Regional bone density variations in osteoarthritic glenoids: A comparison of symmetric to asymmetric (type B2) erosion patterns

Background: Accurate characterization of regional variations in bone density in symmetric and asymmetric (B2) glenoid erosion patterns can assist with surgical planning, reaming, and component implantation. The purpose of this study was to characterize regional bone density and porosity in symmetric and asymmetric (B2) osteoarthritic glenoids. Methods: Symmetric (n=25) and asymmetric (B2) (n=25) erosion patterns were compared by computed tomography-based imaging software. An orthogonal coordinate system separated each glenoid into quadrants. In addition, a linear best-fit line defined the line-of-erosion between the paleoglenoid and neoglenoid in the asymmetric cohort. All glenoids were further divided into volumes at depths of 0 to 2.5mm and 2.5 to 5mm. Average bone density was measured in Hounsfield units. Bone voids or cysts were included to quantify regional porosity as the fraction of void volume to total glenoid volume. Results: For the symmetric cohort, there were no significant differences in bone density between quadrants at either depth (. P≥.089). For the asymmetric cohort, bone density was significantly higher in the posterior quadrants compared with the anterior quadrants (. P<.001), especially posteroinferiorly (. P≤.007) at both depths. In addition, the neoglenoid had significantly higher density and lower void fraction compared with the paleoglenoid (. P<.001). There were also significant differences in void fraction between quadrants for both cohorts, at both depths (. P≤.004). Conclusions: This study demonstrates that osteoarthritic glenoids with symmetric erosion have uniform subarticular bone density. However, asymmetric (B2) erosion patterns have potentially important regional variations in bone density and porosity, with the densest bone with the least porosity found posteroinferiorly or in the neoglenoid region.