Patterns of ordering diagnostic tests for patients with acute low back pain

Background: Low back pain is a common reason for visiting a physician. Authors of guidelines and insurance payers are currently scrutinizing use of radiography and computed tomography (CT) or magnetic resonance imaging (MRI). Objective: To study the determinants of the use of lumbar spine radiography and either CT or MRI in patients with acute low back pain. Design: Prospective cohort study. Setting: Community-based practices in North Carolina in six strata: urban primary care physicians, rural primary care physicians, urban chiropractors, rural chiropractors, orthopedic surgeons, and practitioners at a group-model health maintenance organization. Patients: 1580 patients with acute low back pain. Measurements: Telephone interviews done after the index office visit and at 2, 4, 8, 12, and 24 weeks or until complete recovery; survey of practitioners; and chart abstraction. Results: During the acute back pain episode, 46% of patients had radiography and 9% had CT or MRI. Patient variables related to use of radiography included pain that began more than 2 weeks before the index visit and no previous episodes of low back pain. Practitioner variables associated with use of radiography were being a chiropractor or orthopedic surgeon and having a solo practice. Use of CT or MRI was associated with white race, neurologic deficit at baseline, sciatica, poor functional status at baseline, and small group-practice size. Practitioners' responses to clinical vignettes were associated with aggregate practitioner behavior: In the vignettes and in real life, practitioners were more likely to order CT for patients with sciatica. However, a practitioner's response to a vignette did not predict that practitioner's use of CT or MRI for similar patients in his or her own practice. Conclusion: Radiography is commonly used as a diagnostic test for patients with acute back pain. Clinical factors and provider specialty are major correlates of the use of imaging studies.