title: Rotator cuff strength in recurrent anterior shoulder instability.
abstract: BACKGROUND
  Although rotator-cuff muscle contraction plays an important role in stabilizing the glenohumeral joint, little is known about the role of these muscles in the pathophysiology of recurrent anterior instability. We intended to analyze the association between isokinetic internal rotator and external rotator muscle strength and glenohumeral joint instability in patients with recurrent anterior instability that was not previously treated surgically.
  
  
  METHODS
  We enrolled thirty-seven patients with unilateral recurrent anterior posttraumatic shoulder dislocation and eleven healthy nonathletic subjects in this controlled study. The association between internal rotator and external rotator strength and shoulder instability was analyzed by side-to-side comparisons and comparisons with a control group. Isokinetic internal rotator and external rotator strength was evaluated with a Con-Trex dynamometer, with the subject seated and the shoulder abducted 45° in the scapular plane. Tests were performed at 180°/s, 120°/s, and 60°/s in concentric mode for both sides. Peak torque normalized to body weight and external rotator to internal rotator ratio were calculated for each angular velocity. Clinical and isokinetic evaluation was done by the same rehabilitation physician.
  
  
  RESULTS
  The association between shoulder instability and internal rotator and external rotator strength was associated with side-to-side differences (p < 0.05). Compared with a control group, strength values were lower on the pathological shoulder side of the patients with shoulder instability than on the healthy contralateral shoulder of control subjects at 180°/s and 120°/s (p < 0.05). The side-to-side differences were increased when the nondominant upper-extremity side was involved and were decreased when the dominant side was involved. There was no association between glenohumeral joint instability and external rotator to internal rotator ratio.
  
  
  CONCLUSIONS
  Internal rotator and external rotator weakness was associated with recurrent anterior instability, and side-to-side differences depended on the side of hand dominance. Use of a control group may help in the analysis of the influence of constraints on shoulder strength. Further prospective studies are necessary to determine whether the weakness is a cause or an effect of the instability.
authors.affiliation: Department of Physical Medicine and Rehabilitation, Laboratory of Exercise Physiology (LPE EA 4338), University Hospital of Saint-Etienne, 42055 Saint-Etienne CEDEX 2, France. Pascal.Edouard42@gmail.com
authors.forename: Pascal
authors.initials: P
authors.lastname: Edouard
authors.forename: Francis
authors.initials: F
authors.lastname: Degache
authors.forename: Laurent
authors.initials: L
authors.lastname: Beguin
authors.forename: Pierre
authors.initials: P
authors.lastname: Samozino
authors.forename: Giorgio
authors.initials: G
authors.lastname: Gresta
authors.forename: Isabelle
authors.initials: I
authors.lastname: Fayolle-Minon
authors.forename: Frédéric
authors.initials: F
authors.lastname: Farizon
authors.forename: Paul
authors.initials: P
authors.lastname: Calmels
mesh_terms: D000293:Adolescent; D000328:Adult; D000704:Analysis of Variance; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D007593:Joint Instability / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D009119:Muscle Contraction / Q000502:physiology; D016059:Range of Motion, Articular / Q000502:physiology; D017006:Rotator Cuff / Q000503:physiopathology*; D012540:Scapula / Q000503:physiopathology; D012783:Shoulder Dislocation / Q000503:physiopathology; D012785:Shoulder Joint / Q000503:physiopathology*