Association Between Multimorbidity and Walking Independence After Total Knee Arthroplasty in Adults Aged ≥80 Years: A Retrospective Cohort Study

Background The demand for total knee arthroplasty, an established treatment for advanced knee osteoarthritis, is anticipated to increase among individuals aged ≥80 years. Given the high prevalence of multimorbidity among older adults in Japan, in this study, we aimed to elucidate the relationship between multimorbidity and post-operative walking independence in this demographic. Methods This retrospective cohort study included patients who underwent total knee arthroplasty for knee osteoarthritis between October 2023 and September 2024; those who underwent other surgeries or had significant mobility limitations were excluded. Patients aged ≥80 years with a Charlson Comorbidity Index of ≥2 were categorized into the “older patients with multimorbidity” group. The primary outcome was walking independence, which was assessed using the Functional Ambulation Category. Demographic and clinical variables were evaluated as potential confounders. Statistical tests included Student’s t -test, Mann–Whitney U test, chi-square test, and hierarchical multiple regression analysis; a p -value of <0.05 was considered significant. Results Thirteen and 42 patients were classified as “older patients with multimorbidity” and controls, respectively. Significant intergroup differences were observed in age, height, weight, and hemoglobin levels but not in the length of hospital stay and overall outcomes. Functional Ambulation Category scores declined postoperatively in both groups, with no significant intergroup difference in independent walking ability. Hierarchical multiple regression analysis of pooled data revealed no significant association between age or multimorbidity and walking independence at discharge. Conclusion The findings indicate that age and multimorbidity are not primary determinants of post-operative walking independence. Individualized rehabilitation may improve recovery outcomes, underscoring the potential benefits of standardizing postoperative care for older patients with multimorbidity who have undergone total knee arthroplasty.