Is the Effect of Chronological Age on Postoperative Complications Related to Comorbidity Burden? A Population Study of Revision Total Knee Arthroplasty Patients
Study Design, Data Source, and Sample This retrospective study analyzed data from the Premier Healthcare Database between 2006 and 2022 to identify patients who underwent elective revision TKA procedures. The Premier Health Database is a comprehensive all-payer database that includes data from nearly 1,200 participating hospitals, accounting for approximately 25% of all inpatient discharges. It provides detailed information such as diagnosis codes, procedure codes, and billing information. To identify patients undergoing revision TKA procedures, we used International Classification of Disease ninth Revision or International Classification of Disease 10th Revision procedure codes (Supplemental Table 1, http://links.lww.com/JG9/A393 ). Overall, 187,172 patients received revision TKA surgery from 2006 to 2022. We excluded patients younger than 18 years or missing age (n = 253) and nonelective surgery status (n = 42,517). The final cohort included 144,402 patients who underwent elective revision TKA. Study Variables The primary objective of this study was to examine the effect of chronologic age, CDI, and if the effect of chronologic age on outcomes was influenced by CDI. Age was assessed as both a continuous variable and a categorical variable (<80 years versus 80+ years). The CDI is a validated scoring system used to assess comorbidity-associated survival during preoperative evaluations. It assigns scores to various chronic medical conditions and uses the sum to predict long-term mortality. Postoperative complications assessed in this study included cardiac complications, postoperative pneumonia, AKI, infections, central nervous system (CNS) complications, and intensive care unit (ICU) admissions. Data Analysis We used Spearman rank correlation coefficients and logistic regression models to assess the effect of chronologic age, CDI, and their combination on postoperative complications following revision TKA. We also conducted a similar sensitivity analysis with age converted into categorical variable (<60, 60 to 69, 70 to 79, and 80+ years) while other variables remained the same. Logistic regression models were also employed to assess the primary outcome using chronological age as a categorical variable (<80 years versus 80+ years). As a sensitivity analysis, we estimated the age cutoff associated with an increased risk for each complication using Youden statistic. A P value of <0.05 was considered statistically significant. All statistical analyses were done using SAS version 9.4 (SAS Institute).   This retrospective study analyzed data from the Premier Healthcare Database between 2006 and 2022 to identify patients who underwent elective revision TKA procedures. The Premier Health Database is a comprehensive all-payer database that includes data from nearly 1,200 participating hospitals, accounting for approximately 25% of all inpatient discharges. It provides detailed information such as diagnosis codes, procedure codes, and billing information. To identify patients undergoing revision TKA procedures, we used International Classification of Disease ninth Revision or International Classification of Disease 10th Revision procedure codes (Supplemental Table 1, http://links.lww.com/JG9/A393 ). Overall, 187,172 patients received revision TKA surgery from 2006 to 2022. We excluded patients younger than 18 years or missing age (n = 253) and nonelective surgery status (n = 42,517). The final cohort included 144,402 patients who underwent elective revision TKA.   The primary objective of this study was to examine the effect of chronologic age, CDI, and if the effect of chronologic age on outcomes was influenced by CDI. Age was assessed as both a continuous variable and a categorical variable (<80 years versus 80+ years). The CDI is a validated scoring system used to assess comorbidity-associated survival during preoperative evaluations. It assigns scores to various chronic medical conditions and uses the sum to predict long-term mortality. Postoperative complications assessed in this study included cardiac complications, postoperative pneumonia, AKI, infections, central nervous system (CNS) complications, and intensive care unit (ICU) admissions.   We used Spearman rank correlation coefficients and logistic regression models to assess the effect of chronologic age, CDI, and their combination on postoperative complications following revision TKA. We also conducted a similar sensitivity analysis with age converted into categorical variable (<60, 60 to 69, 70 to 79, and 80+ years) while other variables remained the same. Logistic regression models were also employed to assess the primary outcome using chronological age as a categorical variable (<80 years versus 80+ years). As a sensitivity analysis, we estimated the age cutoff associated with an increased risk for each complication using Youden statistic. A P value of <0.05 was considered statistically significant. All statistical analyses were done using SAS version 9.4 (SAS Institute).   The primary diagnosis for elective revision TKA were summarized in Table . The common diagnosis included mechanical complications (65.62%) and infection (22.76%). We studied five outcomes after revision TKA, including postoperative cardiac complications, pneumonia, AKI, CNS complications, and ICU admissions. The odds ratio (OR) of CDI on postoperative complications following revision TKA ranged from 1.370 to 1.829 (Table ), whereas the OR of postoperative complications for the impact from chronological age ranged from 1.015 to 1.070 (Table ). Increased CDI was associated with higher odds of all complications (Figure ). Chronological age did not show an escalation of odds for complications with the increase in CDI (Figure and Table ). The odds of postoperative complications from chronological age were relatively stable across various CDI categories, such as 1.034 to 1.067 for cardiac complications (Table ). Sensitivity analysis with age converted into categorical variable (<60, 60 to 69, 70 to 79, and 80+ years) showed similar stable ORs for complications across various CDI categories (Supplemental Table 2, http://links.lww.com/JG9/A394 ). The estimated point of age with escalating complication odds on these complications by Youden index indicated 60.1 to 71.7 years of age for these study outcomes (Table ). When age was considered as a categorical variable (<80 years versus 80+ years), the odds of postoperative complications increased markedly in patients older than 80 years (OR 1.698 to 3.695) (Table ).   