title: Topographical mapping and mechanical pain sensitivity of myofascial trigger points in the infraspinatus muscle.
abstract: OBJECTIVE
  To screen for the presence of latent and active myofascial trigger points (MTrPs) in patients with unilateral shoulder and arm pain and perform topographical mapping of mechanical pain sensitivity bilaterally in the infraspinatus muscles.
  
  
  METHODS
  Nineteen patients with unilateral musculoskeletal shoulder pain participated in the study. The area overlying the infraspinatus on each side was divided into 10 adjacent sub-areas of 1cm(2), corresponding to the area of a pressure algometer probe. Pressure pain threshold (PPT) was measured in each sub-area bilaterally in the infraspinatus muscles. Following PPT measurement, an acupuncture needle was inserted into each sub-area five times in different directions in order to induce local twitch response and/or referred pain.
  
  
  RESULTS
  A significantly lower PPT level in the infraspinatus muscle was detected on the painful side compared with the non-painful side (P=0.001). PPT at midfiber region of the infraspinatus muscles was lower than that at other muscle parts (P<0.05). Multiple, but not single, active MTrPs were found in the infraspinatus muscle on the painful side and there were also multiple latent MTrPs bilaterally in the infraspinatus muscles. PPT at active MTrPs was much lower than the latent MTrPs and again lower than the non-MTrPs.
  
  
  CONCLUSIONS
  There exists bilateral mechanical hyperalgesia in patients with unilateral shoulder pain. Further, the association of multiple active MTrPs with unilateral shoulder pain and the heterogeneity of mechanical pain sensitivity distribution suggest a crucial role of peripheral sensitization in chronic myofascial pain conditions. Additionally, the locations of MTrPs identified with dry needling correspond well to PPT topographical mapping, suggesting that dry needling and PPT topographical mapping are sensitive techniques in the identification of MTrPs.
authors.affiliation: Centre for Sensory-Motor Interaction (SMI), Department of Health Science and Technology, Aalborg University, Fredrik Bajers Vej 7 D-3, DK-9220 Aalborg, Denmark. ghy@hst.aau.dk
authors.forename: Hong-You
authors.initials: HY
authors.lastname: Ge
authors.forename: César
authors.initials: C
authors.lastname: Fernández-de-Las-Peñas
authors.forename: Pascal
authors.initials: P
authors.lastname: Madeleine
authors.forename: Lars
authors.initials: L
authors.lastname: Arendt-Nielsen
mesh_terms: D026881:Acupuncture / Q000295:instrumentation; D000328:Adult; D001931:Brain Mapping; D005207:Fasciculation / Q000209:etiology; D005260:Female; D006801:Humans; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000294:innervation / Q000503:physiopathology*; D009209:Myofascial Pain Syndromes / Q000175:diagnosis / Q000503:physiopathology*; D009339:Needles; D010147:Pain Measurement; D017288:Pain Threshold; D053591:Referred Pain / Q000209:etiology; D011312:Pressure / Q000009:adverse effects; D011677:Punctures / Q000009:adverse effects; D020069:Shoulder Pain / Q000503:physiopathology*