BACKGROUND:Universal spinal immobilization has been the standard of prehospital trauma care since the 1960s. Selective immobilization has been shown to be safe and effective for emergency medical services use, but it is unclear whether such protocols reduce unnecessary and potentially harmful immobilization practices. This study evaluated the impact of a selective spinal immobilization protocol on practice patterns in a regional trauma system. METHODS:All encounters for traumatic injury in the Tidewater Emergency Medical Services region from 2010 to 2016 were extracted from the Virginia Pre-Hospital Information Bridge. An interrupted time series analysis was used to assess practice change after systemwide protocol implementation in 2013. Intravenous access was used as a nonequivalent outcome measure in the absence of an appropriate control group. RESULTS:A total of 63,981 encounters were analyzed. At baseline, 16.7% of patients underwent full immobilization. The preprotocol slope was slightly positive (0.2% per month; 95% confidence interval, 0.1-0.2%). Slope and level changes after protocol implementation did not differ from those observed for intravenous access (−0.4% vs. −0.4% per month [p = 0.4917] and −1.6% vs. −1.1% [p = 0.1202], respectively). Cervical spinal immobilization became more common over the postimplementation period (0.1% per month; 95% confidence interval, 0.1-0.1%). Rates of immobilization for isolated penetrating trauma remained unchanged. CONCLUSION:Implementation of a selective spinal immobilization protocol did not reduce prehospital immobilization rates in a regional trauma system. Given the entrenched nature of immobilization practices, more intensive education and training strategies are needed. Efforts should prioritize eliminating immobilization for isolated penetrating trauma given its association with increased mortality.