The validity and reliability of the modified forgotten joint score.

We aim to validate the "Modified Forgotten Joint Score" (MFJS) as a new patient-reported outcome measure (PROM) in hip and knee arthroplasty, against the UK's gold standard Oxford Hip and Knee Scores (OHS/OKS). The original Forgotten Joint Score (FJS) (12 items) was created to assess post-arthroplasty joint awareness. We modified the FJS to 10-items to improve its reliability. Postal questionnaires were sent out to 400 total hip or knee replacement (THR/TKR) patients who were 1-2 years' post-op, along with the OHS/OKS. Data, collected from the 212 returned questionnaires (53% response rate), was analysed in relation to construct and content validity. A sub-cohort of 77 patients took part in a test-retest repeatability study, to assess reliability of the MFJS. The MFJS proved to have an increased discriminatory power in high-performing patients in comparison to the OHS and OKS. 30.8% of TKR patients (n = 131) scored highly (87.5% or more) in the OKS compared to just 7.69% in the MFJS TKR patients. The MFJS proved to have increased test-retest repeatability, based upon its intra-class correlation coefficient of 0.968 compared to the Oxford's 0.845, p < 0.001. The MFJS is a more relevant tool, compared to the FJS, with greater discrimination in the assessment of well performing hip and knee arthroplasties in comparison to the OHS/OKS.