Paper 06: The Effect of Anterior Glenoid Cartilage Defects on Anterior Glenohumeral Instability: A Biomechanical Study

OBJECTIVES: While it is well-known that a glenoid osseous defect of >25% glenoid width or 20% of the glenoid length critically destabilizes the shoulder, it is unclear whether glenoid cartilage defects contribute to the shoulder stability, and if so at what size defect the shoulder is critically destabilized. The purpose of this study was to determine the effect of incremental cartilage defect sizes on the anterior shoulder stability. We hypothesized that cartilage defects of equal to or greater than 25% of the glenoid width or 20% of the glenoid length will significantly the decrease the anterior shoulder stability ratio. METHODS: This was a controlled laboratory study testing 12 fresh-frozen shoulders. Specimens were attached to a custom testing device in abduction and neutral rotation with 50N compression applied to the glenoid. The humeral head was translated 10 mm anteriorly, anteroinferiorly, and anterosuperiorly with conditions of intact cartilage and labrum and anterior cartilage defects of 3, 6, and 9 mm width. Translation force was measured continuously. Peak translation force divided by 50 N compression force was defined as the stability ratio. Data were analyzed using ANOVA tests. RESULTS: In the anterior direction, the stability ratio decreased between intact cartilage (36±7%) and all defects 3-mm or larger (32±8%, p=0.023.) In the anteroinferior direction, the stability ratio decreased between intact cartilage (52±7%) and all defects 3-mm or larger (47±7%, P=0.006). In the anterosuperior direction, the stability ratio decreased between intact cartilage (36±4%) and all defects larger than 6-mm (32.6±4%, P = 0.006.) A 3-mm cartilage defect was equivalent to 10% of the glenoid width and 7% of the glenoid length. There were strong negative correlations between the glenoid cartilage defect size and the stability ratio in the anterior direction, the anteroinferior direction and the anterosuperior direction (r= -0.79, -0.63, and -0.58, respectively, P≤0.001). There were strong negative correlations between the ratio of glenoid cartilage defect size to the glenoid width and the stability ratio in all directions (r= -0.81, -0.63, and -0.61, respectively, P≤0.001.) CONCLUSIONS: An anterior cartilage defect of >3 mm or >10% of the glenoid width or 7% of the glenoid length significantly decreases anterior and anteroinferior stability and may require further treatment to restore stability. Cartilage defect size negatively correlates with stability.