title: The reliability of rehabilitative ultrasound imaging in the measurement of infraspinatus muscle function in the symptomatic and asymptomatic shoulders of patients with unilateral shoulder impingement syndrome.
abstract: BACKGROUND
  Rehabilitative ultrasound Imaging (RUSI) is increasingly used in the management of musculoskeletal conditions as it provides an objective measure of muscle function while being less invasive than needle electromyography. While research has documented the ability to reliably measure trunk muscles in patients with back pain, no study to date has used RUSI to quantify infraspinatus muscle function in patients with shoulder impingement syndrome (SIS).
  
  
  OBJECTIVE
  The purpose of this study was to examine the intra-rater and inter-rater reliability of measuring infraspinatus muscle thickness with RUSI and to compare such measures during resting versus contracted muscle states and in the symptomatic versus asymptomatic shoulders in patients with SIS.
  
  
  METHODS
  Cross-sectional, measurement study.
  
  
  METHODS
  Fifty-two participants with unilateral SIS underwent a standard baseline examination to include RUSI of the infraspinatus muscle bilaterally. Images were acquired at rest and during a submaximal isometric contraction, by two novice examiners. The isometric contraction was elicited by having prone participants externally rotate their shoulder from a position of 90° abduction into a dynamometer and hold a static force of 20 mmHg (approximately 20-30% maximal voluntary contraction). Images were captured using a standardized placement of the transducer placed just inferior to the spine of the scapula along the medial scapular border and measured off-line using Image J software (V1.38t, National Institutes of Health, Bethesda, Maryland).
  
  
  RESULTS
  Estimates (ICCs) for thickness measurements ranged between 0.96 and 0.98 for intra-rater reliability and between 0.87 and 0.92 for inter-rater reliability. Reliability was substantially lower (ICC = 0.43 to 0.79) for calculations of percent thickness change. The infraspinatus muscle was significantly thicker when contracted (19.1mm) than during rest (16.2mm) in both shoulders (p < 0.001). There was also a statistically significant interaction between contraction state and shoulder (p = 0.026), indicating that the change in thickness that occurred during contraction was significantly smaller in the symptomatic shoulder than in the asymptomatic shoulder.
  
  
  CONCLUSIONS
  RUSI measurements of infraspinatus muscle thickness appear to be highly reliable, both within the same examiner and between different examiners, in patients with SIS. Moreover, such measurements were different in rested and contracted states of the infraspinatus, as well as, between the symptomatic and asymptomatic shoulders of patients with unilateral SIS.
  
  
  METHODS
  Level 2.
authors.affiliation: U.S. Army-Baylor University Doctoral Program in Physical Therapy, San Antonio, TX, USA.
authors.forename: Shane
authors.initials: S
authors.lastname: Koppenhaver
authors.affiliation: Physical Therapy Student During Study, U.S. Army-Baylor University Doctoral Program in Physical Therapy, San Antonio, TX, USA.
authors.forename: Danny
authors.initials: D
authors.lastname: Harris
authors.affiliation: Physical Therapy Student During Study, U.S. Army-Baylor University Doctoral Program in Physical Therapy, San Antonio, TX, USA.
authors.forename: Amanda
authors.initials: A
authors.lastname: Harris
authors.affiliation: Physical Therapy Student During Study, U.S. Army-Baylor University Doctoral Program in Physical Therapy, San Antonio, TX, USA.
authors.forename: Erin
authors.initials: E
authors.lastname: O'Connor
authors.affiliation: Physical Therapy Student During Study, U.S. Army-Baylor University Doctoral Program in Physical Therapy, San Antonio, TX, USA.
authors.forename: Max
authors.initials: M
authors.lastname: Dummar
authors.affiliation: U.S. Army-Baylor University Doctoral Program in Physical Therapy, San Antonio, TX, USA.
authors.forename: Theodore
authors.initials: T
authors.lastname: Croy
authors.affiliation: South College Doctor of Physical Therapy Program, Knoxville, TN, USA.
authors.forename: Michael
authors.initials: M
authors.lastname: Walker
authors.affiliation: South College Doctor of Physical Therapy Program, Knoxville, TN, USA.
authors.forename: Tim
authors.initials: T
authors.lastname: Flynn
keywords: Infraspinatus muscle; muscle function; reliability; shoulder impingement syndrome; shoulder pain; ultrasound imaging