Trabecular Bone Density Distribution in the Scapula of Patients Undergoing Reverse Shoulder Arthroplasty

Background

To improve implant survival following reverse shoulder arthroplasty (RSA), surgeons need to maximize screw fixation. However, bone density variation and distribution within the scapula is not well understood as it relates to RSA. The three columns of bone in the scapula surrounding the glenoid fossa are the lateral border, the base of the coracoid process, and the spine of the scapula. In our previous study by Daalder et al on cadaveric specimens, the coracoid column was significantly less dense than the lateral border and spine. This study’s objective was to verify whether these results are consistent with CT scan information from patients undergoing RSA.

Methods

Two-dimensional axial computer tomography (CT) images from twelve patients were segmented, and a three-dimensional digital model of the scapula was subsequently created using Mimics 17.0 Materialise Software (Leuven, Belgium). Hounsfield Unit (HU) values representing cortical bone were filtered out to determine the distributions of trabecular bone density. An analysis of variance with post hoc Bonferroni tests determined the differences in bone density between the columns of bone in the scapula.

Results

The coracoid superolateral (270 ± 45.6 HU) to the suprascapular notch was significantly less dense than the inferior (356 ± 63.6 HU, p=0.03, ds=1.54) and anterosuperior portion of the lateral border (353 ± 68.9 HU, p=0.04, ds=1.42), and the posterior (368 ± 70 HU, p=0.007, ds=1.65) and anterior spine (370 ± 78.9 HU, p=0.006, ds=1.54).

Discussion/Conclusion

The higher-density bone in the spine and lateral border compared with the coracoid region may provide better bone purchase for screws when fixing the glenoid baseplate in RSA. This is in agreement with our previous study and indicates that the previous cadaveric results are applicable to clinical CT scan data. When these studies are taken together, they provide robust evidence for clinical applications, including having surgeons aim screws for higher density regions to increase screw fixation, which may decrease micromotion and improve implant longevity.