title: Afferent inhibition and cortical silent periods in shoulder primary motor cortex and effect of a suprascapular nerve block in people experiencing chronic shoulder pain.
abstract: OBJECTIVE
  To characterise short afferent inhibition (SAI) and the cortical silent period (CSP) in the primary motor cortex representations of the infraspinatus muscle in healthy adults and people experiencing chronic shoulder pain, to determine the impact of a suprascapular nerve block (SSNB).
  
  
  METHODS
  Neurophysiological measures were obtained in 18 controls and 8 patients with chronic shoulder pain, pre and post SSNB and 1 week later. Pain intensity was assessed by a visual analogue scale.
  
  
  RESULTS
  SAI was apparent in controls (all P<0.03) and a CSP was observed which reduced in the presence of SAI (all P<0.0001). Compared to controls, shoulder pain patients demonstrated higher active motor threshold (P=0.046), less SAI (P=0.044), a longer CSP (P=0.048) and less modulation of the CSP by SAI (P=0.045). Higher motor thresholds were related to higher pain scores (P=0.009). The SSNB immediately restored SAI (P=0.013), with a positive relationship between increased SAI and reduced pain (P=0.031). The SSNB further reduced modulation of CSP by SAI at 1 week post injection (P=0.006).
  
  
  CONCLUSIONS
  SAI and the CSP were present and demonstrated robust interaction in controls, which was aberrant in patients. The SSNB transiently restored SAI but had no effect on the CSP; however CSP modulation by SAI was further attenuated 1 week post injection.
  
  
  CONCLUSIONS
  The current findings improve understanding of the neurophysiology of the shoulder motor cortex and its modulation by chronic pain. The effect of SSNB in shoulder pain patients should be interpreted with caution until proven in a larger population. Interventions that target intracortical inhibition might increase efficacy in people with chronic shoulder pain.
authors.affiliation: Discipline of Physiotherapy, School of Health Sciences, Faculty of Medicine, Nursing and Health Sciences, Flinders University, South Australia, Australia; Applied Brain Research Laboratory, Centre for Neuroscience, School of Medicine, Faculty of Medicine, Nursing and Health Sciences, Flinders University, South Australia, Australia. Electronic address: lynley.bradnam@flinders.edu.au.
authors.forename: Lynley
authors.initials: L
authors.lastname: Bradnam
authors.affiliation: Department of Rheumatology, Repatriation General Hospital, Adelaide, South Australia, Australia; School of Medicine, Faculty of Medicine, Nursing and Health Sciences, Flinders University, South Australia, Australia.
authors.forename: E Michael
authors.initials: EM
authors.lastname: Shanahan
authors.affiliation: Discipline of Physiotherapy, School of Health Sciences, Faculty of Medicine, Nursing and Health Sciences, Flinders University, South Australia, Australia.
authors.forename: Kirsty
authors.initials: K
authors.lastname: Hendy
authors.affiliation: Discipline of Physiotherapy, School of Health Sciences, Faculty of Medicine, Nursing and Health Sciences, Flinders University, South Australia, Australia.
authors.forename: Amalia
authors.initials: A
authors.lastname: Reed
authors.affiliation: Discipline of Physiotherapy, School of Health Sciences, Faculty of Medicine, Nursing and Health Sciences, Flinders University, South Australia, Australia.
authors.forename: Tegan
authors.initials: T
authors.lastname: Skipworth
authors.affiliation: Discipline of Physiotherapy, School of Health Sciences, Faculty of Medicine, Nursing and Health Sciences, Flinders University, South Australia, Australia.
authors.forename: Anri
authors.initials: A
authors.lastname: Visser
authors.affiliation: Discipline of Physiotherapy, School of Health Sciences, Faculty of Medicine, Nursing and Health Sciences, Flinders University, South Australia, Australia.
authors.forename: Sheila
authors.initials: S
authors.lastname: Lennon
mesh_terms: D000328:Adult; D000344:Afferent Pathways / Q000502:physiology; D000368:Aged; D059350:Chronic Pain / Q000175:diagnosis / Q000503:physiopathology / Q000628:therapy*; D015331:Cohort Studies; D004576:Electromyography / Q000379:methods; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009044:Motor Cortex / Q000502:physiology*; D009407:Nerve Block / Q000379:methods*; D009433:Neural Inhibition / Q000502:physiology*; D010147:Pain Measurement / Q000379:methods; D012540:Scapula / Q000294:innervation / Q000502:physiology; D020069:Shoulder Pain / Q000175:diagnosis / Q000503:physiopathology / Q000628:therapy*; D050781:Transcranial Magnetic Stimulation / Q000379:methods*; D016896:Treatment Outcome; D055815:Young Adult
keywords: Chronic shoulder pain; Cortical silent period; Infraspinatus; Short afferent inhibition; Suprascapular nerve block; Transcranial magnetic stimulation