sacroiliitis

Sacroiliitis is inflammation of one or both sacroiliac joints, which connect the lower spine (sacrum) to the pelvic bones (iliac crests). The condition can cause pain in the buttocks, lower back, and sometimes the groin or posterior thigh. It may occur on one side (unilateral) or both sides (bilateral) and can be acute or chronic.

Causes and classification include inflammatory, infectious, and mechanical categories. Inflammatory sacroiliitis is commonly associated with axial spondyloarthritis, including ankylosing spondylitis and related conditions such as psoriatic arthritis or inflammatory bowel disease. Mechanical causes involve overuse, trauma, pregnancy-related stress, or degenerative changes. Septic sacroiliitis, caused by bacterial infection, is less common but requires urgent treatment. Other less frequent etiologies include crystal arthropathies and referred pain from other structures.

Clinical features typically include buttock or lower back pain that worsens with weight bearing or transitional movements, morning stiffness, and limited hip or spine mobility. Pain may be aggravated by prolonged sitting or standing. Because symptoms can resemble other back or hip disorders, a thorough evaluation is necessary.

Diagnosis relies on history, physical examination, and imaging. Physical findings may include positive provocative maneuvers for the sacroiliac joint (such as Flexion, ABduction, External Rotation). X-rays can be normal early on; MRI best identifies active inflammation, while CT helps assess structural damage. Laboratory tests (inflammatory markers like ESR/CRP and HLA-B27 status) support but do not confirm the diagnosis; blood cultures are essential if infection is suspected.

Management aims at the underlying cause. NSAIDs and physical therapy are first-line for inflammatory sacroiliitis. Corticosteroid injections into the SI joint may provide relief. Disease-modifying antirheumatic drugs or biologics are used for inflammatory spondyloarthritis. Septic sacroiliitis requires antibiotics and often hospitalization. Severe or refractory cases may benefit from surgical fusion of the joint. Prognosis varies with the cause and early treatment improves outcomes.