Imaging the back pain patient.

Imaging is an integral part of the clinical examination of the patient with back pain; it is, however, often used excessively and without consideration of the underlying literature. The primary role of imaging is the identification of systemic disease as a cause of the back or limb pain; magnetic resonance imaging (MRI) excels at this. Systemic disease as a cause of back or limb pain is, however, rare. Most back and radiating limb pain is of benign nature, owing to degenerative phenomena. There is no role for imaging in the initial evaluation of the patient with back pain in the absence of signs or symptoms of systemic disease. When conservative care fails, imaging may be undertaken with due consideration of its risks: labeling the patient as suffering from a degenerative disease, cost, radiation exposure, and provoking unwarranted minimally invasive or surgical intervention. Imaging can well depict disc degeneration and disc herniation. Imaging can suggest the presence of discogenic pain, but the lack of a pathoanatomic gold standard obviates any definitive conclusions. The imaging natural history of disc herniation is resolution. There is very poor correlation between imaging findings of disc herniation and the clinical presentation or course. Psychosocial factors predict functional disability due to disc herniation better than imaging. Imaging with MRI, computed tomography (CT), or CT myelography can readily identify central canal, lateral recess, or foraminal compromise. Only when an imaging finding is concordant with the patient's pain pattern or neurologic deficit can causation be considered. The zygapophysial (facet) and sacroiliac joint are thought to be responsible for axial back pain, although with less frequency than the disc. Imaging findings of the structural changes of osteoarthritis do not correlate with pain production. Physiologic imaging, either with single-photon emission CT bone scan, heavily T2-weighted MRI sequences (short-tau inversion recovery), or gadolinium enhancement, can detect inflammation and are more predictive of an axial pain generator.