• Heavy lifting, especially incorrect training or when muscles aren’t prepared for the activity
• A traumatic injury or sudden impact, such as a motor vehicle accident or a fall, affecting your spine, lower back, pelvis or buttocks
• Spondyloarthropathies, which include ankylosing spondylitis, arthritis associated with psoriasis and others
• Degenerative arthritis, also called osteoarthritis of the spine, causing degeneration of the sacroiliac joints, which can cause mild inflammation and pain
• Pregnancy, because the pelvis must stretch to accommodate childbirth
• Infection of the sacroiliac joint, sometimes caused by bacteria in food (brucellosis)

Another method of classifying its causes is-

• Bilateral & symmetrical

• Ankylosing spondylitis
• Reiter’s syndrome
• Enteropathic

• Bilateral & assymetrical

• Psoriatic arthritis
• Rheumatoid arthritis
• Juvenile rheumatoid arthritis

• Unilateral

• Gout
• Infection
• Osteoarthritis