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Open Access Highly Accessed Research article

The mechanical and inflammatory low back pain (MIL) index: development and validation

Antonio Cuesta-Vargas126*, Andre Farasyn3, Charles Philip Gabel4 and Juan V Luciano56

Author Affiliations

1 School Clinical Science at Queensland University of Technology, Brisbane, Australia

2 Faculty of Health Science, University of Malaga, Malaga, Spain

3 Department of Human Physiology and Sport Medicine, Vrije Universiteit Brussel (VUB), Brussels, Belgium

4 Faculty of Science, Health and Education, Centre for Healthy Activities, Sport and Exercise, University of the Sunshine Coast, Sippy Downs, Australia

5 Parc Sanitari Sant Joan de Déu & Fundació Sant Joan de Déu, Sant Boi de Llobregat, Spain

6 Red de Investigación en Actividades Preventivas y Promoción de la Salud (RedIAPP), Sant Boi de Llobregat, Spain

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BMC Musculoskeletal Disorders 2014, 15:12  doi:10.1186/1471-2474-15-12

Published: 9 January 2014



The purpose of this study was the development of a valid and reliable “Mechanical and Inflammatory Low Back Pain Index” (MIL) for assessment of non-specific low back pain (NSLBP). This 7-item tool assists practitioners in determining whether symptoms are predominantly mechanical or inflammatory.


Participants (n = 170, 96 females, age = 38 ± 14 years-old) with NSLP were referred to two Spanish physiotherapy clinics and completed the MIL and the following measures: the Roland Morris Questionnaire (RMQ), SF-12 and “Backache Index” (BAI) physical assessment test. For test-retest reliability, 37 consecutive patients were assessed at baseline and three days later during a non-treatment period. Face and content validity, practical characteristics, factor analysis, internal consistency, discriminant validity and convergent validity were assessed from the full sample.


A total of 27 potential items that had been identified for inclusion were subsequently reduced to 11 by an expert panel. Four items were then removed due to cross-loading under confirmatory factor analysis where a two-factor model yielded a good fit to the data (χ2 = 14.80, df = 13, p = 0.37, CFI = 0.98, and RMSEA = 0.029). The internal consistency was moderate (α = 0.68 for MLBP; 0.72 for ILBP), test-retest reliability high (ICC = 0.91; 95%CI = 0.88-0.93) and discriminant validity good for either MLBP (AUC = 0.74) and ILBP (AUC = 0.92). Convergent validity was demonstrated through similar but weak correlations between the ILBP and both the RMQ and BAI (r = 0.34, p < 0.001) and the MLBP and BAI (r = 0.38, p < 0.001).


The MIL is a valid and reliable clinical tool for patients with NSLBP that discriminates between mechanical and inflammatory LBP.

Low back pain; Psychometrics properties; Pain measurement; Screening tool; Inflammatory; Mechanical