A sacroiliac joint injection can be used to diagnose or treat lower back pain that comes from your sacroiliac joint. This joint is the place where your spine (sacrum) connects to your pelvis (ilium). For the procedure, an x-ray machine is used for needle placement to ensure accuracy and safety. This injection can be performed with use of a steroid to decrease pain and inflammation, or PRP (platelet rich plasma) for regenerative treatment.