These nerves can become irritated due to inflammation in the area. Also, if the joint capsule ruptures, the infected material can track through soft tissue anteriorly, posteriorly, or inferiorly. Abscess formation may develop in the gluteal region, the subgluteal region, the retroperitoneum, along the iliopsoas either with or without peritonitis or through the pelvic floor to the thigh, hip joint or the vaginal area. Conditions predisposing to pyogenic sacroilitis include trauma, pregnancy, infections of the skin, osteomyelitis, urinary tract infection, endocarditis, and drug addiction. The hormonal changes of pregnancy induce laxity of the SI joint ligaments and allow increased movement with the joint.
Inflammation occurs which enhances susceptibility to hematogenous seeding of bacteria.
Patients present in a variety of ways. The acute onset is characterized by sudden onset of fever, pain, and decreased range of motion. Subacute presentation may be with or without fever. There is often malaise, pain, limp and some decreased range of motion, but in general symptoms are vague. All patients have SI joint pain, but this may be overlooked because of their reluctance to move.