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

Abstract

Background: 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.

Methods: 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.

Results: 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).

Conclusion: 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.

Keywords: Glenoid inclination; Glenoid fossa; Glenoid labrum; Soft tissue compensation; Glenoid surface; Passive shoulder stability.

Figure 1

Multiplanar image reformatting was performed to obtain a standardized coronal plane aligned to the scapular axis and the longitudinal axis of the glenoid (yellow line on sagittal view). The defined coronal plane passes through the center of the best fitting circle of the lower glenoid. The glenoid plane was defined (red line) to enable an en-face view of the glenoid in sagittal scans.

Figure 2

Measurements for (a) bony glenoid inclination, (b) glenoid surface inclination, (c) bony glenoid concavity depth, (d) glenoid surface concavity depth, (e) radius of the bony glenoid, (f) radius of the glenoid surface.

Figure 3

In this figure, the Pearson correlation between bony glenoid inclination and its angle difference to glenoid surface inclination is depicted. An increase in superior bony glenoid inclination is associated with an increase in difference between bony and surface inclination angles.

Figure 4

This figure shows the Pearson correlation between bony glenoid radius of curvature and its radius difference to the glenoid surface radius. Similarly to bony inclination, an increase in bony glenoid radius of curvature is associated with an increase in difference between bony and surface radius of curvature.

Figure 5

This image shows the X-ray and MRI scan of the shoulder of a 10-year-old individual. While the underlying bony glenoid is flat-shaped with pronounced superior inclination, the cartilage forms a concave articular surface of the glenoid fossa and neutralizes the inclination angle together with the superior labral complex. MRI, magnetic resonance imaging.