Cite This Article

What is the diagnosis?

Sacroiliitis (unilateral or bilateral) is an inflammatory condition of the SI joints that can lead to sclerosis, fibrosis, and ossification/fusion of the SI joints. It typically presents as subacute to chronic lower back or posterior pelvic pain depending on correlated pathologies.

The differential diagnosis includes lumbar spondylopathy,  lumbar spasm, radiculopathy, piriformis syndrome, gluteus medius tendinitis, hyperparathyroidism, and malignancy [1].

What is the mechanism of injury?

Sacroiliitis can be caused by mechanical stress, OA, or trauma. However, it can also present secondary to inflammatory bowel disease, ankylosing spondylitis, rheumatoid arthritis, psoriatic arthritis, gout, reactive arthritis, Behçet disease, infective processes, malignancy, or pregnancy.

• Pearl: Laterality and symmetry of sacroiliitis can help differentiate etiology as below. 
• Bilateral and Symmetric: IBD, ankylosing spondylitis, RA
• Bilateral and Asymmetric: gout, reactive arthritis, PsA, OA, Behçet
• Unilateral: Infective, neoplastic

What physical exam findings are expected?

Several exam maneuvers can assist in isolating pain to the SI joint as opposed to the lower back, external rotators, or femoroacetabular joint.

Which imaging modalities can be used?

Frontal and lateral radiographs with oblique views are helpful, but not sensitive in the acute setting. MRI w/contrast remains the gold standard for diagnosis, and can identify subchondral edema, which is the earliest sign of sacroiliitis.

MRI does not need to routinely be utilized for diagnosis but can help rule out abscess formation, lumbar disk herniation, and differentiate between inflammatory and structural etiologies.

What is the management in the ED?

Investigation to rule out correlated or syndromic pathology largely determines plan of care. Labs including urine pregnancy, WBC, ESR/CRP, and blood cultures can help determine the etiology and guide further diagnostics. Infectious etiologies can require surgical debridement or abscess drainage. If chronic inflammatory etiology is suspected, rheumatoid factor and HLA-B27 testing can be performed in the outpatient setting.

• Pearl: Inflammatory and traumatic etiologies are most common, and typically do not warrant radiographs for confirmation. 

When should you consult orthopedics?

In the setting of aggressive or recurrent infection or a large (3-5cm) abscess, surgical consultation should be considered. In the setting of recurrent or severe symptomatology that is refractory to conservative medical management, SI joint injections, physical therapy, and TNF inhibitors should be considered. Surgical consultation for SI joint fusion has mixed evidence to support a modest reduction in pain.