STUDY DESIGN: Retrospective cohort.
OBJECTIVE: To evaluate for the presence and magnitude of the "July effect" 
within elective spine surgery.
SUMMARY OF BACKGROUND DATA: The July effect is the hypothetical increase in 
morbidity and mortality thought to be associated with the influx of new (or 
newly promoted) trainees during the first portion of the academic year. Studies 
evaluating for the presence and magnitude of the July effect have demonstrated 
conflicting results.
METHODS: We accessed the American College of Surgeons National Surgical Quality 
Improvement Program database from 2005-2010. Statistical analyses were conducted 
using bivariate and multivariate logistic regression.
RESULTS: A total of 14,986 cases met inclusion criteria and constitute the study 
population. Of these, 26.5% occurred in the first academic quarter and 25.3% had 
resident involvement. The rate of serious adverse events was 1.9 times higher 
and the rate of any adverse events was 1.6 times higher among cases with 
resident involvement than among those without (P < 0.001 for both). Among cases 
without resident involvement, the rates of serious adverse events and any 
adverse events did not differ by academic quarter. Similarly, among cases with 
resident involvement, the rates of serious adverse events and any adverse events 
did not differ by academic quarter.
CONCLUSION: We could not demonstrate that the training of new (or newly 
promoted) residents is associated with an increase in the adverse events of 
spine surgery. Safeguards that have been put in place to ensure patient safety 
during this training period seem to be effective. Although adverse events were 
more common among cases with resident involvement than among cases without 
resident involvement, our data suggest that this association is more likely a 
product of the riskier population of cases in which residents participate than 
of the resident involvement itself.