J Manipulative Physiol Ther. 2017 (Jul); 40 (6): 427–433 ~ FULL TEXT
Christina Knecht, BMed,
Barry Kim Humphreys, DC, PhD,
Brigitte Wirth, PT, MSc, PhD
Chiropractic Medicine Department,
Faculty of Medicine,
University of Zürich and University Hospital Balgrist,
OBJECTIVES: The purpose of this study was to investigate recurrence rate and prognostic factors in a large population of patients with low back pain (LBP) up to 1 year after chiropractic care using standardized definitions.
METHODS: In Switzerland, 722 patients with LBP (375 male; mean age = 44.5 ± 13.8 years) completed the Numeric Rating Scale for pain (NRS) and the Oswestry Disability Index (ODI) before treatment and 1, 3, 6, and 12 months later (ODI up to 3 months). Based on NRS values, patients were categorized as "fast recovery," "slow recovery," "recurrent," "chronic," and "others." In multivariable logistic regression models, age, sex, work status, duration of complaint (subacute: ≥14 days to <3 months; chronic: ≥3 months), previous episodes, baseline NRS, and baseline ODI were investigated as predictors.
RESULTS: Based on NRS values, 13.4% of the patients were categorized as recurrent. The recurrent pattern significantly differed from fast recovery in duration of complaint (subacute: odds ratio [OR] = 3.3; chronic: OR = 10.1). The recurrent and chronic pattern significantly differed in duration of complaint (chronic: OR = 0.14) and baseline NRS (OR = 0.75).
CONCLUSION: Recurrence rate was low in this LBP patient population. The duration of complaint before treatment was the main predictor for recurrence. The fact that even subacute duration significantly increased the odds for an unfavorable course of LBP is of clinical relevance.
KEYWORDS: Chiropractic, Low Back Pain, Recurrence
From the Full-Text Article:
Low back pain (LBP) is the leading cause for years lived with a disability globally,  and the burden of LBP is expected to rise as the population ages. [1, 2] Only about 1 in 3 LBP episodes completely resolves within a year, [3, 4] and the percentage of LBP that goes from acute to chronic varies among studies from 2% to 34%.  However, apart from the quickly resolving acute and the lengthy chronic course there are vast numbers of patients — approximately 3 in 53 — who suffer from recurrent LBP episodes. [6-10] It is difficult to predict which patients will experience LBP recurrence within the next year  because the pattern of recurrent episodes is unpredictable and still not fully understood. Nevertheless, recurrent LBP episodes have a tremendous impact on physical and social functioning  and are considerably more expensive than the original episode.  Thus, the prevention of future relapse episodes is crucial.
Solid evidence about risk factors for recurrence of LBP is sparse because the majority of research has focused on prognostic factors for poor outcome, disability, or chronicity instead of recurrence. Those that did find prognostic factors for the recurrent course have reported conflicting information, most probably because a variety of definitions for recurrent LBP have been used. A systematic review concluded that among the studies in this field, only 38% used a specific but self-created definition for recurrence, whereas in 62% it was unclear how recurrence had been measured.  This lack of standardization is reflected in the 1-year recurrence rate ranging from 25% to 73%. [9, 10] Moreover, most studies lacked a definition of recovery as part of the definition of recurrence, probably including patients with persistent pain instead of recurrent episodes.  Thus, the following consensus definition for a recurrence of an episode of LBP was reached in a modified Delphi approach: “return of LBP lasting at least 24 hours with a pain intensity of >2 on an 11-point Numeric Rating Scale (NRS) following a period of at least 30 days pain-free.” 
Thus, the main aim of this study was to determine the amount of LBP recurrences using the consensus definition of recurrence, according to Stanton et al,  in patients up to 1 year after chiropractic care based on pain intensity (NRS). The second aim was to compare the recurrent patients to all other patients (grouped according to various trajectories) in terms of certain baseline factors and to investigate whether certain baseline factors increased the risk for LBP recurrence.
In this population of patients with LBP undergoing chiropractic care, recurrences during the first year were sparse. The regression models could distinguish the recurrent patients from those who recovered quickly and those who became chronic, mainly based on the duration of the current complaint. The chronic patients and those with a subacute problem (≥14 days) at baseline were at considerably higher odds to experience recurrence rather than a fast recovery. Also, a chronic, but not a subacute problem at baseline increased the odds for a chronic course. High pain intensity at baseline more likely resulted in a chronic rather than in a recurrent course.
Using a standardized definition of recurrence, a recurrence rate of 13.4% was low. Recurrence was defined as NRS ≤1 at a preceding assessment and NRS >2 at the consecutive assessment, which only includes the aspect of pain intensity. However, because of lack of information, the aspect of pain duration as required in the definition by Stanton et al  (ie, “return of LBP lasting at least 24 hours with a pain intensity of >2 on an 11-point NRS following a period of at least 30 days pain-free”) was not included. In a similar study, Stanton et al  found a recurrence rate of 33%. They asked their patients at 3 and 12 months after recovering from an acute LBP episode whether they had a recurrence of LBP lasting for more than 24 hours. This definition included the duration aspect of the recurrence definition but disregarded pain intensity. Thus, patients with NRS ≤2 in the new LBP pain episode were classified as recurrent, which might explain the lower recurrence rate in the present study.
In fact, the present study might underestimate the true recurrence rate because there were only 5 assessments during the follow-up and some recurrences might have been missed. Nevertheless, the comparable study by Stanton only assessed LBP at 2 points in time (at 3 and 12 months after recovery) and found a higher recurrence rate. Similarly, a recent study by Hancock et al  used the definition of recurrence as “return of LBP lasting at least 24 hours with a pain intensity of 3 or more on a 0-10 numerical pain rating scale.” This definition corresponded to the first part of the consensus definition by Stanton et al  but did not, to our understanding, consider the second part (“following a period of at least 30 days pain-free”). Thus, in contrast to the present study, that definition of recurrence did not include recovery.
