While the bony glenoid is superiorly inclined, the glenoid surface is not

The labral complex plays a crucial role in shaping the glenoid fossa morphology, thereby enhancing passive joint stability. This study aimed to investigate the influence of the labrum on glenoid inclination, a key determinant for load distribution within the joint. In addition, the labral influence on glenoid concavity depth and radius of curvature in the supero-inferior plane was evaluated.

Forty-three patients (mean age: 42 years [range 21-64 years]; 35 males, 8 females) with acromioclavicular (AC)-joint dislocation and no glenohumeral pathologies, who received a full series of magnetic resonance imaging or magnetic resonance arthrography, were retrospectively included. For each patient, the glenoid surface inclination, concavity depth, and radius of curvature was measured and compared to their respective values of the bony glenoid. In addition, the bony humeral head radius was measured to evaluate the influence of the labrum on joint congruency. Paired t-tests were used to assess the differences between bony and glenoid surface inclination and concavity depth. Repeated measures analysis of variance and pairwise comparisons were made to compare radius of curvature measurements. The correlation between the bony glenoid inclination and its difference to glenoid surface inclination, as well as between the bony glenoid radius and its difference to glenoid surface radius, was analyzed.

The bony glenoid inclination measured 7.1° ( ± 4.1° standard deviation [SD]), the glenoid surface inclination 1.6° ( ± 3.2° SD); the bony glenoid concavity depth measured 4.0 mm ( ± 0.8 mm SD), the glenoid surface concavity depth 7.1 mm ( ± 0.9 mm SD). The bony glenoid radius of curvature measured 33.4 mm ( ± 3.3 mm SD), the glenoid surface radius 25 mm ( ± 2.1 mm SD) and the humeral head radius 24.1 mm ( ± 1.7 mm SD). The labrum significantly decreased the glenoid fossa inclination by 5.5° (P < .001), significantly decreased the glenoid fossa radius by 8.4 mm (P < .001) and significantly increased the concavity depth by 3.2 mm (P < .001). There was a positive correlation between the bony glenoid inclination and its respective difference to the glenoid surface inclination (r = 0.71, P < .001). Also, there was a positive correlation between bony glenoid radius of curvature and its respective difference to the glenoid surface radius (r = 0.77, P < .001).

The labral complex decreases glenoid inclination and increases joint concavity and congruency in the supero-inferior plane. Differences between bony and surface glenoid measures were higher in individuals with increased superior bony inclination and larger bony radii, suggesting a compensatory role to the labrum for the underlying bony morphology.