In this analysis based on the Premier Healthcare Database, we found that the risk of postoperative complications following revision TKA was associated with both CDI and chronological age. Chronological age and CDI did not exhibit a synergistic effect on postoperative complications following revision TKA. The prevalence of TKA procedures, coupled with an increasing life expectancy, has led to a surge in demand for revision surgeries, especially among the elderly. , Revision TKA are more complex than primary procedures and carry a much higher risk of complications. Moreover, revision TKA imposes a notable financial strain on healthcare systems. These factors underscore the critical importance of judicious decision making when considering revision surgery. Previous research has identified age and comorbidity as key risk factors for postoperative complications. Therefore, it is imperative to enhance our understanding of how chronological age, CDI, and their interplay influence postoperative outcomes to devise decision making on surgical intervention and strategies to improve outcomes in patients undergoing revision TKA. In this study, we found that the risk of complications following revision TKA was both closely associated with CDI and chronological age. The assessment of risk factors, including patient's comorbidities, has been described by frailty scores, CDI, hospital frailty risk score, and age-adjusted modified frailty index. Previous studies have indicated that common medical comorbidities associated with revision TKA include hypertension, obesity, uncomplicated diabetes, hypothyroidism, chronic pulmonary disease, and depression. These comorbidities, as risk factors, can potentially be mitigated through patient screening, medical interventions, and risk assessments for optimization. The assessment of patient comorbidities is increasingly vital for clinical decision making and prognostication. Interestingly, when chronological age was analyzed as a categorical variable (<80 years versus 80+ years), it emerged as the most impactful factor for postoperative complications. Our findings align with previous studies, indicating an increased risk of postoperative cardiac complications, postoperative pneumonia, CNS complications, and ICU admission in elderly patients older than 80 years. Zamanzadeh et al reported that individuals aged 73 years or older had a markedly higher risk of postoperative complications. Sinclair et al also noted a notable mortality risk in patients aged 70 years or older undergoing revision procedures. Our findings confirm that age is an independent risk factor for postoperative complications, with an escalating point of complications around 60.1 to 71.7 years of age. We electively adopted 80 years of age as the cutoff for its clinical popularity at our clinical practice. Age serves as a more comprehensive indicator of a patient's overall physiological reserve than individual comorbidities, reflecting the cumulative effect of aging, common risk factors, lifestyle choices, frailty, socioeconomic challenges, and cognitive decline. Given that chronological age is a nonmodifiable risk factor, careful consideration should be given when advising patients aged 80 years and older about revision TKA, with enhanced monitoring and preoperative optimization recommended. A common assumption is that patients with advanced-age and notable comorbidity burdens may not be suitable candidates for elective revision TKA. Our study showed that chronological age and CDI did not exhibit a synergistic effect on outcomes after revision TKA as the trends of impact from chronological age on outcome remained similar across different CDI categories. Sensitivity analysis with age converted into categorical variable showed similar patterns on outcomes without synergistic effect. Previous research indicated that the incidence of 30 days mortality had no difference between the 80 to 89 years old and 65 to 79 years old hypertensive patients following revision TKA. Song et al examined postoperative complications and midterm survival in octogenarians undergoing primary and revision TKA. They noted that the age-adjusted Charlson comorbidity index was significantly higher in the revision group preoperatively. However, they found no differences in TKA-related complication rates or mid-term lifetime survival between the two groups. Similarly, Bovonratwet et al indicated that octogenarians undergoing TKA had higher rates of blood transfusion and slightly longer hospital stays compared with younger patients. Nevertheless, they observed no disparities in mortality or readmission rates between octogenarians and younger populations. Our findings indicate that both CDI and chronological age are independent risk factors for postoperative complications following revision TKA. However, no synergistic effect was observed between CDI and chronological age. Our study has several limitations. First, our analysis is influenced by the quality of the Premier data set, such as sampling bias, especially on these Medicare patients, and geographic bias as the Premier database only included approximately 25% of all healthcare systems in the United States, which may limit the generalizability of our findings to the broader U.S. population. Second, we did not include surgical complications and readmissions, which would result in an underestimation of complication outcomes. Third, we did not include hospital characteristics and surgeon characteristics (specialty, volume, experience, etc) in the model, which could influence these outcomes.   In summary, both chronological age and CDI were independent risk factors for postoperative complications in patients after revision TKA. Chronological age and CDI did not exhibit a synergistic effect on outcomes after revision TKA as the trends of impact from chronological age on outcome remained similar across different CDI categories.      