A sacroiliac joint injection is an injection of local anesthetic and a steroid medication into the sacroiliac joint.Quoted From: https://www.soundpainalliance.com/injections/sacroiliac-joint-injections/
"A sacroiliac joint injections (SI) are injections of local anesthetic and a steroid medication into the sacroiliac joint. Due to the numbing medicine used during this procedure, you may experience temporary pain relief afterwards that may last several hours. Once the numbing medicine wears off, however, your pain will most likely return. The steroid medication may give longer lasting pain relief and usually begins working after 24-48 hours."