Linda J. Carroll, PhD, Sheilah Hogg-Johnson, PhD, Gabrielle van der Velde, DC,
Scott Haldeman, DC, MD, PhD, Lena W. Holm, DrMedSc, Eugene J. Carragee, MD, FACS,
Eric L. Hurwitz, DC, PhD, Pierre Côté, DC, PhD, Margareta Nordin, PT, DrMedSc,
Paul M. Peloso, MD, MSc, FRCP(C), Jaime Guzman, MD, MSc, FRCP(C),
J. David Cassidy, DC, PhD, DrMedSc
Department of Public Health Sciences,
School of Public Health,
University of Alberta, Canada.
STUDY DESIGN: Best evidence synthesis.
OBJECTIVE: To perform a best evidence synthesis on the course and prognostic factors for neck pain and its associated disorders in Grades I-III whiplash-associated disorders (WAD).
SUMMARY OF BACKGROUND DATA: Knowledge of the course of recovery of WAD guides expectations for recovery. Identifying prognostic factors assists in planning management and intervention strategies and effective compensation policies to decrease the burden of WAD.
METHODS: The Bone and Joint Decade 2000-2010 Task Force on Neck Pain and its Associated Disorders (Neck Pain Task Force) conducted a critical review of the literature published between 1980 and 2006 to assemble the best evidence on neck pain and its associated disorders. Studies meeting criteria for scientific validity were included in a best evidence synthesis.
RESULTS: We found 226 articles related to course and prognostic factors in neck pain and its associated disorders. After a critical review, 70 (31%) were accepted on scientific merit; 47 of these studies related to course and prognostic factors in WAD. The evidence suggests that approximately 50% of those with WAD will report neck pain symptoms 1 year after their injuries. Greater initial pain, more symptoms, and greater initial disability predicted slower recovery. Few factors related to the collision itself (for example, direction of the collision, headrest type) were prognostic; however, postinjury psychological factors such as passive coping style, depressed mood, and fear of movement were prognostic for slower or less complete recovery. There is also preliminary evidence that the prevailing compensation system is prognostic for recovery in WAD.
CONCLUSION: The Neck Pain Task Force undertook a best evidence synthesis to establish a baseline of the current best evidence on the course and prognosis for WAD. Recovery of WAD seems to be multifactorial.
From the Full-Text Article:
Like neck pain in workers and neck pain in WAD, neck pain in the general population is frequently persistent and/or recurrent. [9, 10] Studies suggest that between 50% and 85% of people in the general population (or in primary care setting) who experience neck pain at some initial point will report neck pain 1 to 5 years later. Estimates varied by populations studied and across case definitions for neck pain. Moreover, in all but 1 study (Côté et al),  it was impossible to determine what proportion of participants experienced persistent versus recurrent neck pain. This particular study assessed 6-month period prevalence of neck pain at 6-month intervals in a general population, and thus provides more detailed information on the course of neck pain.  In this sample, approximately 10% of subjects with initially mild or intense but non-disabling neck pain reported neck pain that became disabling over the follow-up period; whereas one-fifth experienced recovery followed by worsening; and almost 40% experienced persistent levels of neck pain. However, even in this study, it is unclear what proportion of individuals experienced continuous neck pain. Even so, the evidence is clear that most people with neck pain do not experience a complete resolution of this problem.
Like the studies examining gender as a risk factor for new onset of neck pain in these populations,  the evidence on gender as a predictor of recovery from neck pain is equivocal—approximately half the studies examining this issue found that women had poorer outcomes compared to men, whereas the remaining studies noted no effect of gender. Interestingly, although Bot et al reported a higher incidence of neck pain among women found no gender differences in prognosis. [19, 29] No study found that men with neck pain had a poorer prognosis. However, even in the studies reporting poorer prognosis for women with neck pain, the impact was generally modest. We conclude, therefore, that gender is, at best, a weak predictor of recovery for neck pain in this population.
The evidence regarding age as a prognostic factor in neck pain was consistent: young age was associated with better prognosis in all studies examining this issue. However, again, there was not a large impact of age, suggesting that although older age played a consistent role in predicting poorer prognosis for neck pain, it was a weak predictor of recovery. Although most studies of age dichotomized younger versus older or examined age as a continuous variable, 1 study which trichotomized age (divided people into 3 age groups) reported the largest impact on recovery in the middle group (those aged 45–59 years).  This group was almost 4 times more likely to experience chronic, recurrent, or continuous neck pain compared with the older or younger groups. This is congruent with the literature on risk,  and provides preliminary evidence suggesting that the highest risk and poorest prognosis for neck pain is during the middle aged years. This should be confirmed in further studies.
There was a wide variety of indexes of health and health-related factors in the reviewed literature. In general, prior pain and/or injuries and poor health predicted greater presence and/or greater intensity of neck pain at follow-up, although the associations were modest. Despite preliminary findings that regular physical activity protects against onset of neck pain in the general population,  and that exercise is an important component of treatment for neck pain,  the prognostic studies evaluating this factor found that initial levels of exercise were not associated with persistence or with recurrence of neck pain at follow-up. In fact, regular bicycling was associated with poorer prognosis in 1 study.  However, physical fitness and exercise levels are difficult to measure in self-report questionnaires; and, moreover, increases in exercise levels over the follow-up period have not been evaluated. Prognosis may also depend on whether or not the exercises themselves were designed to impact the neck and shoulder areas.
