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 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. STUDY DESIGN 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. CONCLUSION 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. CLINICAL RELEVANCE 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.