The "July effect" in primary total hip and knee arthroplasty: analysis of 21,434 cases from the ACS-NSQIP database.

The "July effect" is the hypothetical increase in morbidity thought to be associated with the training of new residents during the first portion of the academic year. We evaluated for the presence of the July effect in the American College of Surgeons National Surgical Quality Improvement Program (ACS-NSQIP) database among 21,434 patients who underwent primary total hip or knee arthroplasty. There was no association of an interaction term for academic quarter and resident involvement with "serious adverse events" (P = 0.656) or "any adverse events" (P = 0.578). As a result, this study could not demonstrate a July effect. Patients can be reassured that undergoing total joint arthroplasty during the first part of the academic year is without increased risk of adverse events related to the training of residents.