“Can clinically relevant subgroups of low back pain be identified?” Amongst other very important questions this was highlighted by an international panel of leading low back pain (LBP) researchers in primary care, as a relevant area of research to tackle the enormous burden of LBP. Many classification systems have been published, where researchers and clinicians have subgrouped LBP patients into groups of people with similar characteristics, with the aim of optimising management and improving outcomes. We were interested in patients with low back-related leg pain, a group which has received less attention in the literature despite its association with greater disability, recovery time, time off work and higher health care costs than pain in the back alone.
The reason for undertaking this systematic review was firstly to identify and appraise existing classification systems for patients with low back-related leg pain and secondly to summarise how leg pain due to nerve root involvement (commonly called sciatica), is identified and described in the various classification systems.
Following our search of electronic databases and reference lists of eligible studies and reviews, we identified 13,358 potentially relevant titles. Following screening, we included 50 papers in the review which reported on 22 classification systems. Two reviewers independently appraised the quality of these papers and we grouped the classification systems according to the purpose and criteria of the systems. Five themes emerged: (i) clinical features (ii) pathoanatomy (iii) treatment based approach (iv) screening tools and prediction rules and (v) pain mechanisms. Only three of the 22 systems focused specifically on populations with low back-related leg pain.
We found that systems that included statistical methods to develop their classification and that also explored the validity, reliability and generalisability of their systems, reached higher scores in the quality appraisal. There was a clear lack of consistency in how leg pain due to nerve root involvement was described and diagnosed within the systems. A table in the paper illustrates this variation.
There was evidence that some of the systems were being used in different settings but mainly to test issues of validity and reliability. To our knowledge, only one system is currently being implemented in primary care: in the Canadian province of Saskatchewan as part of a pathway to manage LBP.
Some reflections on the reviewing process and the results:
Firstly, our search identified a large number of papers to initially screen (13358). This reflects the breadth of the search strategy which was necessary to include all possible terms to cover the vast nomenclature describing low back-related leg pain.
Secondly, a striking finding was the variability in definitions and criteria to identify leg pain due to nerve root involvement (sciatica) within the systems. This mirrors findings from previous reviews which found variable eligibility criteria in studies involving sciatica patients. Agreement is needed on how clinicians and researchers define leg pain due to nerve root involvement and the clinical criteria used to that effect.
Thirdly, most of the classification systems were developed using a “judgement” approach i.e the authors’ opinions or an expert consensus approach. Very few included statistical methods to identify clusters of patients using patient data, a method that gives a more objective approach and helps reduce bias compared to “judgement” and expert approaches.
It is appreciated that the literature may be slightly saturated with subgroups, and current discussions around subgrouping highlight the limited carry-over or success stories from these groups.
In my view it is an important approach to continue to pursue, as long as it is done with methodological rigour and appropriate follow up. The main drive behind classification or subgrouping is to guide management and ultimately improve outcomes for patients. Identification of subgroups needs to be more than an expert’s opinion and any identified subgroups should ultimately be evaluated in a robust manner i.e. clinical trials.
In summary, our systematic review identified a number of classification systems that included patients with low back-related leg pain, but we were not convinced that the review findings identified ‘clinically relevant subgroups’ of LBLP. Only a few of the systems focused specifically on distinguishing between different presentations of leg pain. Further work is needed to identify subgroups in this population. For groups to be clinically meaningful, they should be based on data from large cohort populations, using recommended methods for classification system development.
About Siobhán Stynes
Siobhán currently works in the Research Institute for Primary Care and Health Sciences at Keele University. Her research interests are in the assessment and management of musculoskeletal conditions, in particular spinal pain and sciatica. In 2012 she was awarded a NIHR Clinical Doctoral Research Fellowship and has recently completed her PhD on the diagnosis and classification of low back-related leg pain. She is a physiotherapist and also works clinically within a local Spinal Interface Service.
 Stynes, S., Konstantinou, K., & Dunn, K. M. (2016). Classification of patients with low back-related leg pain: a systematic review. BMC Musculoskeletal Disorders, 17, 226. http://doi.org/10.1186/s12891-016-1074-z
Commissioning Editor: Neil O’Connel; Associate Editor JP Caneiro