Attachments of muscles as landmarks for implantation of shoulder hemiarthoplasty in fractures

Repositioning of the humeral tuberosities can be guided by pectoralis major insertion

In complex proximal humerus fractures, positioning of the tuberosities can be a challenge. This study demonstrates the constant angle between the pectoralis major (PM) and the medial lip of the bicipital groove (BG) on the horizontal axial plane. This angle can be used to determine the rotation, as well as the positioning of the tuberosities, when planning a hemiarthroplasty or a reconstruction. Thirty-one shoulder MRIs were reviewed by three independent observers. The measurements were taken by superposing the axial cut of the proximal humerus, at the level of the distal bicipital groove, and the cut at the top of the PM insertion. By aligning the centers of rotation, we could determine the arcs of rotation between the insertion of the PM and the lips of the medial and lateral bicipital groove (MBG and LBG). Both angles were compared in terms of reliability, reproducibility, and precision. The mean PM-MBG angle was 3.7° [standard deviation (SD) 14.7°] and 27.4° (SD 14.4°) for the PM-LBG angle. We obtained good and very good intra-class correlation coefficient (ICC) results for inter- (0.675) and intra-observer (0.793) reliabilities on the medial angle, plus excellent results for the lateral angle (inter-observers 0.962 and intra-observer 0.895). This study demonstrates that the repositioning of humeral tuberosities can be guided by pectoralis major insertion. This will help achieve proper positioning of the metaphysis in relation to the diaphysis during surgery for complex proximal humerus fractures.

Three-dimensional analysis of the orientation and the inclination of the rotator cuff footprint

HYPOTHESIS

The tuberosities of the proximal humerus relate geometrically to the humeral head in an anteroposterior symmetry.

MATERIAL AND METHODS

Twenty-eight cadaveric shoulders were scanned with computed tomography and reconstructed digitally in 3 dimensions. On both tuberosities, 5 facets were identified. An orthogonal planar system using the center of the humeral head as its origin was created to calculate the coordinates of the centre of each facet. The angular position of the center of each facet was measured with reference to the sagittal plane. The inclination of each facet was measured to the axial plane.

RESULTS

The presence of 5 distinct facets with a different inclination was confirmed (lesser tuberosity: inferior facet: 77.8° [sd 7.8°]; superior facet: 50.3° [sd 9.3°] - greater tuberosity: superior facet: 20.4° (sd 5.6°); middle facet: 48.6° (sd 5.2°); inferior facet: 92.7° [sd 7.7°]). The angular position of the centers of the facets was less variable (lesser tuberosity: inferior facet: 22.6° [sd 4.3°]; superior facet: 39.2° [sd 4.4°] - greater tuberosity: superior facet: 89.9° [sd 5.9°]; middle facet: 131.6° [sd 6.1°]; inferior facet: 155.1° [sd 6.8°]).

CONCLUSION

Our study contributes to the knowledge of the anatomy of the proximal humerus, more specifically of the position of the rotator cuff insertion in relation to the humeral head. These insights are useful in the development of shoulder trauma prostheses.