Association of Bundled Payments for Joint Replacement Surgery and Patient Outcomes With Simultaneous Hospital Participation in Accountable Care Organizations

IMPORTANCE An increasing number of hospitals have participated in Medicare's bundled payment and accountable care organization (ACO) programs. Although participation in bundled payments has been associated with savings for lower-extremity joint replacement (LEJR) surgery, simultaneous participation in ACOs may be associated with different outcomes given the prevalence of LEJR among patients receiving care at ACO participant organizations and potential overlap in care redesign strategies adopted under the 2 payment models. OBJECTIVE To examine whether simultaneous participation in a Medicare Shared Savings Program (MSSP) ACO affects the association between hospitals' participation in LEJR episodes under the Bundled Payments for Care Improvement (BPCI) initiative and patient outcomes compared with participation in the BPCI initiative alone. DESIGN, SETTING, AND PARTICIPANTS This cohort study, conducted from January 1 to May 31, 2019, used 2011 to 2016 Medicare claims data and incorporated an instrumental variable with a difference-in-differences method among 483 008 fee-for-service Medicare beneficiaries undergoing LEJR surgery at 212 bundled payment participant hospitals, 105 coparticipant hospitals, and 1413 nonparticipant hospitals in the United States. EXPOSURES Hospital participation in both the BPCI initiative and the MSSP (coparticipants), BPCI only (bundled payment participants), or neither (nonparticipants). MAIN OUTCOMES AND MEASURES Changes in clinical outcomes and mean LEJR episode spending. RESULTS A total of 483 008 patients (mean [SD] age, 73.0 [8.4] years; 308 173 [63.8%] female) were included in the study. No differential changes were found in patient and hospital characteristics across participation groups. In adjusted analysis, coparticipants had 1.5%(95% CI, 0.7%-2.2%; P<.001) more unplanned readmissions than did bundled payment participants. Compared with bundled payment participants, coparticipants also had differentially greater decreases in hospital length of stay (adjusted difference-in-differences value, -5.3%; 95% CI, -7.1% to -3.5%; P<.001) and home health care use (adjusted difference-in-differences value, -3.4%; 95% CI, -4.5% to -2.3%; P<.001) and greater increases in postdischarge outpatient follow-up (adjusted difference-indifferences value, 2.1%; 95% CI, 0.9%-3.3%; P<.001). Coparticipants and bundled payment participants did not have differential changes in episode spending (adjusted difference-indifferences value, 0.4%; 95% CI, -0.7% to 1.6%; P=.46), although both groups had more decreased spending compared with nonparticipants. CONCLUSIONS AND RELEVANCE Among bundled payment participants, coparticipation in ACOs was not associated with LEJR episode savings but was associated with differential changes in postacute care use patterns and unplanned readmissions. These findings support the longer-term benefits of LEJR bundles and suggest that coparticipants may adopt care redesign strategies that differ from hospitals with bundled payments only.