The sacroiliac (SI) joint has several unique anatomical features that make it one of the more challenging joints to image. The joint is difficult to profile well on radiographic views, and therefore the radiographic findings of
sacroiliitis are often equivocal. Computed tomography images can usually show the findings of
sacroiliitis and
osteoarthritis earlier than radiographs. Magnetic resonance imaging performed with proper sequences is excellent for diagnosing even very early
sacroiliitis and for following treatment response. The SI joint is often involved in patients with
osteoarthritis or one of the inflammatory spondyloarthritides, most notably
ankylosing spondylitis.
Ankylosing spondylitis often presents with
sacroiliitis, which appears as erosions,
sclerosis, and joint space narrowing, eventually leading to
ankylosis. Several disorders can cause
sacroiliitis-like changes of the joint, including
hyperparathyroidism and repetitive shear-stress
injuries in athletes. The joint can become painful during pregnancy as it widens and develops increased motion, and some postpartum women develop iliac
sclerosis adjacent to the joint termed
osteitis condensans ilii. Another cause of SI
joint pain is a disorder called sacroiliac joint dysfunction, which typically has few abnormal imaging findings. Patients with SI joint dysfunction, as well as
sacroiliitis, often get relief from image-guided SI joint therapeutic
injections.