This study will compare two different corticosteroids (dexamethasone and methylprednisolone) for use in sacroiliac joint injections to treat SI joint pain.

Patients who are screened for inclusion will be randomized into one of two groups; dexamethasone or methylprednisolone. Patients will report their pain immediately after the procedure to confirm the diagnosis of sacroiliac joint pain, then be followed for three months to compare the efficacy and safety of the two medications.

Inclusion Criteria:

• Aged >18, capable of understanding and providing consent in English, capable of complying with the outcome instruments used, capable of attending all planned follow up visits
• Unilateral low back/buttocks pain of at least 2 weeks.
• Patient reported 7 day average of numeric pain rating score (NPRS) low back/buttocks pain of at least 5/10 at baseline evaluation
• Clinical diagnosis of sacroiliac joint pain as diagnosed by a board certified Physiatrist including history of low back/buttocks pain and at least 2 positive physical exam findings (including positive fortin finger sign, pain with palpation of posterior superior iliac spine, positive FABER's test, positive Gaenslan's test, positive sacral distraction, positive thigh thrust, positive lateral compression, positive sacral thrust)
• Patient consents to sacroiliac joint corticosteroid injection in a shared decision-making process with the treating physician.
• 80% or more relief of index pain within first 5-15 minutes after injection

Exclusion Criteria:

• Clinical suspicion of alternative process is greater than clinical suspicion of sacroiliac joint pain
• Those receiving remuneration for their pain treatment (e.g., disability, worker's compensation).
• Those involved in active litigation relevant to their pain.
• Those unable to read English and complete the assessment instruments.
• Those unable to attend follow up appointments
• The patient is incarcerated.
• History of prior sacroiliac joint fusion
• Progressive lower extremity neurologic deficit (from active radiculopathy, unhealed radiculopathy, or neuromuscular disease)
• Sacroiliac joint steroid injection within the prior 12 months
• 2 Positive lumbar medial branch blocks within the past 12 months
• Radiofrequency ablation of the lumbar spine within the past 12 months
• Lumbar facet steroid injections within the past 12 months
• Prior epidural steroid injection within the prior 3 months in any location within the spine.
• Possible pregnancy or other reason that precludes the use of fluoroscopy.
• Allergy to steroid, contrast media, or local anesthetics.
• BMI>40.
• Systemic inflammatory arthritis (e.g., rheumatoid arthritis, ankylosing spondylitis, lupus).
• Active infection or treatment of infection with antibiotics within the past 7 days.
• Medical conditions causing significant functional disability (e.g., stroke, decompensated ---COPD, decompensated heart failure)
• Chronic widespread pain or somatoform disorder (e.g. fibromyalgia).
• Addictive behavior, severe clinical depression, or psychotic features.