Research strategy and selection criteria

A systematic literature review was performed by following the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines [24] (checklist is shown in Supplementary Table 1). Relevant studies (by January 17, 2021) in PubMed, Embase, Cochrane Library, China National Knowledge Internet (CNKI), Wanfang Data and Chongqing VIP database (CQVIP) were retrieved to identify studies comparing MIS-TLIF and OLIF for the treatment of lumbar degenerative disorders. The following search terms were used: ((((oblique) OR (retroperitoneal)) OR (OLIF)) AND ((transforaminal) OR (TLIF))) AND (((((((((Spinal Fusion [MeSH Terms]) OR (Spinal Fusion [Title/Abstract])) OR (Fusion, Spinal [Title/Abstract])) OR (Fusions, Spinal [Title/Abstract])) OR (Spinal Fusions [Title/Abstract])) OR (Spondylodesis [Title/Abstract])) OR (Spondylodeses [Title/Abstract])) OR (Spondylosyndesis [Title/Abstract])) OR (Spondylosyndeses [Title/Abstract])). Relevant studies from references were also checked to broaden our search. The inclusion criteria were as follows: (1) prospective or retrospective studies that compared single-level MIS-TLIF and OLIF for the treatment of lumbar degenerative disorders; (2) studies that provided information in regard to clinical and radiographic efficacy (including at least one of the following: operation time, intraoperative blood loss, Visual Analogue Scale (VAS), Oswestry Disability Index (ODI), Japanese Orthopaedic Association Back Pain Evaluation Questionnaire (JOABPEQ) effectiveness rate, complications, disc height, disc angle, lumbar lordosis, fusion rate and subsidence); (3) studies with a mean follow-up of more than 6 months; and (4) studies published in English or Chinese. Studies that met the following criteria were excluded: (1) noncomparative study; (2) combination of both techniques in the same treatment; and (3) case report, letter, comment, review and conference papers.