A new subgrouping of low back pain to explain alterations in lumbar muscle function and morphology

A NEW SUBGROUPING OF LOW BACK PAIN TO EXPLAIN ALTERATIONS IN LUMBAR MUSCLE FUNCTION AND MORPHOLOGY Van Oosterwijck S.1, Adnan R.1,2, Danneels L.1, Willems T.1, Dhondt E.1,3, Goubert D.1,3, Van Oosterwijck J.1,3,4 1Ghent University, Faculty of Medicine and Health Sciences, Department of Rehabilitation Sciences, SPINE Research Unit Ghent, Ghent, Belgium; 2Universiti Teknologi MARA, Faculty of Sports Science and Recreation, Shah Alam, Malaysia; 3Pain in Motion international research group, www.paininmotion.be; 4Research Foundation – Flanders (FWO), Brussels, Belgium Introduction: Evidence concerning paraspinal muscle structural and functional alterations in nonspecific low back pain (LBP) patients is inconclusive. Furthermore, the traditional means of classifying nonspecific LBP (i.e. chronic vs. recurrent nonspecific LBP) is subjective and often neglects physiological, psychological, attentional, and functional characteristics that may influence muscle structure and function. Purpose/Aim: To empirically test a new nonspecific LBP classification and explore associations with structural and functional alterations in paraspinal muscles. Materials and Methods: Fifty-nine women, pain-free (n=14) or having nonspecific LBP (n=45) underwent MRI. Total, lean muscle, and fat cross-sectional area (CSA) and muscle fat index (MFI) of the lumbar multifidus (MF) and erector spinae (ES) were calculated using T1-weighted MRI. Using functional MRI, the metabolic tissue characteristics of these muscles at rest (T2-rest) and following trunk extension (T2-shift) were examined. To obtain information on physiological characteristics, a self-constructed questionnaire was administered (i.e. age, BMI, LBP symptom duration, LBP intensity) and algometry was performed to determine pressure pain thresholds. Patients provided information on various characteristics by means of the Hospital Anxiety and Depression Scale to assess psychological characteristics (i.e. anxiety and depression), the Pain Catastrophizing Scale to evaluate attentional characteristics (i.e. catastrophizing), and the Roland Morris Disability Questionnaire to assess functional (i.e. disability) characteristics. Results: Cluster analysis yielded a classification with four subgroups, i.e. a neutral affected (NT), a physiological affected (PA), an attentional affected (AA), and a physiological-psychological-attentional-functional affected (PPAFA) subgroup. Muscle structural findings include 1) higher fat CSA of the MF and ES in the PA compared to the NT and AA subgroup, 2) higher fat CSA of the ES in the PA, AA, and PPAFA subgroups, 3) higher MFI of the MF in the PA, AA, and PPAFA subgroups. Muscle functional findings include 1) lower T2-rest of the MF in the PA and AA compared to the NT subgroup, 2) higher T2-shift of the ES in the PA and AA versus NT subgroup, 3) higher T2-shift of the MF and ES in the PA compared to the NT, AA, and PPAFA subgroups. Conclusion: A new classification of nonspecific LBP patients was derived based on physiological, psychological, attentional, and functional characteristics. Using this classification, group-specific structural and functional alterations of the MF and ES were found. This comprehensive classification helps clarify previous inconsistent findings regarding structural and functional alterations observed in the lumbar muscles of nonspecific LBP patients. A clinically diverse nonspecific LBP population exists, for whom treatment should be tailored to the presence of physiological, psychological, attentional, and functional characteristics. Keywords: nonspecific low back pain, classification, MRI, muscle structure, muscle function