title: Identification of subgroups of inflammatory and degenerative MRI findings in the spine and sacroiliac joints: a latent class analysis of 1037 patients with persistent low back pain.
abstract: The aim of this study was to investigate subgroups of magnetic resonance imaging (MRI) findings for the spine and sacroiliac joints (SIJs) using latent class analysis (LCA), and to investigate whether these subgroups differ in their demographic and clinical characteristics.
  
  
  
  The sample included 1037 patients aged 18-40 years with persistent low back pain (LBP). LCA was applied to MRI findings of the spine and SIJs. The resulting subgroups were tested for differences in self-reported demographic and clinical characteristics.
  
  
  
  A five-class model was identified: Subgroup 1, 'No or few findings' (n = 116); Subgroup 2, 'Mild spinal degeneration' (n = 540); Subgroup 3, 'Moderate to severe spinal degeneration' (n = 229); Subgroup 4, 'Moderate to severe spinal degeneration with mild SIJ findings' (n = 68); and Subgroup 5, 'Mild spinal degeneration with moderate to severe SIJ findings' (n = 84). The two SIJ subgroups (Subgroups 4 and 5) had a higher median activity limitation score (Roland Morris Disability Questionnaire calculated as a proportional score: 65 (IQR 48-78)/65 (48-78)) compared with Subgroups 1-3 (48 (35-74)/57 (39-74)/57 (39-74)), a higher prevalence of women (68 % (95 % CI 56-79)/68 % (58-78)) compared with Subgroups 2 and 3 (51 % (47-55)/40 % (33-46)), a higher prevalence of being overweight (67 % (95 % CI 55-79)/53 % (41-65)) compared with Subgroup 1 (36 % (26-46)) and a higher prevalence of previous LBP episodes (yes/no: 81 % (95 % CI 71-91)/79 % (70-89)) compared with Subgroup 1 (58 % (48-67)). Subgroup 5 was younger than Subgroup 4 (median age 29 years (IQR 25-33) versus 34 years (30-37)) and had a higher prevalence of HLA-B27 (40 % (95 % CI 29-50)) compared with the other subgroups (Subgroups 1-4: 12 % (6-18)/7 % (5-10)/6 % (3-9)/12 % (4-20)). Across the subgroups with predominantly spinal findings (Subgroups 1-3), median age, prevalence of men, being overweight and previous LBP episodes were statistically significantly lower in Subgroup 1, higher in Subgroup 2 and highest in Subgroup 3.
  
  
  
  Five distinct subgroups of MRI findings in the spine and SIJs were identified. The results indicate that SIJ MRI findings not only can be seen as a part of the spondyloarthritis disease entity, but also are associated with age, gender and being overweight. Furthermore, the results indicate that LBP patients with SIJ MRI findings are more disabled compared with patients without SIJ MRI findings, and that moderate to severe spinal degeneration and/or SIJ MRI findings may be associated with recurrent pain.
authors.affiliation: Research Department, Spine Centre of Southern Denmark, Hospital Lillebaelt, Oestre Hougvej 55, Middelfart, 5500, Denmark. bodil.arnbak@rsyd.dk.|Institute of Regional Health Research, University of Southern Denmark, Winsloewparken 19-3, Odense C, 5000, Denmark. bodil.arnbak@rsyd.dk.
authors.forename: Bodil
authors.initials: B
authors.lastname: Arnbak
authors.affiliation: Research Department, Spine Centre of Southern Denmark, Hospital Lillebaelt, Oestre Hougvej 55, Middelfart, 5500, Denmark.|Institute of Regional Health Research, University of Southern Denmark, Winsloewparken 19-3, Odense C, 5000, Denmark.
authors.forename: Rikke Krüger
authors.initials: RK
authors.lastname: Jensen
authors.affiliation: Research Department, Spine Centre of Southern Denmark, Hospital Lillebaelt, Oestre Hougvej 55, Middelfart, 5500, Denmark.|Institute of Regional Health Research, University of Southern Denmark, Winsloewparken 19-3, Odense C, 5000, Denmark.
authors.forename: Claus
authors.initials: C
authors.lastname: Manniche
authors.affiliation: Institute of Regional Health Research, University of Southern Denmark, Winsloewparken 19-3, Odense C, 5000, Denmark.|King Christian 10th Hospital for Rheumatic Diseases, Toldbodgade 3, Graasten, 6300, Denmark.
authors.forename: Oliver
authors.initials: O
authors.lastname: Hendricks
authors.affiliation: School of Physiotherapy and Exercise Science, Curtin University, Kent Street, Bentley, Perth, Western Australia, 6102, Australia.|Department of Sports Science and Clinical Biomechanics, University of Southern Denmark, Campusvej 55, Odense M, 5230, Denmark.
authors.forename: Peter
authors.initials: P
authors.lastname: Kent
authors.affiliation: Research Department, Spine Centre of Southern Denmark, Hospital Lillebaelt, Oestre Hougvej 55, Middelfart, 5500, Denmark.|Institute of Regional Health Research, University of Southern Denmark, Winsloewparken 19-3, Odense C, 5000, Denmark.|Department of Radiology, Aarhus University Hospital, Noerrebrogade 44, Aarhus C, 8000, Denmark.
authors.forename: Anne Grethe
authors.initials: AG
authors.lastname: Jurik
authors.affiliation: Research Department, Spine Centre of Southern Denmark, Hospital Lillebaelt, Oestre Hougvej 55, Middelfart, 5500, Denmark.|Institute of Regional Health Research, University of Southern Denmark, Winsloewparken 19-3, Odense C, 5000, Denmark.|Nordic Institute of Chiropractic and Clinical Biomechanics, Campusvej 55, Odense M, 5230, Denmark.
authors.forename: Tue Secher
authors.initials: TS
authors.lastname: Jensen
mesh_terms: D000293:Adolescent; D000328:Adult; D005260:Female; D006801:Humans; D017116:Low Back Pain / Q000000981:diagnostic imaging* / Q000473:pathology; D008279:Magnetic Resonance Imaging; D008297:Male; D012446:Sacroiliac Joint / Q000000981:diagnostic imaging* / Q000473:pathology; D013131:Spine / Q000000981:diagnostic imaging* / Q000473:pathology; D055815:Young Adult
keywords: Cluster analysis; Low back pain; Magnetic resonance imaging; Sacroiliac joints; Spine; Spondyloarthritis