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Background: It is well known that glenoid osseous defects >13.5% of the glenoid width critically destabilize the shoulder, as do labral tears. Chondrolabral defects often occur with anterior dislocation of the shoulder. It is unclear whether glenoid chondrolabral defects contribute to shoulder stability and, if so, at what size they become critical. Purpose/Hypothesis: The purpose of this study was to determine the effect of incremental chondrolabral defect sizes on anterior shoulder stability in the setting of labral deficiency. The hypothesis was that chondrolabral defects ≥13.5% of the glenoid width will decrease anterior shoulder stability. Study Design: Controlled laboratory study. Methods: This controlled laboratory study tested 12 fresh-frozen shoulders. Specimens were attached to a custom testing device in abduction and neutral rotation with 50-N compression applied to the glenoid. The humeral head was translated 10 mm anterior, anteroinferior, and anterosuperior with the conditions of intact cartilage and labrum and anterior full-thickness chondrolabral defects of 3-, 6-, and 9-mm width. Translation force was measured continuously. Peak translation force divided by 50-N compressive force defined the stability ratio. Data were analyzed using analysis of variance. Results: The anterior stability ratio decreased between the intact state (36% ± 7%) and all defects ≥3 mm (≤32% ± 8%; P ≤ .023). The anteroinferior stability ratio decreased between the intact state (52% ± 7%) and all defects ≥3 mm (≤47% ± 7%; P ≤ .006). The anterosuperior stability ratio decreased between the intact state (36% ± 4%) and all defects ≥6 mm (≤33% ± 4%; P ≤ .006). A 3-mm defect equated to 10% of the glenoid width. There were moderate to strong negative correlations between chondrolabral defect size and stability ratio in the anterior, anteroinferior, and anterosuperior directions ( r = –0.79, –0.63, and –0.58, respectively; P ≤ .001). There were moderate to strong negative correlations between the percentage of glenoid chondrolabral defect size to the glenoid width and the stability percentage in all directions ( r = –0.81, –0.63, and –0.61; P ≤ .001). Conclusion: An anterior glenoid chondrolabral defect ≥3 mm (>10% of the glenoid width) significantly decreased anterior and anteroinferior stability. Chondrolabral defect size negatively correlated with stability. Clinical Relevance: To fully restore glenohumeral stability, in addition to labral repair, it may be necessary to reconstruct chondrolabral defects as small as 3 mm (10% of the glenoid width).

In vitro simulation of 3D shoulder motion using in vivo kinematics obtained from human subjects allows investigation of clinical conditions in the context of physiologically relevant biomechanics. Herein we present a framework for laboratory simulation of subject-specific kinematics that combines individual 3D scapular and humeral control in cadavers. The objectives were to: 1) robotically simulate 7 healthy subject-specific 3D scapulothoracic and glenohumeral kinematic trajectories in 6 cadavers, 2) characterize system performance using kinematic orientation accuracy and repeatability, and muscle force repeatability metrics and 3) analyze effects of input kinematics and cadaver specimen variability. Using an industrial robot to orient the scapula range of motion (ROM), errors with repeatability of ±0.1 mm and <0.5° were achieved. Using a custom robot and a trajectory prediction algorithm to orient the humerus relative to the scapula, orientation accuracy for glenohumeral elevation, plane of elevation, and axial rotation of <3° mean absolute error was achieved. Kinematic accuracy was not affected by varying input kinematics or cadaver specimens. Muscle forces over 5 repeated setups showed variability typically <33% relative to the overall simulations. Varying cadaver specimens and subject-specific human motions showed effects on muscle forces, illustrating that the system was capable of differentiating changes in forces due to input conditions. The anterior and middle deltoid, specifically, showed notable variations in patterns across the ROM that were affected by subject-specific motion. This machine provides a platform...(truncated to fit word count, missing text in main PDF includes R2 changes).

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.