title: Comparison of location, depth, quality, and intensity of experimentally induced pain in 6 low back muscles.
abstract: BACKGROUND
  The pattern of pain originating from experimentally induced low back pain appears diffuse. This may be because sensory information from low back muscles converges, sensory innervation extends over multiple vertebral levels, or people have difficulty accurately representing the painful location on standardized pain maps.
  
  
  OBJECTIVE
  The aim of this study was to provide insight into the perception of pain from noxious stimulation of a range of low back muscles using novel depth and location measures.
  
  
  METHODS
  Hypertonic saline (1 mL, 7% NaCl) was injected into bellies of longissimus (LO), quadratus lumborum (QL), superficial multifidus (SM), and deep multifidus (DM) at the level of the fourth lumbar vertebrae (L4) and in SM and DM at L5 using ultrasound guidance over 6 sessions. Fifteen participants reported depth, location, intensity, size, and descriptive quality of pain throughout the painful period (∼14 min).
  
  
  RESULTS
  Pain was reported deeper (P<0.04) for DML4/L5 compared with SML4/L5, LO and QL; more cranial for LO compared with DML4 and QL (P<0.01); more lateral for LO compared with DML4 (P<0.02); and more lateral for QL compared with all other muscles at L4 (P<0.0001). Pain intensity was higher in DML4/L5 than all other muscles (P<0.04) for ∼3 minutes. Descriptive qualities varied slightly between muscles.
  
  
  CONCLUSIONS
  Depth and lateral position may be the most critical descriptors to determine the source of acute lumbar muscular pain. Overlapping regions of pain may be explained by convergence of receptive fields, innervation of multifidus fascicles at multiple lumbar segments, and convergence of sensory input from different muscles to the same sensory cell bodies as demonstrated in the lumbar spine of animal preparations.
authors.affiliation: School of Health and Rehabilitation Sciences, NHMRC Centre of Clinical Research Excellence in Spinal Pain, Injury and Health, The University of Queensland, Brisbane, Qld, Australia.
authors.forename: Kylie J
authors.initials: KJ
authors.lastname: Tucker
authors.forename: Matthew
authors.initials: M
authors.lastname: Fels
authors.forename: Scott R
authors.initials: SR
authors.lastname: Walker
authors.forename: Paul W
authors.initials: PW
authors.lastname: Hodges
mesh_terms: D064131:Back Muscles / Q000503:physiopathology*; D005260:Female; D006801:Humans; D017116:Low Back Pain / Q000503:physiopathology*; D008297:Male; D059226:Nociceptive Pain / Q000503:physiopathology*; D010147:Pain Measurement; D058748:Pain Perception / Q000502:physiology*; D016684:Prone Position; D012462:Saline Solution, Hypertonic; D011795:Surveys and Questionnaires; D055815:Young Adult
chemical_list: D012462:Saline Solution, Hypertonic