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

Introduction : Evidence concerning paraspinal muscle structural and functional alterations in nonspecific low back pain (LBP) patients is inconclusive. Furthermore, the traditional means of classifying LBP is subjective and neglects physiological, psychological, attentional, and functional characteristics that may influence muscle structure and function. Purpose/Aim : To empirically test a new 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 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. The metabolic tissue characteristics of these muscles at rest (T2-rest) and following trunk extension (T2-shift) were examined. Physiological (age, BMI, symptom duration, pain intensity, pressure pain thresholds), psychological (anxiety and depression), attentional (catastrophizing), and functional (disability) characteristics were assessed. Results :Using cluster analysis, a classification with 4 subgroups was made, i.e. a neutral (NT), a physiologically affected (PA), a physiological-attentional affected (PAA), and a physiological-psychological-attentional-functional affected (PPAFA) subgroup. Muscle structural findings include 1) higher MF and ES fat CSA in the PA subgroup, 2) higher ES fat CSA in PAA and PPAFA versus NT, 3) higher MF MFI in PA, PPA, and PPAFA. Muscle functional findings include 1) lower MF and ES T2-rest in PA and PAA compared to the NT subgroup, 2) higher MF and ES T2-shift in PA versus NT and PPA, 3) higher ES T2-shift in PA compared to PPAFA, 4) higher ES T2-shift in PPA versus NT. Relevance : This comprehensive classification of LBP clarifies the inconclusive evidence regarding structural and functional alterations found in lumbar muscles of LBP patients. Conclusions : A new classification of LBP patients was derived based on the aforementioned characteristics. Using this classification group-specific structural and functional alterations of MF and ES were found. Implications : A clinically diverse LBP population exists, for whom treatment should be tailored to the presence of physiological, psychological, attentional, and functional characteristic