Laboratory Studies
In a patient with sacroiliitis, inflammatory origins (eg, ankylosing spondylitis [AS], psoriatic arthritis) must be considered. The following laboratory studies are appropriate when an inflammatory disorder is suspected in a young patient:
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Complete blood cell (CBC) count
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Erythrocyte sedimentation rate (ESR)
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C-reactive protein (CRP) level
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Antinuclear antibody (ANA) profile
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Human leukocyte antigen (HLA)-B27 status
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Rheumatoid factor (RF) value
In patients in whom the pain has become chronic, clinicians need to consider whether the patients may have secondary reactive depression. Testing for hypothyroidism, cortisol abnormalities, or other metabolic or endocrine imbalances may be appropriate as part of the workup for a patient with depression.
Prostate-specific antigen (PSA) testing, serum protein electrophoresis/urine protein electrophoresis, and other laboratory tests used to investigate for malignancy are appropriate for older patients who have not improved with initial care and may have symptoms warranting further investigation.
Imaging Studies
Use of imaging studies when evaluating sacroiliac pathology is a source of controversy among clinicians because whether normal and abnormal radiographic studies can help differentiate symptomatic versus nonsymptomatic patients is unclear. This is probably due to the great variability in joint anatomy among patients. Additional disagreement exists on the significance of inflammatory findings and degenerative findings (sclerosis) being diagnostic of pain within the joint.
The usual SIJ examination is performed using anteroposterior pelvis/lumbar spine radiography. Sclerosis or obliteration of the SIJ can be observed in older patients.
Patients with AS usually have normal radiographic findings; in older patients with this disease, the joint can appear fused.
Specific sacroiliac views superimpose the anterior and posterior joint margins, which may increase the sensitivity for detecting abnormalities. These radiographs are taken at a 25-30° angle to the anteroposterior plane. Joint widening with erosive and sclerotic changes at the bony margins may be suggestive of inflammatory sacroiliitis.
Computed tomography (CT) scanning can often be used to document reactive spurring, sclerosis, or even subluxation. Many clinicians believe reactive spurring is due to prolonged abnormal motion within the joint.
In persons with inflammatory conditions (eg, AS), bone scanning can show enhancement within the SIJ (often bilaterally).
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Nuclear medicine bone scanning with single photon emission computed tomography (SPECT) can also be used to rule out femur and pelvic stress fractures and most bony metastatic disease.
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Some clinicians view enhancement observed in the SIJ unilaterally in a patient with suspected SIJ conditions as an indicator of SIJ dysfunction or inflammation. Slipman et al found nuclear imaging under these circumstances to be very low in sensitivity but high in specificity for sacroiliac-mediated pain. [17] Painful SIJs were confirmed with an intra-articular injection of anesthetic. Therefore, bone scanning was of little value in the diagnostic algorithm for SIJ pain.
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Adding SPECT scanning may increase the sensitivity of nuclear imaging for SIJ injuries; however, this has not been studied.
Magnetic resonance imaging (MRI) is not generally used for evaluating the SIJ, although it can be a valuable tool to help exclude disc herniation (especially at L5-S1) as part of the SIJ dysfunction differential diagnosis (see Differentials and Other Problems to Be Considered). MRI can occasionally show inflammatory signs within the SIJ. MRI can also be used to investigate pelvic stress fracture, femoral neck stress fracture, or femoral head avascular necrosis.
Procedures
For discussion of diagnostic and therapeutic SIJ injection, see Acute Phase, Other Treatments.
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Flouroscopically guided sacroiliac joint injection. Contrast seen throughout the joint.
