Introduction

Low back pain (LBP) is a major problem globally.1 It is associated with lost work productivity, disability and considerable health care costs.2 In 2009, estimates of treatment costs alone for chronic LBP (defined as LBP lasting 180 days or more) were [pounds]2.8 billion per annum in the United Kingdom.3

Merskey and Bogduk4 highlighted how chronic pain was distinct from acute pain, with chronic pain defined by its persistence beyond usual healing times. Although other approaches to classifying chronicity have been identified that incorporate psychosocial aspects and interference with activities of daily living,5 the vast majority of journal articles and systematic reviews use pain duration alone to categorize patients. However, there is little agreement on the definitions of acute, subacute and chronic LBP, despite these terms being frequently used as criteria to establish the sample population in clinical and epidemiological research and in studies focusing on the prevalence of LBP.6-8 More recently, terms such as persistent LBP have been used to describe patients' pain duration category.9 A recent systematic review looking at the prevalence of chronic LBP highlighted the lack of consensus in the definitions of acute and chronic LBP, as the pain duration criteria used in studies varied significantly.8 These inconsistencies lead to heterogeneity in study results, making it difficult to compare or summarize findings.7 This could have implications for clinicians who are trying to use the research to implement the best management for patients with LBP. Foster et al.9 emphasize the extensive gaps between evidence and clinical practice worldwide.

Although the revised National Institute for Health and Care Excellence (NICE) guidelines no longer consider duration of pain when making management recommendations for patients with LBP,10 there is little empirical evidence to support this decision. The small amount of existing literature is, at least in part, conflicting. Findings from Dunn and Croft6 identified duration of pain at baseline as a predictor of outcome regardless of baseline severity of pain and psychological status. They demonstrated that patients with increasing pain duration were associated with poorer clinical outcomes; those with pain for more than three years at baseline took significantly longer to improve than those who had pain for a shorter duration. In contrast, recent work published by our group found that regardless of the duration of pain, all patients with LBP who were managed with an evidence-based pathway showed clinically relevant short-term improvement. However, there was a trend for those with shorter pain duration to demonstrate better outcomes.11 A key difference between these studies is that patients in the Dunn and Croft6 study received a broad battery of usual care from their general practitioner, while those in the study by Jess et al.11 were managed on an evidenced-based pathway.

The updated NICE guidelines for LBP now recommend the use of risk stratification to classify patients, rather than the previous duration-based classification (acute, subacute and chronic).10 While there is emerging evidence demonstrating that interventions aligned with stratification can improve disability in samples with largely chronic LBP,12 Traegar et al.13 highlighted that it is uncertain whether this prognostic approach can prevent the onset of chronic LBP. This indicates that using risk stratification to classify LBP requires further research. Many other clinical guidelines still separate the management of acute, subacute and chronic LBP,14-15 and research studies in LBP continue to differentiate patients based on duration of pain.8

Commonly used definitions of the duration of LBP are as follows: acute LBP is pain that lasts for less than four weeks, subacute pain lasts four to 12 weeks and chronic back pain lasts for more than 12 weeks.14 In contrast, the systematic review by Meucci et al.8 found numerous variations in the definition of chronic LBP, including pain lasting for more than six weeks, more than seven weeks, more than three months, more than six months and continuous pain.8 With the current variability in pain duration definitions, it would be beneficial to conduct a scoping review of the literature to map the different working definitions currently used for the duration of acute, subacute and chronic LBP. Dionne et al.7 emphasize the importance of standardized definitions for comparing and summarizing research results to implement appropriate findings into clinical practice. The scoping review will not aim to count all the different definitions, but it will focus on facilitating a better understanding of the origins of the commonly used categorizations. By examining the rationale provided for the timeframes used, this scoping review will aim to establish why the variations in categorizations exist and try to inform their use in future research and clinical practice.

A preliminary search for existing scoping reviews on the topic has been conducted, and no existing reviews were identified. Due to the type of research question, and the variation of studies to be included, the quality of the evidence will not be graded. Armstrong et al.16 highlighted that assessing the quality of evidence is not a priority of a scoping review.

Review objectives

The primary aim of this review is to identify the different definitions of the duration of acute, subacute and chronic low back pain. It will aim to establish where the definitions originated, the rationale provided for the timelines used and why the variations in the definitions exist. The secondary aim of the review is to identify which other terms have been used to denote the individuals' duration of pain, for example persistent low back pain.

Inclusion criteria

The JBI methodology for scoping reviews will be followed for this systematic scoping review protocol.17

Participants

Studies that include participants with non-specific LBP regardless of the sex of participants will be considered. LBP is defined as pain focused between the lower rib margins and the inferior gluteal folds, with or without leg pain, that can be associated with neurological symptoms in the lower limbs.18 Studies that include children (younger than 18 years) or participants with specific causes of LBP (malignancy, infection, osteoporosis, fracture, inflammatory disease, pregnancy, nerve root pain or cauda equina) will be excluded, as these may incorporate more complex reasons for the LBP and are outside the scope of non-specific low back pain, which accounts for 90%-95% of LBP seen in primary care.19

Concept

The main outcome of interest for this review is the proposal of an original definition of the duration of acute, subacute or chronic LBP-that is, the first identifiable study to propose a specific duration with some reasoning as to why the timeframes have been proposed. If the study states that it is using a particular timeframe because of another reference from the literature, then we will search for the reference it provides to try to establish the origin. If a study suggests another term denoting duration of pain (e.g. persistent LBP), it will also be included. Studies that propose a specific duration but do not provide any rationale as to why the specific timeframe has been used will be excluded.

