Inpatient resource use and principal-diagnosis categories in revision total knee arthroplasty: A 2020–2022 national inpatient sample analysis

Abstract Background Administrative definitions can affect the estimated inpatient burden and indication distribution of revision total knee arthroplasty (TKA). We examined resource use and coded morbidity in primary and revision TKA admissions from 2020 to 2022, with sensitivity analyses of surgical and diagnosis classifications. Methods A previously assembled National Inpatient Sample extract was reanalyzed using laterality-specific procedure definitions. Revision admissions included direct revision or ipsilateral prosthesis/spacer removal with replacement. Explicit partial-arthroplasty and ambiguous mixed-procedure patterns were excluded. Diagnosis definitions were narrowed, and principal-diagnosis categories were compared with all-diagnosis classifications. Discharge weights were used for descriptive estimates; charges were converted to 2022 U.S. dollars. Results The audited extract included 152,085 admissions (130,235 primary and 21,850 revision), representing 760,424 weighted admissions. Revision accounted for 14.4%. Mean length of stay was 3.30 versus 2.09 days (difference, 1.21 days), and mean charges were $151,287 versus $80,623 (difference, $70,664). Acute kidney injury was coded in 6.80% versus 2.62%. Mechanical loosening was the largest principal-diagnosis category (29.4%). Knee periprosthetic fracture comprised 1.24% using the principal diagnosis and 6.57% using any diagnosis. Restriction to elective admissions attenuated several morbidity differences. Conclusions Among the analyzed inpatient admissions, revision TKA was accompanied by longer hospital stays and greater charges than primary TKA. Indication distributions and coded morbidity varied with diagnosis definitions and admission selection. These findings describe inpatient resource use and coding patterns rather than independent effects of revision surgery or longitudinal revision risk.