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Differences Between Inpatient and Outpatient Medicare Total Knee Arthroplasty: Substantial Clinical Benefit
Shlok V Patel1, Ignacio Pasqualini1, Shujaa T Khan1
1Department of Orthopaedic Surgery, Cleveland Clinic, Cleveland, Ohio.
Background:
The Centers for Medicare and Medicaid Services patient-reported outcome-based performance measure mandates collection of patient-reported outcome measures after total knee arthroplasty (TKA) and defines success as achieving substantial clinical benefit (SCB) on the Knee injury and Osteoarthritis Outcome Score for Joint Replacement (KOOS-JR) of ≥ 20 points. As TKA increasingly shifts to outpatient care and patient complexity varies by care setting, a single universal threshold may misclassify improvement. This study estimated specific KOOS-JR SCB thresholds in separate Medicare inpatient and outpatient cohorts and compared the performance of these thresholds between settings.
Methods:
A retrospective analysis of prospectively collected data on 7,926 Medicare beneficiaries ≥ 65 years who underwent primary elective TKA from 2016 to 2022 was performed. Patients were stratified by care setting into inpatient (n = 2,812) and outpatient (n = 5,114) cohorts. The SCB thresholds on KOOS-JR were derived using an anchor-based approach with the Veterans RAND 12-Item, "Compared to 1 year ago, how would you rate your physical health now?" as the anchor. Receiver operating characteristic analysis with Youden's index identified setting-specific cut points.
Results:
The KOOS-JR SCB threshold for the inpatient Medicare cohort was 29.3 points (Youden's index 0.303 and area under the curve 0.705). Using this threshold, 64.3% of inpatients achieved SCB. For outpatients, the SCB threshold was 21.5 points (Youden's index 0.317 and area under the curve 0.706). With this threshold, 65.6% of outpatients attained SCB.
Conclusions:
Calculating separate inpatient and outpatient KOOS-JR SCB thresholds for Medicare TKA patients yielded notably different cut points, with the inpatient threshold being nearly eight points higher than the outpatient. This gap possibly reflects underlying differences in baseline status and comorbidity burden between care settings. Threshold interpretation adjusted for such patient factors rather than a single universal cut point may support more equitable and fair performance evaluation.