Comprehensive review Do various baseline characteristics of transversus abdominis and lumbar multifidus predict clinical outcomes in nonspecific low back pain? A systematic review Arnold Y.L. Wong a , Eric C. Parent a,b , Martha Funabashi a , Tasha R. Stanton c , Gregory N. Kawchuk a,⇑ a Department of Physical Therapy, University of Alberta, Edmonton, Alberta, Canada b Glenrose Rehabilitation Hospital, Edmonton, Alberta, Canada c Sansom Institute for Health Research, School of Health Sciences, University of South Australia, Adelaide, South Australia, Australia Sponsorships or competing interests that may be relevant to content are disclosed at the end of this article. article info Article history: Received 26 March 2013 Received in revised form 5 July 2013 Accepted 10 July 2013 Available online xxxx Keywords: Effect modifier Low back pain Lumbar multifidus Prognostic factor Systematic review Transversus abdominis Treatment abstract Although individual reports suggest that baseline morphometry or activity of transversus abdominis or lumbar multifidus predict clinical outcome of low back pain (LBP), a related systematic review is unavail- able. Therefore, this review summarized evidence regarding the predictive value of these muscular char- acteristics. Candidate publications were identified from 6 electronic medical databases. After review, 5 cohort studies were included. Although this review intended to encompass studies using different muscle assessment methods, all included studies coincidentally used ultrasound imaging. No research investi- gated the relation between static morphometry and clinical outcomes. Evidence synthesis showed lim- ited evidence supporting poor baseline transversus abdominis contraction thickness ratio as a treatment effect modifier favoring motor control exercise. Limited evidence supported that high baseline transversus abdominis lateral slide was associated with higher pain intensity after various exercise inter- ventions at 1-year follow-up. However, there was limited evidence for the absence of relation between the contraction thickness ratio of transversus abdominis or anticipatory onset of lateral abdominal mus- cles at baseline and the short- or long-term LBP intensity after exercise interventions. There was conflict- ing evidence for a relation between baseline percent thickness change of lumbar multifidus during contraction and the clinical outcomes of patients after various conservative treatments. Given study het- erogeneity, the small number of included studies and the inability of conventional greyscale B-mode ultrasound imaging to measure muscle activity, our findings should be interpreted with caution. Further large-scale prospective studies that use appropriate technology (ie, electromyography to assess muscle activity) should be conducted to investigate the predictive value of morphometry or activity of these muscles with respect to LBP-related outcomes measures. Ó 2013 International Association for the Study of Pain. Published by Elsevier B.V. All rights reserved. 1. Introduction Approximately 9.2% of the global population is affected by low back pain (LBP), while LBP-related disability is the leading cause of disability in the world [91]. Although certain cases of LBP are ascribed to specific pathology, 90% of those with LBP experience LBP of unknown origin or pathology, known as nonspecific LBP [24]. Notwithstanding the lack of consensus regarding the causal rela- tion between deficits in spinal muscles and the onset of LBP, the transversus abdominis (TrA) and lumbar multifidus (LM) play important roles in intersegmental spinal control [32,46,53,73, 75,100] and may affect the progression and recurrence of LBP. Ana- tomically, TrA connects to the lumbar vertebrae through the thora- columbar fascia, forming a corset-like structure encircling the trunk, which controls intra-abdominal pressure and vertebral stiffness [4,31,34,43]. In contrast, the LM muscles are deep paraspinal mus- cles with densely packed short muscle fibers that generate large forces over short distances [20] for intersegmental control [9,100]. Various investigations have demonstrated associations between LBP and the characteristics of TrA/LM [15,18,57]. Research has re- vealed that patients with acute or chronic LBP have increased fat infiltration and abnormal changes of type I and II fibers in LM [2,3,42,56,58,70], while patients with unilateral LBP display localized asymmetrical LM atrophy at the painful vertebral level [15,33,70,92]. Functionally, patients with LBP demonstrate 0304-3959/$36.00 Ó 2013 International Association for the Study of Pain. Published by Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.pain.2013.07.010 ⇑ Corresponding author. Address: Department of Physical Therapy, University of Alberta, 3-48 Corbett Hall, Edmonton, Alberta T6G 2G4, Canada. Tel.: +1 780 492 6891; fax: +1 780 492 4429. E-mail address: greg.kawchuk@ualberta.ca (G.N. Kawchuk). PAIN Ò xxx (2013) xxx–xxx www.elsevier.com/locate/pain Please cite this article in press as: Wong AYL et al. Do various baseline characteristics of transversus abdominis and lumbar multifidus predict clinical out- comes in nonspecific low back pain? A systematic review. PAIN Ò (2013), http://dx.doi.org/10.1016/j.pain.2013.07.010