Can KOOS-PS be replaced with a simple anchor question in patients after total knee arthroplasty?: an agreement study of 2,478 primary surgeries.

Background and purpose:  Physical function and pain are the most important outcomes following total knee arthroplasty (TKA). These can be evaluated by patient-reported outcome measures (PROMs), or by an anchor question. The primary aim of the study was to evaluate whether a simple anchor question can replace KOOS-PS in assessing postoperative knee function until 1-year follow-up, evaluated by analyzing the agreement between the 2 methods using the diagnostic odds ratio (DOR). Secondary aims were pain (NRS) at rest and during mobilization.

Methods:  This is a diagnostic accuracy study with primary TKAs performed between 2010 and 2022. The surgeries were categorized as improved (I) or worsened (W) based on a dichotomized anchor question related to self-perceived change in physical function, and the dichotomized change in KOOS-PS until 1-year follow-up. This led to 4 groups: (II, IW, WI, and WW).

Results:  Agreement was found with a DOR of 11.3 (CI 7.9-16.2). 2,335 (94%) reported improved function on the anchor question and 143 (6%) worsened function. Among those with improved anchor 2,132 (91%) had improved KOOS-PS, but among those with worsened anchor only 74 (52%) had worsened KOOS-PS. Pain at 1-year follow-up was lower in the groups reporting improved anchor.

Conclusion:  The KOOS-PS can be replaced with an anchor question to assess change in function until 1 year. However, the KOOS-PS might be a valuable supplement in patients reporting worsened anchor as only half of those had worsened KOOS-PS.