RECOVERY PLATEAUS AND CEILING EFFECTS OF COMMONLY USED PATIENT-REPORTED OUTCOME MEASURES FOLLOWING TOTAL KNEE ARTHROPLASTY

Various patient-reported outcome measures (PROMs) are used to assess recovery following total knee arthroplasty (TKA), but the timing of recovery plateaus and the magnitude of ceiling effects remain unclear. A retrospective observational cohort study was undertaken, involving 229 patients (115 male, 114 female) who underwent TKA from three centres, after screening 287 patients for eligibility. PROMs were assessed pre-operatively, at 6-weeks, 6-months, and annually from 1- to 4-years using the Oxford Knee Score (OKS), Forgotten Joint Score (FJS), Knee Injury and Osteoarthritis Outcome Score (KOOS), EQ-5D and EQVAS. The Objective Knee Society Score (KSS), and range of motion (ROM) were also assessed as physical outcome measures. All knee-specific PROMs plateaued between 1 and 2 years post-operatively, with the derivative score approaching zero. Plateaus were statistically confirmed by 2 years for all knee-specific PROMs, by 6 months for EQ-5D and EQ VAS, and by 1 year for Objective KSS and ROM. The proportion of patients achieving the Patient Acceptable Symptom State (PASS) typically stabilised by 2 years; the Minimal Important Change (MIC) by 1 year; and the ceiling (maximum) score by 2-3 years. Substantial ceiling effects emerged between 6 months and 3 years for all knee-specific PROMs except the OKS, which remained unaffected. Following TKA, knee-specific PROMs plateau by 2 years postoperatively, with no further improvement in the proportion of patients achieving the PASS. However, substantial ceiling effects may contribute to this observed plateau. Additional research is needed to determine whether new PROMs could better capture postoperative recovery following TKA.