Three-year incidence of low back pain in an initially asymptomatic cohort: clinical and imaging risk factors.

STUDY DESIGN: Prospective cohort study of randomly selected Veterans Affairs out-patients without baseline low back pain (LBP).

OBJECTIVE: To determine predictors of new LBP as well as the 3-year incidence of magnetic resonance imaging (MRI) findings.

SUMMARY OF BACKGROUND DATA: Few prospective studies have examined clinical and anatomic risk factors for the development of LBP, or the incidence of new imaging findings and their relationship to back pain onset.

METHODS: We randomly selected 148 Veterans Affairs out-patients (aged 35 to 70) without LBP in the past 4 months. We compared baseline and 3-year lumbar spine MRI. Using data collected every 4 months, we developed a prediction model of back pain-free survival.

RESULTS: After 3 years, 131 subjects were contacted, and 123 had repeat MRI. The 3-year incidence of pain was 67% (88 of 131). Depression had the largest hazard ratio (2.3, 95% CI = 1.2-4.4) of any baseline predictor of inci-dent back pain. Among baseline imaging findings, central spinal stenosis and nerve root contact had the highest, though nonsignificant, hazard ratios. We did not find an association between new LBP and type 1 endplate changes, disc degeneration, annular tears, or facet degeneration. The incidence of new MRI findings was low, with the most common new finding being disc signal loss in 11 (9%) subjects. All five subjects with new disc extrusions and all four subjects with new nerve root impingement had new pain.

CONCLUSION: Depression is an important predictor of new LBP, with MRI findings likely less important. New imaging findings have a low incidence; disc extrusions and nerve root contact may be the most important of these findings.