Context

The context for this review will be any healthcare and workplace settings, due to the wide impact of LBP in society. Definitions can be those given by clinicians or researchers.

Types of studies

This review will consider peer-reviewed journal articles as well as books and book chapters if referenced in studies that are included, as original duration definitions may have been published in books. Study types can include quantitative studies, qualitative designs and systematic reviews. Studies will include, but are not limited to, randomized controlled trials, case studies, feasibility studies and observational studies. A study will be included if it gives a proposal for an original definition of duration-as well as some reasoning as to why the duration has been used-in the title, abstract or body of the paper, regardless of publication date or methods. The terms for duration will include acute, subacute or chronic LBP, or another term relating to duration (e.g. persistent). Studies will be limited to those published in English.

Methods

Search strategy

An initial limited search of MEDLINE (via Ovid) has been undertaken, followed by analysis of the text words contained in the title and abstract, and of the index terms used to describe the article. This informed the development of a search strategy, which will be tailored for each information source. The search strategy was developed by one reviewer (MAJ), with assistance from a professional librarian. To focus the search, Boolean operators and truncation terms will be used. An asterisk used at the end of keywords represents a wild card to enable alternative suffixes for the word to be searched. To ensure that the search strategy is specific enough to meet the aims of this scoping review, an approach using proximity of 20 words will be applied. Phrases with 'n20' indicate a proximity search, whereby the two words must fall within 20 words of each another. There are no guidelines for using proximity searching. After exploring different proximity search strategies, the use of 20 words was chosen to make the search sufficiently specific to the aims of the scoping review while ensuring a broad enough range to identify relevant articles. An example of the full search strategy for MEDLINE is detailed in Appendix I. A total of 2984 records were retrieved that met the search parameters. Hand searching and screening of reference lists of included studies will be performed to identify other potential studies that meet the inclusion criteria.

Information sources

The databases to be electronically searched include MEDLINE, Excerpta Medica Database (Embase), Cumulative Index to Nursing and Allied Health Literature (CINAHL) and PsycINFO from the start of each database to the present. There is no lower date limit to ensure that original sources can be included.

Study selection

Following the search, all identified citations will be collated and uploaded into EndNote X9 (Clarivate Analytics, PA, USA) and duplicates removed. Titles and abstracts will then be screened by two independent reviewers for assessment against the inclusion/exclusion criteria for the review. Studies that may meet the inclusion criteria will be retrieved in full and their details imported into the JBI System for the Unified Management, Assessment and Review of Information (JBI SUMARI; Joanna Briggs Institute, Adelaide, Australia). The full text of selected studies will be retrieved and assessed in detail against the inclusion/exclusion criteria by two independent reviewers. Full-text studies that do not meet the inclusion criteria will be excluded, and reasons for exclusion will be provided in an appendix in the final scoping review report. The results of the search will be reported in full in the final report and presented in a PRISMA flow diagram.20 Any disagreements that arise between the reviewers will be resolved through discussion or with a third reviewer.

Data extraction

A data extraction table (Appendix II) will be created to include general information from each source (author, year of publication, country of publication, type of report, timeframes given for acute, subacute and chronic pain durations, and any other term used for pain duration, where the duration originated, rationale for timeframes and any additional relevant information). The data to be included will be further refined at the review stage, and the charting table will be updated accordingly. Two reviewers will read each included article and independently extract the aforementioned data from each source. Any disagreements that arise between the reviewers will be resolved through discussion or with a third reviewer. Authors of papers will be contacted to request missing or additional data where required.

Data presentation

Once the results have been organized and displayed in a table (Appendix II), a chronological narrative synthesis of the data will describe how the results relate to the objectives of the scoping review. We will aim to discuss where the current, frequently used LBP duration categorizations originated, and the rationale provided for them, to facilitate an understanding of their use in clinical practice and research. Because of the large variability of LBP duration categorizations, by establishing the origin and rationale, this scoping review will try to provide some insight into why this variability exists. This should help to inform use of these terms in future research and clinical practice. To establish a level of credibility, a brief description of the source or study background will be given.

Acknowledgments

Julie Hogg assisted with developing the search strategies in conjunction with the main researcher (MAJ).

Appendix I: Search strategy for MEDLINE

(defin^* OR duration^* OR categor^* OR classif^* OR "natural history" OR timeframe) n20 (acute OR subacute OR chronic OR persistent) n20 (pain OR "back pain")

Appendix II: Charting table for data extraction

References