Changes in chronic preoperative opioid use. The proportion of patients with chronic preoperative opioid use (per 1,000 total knee arthroplasties) decreased every month, gradually, up to October 2013, with a significant decline after roll out of the Opioid Safety Initiative (interrupted vertical line) ~13% fewer patients versus the number expected based on pre–Opioid Safety Initiative trends (observed n = 5,861 vs. expected n = 6,724). TKA, total knee arthroplasty.