Categorization of changes in the Oxford Knee Score after total knee replacement: an interpretive tool developed from...

The objective of the study was to create an interpretive categorical classification for the transition in the Oxford Knee Score (OKS) change score (ΔOKS) using the anchor-based method.

Registry data from 46,094 total knee replacements from the year 2014/15, were accessed via the Health and Social Care Information Center official website. Data included preoperative and 6-month follow-up OKS and response to the transition anchor question. Categories were determined using Gaussian approximation probability and k-fold cross-validation.

Four categories were identified with the corresponding ΔOKS intervals: "1. much better" (≥16), "2. a little better" (7-15), "3. about the same" (1-6), and "4. much worse" (≤0) based on the anchor questions' original five categories. The mean 10-fold cross-validation error was 0.35 OKS points (95% confidence interval 0.12 to 0.63). Sensitivity ranged from 0.34 to 0.68; specificity ranged from 0.74 to 0.95.

We have categorized the change score into a clinically meaningful classification. We argue it should be an addition to the continuous OKS outcome to contextualize the results in a way more applicable to the shared decision-making process and for interpreting research results.