Selection of studies
A total of 6542 citations were screened (EMBASE and MEDLINE 4230, CINAHL 2012, PsychINFO 300), providing 349 abstracts that appeared to meet the inclusion criteria. Of these 349 abstracts, 276 were excluded (102 not musculoskeletal, 88 randomised controlled trials, 32 duplicates and 54 not conducted in primary care), leaving 73 full text articles. A further 30 studies were excluded after reading the whole article (16 randomised controlled trials, 12 not conducted in primary care and two not relevant). Local experts identified a further two studies, giving a total of 45 included studies (Figure 1).
Figure 1 Results of systematic search and selection of studies.
Study characteristics
Forty-five studies were included in the systematic review. Approximately half of the studies were of low back pain prognosis (27 studies), with a smaller number relating to spinal pain (six studies), shoulder and/or shoulder-neck pain (four studies), hip pain (two studies), elbow pain (one study), and knee pain (one study). Four studies were of prognosis for general musculoskeletal pain. No primary care-based observational studies of hand or foot pain were identified. Study size varied greatly, ranging from 44 to 3197 participants. Articles included in the review used 14 different outcome domains at follow up. The most frequently used were self-reported disability (22 studies), persistence of symptoms (10 studies), pain severity (10 studies), work absence (eight studies), and patient perceived recovery (eight studies).
Other outcomes included healthcare utilisation (three studies), return to work (three studies), recurrence (two studies), medication use (two studies), bed rest, catastrophising, pain-related fear, quality of life, and hip replacement (all used as outcomes in one study). Studies using the same outcome domain (for example, disability), frequently used different outcome measures (for example, for low back pain studies including disability as an outcome domain, three different measures were used). The length of time participants were followed up for ranged from 2 weeks to 5 years (Supplementary Table 1). Seventeen studies were restricted to patients with a new pain episode (defined variously as ‘never having had that pain before’, or having had no pain in the previous 28 days, 2, 3, 6, 12, or 24 months), five studies included only patients with chronic pain complaints, 10 studies included patients with a combination of chronic and acute pain, and for 13 studies, no explicit details were provided.
Prognostic indicators
In total, 63 different prognostic indicators were identified, which had been investigated in at least one study and shown to be associated with outcome. Eleven of these prognostic indicators were associated with outcome in at least two different studies of pain at different anatomical sites, (although low back pain and spinal pain were presented separately, they were regarded as one site for the purposes of this analysis because of the overlap between them; supplementary Table 1).
The other 49 prognostic indicators were associated with outcome in at least one study, but only for a single anatomical site. Of the eleven indicators at baseline that were associated with poor outcome across more than one anatomical site, four were pain characteristics (higher pain intensity, longer pain duration, multiple-site or widespread pain and previous episode of pain), and two were related to psychological conditions (higher levels of anxiety or depression and higher somatic perceptions or psychological distress).
Other indicators identified as being associated with a poor prognosis were movement restriction, adverse coping strategies, low levels of social support, and older age. Higher baseline pain intensity and disability were associated with poor outcome at all of the anatomical sites in this review (general musculoskeletal, spinal, low back, shoulder-neck, hip, knee, and elbow). Longer pain duration at baseline was indicative of poor prognosis for spinal pain, low back pain, shoulder pain, and hip pain, while the presence of widespread pain was a prognostic indicator for poor outcome in spinal pain, low back pain, and shoulder pain. To assess whether study quality was associated with the prognostic indicators identified, the analysis was repeated after excluding 11 studies with quality assessment scores of less than 11.12,18,21,23,33,38,42,44,48,51,54 This did not alter the pattern of findings on generic prognostic indicators.
Heterogeneity in either study populations, outcomes, the specific measurement of each prognostic indicator, or approaches to statistical analysis, prevent any meaningful pooled quantitative estimate of the association between prognostic indicator and poor outcome. For example, in eight of the studies reporting a positive association between higher pain intensity and outcomes at 1 year, two provided unadjusted P-values <0.05,35,45 (two provided adjusted OR = 8.1: no CI;19 OR = 2.0; 95% CI = 1.2 to 3.3,25 two provided unadjusted RR = 0.93, 95% CI = 0.88 to 0.98;37 RR = 2.8, 95% CI = 1.8 to 4.2,44 one provided adjusted hazard ratios for time to recovery, 0.99, 95% CI = 0.99 to 1.00),27 and one provided a percentage of variance in outcome explained by pain intensity within a multivariate model (5%).21