Abstract. Background. The Forgotten Joint Score (FJS) is a 12-item patient reported outcome measurement instrument. It was developed with classical test theory, without testing assumptions such as unidimensionality (all items reflect one underlying factor), appropriate weighting of each item, no differential item function (DIF, different groups answer the same way), and monotonicity (people with higher function have higher score). We applied item response theory (IRT) to improve the validity of FJS to contemporary standards to optimise it for ongoing use. Research Questions. Does the FJS reflect one latent trait? Can an IRT model be fitted to the FJS to provide interval-scaled measurement?. Methodology. Participants undergoing primary total knee replacement provided pre-operative and post-operative (6-months) responses for FJS. An exploratory factor analysis (EFA), confirmatory factor analysis (CFA) and Mokken analysis were conducted. The data were fitted to a graded response model (GRM). Results. 1288 response patterns were analysed. EFA showed a one factor model (all 12 items load to one underlying trait). CFA demonstrated excellent model fit (X2 <0.001, Tucker Lewis Index=0.96, Comparative Fit Index=0.96). Items did not have equal weighting. The FJS demonstrated good monotonicity with no differential item functioning by sex, age, or body mass index. Conclusions. The FJS meets key validity assumptions supporting its use in clinical practice and research. The IRT-adapted FJS provides continuous measurements with greater granularity including individual measurement error. This adapted score has advantages over traditional FJS scoring, being interval scaled (using GRM) and can be retrospectively applied to existing response sets

Aims

To map the Oxford Knee Score (OKS) and High Activity Arthroplasty Score (HAAS) items to a common scale, and to investigate the psychometric properties of this new scale for the measurement of knee health.

The routine use of patient reported outcome measures (PROMs) in evaluating the outcome after arthroplasty by healthcare organisations reflects a growing recognition of the importance of patients’ perspectives in improving treatment. Although widely embraced in the NHS, there are concerns that PROMs are being used beyond their means due to a poor understanding of their limitations.

This paper reviews some of the current challenges in using PROMs to evaluate total knee arthroplasty. It highlights alternative methods that have been used to improve the assessment of outcome.

Cite this article: Bone Joint J 2015;97-B:3–9.