Bone densities in type E3 glenoids: quantitative assessments and topographical distributions

Favard E3 type glenoids are characterized by superior and global erosion patterns and can be successfully treated with reverse total shoulder arthroplasty. However, with severe bone loss, implant loosening remains a concern. Since little is known about the regional density variations of Favard type glenoids, this study analyzed E3 types from central to peripheral regions of the glenoid. The study worked with the following hypotheses: First, that regional variations of cortical as well as trabecular bone densities of E3 type glenoids exist; second, that a novel three-dimensional orientational grid can assess and show significant variability in topographical density distributions from central to peripheral regions of the glenoid; third, that the density distributions of E3 types correlate with their erosion pattern. This study used computer tomography scans of 28 patients (5 males, 23 females, mean age 78) that were classified as E3 type glenoids by an experienced shoulder surgeon. A novel three-dimensional grid of 40 different segments, combining quadrants (superior, anterior, posterior, and inferior) as well as 10 concentric rings with a single depth layer of 18 mm into the glenoid vault, mapped the glenoid bone density variations in fine detail. A mixed repeated-measures multiple analysis of variance was conducted to assess the variations in bone density between each quadrant, ring, and bone type (either cortical or trabecular). The results showed that both cortical as well as trabecular bone densities peaked in the periphery (ie, in rings 8 and 9) of the superior-anterior glenoid regions (P < .001) and conversely showed low densities in the periphery of inferior-posterior glenoid regions (P < .001). Greater bone densities in the periphery of the superior-anterior regions in type E3 glenoids suggest that joint loading occurs preferentially in these areas. These density results therefore only partially coincide with the Favard E3 type erosion description. The density data may also help optimize future implant designs that leverage these high-density regions. Anchoring augmented baseplates in adequately dense bone at time-zero has shown to decrease implant loosening, minimizing the likelihood of surgical revisions by improving fixation and reducing micromotion. Also, the three-dimensional grid can be used to revisit other Favard subtypes to compare and correlate densities to gain further insight into the pathophysiology of cuff tear arthropathy.