An Anatomical Study of the Trabecular Bone Density Distribution in the Scapula Adjacent to the Glenoid Fossa
Authors: Daalder Matt , Venne Gabriel , Rainbow Michael , Bryant Timothy , Bicknell Ryan T. , MacKenzie Leslie 
Published: November 2023

Purpose

Several orthopaedic surgical procedures performed on the shoulder joint require the fixation of implants by means of screw placement in the scapula. Secure anchoring in adequate bone‐quality is crucial for prosthetic stability. However, loss of implant fixation can occur due to screw loosening. This study examines the anatomic distribution of cancellous bone density in regions of the scapula adjacent to the glenoid available for screw placement.

Method

With approval of IRB, seven cadaveric shoulders were CT scanned at a slice thickness of 0.625mm and reconstructed in 3D using the commercially available image processing software (Mimics 15.0 Materialise, Leuven, Belgium). Volumetric regions of interest (ROI) for potential screw placement sites were identified: base of the coracoid process (lateral and inferior regions of the suprascapular notch), posterior and anterior aspect of the lateral spine and anterosuperior and posteroinferior aspect of the lateral border. Hounsfield Units (HU) values were extracted from voxels of the reconstructed 3D model corresponding to trabecular bone within each ROI. Overall bone density was summarized as the frequency of HU values above 80% of the ROI's maximum density value. Paired, two‐tailed t‐tests assuming unequal variance were used for pairwise comparisons (P≤0.05). Intra‐region analyses compared two ROIs within the same broad anatomical structure; inter‐region analyses compared ROIs between anatomical structures.

Results

Intra‐region comparisons were conducted and evaluated with the following results: base of coracoid P=0.43, spine P=0.95, lateral border P=0.41. Therefore, no significant differences were determined for intra‐regions comparisons.

Inter region comparisons were also conducted and evaluated. Evaluation of the ROI inferior to the suprascapular notch determined this area was on average 3.78% (P=0.08) and 6% (P=0.04) less dense than the anterosuperior and posteroinferior lateral border and 7.59% (P=0.006) and 7.72% (P=0.01) less dense than the anterior and posterior lateral spine. This indicates that the cancellous bone inferior to the suprascapular notch is significantly less dense than that of the spine and lateral border.

Evaluation of the ROI lateral to the suprascapular notch determined this area was on average 6% (P=0.05) and 8.21% (P=0.02) less dense than the anterosuperior and posteroinferior lateral border and 9.8% (P=0.006) and 9.94% (P=0.008) less dense than the anterior and posterior lateral spine. Therefore, the cancellous bone of the ROI lateral to the suprascapular notch is significantly less dense than that of the spine and lateral border.

Finally, there was no significant difference between the anterior spine and anterosuperior and posteroinferior lateral border (P=0.12, P=0.58), nor between the posterior spine and anterosuperior and posteroinferior lateral border (P=0.14, P=0.57). This indicates the spine and lateral border do not have significantly different cancellous bone densities.

Conclusion

Results from this study indicate that the spine and lateral border of the scapula contain denser trabecular bone relative to the base of the coracoid process. Further research should be conducted in the areas studied to determine if screw purchase is increased in these areas of higher cancellous bone quality.

Support or Funding Information

Ryan T. Bicknell: Consulting for DePuy Orthopaedics and Zimmer Inc. Tim Bryant, Michael Rainbow, Ryan T. Bicknell: Research support from DePuy Orthopaedics.