IntroductionThe progression of medical knowledge competency during surgical residency training is poorly understood. This study measures the acquisition of medical knowledge as orthopedic surgery residents advance during training and the impact of accreditation status on orthopedic in-training examination (OITE) performance.MethodsOrthopedic surgery residents taking the OITE during 2020 and 2021 were included. Residents were grouped into cohorts by post-graduate year (PGY) and Accreditation Council for Graduate Medical Education (ACGME) accreditation status. Comparisons were made with parametric tests.ResultsEight thousand eight hundred and seventy-one ACGME-accredited residents (89%) and 1,057 non-ACGME-accredited residents (11%) were evenly distributed by the PGY level (range, 19-21%). Residents in both ACGME- and non-ACGME-accredited residency programs had a significant increase in OITE performance at each PGY level (P<0.001). At ACGME-accredited programs, OITE performance increased from PGY1 (51%), PGY2 (59%), PGY3 (65%), PGY4 (68%), and PGY5 (70%) (P<0.001). There were progressively smaller percentage increases in OITE performance during accredited residency training (range, 2-8%), but this increase was linear in non-accredited residency training (range, 4%). At each PGY level, residents at accredited programs outperformed their counterparts at non-accredited programs (P<0.001).ConclusionOITE performance increases during residency training. Among ACGME-accredited residents, performance on the OITE progresses rapidly during junior years and plateaus during senior years. Residents in ACGME-accredited residency programs outperform their counterparts in non-accredited residency programs. More research is needed to understand optimal training environments that promote medical knowledge acquisition during orthopedic surgery residency.