatoid arthritis or osteoarthritis patients. Outcomes of principle interest were physical functioning and quality of life. Since the last decade, IRT has also been applied to clinical measures more frequently. IRT was mostly used for evaluating model fit, unidimensionality and differential item functioning, the distribution of items and persons along the underlying scale, and reliability. Less frequently used IRT applications were the evaluation of local independence, the threshold ordering of items, and the measurement precision along the scale.

CONCLUSION

IRT applications have markedly increased within rheumatology over the past decades. To date, IRT has primarily been applied to patient-reported outcomes, however, applications to clinical measures are gaining interest. Useful IRT applications not yet widely used within rheumatology include the cross-calibration of instrument scores and the development of computerized adaptive tests which may reduce the measurement burden for both the patient and the clinician. Also, the measurement precision of outcome measures along the scale was only evaluated occasionally. Performed IRT analyses should be adequately explained, justified, and reported. A global consensus about uniform guidelines should be reached concerning the minimum number of assumptions which should be met and best ways of testing these assumptions, in order to stimulate the quality appraisal of performed IRT analyses.

Rasch analysis of the intermittent and constant osteoarthritis pain (ICOAP) scale

OBJECTIVES

The intermittent and constant osteoarthritis pain (ICOAP) questionnaire was developed to assess two forms of pain reported by people with osteoarthritis: intermittent and constant pain. Studies examining its measurement qualities have provided some support for its use as separate and total scales. However, it has not been previously evaluated using Rasch analysis. The current study examined the fit between data obtained from the ICOAP questionnaire and the Rasch model to determine whether it meets the requirements of interval-level measurement.

DESIGN

ICOAP responses from 175 participants with knee osteoarthritis were collected in a cross-sectional questionnaire study. Participants were recruited from hospital clinics and a group who had taken part in previous research. The questionnaires were completed at home and returned by pre-paid envelope and the data were analysed using RUMM2020.

RESULTS

Fit to the Rasch model was achieved for both the constant and intermittent subscales following removal of a small number of items. The Total scale initially resulted in substantial misfit to the model, but fit was improved by removing four items that misfit the model. However, several participants presented with high fit residuals, which is consistent with misfit.

CONCLUSIONS

The results support the use of Constant and Intermittent subscales as unidimensional measures of pain. The Total scale can be adapted to improve fit to the Rasch model, but there are concerns over participant misfit.

An overview of OA research in two urban APLAR populations

Osteoarthritis (OA), the most prevalent type of arthritis in the elderly, is also among the first five leading causes of disability in developed countries. With the 'Westernized' living environment and lifestyle among Southeast Asian urbanized cities, where obesity is on the rise and the populations are ageing, the incidence of OA is expected to rise in the next decades. There is need to summarize research work within these places. This article summarizes some of the research aspects of OA in Southeast Asian cities. These data may form a useful basis for future planning of medical resource and needs.

The AUSCAN subscales, AIMS-2 hand/finger subscale, and FIOHA were not unidimensional scales

OBJECTIVES

Evaluate the internal construct validity of the Australian/Canadian (AUSCAN) index for hand osteoarthritis (HOA) and identify the physical function instrument with best performance.

STUDY DESIGN AND SETTING

AUSCAN, AIMS-2 (Arthritis Impact Measurement Scale 2), and Functional Index of HOA (FIHOA) were self-completed by 209 HOA patients (mean [standard deviation] age 61.6 [5.7] years) at baseline and 128 at follow-up. Rasch analysis was performed.

RESULTS

AUSCAN pain, physical function, and stiffness subscales comprised three constructs. AUSCAN scale performance was improved after removal of "Pain at rest" from the pain scale and division of physical function into two scales of high precision and grip strength tasks. AIMS-2 hand/finger subscale and FIHOA were improved after removal of one and two items, respectively and collapse of two AIMS-2 response categories. AUSCAN physical function scale showed better targeting to the sample and higher person reliability compared with FIHOA and especially AIMS-2 because of less "severe" items concerning grip strength tasks as opposed to precision tasks.

CONCLUSION

The AUSCAN subscales, AIMS-2 hand/finger scale, and FIHOA were not unidimensional. However, deletion of misfitting items improved scale performance. The revised AUSCAN physical function and FIHOA scales are preferable for measurement of grip strength and precision tasks, respectively.