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Obesity is Associated With Greater Improvement in Patient-Reported Outcomes Following Revision Total Knee Arthroplasty
Background Body mass index (BMI) cutoffs are frequently implemented for total knee arthroplasty (TKA) candidates. However, recent data in primary TKA suggest obese patients have greater improvement in patient-reported outcome measures (PROMs) and no difference in postoperative complications when utilizing standardized medical optimization protocols. This study evaluated the influence of BMI on PROMs following revision TKA using these optimization protocols. The null hypothesis of the study was there would be no difference in PROMs based on BMI following revision TKA.
Methods Between 2010 and 2022, 572 consecutive revision TKAs were retrospectively reviewed. All patients underwent risk assessment and medical clearance prior to surgery by a designated internal medicine specialist. Cases were dichotomized into two BMI groups, ≥35kg/m2 and <35kg/m2 (range, 20 to 65kg/m2). Activity level, pain, function, and satisfaction were compared between groups, controlling for multiple comorbidities and case characteristics. The BMI ≥35kg/m2 group was younger; had a higher prevalence of depression/anxiety and pre-revision narcotics; and worse pre-revision PROMs (P≤0.090). Multivariate statistical analysis was performed with P<0.05 as significant.
Results Patients with a BMI ≥35 demonstrated greater improvement in their Knee injury and Osteoarthritis Outcome Score for Joint Replacement (KOOS-JR) and experienced less pain when walking and climbing stairs (P≤0.071) over an average of 2.0 years. A higher percentage of patients in the BMI ≥35 group also achieved Minimal Clinically Important Differences (MCIDs) for PROMs (46-67% compared to 59-70%). Moreover, the BMI ≥35 group reported higher satisfaction levels (72.2% versus 66.5%, P=0.254), and more patients indicated that their knee 'always' feels normal (28.4% versus 19.8%, P=0.149). The groups did not differ by the indication for revision surgery or the number of components revised (P≥0.108). However, those who needed revision due to aseptic loosening showed significantly greater improvements in PROMs. There was no difference in the rate of re-revisions between the two groups for aseptic loosening or infection.
Conclusion Despite being more debilitated preoperatively, revision TKA patients with a BMI ≥35 experienced greater improvements in PROMs compared to patients with lower BMIs, independent of revision indication. Given the significant improvements in PROMs with appropriate perioperative optimization, obese patients should not be restricted access to revision TKA when appropriately indicated.