title: Factors Expressed in an Animal Model of Anteroinferior Glenohumeral Instability.
abstract: BACKGROUND
  There is little information on the molecular factors important in healing and changes that occur in the glenoid labrum in response to injury. Using a novel animal model of acute anterior shoulder dislocation, this study characterizes the factors expressed in the glenoid labrum in response to injury and correlates their expression to glenohumeral stability.
  
  
  OBJECTIVE
  To study the response of the glenoid labrum to injury both biomechanically and with immunohistochemical testing.
  
  
  METHODS
  An injury to the anteroinferior labrum was surgically induced in 50 male Lewis rats. Rats were sacrificed at 3, 7, 14, 28, or 42 days. Immunolocalization experiments were performed to localize the expression of growth factors and cytokines. For biomechanical testing, dynamic stiffness for anterior and posterior laxity, load to failure, stiffness, and maximum load were recorded. Statistical differences were determined at P < .05.
  
  
  METHODS
  Descriptive laboratory study.
  
  
  RESULTS
  Expression of interleukin-1 beta (IL-1β), transforming growth factor-beta 1 (TGF-β1), matrix metalloproteinase 3 (MMP3), and matrix metalloproteinase 13 (MMP13) were increased in injured compared with uninjured specimens. Collagen III expression was increased early and decreased with time. Biomechanical testing verified instability by demonstrating increased anterior displacement and decreased stiffness in injured shoulders at all time points.
  
  
  CONCLUSIONS
  This novel animal model of acute anterior shoulder dislocation showed increased expression of IL-1β, TGF-β1, MMP3, MMP13, and collagen III in the injured labral tissue at early time points. Increased anterior laxity and decreased stiffness and maximum load to failure were seen after anterior labral injury, supporting the model's ability to re-create anterior glenohumeral instability. These data provide important information on the temporal changes occurring in a rat model of anterior glenohumeral dislocation.
  
  
  CONCLUSIONS
  Identification of factors expressed in the anterior capsule and glenoid labrum in response to injury may lead to the development of novel agents that can be used to augment glenoid labrum healing and ultimately improve both surgical and nonsurgical treatment of this common shoulder injury.
authors.affiliation: Drexel University College of Medicine, Philadelphia, Pennsylvania, USA.
authors.forename: Mary K
authors.initials: MK
authors.lastname: Mulcahey
authors.affiliation: EpiVax Inc, Providence, Rhode Island, USA.
authors.forename: Mindy
authors.initials: M
authors.lastname: Marshall
authors.affiliation: Yale University School of Medicine, New Haven, Connecticut, USA.
authors.forename: Stacey E
authors.initials: SE
authors.lastname: Gallacher
authors.affiliation: OrthoNY, Albany, New York, USA.
authors.forename: Lee A
authors.initials: LA
authors.lastname: Kaback
authors.affiliation: Yale University School of Medicine, New Haven, Connecticut, USA.
authors.forename: Theodore A
authors.initials: TA
authors.lastname: Blaine
keywords: animal model; anterior shoulder dislocation; biomechanical testing; cytokines; glenoid labrum; growth factors; shoulder instability