Introduction: Shoulder hemiarthroplasty is an established treatment for complex proximal humeral fractures but the functional results of these hemiarthroplasties in proximal humeral fractures are often poor and unpredictable. The capacity of restoring proximal humeral anatomy in such these complex fractures is of capital importance to obtain proper placement and secure fixation of the tuberosities to the prosthesis. The purpose of this study was to determine the value of the upper edge of the pectoralis major insertion as a landmark to determine proper height and version of hemiarthroplasties implanted for proximal humeral fractures.
Material and Methods: The upper edge of the pectoralis major insertion was referenced with a metallic device in 20 cadaveric humerus. A Computed Tomography study was performed in all the specimens. Total humeral length was recorded in all the specimens. The distance between the upper pectoralis major insertion and the tangent to the humeral head was also recorded. The anatomical neck of the humeral head was determined in the axial plane of the CT scan and a perpendicular line was drawn to represent the posterior fin of the prosthesis. To that image, the CT scan slice showing the upper insertion of the pectoralis major was superimposed and the distance of the metallic reference to the posterior fin of the prosthesis was recorded as it was the angle formed by the line connecting the upper pectoralis major insertion with the center of the anatomical neck diameter and with the posterior fin of the prosthesis.
Qualitative variables are presented in absolute and percentage values. Quantitative variables are presented with mean values and standard deviation.
Results: Mean total humeral length was 32,13 cm. The mean distance from the upper pectoralis major insertion to the tangent to the humeral head was of 5,64. The mean distance from the upper pectoralis major insertion to the tangent to the humeral head represents the 17,55% of the total humeral length. The mean distance of the upper pectoralis major insertion to the posterior fin of the prosthesis was of 1,06 cm. The angle between the upper pectoralis major insertion and the posterior fin of the prosthesis was of 24,65º.
Conclusions: Mean distance from the upper part of the pectoralis major insertion to the top of the humeral head of 5, 6 cm with a 95% confidence interval.
Placement of the prosthesis in the proper retroversion can be achieved by placing the posterior fin 1,06 cm posterior to the upper insertion of the pectoralis major or by placing the posterior fin at 24,65º with respect to the upper insertion line.
Upper insertion of the pectoralis major constitutes a reliable reference to reproduce anatomy in hemiarthroplasties for proximal humeral fractures.
