The eligibility criteria for study selection used in this review are summarised in Table 1. Titles were initially screened by one reviewer (SS). When eligibility could not be determined on the basis of the title, abstracts were reviewed. To select full text papers, two reviewers (SS, KK) independently screened titles and abstracts of the remaining citations. Any disagreements were resolved through discussion and consensus. Selected full text papers and additional papers identified in reference lists of the included full text papers were screened by the same two reviewers and final agreement was reached on which papers to be included in the review.

Study eligibility criteria

Published studies were included if they fulfilled any of the following criteria:
 • Developed and described an original classification system for back pain that included adult patients with low back related leg pain (LBLP). Leg pain was defined as pain below the gluteal fold. • Adapted an existing classification system that was designed for or included LBLP patients. • Provided approaches to appraising or validating an existing classification system for LBLP.
Exclusion criteria:
 • Studies looking at specific spinal “red flag” conditions such as cauda equina syndrome, tumours or spinal fractures or a specific disease cohort such as diabetes. • Studies that only used expensive or advanced investigations or technology more likely to be feasible for secondary care settings (e.g. electromyography, surgical findings, imaging or expensive kinematic equipment) for classification of patients. • Case studies and case series design studies.
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