Background/Purpose: The elective nature of knee replacement (KR) creates difficult decisions and the potential for both overuse and underuse. We examined the temporal relationship between needing a KR and actually undergoing one to determine the rates and investigate predicotrs of overuse and underuse.

Methods: We pooled longitudinal data from the Osteoarthritis Initiative (OAI) and the Multicenter Osteoarthritis (MOST) Study to estimate KR overuse and underuse.  These cohorts closely followed 8,002 participants with or at risk of knee OA over multiple years and collected demographic, patient-reported, radiographic, and clinical exam information. To determine need for KR, we longitudinally applied the modified and validated Escobar KR appropriateness criteria (AC) to classify participants as either appropriate or inappropriate for KR (Table 1). Examining the temporal relationship between appropriateness status and KR utilization, we classified participants into: 1) appropriate and had KR (appropriate use), 2) appropriate but did not have KR (potential underuse), and 3) inappropriate but had KR (potential overuse). We used multinomial logistic regression to estimate the association between overuse and underuse and age, sex, race, educational status, obesity categories, CESD depression score>16, SF-12 PCS, Charlson comorbidity score, and living alone. We repeated our analyses by dividing potential underusers into those with and without extreme pain (an indicator of necessity and a likely substantial benefit from KR).

Table 1: Elements of the modified Escobar appropriateness criteria for KR*

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Results: 3,449 of 8,002 participants fell into one of the 3 groups, with 843 (24.4%) classified as appropriate users, 2256 (65.4%) as potential underusers, and 350 (10.1%) as potential overusers. Of potential underusers, 988 (43.8%) were deemed likely to receive substantial benefit.  Compared to appropriate use, the odds of underuse were greater in blacks (OR=2.9, 95% CI [2.3, 3.8]). The odds of overuse increased with postgraduate degree, higher SF-12 PCS score, living alone, and decreased with being overweight or obese, having depressive symptoms, and having comorbidities.  Distinguishing necessary from not necessary but appropriate in the underuser group increased racial disparities in KR underuse (blacks OR=4.9, 95% CI[3.8, 6.5]), without significantly affecting findings related to the other predictors.

Conclusion: We found a substantial proportion of patients either overuse or underuse KR. For the underusers, almost 50% would likely receive substantial benefit if they underwent KR and of these, African Americans are at greatest risk for underuse. Overuse appears to be less of a issue but still occurs approximately 10% of the time. Future work needs to focus on ways of  reducing rates of overuse and underuse of KR given the substantial costs and consequences of the procedure.