Introduction: The American Academy of Orthopaedic Surgeons American Joint Replacement Registry (AJRR) is the largest registry of total hip and knee arthroplasty (THA and TKA) procedures performed in the United States. The purpose of this study was to examine whether AJRR data are representative of the national experience with hip and knee arthroplasty as represented in the National (Nationwide) Inpatient Sample (NIS).
Methods: All patients undergoing a THA or TKA procedure between 2012 to 2018 (AJRR) and 2012 to 2016 (NIS) were identified. Cohen d effect sizes were computed to ascertain the magnitude of differences in demographics, hospital volume (in 50 patient increments), and geographic characteristics between the AJRR and NIS databases.
Results: The study included (NIS: 2,316,345 versus AJRR: 557,684) primary THA and (NIS: 3,417,700 versus AJRR: 809,494) TKA procedures. The magnitude of distribution, as determined by the Cohen d effect size, showed that the proportions of AJRR and NIS patients were similar based on overall sex (THAs [d = 0.03] and TKAs [d = 0.02]) and age (THAs [d = 0.17] and TKAs [d = 0.12]). Similarly, only small differences (d = 0.34 or less) were identified between databases considering hospital volume and geography. The AJRR was underrepresented in Southern regions and hospitals with low procedure volume and overrepresented in Northern hospitals and those with larger volume. Both the NIS and the AJRR followed a similar overall trend, with most procedures performed at hospitals with <50 cases per year.
Discussion: Distributions across hospital volume, age, and geography were proportionally similar between the AJRR and NIS databases, supporting the generalizability of AJRR findings to the larger US cohort.
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