Epidemiological Trends and Age-Related Outcomes in Reverse Total Shoulder Arthroplasty: A U.S. Nationwide Inpatient Analysis of 9692 Patients

<b>Background/Objectives</b>: Reverse total shoulder arthroplasty (RTSA) is increasingly common, but large-scale studies on age-related differences in outcomes are limited. This study aims to evaluate epidemiological trends, clinical indications, and postoperative outcomes in patients under 65 undergoing RTSA. <b>Methods</b>: We analyzed data from the Nationwide Inpatient Sample (NIS) from 2016-2021, including 48,460 patients aged 35-64 undergoing shoulder arthroplasty. Patients were stratified into three age groups: 35-45, 46-55, and 56-65 years. We assessed trends, clinical indications, comorbidities, hospital stay metrics, and postoperative complications using chi-square tests, ANOVA, and multivariate logistic regression. <b>Results</b>: Procedure volumes increased from 2016 to 2019, peaking at 2007 cases, but declined in 2020 and 2021 (924 cases). The 56-65 age group consistently comprised the majority of procedures (81.7% in 2016 to 88.3% in 2021). Comorbidities like type 2 diabetes (5.9% to 22.8%), hypertension (27.9% to 55.3%), and dyslipidemia (10.3% to 40.5%) increased with age (<i>p</i> < 0.001). Rotator cuff tears were more prevalent in older patients (25% to 48.5%, <i>p</i> < 0.001), while instability was higher in the youngest group (8.8%, <i>p</i> < 0.001). Osteoarthritis was the most common indication, increasing with age (56.6% to 62.5%, <i>p</i> < 0.001). Cardiac complications increased with age (2.2% to 5.1%, <i>p</i> = 0.04). Female gender (OR = 1.548, <i>p</i> < 0.001), private insurance (OR = 1.570, <i>p</i> < 0.001), and small hospital size were associated with higher odds of cardiac complications. Native American race showed lower odds (OR = 0.308, <i>p</i> = 0.009) compared to White patients. <b>Conclusions</b>: Significant age-related differences exist in comorbidities, clinical indications, and postoperative complications following RTSA. Older patients had higher rates of comorbidities and cardiac complications, while younger patients presented with instability. These findings highlight the importance of age-specific perioperative management to optimize outcomes.