Original Research Factors Expressed in an Animal Model of Anteroinferior Glenohumeral Instability

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. Purpose: 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 bio-mechanical testing, dynamic stiffness for anterior and posterior laxity, load to failure, stiffness, and maximum load were recorded. Statistical differences were determined at P <.05. Study Design: Descriptive laboratory study. Results: Expression of interleukin–1 beta (IL-1b), transforming growth factor–beta 1 (TGF-b1), 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. Conclusion: This novel animal model of acute anterior shoulder dislocation showed increased expression of IL-1b, TGF-b1, MMP3, MMP13, and collagen III in the injured labral tissue at early time points. Increased anterior laxity and decreased stiffness andmaximu