Sacroiliitis is an osteoarticular inflammatory disease of the sacroiliac joint or joints. May be caused by degenerative disorder, infection, or related to prior injury. Bacterial infection is a more common cause in late childhood, as in pyogenic sacroiliitis, with Staphylococcus aureus a common pathogen. Other infectious causes include Salmonella or clostridial sepsis, tuberculous, Streptococcus B, and pneumococcus. Sacroiliitis may be associated with ankylosing spondylitis, arthritis, ulcerative colitis, or related diseases. Characterized by pain and inflammation in one or both sacroiliac joints, with or without fever. Buttocks pain, pelvic instability, and decrease in weight-bearing ability are common.