title: EMG and MRI are independently related to shoulder external rotation function in neonatal brachial plexus palsy.
abstract: BACKGROUND
  Few studies exist with regard to the ability of electromyography (EMG) and volumetric magnetic resonance imaging (MRI) of the infraspinatus muscle to complement the physical assessment of active global shoulder external rotation (GER) in the neonatal brachial plexus palsy (NBPP) population. Therefore, the purpose of this study was to evaluate the relationships of EMG and MRI with active GER based on analysis of the infraspinatus muscle.
  
  
  METHODS
  Seventy-four NBPP patients (mean age, 5 y 1 m; range, 1 y 1 m to 13 y 3 m) who had undergone physical examination of the shoulder, EMG evaluation of the infraspinatus muscle, and shoulder MRI were included in this study. The outcome variable active GER was dichotomized into <0 degree active GER (poor) and ≥0 degree active GER (good). The interference pattern on EMG of the infraspinatus muscle was graded on a 6-point scale and dichotomized into ≤4 and ≥5. On shoulder MRI, infraspinatus muscle volume was measured. The infraspinatus muscle interference pattern and volume were compared with active GER.
  
  
  RESULTS
  Interference pattern on EMG of the infraspinatus muscle was significantly related to the Mallet Score (P=0.0022), with a poor interference pattern associated with an approximately 7 times higher likelihood [odds ratio=7.391; 95% confidence interval (2.054, 26.588)] of poor active GER. Infraspinatus muscle volume decrease on MRI was also significantly related to active GER (P=0.0413), with each percent volume decrease corresponding to an increase of 0.094 in the odds of having a poor Mallet Score for active GER [odds ratio=1.094; 95% confidence interval (1.004, 1.193)].
  
  
  CONCLUSIONS
  The interference pattern of the infraspinatus muscle on EMG and the infraspinatus muscle volume on MRI are strongly related to active GER as assessed by the Mallet Score. Integrating clinical assessment with electrophysiological and imaging findings may improve the accuracy in evaluating shoulder dysfunction in NBPP and provide improved guidance in selecting interventions specific to the patient's pattern of deficits.
  
  
  METHODS
  Diagnostic study, level II.
authors.affiliation: Division of Pediatric Orthopaedics, Cincinnati Children’s Hospital Medical Center, 3333 Burnet Avenue, MLC 2017, Cincinnati, OH 45229, USA.
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Talbert
authors.forename: Linda J
authors.initials: LJ
authors.lastname: Michaud
authors.forename: Charles T
authors.initials: CT
authors.lastname: Mehlman
authors.forename: Douglas G
authors.initials: DG
authors.lastname: Kinnett
authors.forename: Tal
authors.initials: T
authors.lastname: Laor
authors.forename: Susan L
authors.initials: SL
authors.lastname: Foad
authors.forename: Beverly
authors.initials: B
authors.lastname: Schnell
authors.forename: Shelia
authors.initials: S
authors.lastname: Salisbury
mesh_terms: D000293:Adolescent; D001720:Birth Injuries / Q000150:complications; D020516:Brachial Plexus Neuropathies / Q000150:complications*; D002648:Child; D002675:Child, Preschool; D004576:Electromyography / Q000379:methods*; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D016059:Range of Motion, Articular; D012189:Retrospective Studies; D012399:Rotation; D012785:Shoulder Joint / Q000503:physiopathology*