Recovery plateaus and ceiling effects of commonly used patient-reported outcome measures following primary total knee arthroplasty

Background
Various patient-reported outcome measures (PROMs) are used following total knee arthroplasty (TKA), but the timing of recovery plateaus and the presence of ceiling effects remain unclear. This study aimed to describe these characteristics of commonly used PROMs following TKA.

Methods
This retrospective analysis of prospective data included 229 patients (mean age, 64 years; range, 43 to 75) who underwent primary TKA. Outcomes were collected preoperatively, at six weeks, six months, and annually up to four years using the Oxford Knee Score (OKS), Forgotten Joint Score (FJS), Knee Injury and Osteoarthritis Outcome Score subscales, EuroQol 5-Dimension (EQ-5D), EuroQol Visual Analogue Scale (EQ-VAS), Objective Knee Society Score, and range of motion. Recovery trajectories were modeled using linear mixed-effects models, and plateaus were identified through pairwise comparisons. Ceiling effects and proportions of patients achieving the minimal important change (MIC), patient acceptable symptom state (PASS), and maximum scores were tracked over time. 

Results 
Knee-specific PROMs plateaued by two years, while health-related quality of life measures plateaued earlier (EQ-5D at one year, EQ-VAS at six months), as did physical outcome measures (one year). For knee-specific PROMs, the proportions achieving the MIC and PASS stabilized by one and two years, respectively, while maximum score achievement increased up to three years for all except the OKS. Ceiling effects emerged for all knee-specific PROMs except the OKS, developing between six months and three years. The FJS exhibited a ceiling effect by three years. 

Conclusion 
Current knee-specific PROMs plateau by two years following TKA. However, ceiling effects and increases in maximum score achievement up to three years suggest that further improvements are masked by instrument limitations. Routine collection of current PROMs beyond two years provides limited value, but extended follow-up remains important for research. Future PROM development should prioritize improved postoperative score distributions and assessment of high-level function.