title: Shoulder magnetic resonance imaging abnormalities, wheelchair propulsion, and gender.
abstract: OBJECTIVE
  To investigate the relationship between pushrim forces and the progression of shoulder injuries in manual wheelchair users.
  
  
  METHODS
  Longitudinal case series.
  
  
  METHODS
  Biomechanics laboratory and magnetic resonance imaging (MRI) facility at a Veterans Health Administration medical center and university hospital, respectively.
  
  
  METHODS
  Fourteen individuals with spinal cord injury (8 men, 6 women) who used manual wheelchairs.
  
  
  METHODS
  Subjects propelled their own wheelchairs on a dynamometer at 0.9 and 1.8m/s. Bilateral biomechanical data were obtained by using force and moment sensing pushrims at time 1. Bilateral shoulder MR images were also completed on 2 occasions, at time 1 and, approximately 2 years later, at time 2.
  
  
  METHODS
  The peak pushrim forces in a pushrim coordinate system were calculated, weight normalized and averaged over 5 strokes (presented as % body weight). MRI abnormalities were graded by using a summated scale. Differences between scores between times 1 and 2 were calculated.
  
  
  RESULTS
  Subjects were divided into 2 groups based on change in MRI score. Seven subjects were in the group with worsening scores (MRI+; mean, 8.14 points; range, 5-16), and 7 were in the group with improving or unchanging scores (MRI-; mean, -1.00 point; range, -5 to 1). There was no significant difference between groups with respect to age, body mass index, or years from injury. There were significantly more women in the MRI+ group (6 women, 1 man) than in the MRI- group (7 men) (P=.001). The MRI+ group used significantly greater weight-normalized radial force, or force directed toward the axle at time 1, to propel their wheelchairs at each speed (P<.01): MRI+ at 0.9m/s (mean radial force +/- standard deviation, 5.2%+/-1.0%) and MRI- at 0.9m/s (mean radial force, 3.2%+/-1.7%) (P=.028); and MRI+ at 1.8m/s (mean radial force, 6.6%+/-1.2%) (P=.023) and MRI- at 1.8m/s (mean radial force, 4.1%+/-2.2%). In a separate analysis, women were found to propel with a significantly higher radial force. A logistic regression found a significant relationship between radial force at time 1 and increased risk of progression of MRI findings over time.
  
  
  CONCLUSIONS
  Individuals who propel with a greater percentage of force directed toward the axle were at increased risk of progression of MRI findings over time. Most people in this group were women. Clinicians should instruct wheelchair users in effective propulsion techniques and should pay particular attention to women who use wheelchairs. Reducing forces during wheelchair propulsion may minimize the likelihood of developing shoulder injuries.
authors.affiliation: Department of Physical Medicine and Rehabilitation, School of Medicine, University of Pittsburgh, and VA Piitsburgh Health Care System Center of Excellence in Wheelchairs and Related Technology, PA 15206, USA.
authors.forename: Michael L
authors.initials: ML
authors.lastname: Boninger
authors.forename: Brad E
authors.initials: BE
authors.lastname: Dicianno
authors.forename: Rory A
authors.initials: RA
authors.lastname: Cooper
authors.forename: Jeffrey D
authors.initials: JD
authors.lastname: Towers
authors.forename: Alicia M
authors.initials: AM
authors.lastname: Koontz
authors.forename: Aaron L
authors.initials: AL
authors.lastname: Souza
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena; D005260:Female; D006801:Humans; D016015:Logistic Models; D008137:Longitudinal Studies; D008279:Magnetic Resonance Imaging; D008297:Male; D011859:Radiography; D012737:Sex Factors; D012782:Shoulder / Q000002:abnormalities* / Q000000981:diagnostic imaging; D013119:Spinal Cord Injuries / Q000534:rehabilitation*; D014910:Wheelchairs