The structural validity of the Danish version of the Oxford Knee Score is not substantiated using Rasch analysis and confirmatory factor analysis

Aims The Oxford Knee Score (OKS) is a 12-item patient-reported outcome measure (PROM), developed for patients who are candidates for total knee arthroplasty (TKA). A prerequisite for a PROM to be considered an adequate measurement instrument is a unidimensional structure as demonstrated by a modern test theory (MTT) model, meaning that each (sub)scale reflects one construct (e.g. pain). However, the structural validity of OKS has only been sparsely evaluated with MTT, and with ambiguous results. This study aimed to assess the structural validity of the Danish OKS. Since the OKS includes items addressing both pain and physical function, it was hypothesized that scores were more accurately reported as two separate subscales. Methods OKS responses from a study of 1,059 patients treated with a TKA were obtained. Four random subsamples (each with 400 patients) – female and male, preoperative and three months postoperative – were assessed by confirmatory factor analysis (CFA) and Rasch analysis. CFA model fit was evaluated using the chi-squared statistic and indices of close fit. Rasch fit was evaluated with item fit statistics. Both a one-factor solution and two-factor solutions with scores based on two separate subscales were considered for each subsample. Results OKS data did not fit the original unidimensional model of one total score. Reporting OKS data as the two subscales “pain" and “function” improved CFA fit, but model fit was still inadequate. Results were consistent across subsamples. Conclusion The structural validity of the Danish OKS is inadequate for evaluating patients awaiting TKA or surgically treated with TKA. OKS data should therefore be interpreted with caution. Randomized treatment studies showing no difference in OKS scores may be reanalyzed based on the two domains to reduce the risk of a potential type-2 error. Cite this article: Bone Joint Res 2025;14(11):998–1005.

• Publication year

  2025

• Venue

  Bone & Joint Research

• Publication date

  2025-11-01

• Fields of study

  Not labeled

• Identifiers
  DOI 10.1302/2046-3758.1411.BJR-2025-0060.R1PMCID 12603811
• External record

  Open on Semantic Scholar

• Source metadata

  Semantic Scholar

• No claims are published for this paper.

• No concepts are published for this paper.

• Item response theory validation of the Oxford Knee Score and Activity and Participation Questionnaire: a step towards a common metric.

  2024influential reference
• Item response theory assumptions were adequately met by the Oxford Hip and Knee Scores.

  2023influential reference
• The Minimal Clinically Important Difference Changes Greatly Based on the Different Calculation Methods

  2023cited by this paper
• Hospital variation in revision rates after primary knee arthroplasty was not explained by patient selection: baseline data from 1452 patients in the Danish prospective multicenter cohort study, SPARK

  2023cited by this paper
• Patients in high- and low-revision hospitals have similar outcomes after primary knee arthroplasty: 1-year postoperative results from the Danish prospective multicenter cohort study, SPARK

  2023cited by this paper
• Reliability, Validity, and Efficiency of an Item Response Theory-Based Balance Confidence Patient-Reported Outcome Measure.

  2023cited by this paper
• Patient-reported outcome measures: it is time for authors, reviewers, journal editors and health care strategists to take sufficient responsibility

  2022cited by this paper
• A catalogue of PROMs in sports science: Quality assessment of PROM development and validation

  2021cited by this paper
• Psychometric validation of PROM instruments

  2020influential reference
• Are adequate PROMs used as outcomes in randomized controlled trials? an analysis of 54 trials

  2020cited by this paper
• COSMIN guideline for systematic reviews of patient-reported outcome measures

  2018cited by this paper
• COSMIN methodology for evaluating the content validity of patient-reported outcome measures: a Delphi study

  2018influential reference
• Current Trends in Patient-Reported Outcome Measures in Total Joint Arthroplasty: A Study of 4 Major Orthopaedic Journals.

  2018cited by this paper
• KNEES-ACL has superior responsiveness compared to the most commonly used patient-reported outcome measures for anterior cruciate ligament injury

  2018cited by this paper
• Validation of the Spanish version of the Oxford knee score and assessment of its utility to characterize quality of life of patients suffering from knee osteoarthritis: a multicentric study

  2017influential reference
• COSMIN Risk of Bias checklist for systematic reviews of Patient-Reported Outcome Measures

  2017cited by this paper
• Health Measurement Scales: A Practical Guide to Their Development and Use

  2015cited by this paper
• Extended Rasch Modeling

  2015cited by this paper
• Item Fit Statistics

  2013cited by this paper
• Can pain and function be distinguished in the Oxford Knee Score in a meaningful way? An exploratory and confirmatory factor analysis

  2013influential reference
• Rasch Models in Health

  2013cited by this paper
• Extending the use of PROMs in the NHS—using the Oxford Knee Score in patients undergoing non-operative management for knee osteoarthritis: a validation study

  2013cited by this paper
• lavaan: An R Package for Structural Equation Modeling

  2012cited by this paper
• Rasch analysis of the Oxford Knee Score.

  2009cited by this paper
• The 12-item Oxford Knee Score: cross-cultural adaptation into German and assessment of its psychometric properties in patients with osteoarthritis of the knee.

  2009cited by this paper
• The use of the Oxford hip and knee scores.

  2007cited by this paper
• Translation and validation of the Dutch version of the Oxford 12-item knee questionnaire for knee arthroplasty

  2005cited by this paper
• Translation and validation of the Oxford-12 Item Knee Score for use in Sweden

  2000cited by this paper
• Cutoff criteria for fit indexes in covariance structure analysis : Conventional criteria versus new alternatives

  1999cited by this paper
• Questionnaire on the perceptions of patients about total hip replacement.

  1996cited by this paper
• Observations are always ordinal; measurements, however, must be interval.

  1989influential reference
• THE WORLD HEALTH ORGANIZATION

  1954influential reference

• No citing papers are available for this paper.