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Objectives: Most studies of knee osteoarthritis use isokinetic peak strength as a measure of muscle strength. However, estimated one-repetition maximum (1-RM) may have a stronger relationship than isokinetic peak strength with daily activities. The aim of this study was to test the following hypotheses: first, the estimated 1-RM is more strongly associated than isokinetic peak strength with daily activities; and secondly, the estimated 1-RM is most strongly associated with the 6-minute walk test (6MWT), followed by the Get Up and Go test (GUG test) and the stair-climb test.Methods: Data were used for 177 patients with knee osteoarthritis from a randomized controlled trial on improving muscle strength. The patients had a mean age of 67.6 ± 5.8 years. Isokinetic peak strength was measured using a dynamometer, 1-RM was estimated with the 10-RM test, and physical performance was measured with the 6-minute walk test (6MWT), get-up and go test (GUG) test and stair-climb test, at the start and end of 12 weeks of resistance training. Linear regression analyses provided standardized betas (β) that were comparable between the different associations between measures of muscle strength and daily activities. Results: Compared with the estimated 1-RM, isokinetic peak strength was more strongly associated with all performance-based measures. The associations between the estimated 1-RM and performance-based tests were not ranked in the order hypothesized (6MWT, GUG test, stair-climb test).Conclusion: Contrary to the first hypothesis, isokinetic peak strength showed stronger associations with all daily activities than did estimated 1-RM. In addition, the second hypothesis regarding the activity-specific pattern for the 1-RM with regards walking, chair rising and stair climbing measurements was not confirmed. LAY ABSTRACTIn patients with knee osteoarthritis, greater muscle strength in the upper leg is linked with better performance in daily activities. To test muscle strength, peak muscle strength is usually measured. This study hypothesized that another test (the one-repetition maximum test) would be a more relevant measure. However, this was not confirmed, and therefore peak muscle strength remains the best measure of muscle strength at present.

Additional file 1: Figure S1. Detail of the Item Characteristics Curve for Global 06.

Additional file 1: Figure S2-S3. Empirical plot of items display misfit to the IRT model in at least one subsample.

OBJECTIVE: The Animated Activity Questionnaire (AAQ) assesses activity limitations in patients with hip/knee osteoarthritis (HKOA), and consisting video animations of which patients choose the animation that best matches their own performance. The AAQ has shown good validity and reliability. This study aims to evaluate cross-cultural and construct validity of the AAQ. Methods Cross-cultural validity was assessed using ordinal logistic regression analysis to evaluate Differential Item Functioning (DIF) across 7 languages. Construct validity was assessed by testing correlations between the AAQ, and a Patient Reported Outcome Measure (PROM) and performance-based tests.RESULTS: Data of 1239 patients were available. Compared to Dutch (n=279), none of the 17 items showed DIF in English (n=202), French (n=193), 1 item showed uniform DIF in Spanish (n=99) and Norwegian (n=62), and 2 items showed uniform DIF in Danish (n=201). In all these languages, the occurrence of DIF did not influence the total score, which remained comparable with the original Dutch version. For Italian (n=203) versus Dutch however, 6 items showed uniform DIF, and 1 item showed non-uniform DIF, indicating some problems with the cross-cultural validity between these countries. With regard to construct validity, the correlations with PROM (0.74) and performance-based tests (0.36-0.68) were partly as expected (> 0.60).CONCLUSION: The AAQ, an innovative tool to measure activity limitations that can be placed on the continuum between PROMs and performance-based tests showed a good overall cross-cultural validity, and seems to have great potential for international use in research and daily clinical practice in many European countries. This article is protected by copyright. All rights reserved.

Objective: To evaluate the efficacy on physical functioning and safety of tailored exercise therapy in patients with knee osteoarthritis (OA) and comorbidities. Methods: In a randomized controlled trial, 126 participants were included with a clinical diagnosis of knee OA and at least 1 of the following target comorbidities: coronary disease, heart failure, type 2 diabetes mellitus, chronic obstructive pulmonary disease, or obesity (body mass index ≥30 kg/m2), with severity score ≥2 on the Cumulative Illness Rating Scale. The intervention group received a 20-week, individualized, comorbidity-adapted exercise program consisting of aerobic and strength training and training of daily activities. The control group received their current medical care for knee OA and were placed on a waiting list for exercise therapy. Primary outcome measures were the Western Ontario and McMaster Universities Osteoarthritis Index, subscale physical functioning (WOMAC-pf), and the 6-minute walk test (6MWT). Measurements were performed at baseline, after 20 weeks (directly posttreatment), and at 3 months posttreatment. Results: Statistically significant physical functioning differences over time were found between the intervention and control group (WOMAC: B = −7.43 [95% confidence interval (95% CI) −9.99, −4.87], P < 0.001; and 6MWT: B = 34.16 [95% CI 17.68, 50.64], P < 0.001) in favor of the intervention group. At 3 months followup, the mean improvements in the intervention group were 33% on the WOMAC scale and 15% on the 6MWT. These improvements are of clinical relevance. No serious adverse events occurred during the intervention. Conclusion: This is the first study showing that tailored exercise therapy is efficacious in improving physical functioning and safe in patients with knee OA and severe comorbidities.

