Regional anesthesia provides significant perioperative benefits, including improved pain control and reduced opioid consumption. Clinical trial evidence underpins anesthetic practice, yet inadequate demographic representation and reporting may limit the ability to likely evaluate findings and perpetuate inequities. This systematic review assessed the reporting of race, ethnicity, and sex in randomized controlled trials (RCTs) of regional anesthesia for total joint arthroplasty (TJA). The Aggregate Analysis of Clinical Trials (AACT) database was searched for US-based interventional RCTs of regional anesthesia for TJA published from 2015 to 2025. Trials were required to be registered and published in English. Exclusion criteria included conference abstracts, duplicate publications, and non-peer-reviewed reports. Data on trial characteristics, sample size, interventions, and participant demographics were compared from published articles and ClinicalTrials.gov. The primary outcome was reporting of participant sex, race, and ethnicity in publications and registry entries. Secondary outcomes included demographic distributions across racial and ethnic groups and associations between reporting and study characteristics (funding source, year of publication, center type, US region, sample size) using Fisher's exact test. Twenty-nine RCTs were included in the final analysis, representing 2914 participants. Of 29 journal articles, 28 studies (96.6%) reported sex, 14 (48.3%) reported race, and five (17.2%) reported ethnicity in the published journal articles. Among studies reporting race, 1068 (78.5%) participants identified as White, 253 (18.6%) as Black, 30 (2.2%) as other, 6 (0.4%) as Asian or Pacific Islander, and one (0.07%) as Native Hawaiian/Pacific Islander. Conversely, the data from ClinicalTrials.gov reveals that of the same 29 studies, 22 (75.9%) reported sex, 12 (41.4%) reported race, and seven (24.1%) reported ethnicity. Trial characteristics did not show statistically significant associations when comparing studies that did versus did not report race, ethnicity, or sex. In this review of demographic reporting of US-based regional anesthesia RCTs for TJA, sex was consistently reported, whereas race and ethnicity were infrequently captured. The lack of difference in reporting practices across various trial characteristics points toward a broader issue within the field of regional anesthesia for TJA. Notable inconsistencies in demographic reporting on ClinicalTrials.gov were also observed. The absence of standardized demographic reporting underscores the need for journals to mandate consistent reporting practices in clinical research. Efforts to recruit more diverse study populations are essential to enhance the applicability of trial results and to address ongoing inequities in access to care and patient outcomes following TJA.