Acute low back usually resolves quickly but persistent low back pain often persists.

OBJECTIVE To review the evidence of clinical course of pain and disability in patients with acute and persistent low-back pain, and to investigate whether pain and disability had similar courses. DATA SOURCES MEDLINE, CINAHL and Embase databases were searched from 1950 to November, 2011. This search was supplemented by searching of reference lists from eligible studies. STUDY SELECTION Inception cohort studies involving patients with acute (< 6 weeks) and persistent (≥ 6 weeks) low-back pain in which pain or disability outcomes were reported. DATA EXTRACTION Two reviewers extracted data and discrepancies were resolved by consulting a third reviewer. Methodological quality was assessed using 5 criteria suggested by Altman (2001). A meta-analysis of pain and disability outcome data was conducted, in which pain and disability were modelled as a function of time. DATA SYNTHESIS Of 28 613 studies initially identified by the search, 43 studies (33 cohorts) with a total of 11 166 patients met the selection criteria. Data quality was insufficient in many of the studies; only 52% of the studies explicitly reported methods for assembling a representative sample, 73% had a follow-up of at least 80%, and 88% had a follow-up for at least one prognosis outcome at three months or longer. Based on the quantitative pooling of 24 cohorts and 4994 patients the variance-weighted mean pain score (0-100) was 52 (95% CI 48 to 57) at baseline, 23 (95% CI 21 to 25) at 6 weeks, 12 (95% CI 9 to 15) at 26 weeks, and 6 (95% CI 3 to 10) at 52 weeks after the onset of pain for cohorts with acute pain. Among cohorts with persistent pain, the variance-weighted mean pain score (out of 100) was 51 (95% CI 44 to 59) at baseline, 33 (95% CI 29 to 38) at 6 weeks, 26 (95% CI 20 to 33) at 26 weeks, and 23 (95% CI 16 to 30) at 52 weeks after the onset of pain. The course of disability outcomes was similar to the time course of pain outcomes in the acute pain cohorts, but for persistent pain cohorts disability only improved slowly, despite substantial initial improvement in pain. There were large within-study and between-study variation in outcomes. CONCLUSION Most people who seek care for acute or persistent low-back pain improved markedly within the first six weeks, but afterwards improvement slowed. Low to moderate levels of pain and disability were still present at one year, especially in people with persistent pain.