Objective To systematically summarize the literature on the course of pain in patients with knee osteoarthritis (OA), prognostic factors that predict deterioration of pain, the course of physical functioning, and prognostic factors that predict deterioration of physical functioning in persons with knee OA. Methods A search was conducted in PubMed, CINAHL, Embase, Psych‐INFO, and SPORTDiscus up to January 2014. A meta‐analysis and a qualitative data synthesis were performed. Results Of the 58 studies included, 39 were of high quality. High heterogeneity across studies (I2 >90%) and within study populations (reflected by large SDs of change scores) was found. Therefore, the course of pain and physical functioning was interpreted to be indistinct. We found strong evidence for a number of prognostic factors predicting deterioration in pain (e.g., higher knee pain at baseline, bilateral knee symptoms, and depressive symptoms). We also found strong evidence for a number of prognostic factors predicting deterioration in physical functioning (e.g., worsening in radiographic OA, worsening of knee pain, lower knee extension muscle strength, lower walking speed, and higher comorbidity count). Conclusion Because of high heterogeneity across studies and within study populations, no conclusions can be drawn with regard to the course of pain and physical functioning. These findings support current research efforts to define subgroups or phenotypes within knee OA populations. Strong evidence was found for knee characteristics, clinical factors, and psychosocial factors as prognostics of deterioration of pain and physical functioning.

OBJECTIVES: To systematically summarise the literature on 1) the course of pain in patients with knee OA; 2) prognostic factors that predict deterioration of pain; 3) the course of physical functioning; and 4) prognostic factors that predict deterioration of physical functioning in persons with knee OA. METHODS: A search was conducted in PubMed, CINAHL, Embase, Psych-INFO, and SPORTDiscus up to January 2014. A meta-analysis and a qualitative data synthesis were performed. RESULTS: Of the 58 studies included, 39 were of high quality. High heterogeneity across studies (I(2) > 90%) and within study populations (reflected by large standard deviations of change scores) was found. Therefore, the course of pain and physical functioning was interpreted to be indistinct. We found strong evidence for a number of prognostic factors predicting deterioration in pain (e.g. higher knee pain at baseline, bilateral knee symptoms and depressive symptoms). We also found strong evidence for a number of prognostic factors predicting deterioration in physical functioning (e.g. worsening in radiographic osteoarthritis, worsening of knee pain, lower knee extension strength, lower walking speed and higher comorbidity count). CONCLUSION: Because of high heterogeneity across studies and within study populations, no conclusions can be drawn with regard to the course of pain and physical functioning. These findings support current research efforts to define subgroups or phenotypes within knee osteoarthritis populations. Strong evidence was found for knee characteristics, clinical factors, and psychosocial factors as prognostics of deterioration of pain and physical functioning. This article is protected by copyright. All rights reserved.

OBJECTIVES: To investigate a) the cardiovascular (CV) mortality in a clinical cohort of patients with established rheumatoid arthritis (RA) in comparison with the general population over 15 years, b) the trend in this CV mortality during the study period, and c) for a broad range of predictors, which baseline variables predict CV mortality. METHODS: In 1997, a sample of 1222 patients was randomly selected from the register of a rheumatology outpatient clinic in Amsterdam. Their CV mortality between 1997 and 2012 was obtained from Statistics Netherlands. The standardised mortality ratio (SMR) for CV mortality was calculated. A linear poisson regression analysis was performed to investigate if there was a trend in SMR over time. A Cox regression analysis was performed to determine which baseline variables predicted CV mortality. RESULTS: Mean age of the population at baseline was 60.4 (SD 15.4) years and 72.6% of the patients were women. Estimated SMR (95% confidence interval) for CV mortality was 1.24 (1.05, 1.43). The SMR decreased with 3% annually (p=0.16). Higher age, higher erythrocyte sedimentation rate, having CV comorbidity and diabetes mellitus (DM) were predictors for CV mortality. CONCLUSIONS: CV mortality among patients with RA in the past 15 years was still higher than in the general population. CV mortality decrease was not statistically significant. As CV mortality in RA is still higher than in the general population, continued attention for CV diseases in RA is important. Both tight control of disease activity and good care for comorbid conditions (CV diseases and DM) are advocated.