Better psychologic health (measured in a variety of ways) and greater social support predicted a better outcome in primary care and general population samples with initial neck pain, whereas passive coping predicted a worse outcome. The associations between these psychologic factors and continued pain at follow-up were generally stronger than the associations seen for other types of prognostic factors. These findings are in keeping with the best evidence on risk for new episodes of neck pain, where poor psychologic health was associated with neck pain and was also a risk factor for new episodes. Although psychologic functioning is a potentially modifiable prognostic factor (and therefore a potential intervention target for trials), few trials have explored the impact of psychologic interventions alone, outside the context of multimodal treatment approaches to neck pain.
In summary, to the extent that common factors have been studied, the evidence suggests that most factors which predict poor outcome in persons with neck pain are consistent with those factors that increase the risk for new neck pain (or neck pain episodes).
State of the Literature and Study Limitations
The scientifically admissible literature on prognostic factors within the general population and for persons in primary health care settings is not extensive, although the studies included in the best evidence synthesis were well designed. It is likely that the 2 populations considered here—the general population and patients seeking primary care—are quite similar with respect to prognostic factors for neck pain outcome. Most studies used multivariable analyses to identify the presence and strength of prognostic factors. However, our best evidence synthesis of prognosis in these settings is based on only 6 studies. A seventh study used a distinct sample of persons with longstanding, functionally-limiting pain which had led them to be referred for inpatient rehabilitation. One might expect prognostic factors in this particular population to be different from those in general populations and in primary health care settings.
Identification of prognostic factors can guide expectations for recovery and, where these prognostic factors are modifiable, can guide considerations of what intervention targets will be the most productive. This is especially true when the effect of that factor on neck pain outcome is large. Most of the prognostic factors identified in this literature had only a modest association with outcome of neck pain. In addition, we should point out the wide variety of case definitions of neck pain and prognostic factors that we encountered in the literature. This suggests we should use caution in drawing firm conclusions at this time.
One promising exception involves psychologic factors, although few studies looked at the same psychologic constructs. The importance of this group of prognostic factors needs to be confirmed in additional phase III studies; in addition, if these are to be studied in the context of intervention trials, we need confirmation that they are indeed modifiable. Some such evidence exists for example coping strategies in chronic pain samples have been reported to be amenable to change via cognitive-behavioral or multimodal interventions. [30-32]
Limitations in the literature we reviewed are outlined above. However, the methodology used in the synthesis of the best evidence also has some limitations (outlined in more detail elsewhere). 
In particular, although there is a large overlap among journals indexed in Medline and in other electronic health databases, it is possible that using only Medline resulted in missing studies that may have informed this best evidence synthesis. There is also controversy about whether systematic literature reviews should report findings from all relevant studies or use a best evidence synthesis, as we did. We believe that using a best evidence synthesis approach, that is, reporting evidence only from those studies we judged to have adequate validity, increases the validity of the conclusions.
There are also some limitations specific to our systematic review of prognosis of neck pain in the general population. First, although all articles used in our analysis were judged to be scientifically admissible, the quality and methodology of the studies still varied considerably. In particular, the adequacy of control of confounders varied widely among studies. We attempted to address this potential source of bias by classifying studies into phase I, II, and III and by giving greater scientific weight to studies that explicitly controlled for confounders (i.e., phase III studies).
Second, we made no conclusions about some prognostic factors, indicating that the evidence varied too much among studies to reach firm conclusions. In some cases, this variability may have been due to an attempt to combine studies which diverged because of population-specific effects (that is, the strength and direction of the association varies in the populations in question), and that there was no genuine contradiction between studies.
We propose the following high priorities for future research in this area.
There should be closer tracking of the usual course of neck pain. Although continuous neck pain and recurrent neck pain both reflect failure to recover, there may be different consequences and prognostic factors for these states.
Studies are needed to confirm or refute the suggestion that middle-aged persons are at the greatest risk of persistent neck pain.
Studies to assess the role of degenerative disc changes in recovery from neck pain are required.
Studies examining the role of compensation systems, policies, and legal factors in prognosis for recovery are also required.
Studies examining the effect of genetic factors on neck pain prognosis would be useful.
Further studies are needed to examine the role of exercise and fitness levels on the outcome of neck pain episodes. Given uncertainty about self-reports of fitness or exercise levels, these factors should preferably be assessed using objective criteria rather than self- report. It might also be important to determine the type of exercise as part of this research.
Research priorities and recommendations to improve the quality of prognostic studies are outlined in more detail in Carroll et al. 
Most people (50%– 85%) in the general population with neck pain do not experience a complete resolution of this problem.
Younger people have a better prognosis, and 1 study suggests that those in middle age have the poorest prognosis.
Poor health and prior pain episodes are associated with a poorer prognosis; however, the effect of these factors was modest. Psychologic factors are important in prognosis for neck pain in the general population. Poor psychologic health, and worrying, becoming angry, or becoming frustrated in response to neck pain, were associated with poorer prognosis. Greater optimism, coping that involves self-assurance, and having less need to socialize, were all associated with better prognosis. The impact of psychologic factors was of at least moderate strength (i.e., most ORs in these studies were between 2 and 6).
There is preliminary evidence from 2 studies that general exercise at baseline is not associated with prognosis; however, 1 study found those who engage in regular bicycling have a poorer prognosis.