This implies that patients with fluctuating and persistent pain might be included, which was claimed to be a lack of many studies on LBP recurrence.  Indeed, Hancock et al  reported a recurrence rate of 54%, which corresponds well to the “recurrent” subgroup plus the “others” (fluctuating and persistent mild pain) subgroup in our study. Obviously, using a stringent definition considerably reduces the amount of LBP recurrences. However, this should not hide the fact that the majority of LBP patients in the present study did not become pain free within a year.
About 60% (classified by NRS) of the patients either belonged to the recurrent, chronic or “others” (fluctuating or persisting mild pain) subgroup, indicating that they were not constantly pain free. On the other hand, less than 10% (8%) developed severe chronic pain. These results are in line with a recent study by Kongsted et al,  which found, using latent class analysis, that most patients do not become pain free within a year and a few report constant severe pain. The finding of the present study that the recurrent pattern could be distinguished from the fast-recovering and the chronic courses but not from those patients who slowly recovered or were classified as “others” (fluctuating or persistent low pain) could either reflect that these groups differed in factors that were not investigated in the present study or that there were actually 3 main subgroups, namely a fast recovery subgroup (about 21%), a chronic persistent moderate or severe pain subgroup (about 8%), and a subgroup of patients who experience LBP as a chronic problem but not constantly on a high level (about 71%). Consequently, it might be hypothesized that at least some of the patients who experienced slow recovery in the present study might follow a recurrent pattern later, beyond the follow-up period for the present study. Failure to improve in the initial period after care seeking has previously been reported to negatively affect the prognosis of LBP. [24, 25]
Duration of current complaint emerged from this study as the most powerful factor to distinguish between recurrence and fast recovery and chronic course, respectively. Interestingly and in accordance with other studies, [20, 21] the prognosis deteriorated as early as 2 weeks. Patients presenting with a subacute problem, lasting for more than 14 days at baseline, were at higher odds for a recurrent course, whereas the odds for a chronic course were higher only for patients presenting with a chronic problem (≥3 months) at baseline.
Downie et al  reported that pain duration of more than 5 days was a factor that negatively affects prognosis. Similarly, duration of the current episode emerged as the most consistent factor for prognosis after 1 year in a study by Bekkering et al  and even predicted disability after 5 years.  These findings suggest on the one hand that it might be prudent to seek professional advice early on in the pain episode.  On the other hand, these findings emphasize the importance of change in the early phase of treatment. 
Consequently, every attempt should be made in this initial phase to help the patients experience improvement. This includes not only adequate physical treatment but also addressing coping behaviors,  such as adequate information and education.  Interestingly, the number of previous episodes did not emerge as predictor for recurrence from the present study, which is in contrast to the studies by Stanton et al  and Hancock et al.  However, the hazard ratio reported by Hancock et al  was 1.04, which indicates a limited influence of the previous episodes on recurrence. Still, this discrepancy might be explained by the differences in the definition of “recurrence” that are reflected in the recurrence rates.
Furthermore, the patient sample in the study by Hancock et al  consisted mainly of acute patients, whereas the present study included acute, subacute, and chronic patients about equally. Lastly, higher pain intensity at baseline was associated with a chronic rather than a recurrent course, when assessed by NRS. Accordingly, pain intensity at baseline identified persistent high pain but not fluctuating pain from rapid recovery in the study by Downie et al.  In a review focusing on early prognosis of LBP, all reviewed studies identified patient rating of pain as an important factor for predicting a negative outcome.  Higher pain intensity might lead to reduced activity and might initiate a vicious cycle of inactivity and LBP. 
The present study used, as far as possible, stringent definitions for recurrence and recovery, which is a clear strength. However, information about pain duration of a recurrent episode was not available, and thus, the definition for recurrence could only be fulfilled in terms of pain intensity, not duration. Furthermore, psychosocial factors have not been investigated and some recurrences might have been missed because the number of assessments was limited, which are clear limitations to the study. Although the results might be refined by more numerous assessments, some of the main results were comparable to studies that used weekly assessments.4 Lastly, the presented data do not reflect the natural course of LBP as the patients underwent chiropractic treatment, which was not standardized for methods or number of consultations. However, this was purposely chosen because it better reflects clinical practice.
Nevertheless, future studies on LBP recurrence using a standardized definition should include psychosocial assessments and should further investigate how the recurrent pattern differs from the fluctuating course and from slow recovery. For example, patients who experienced fast and slow recovery from an LBP episode should be followed for longer than 1 year in order to compare the recurrence rates. The findings of this study were only for people from Switzerland and therefore may be limited to this population. Similar studies should be completed in other countries to determine if these data can be extrapolated to other populations.
The recurrence rate of LBP using a stringent definition of recurrence was found to be low in this chiropractic LBP patient population. Nevertheless, the vast majority of patients were not pain free after 1 year. The recurrent course could be distinguished from the fast recovering and chronic patterns, but the differences with respect to the others subgroups were minor. The duration of complaint before treatment was the main predictor for recurrence. Of importance, a subacute duration, defined in the present study as longer than 14 days, significantly increased the odds for an unfavorable course of LBP, which is of clinical relevance.
Duration of complaint before treatment is an important predictor
for recurrence of LBP.
A duration of complaint of >14 days significantly increases the
odds for an unfavorable course of LBP.
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