Abstract: BACKGROUND: There is currently still no absolute standard for internal fixation of plates in the treatment of proximal humerus fractures in clinical practice, but reconstruction of the medial humeral distance and effective resistance to inversion displacement of the humeral head are the key points in achieving strong fixation of proximal humerus fractures.
OBJECTIVE: Finite element analysis techniques were used to obtain the mechanical differences between these three internal fixation modalities acting on proximal humerus fractures and to compare which internal fixation method provides more stable fixation support.
METHODS: A healthy female volunteer was selected to undergo CT scanning of the left shoulder joint, and finite element analysis software was used to construct a model of proximal humerus fracture with medial column support defect. The model was categorized into three groups based on different internal fixation methods. In group A, Philos plate fixation was applied only on the lateral side. In group B, Philos plate fixation was applied on the lateral side combined with miniature straight-locking compression plate fixation on the medial side. In group C, Philos plate fixation was applied on the lateral side combined with miniature straight-locking compression plate fixation on the anterior medial side. The biomechanical stability of these three groups of internal fixation models was evaluated using ANSYS analysis software under the same fixation support and constraint conditions.
RESULTS AND CONCLUSION: (1) The stress of the internal fixation in the three groups of internal fixation models did not exceed 450 MPa. (2) The stress of the humerus and internal fixation in group A was higher than that in groups B and C under different loading conditions, whereas the stress of the humerus and internal fixation in group C was the minimum. (3) Under the flexion loading condition, the relative displacement in group C had a smaller value than that in groups A and B. (4) The relative displacement of the fracture end in group B was the smallest under all the loading conditions. The relative displacement of group B was about half of that of group A under the loading conditions of internal retraction, abduction, and axial compression. (5) The relative displacements between group C and group B were not significantly different, and all of the relative displacements in group C were smaller than those in group A as well. (6) It was found that the combination of the lateral Philos plate and the medial miniature in-line locking compression plate, as well as the combination of the lateral Philos plate and the anterior medial miniature in-line locking compression plate, demonstrated significant stability of the internal fixation system compared with the application of the lateral Philos plate alone. However, when comparing the combination of the lateral Philos plate with the medial miniature in-line locking compression plate and the combination of the lateral Philos plate with the anterior medial miniature in-line locking compression plate, no significant difference in internal fixation system stability was observed. Considering the difficulty of operation in clinical practice, the combination of lateral Philos plate and anterior medial miniature in-line locking compression plate may bring better treatment results in the treatment of proximal humerus fractures. 

中国组织工程研究杂志出版内容重点：人工关节；骨植入物；脊柱；骨折；内固定；数字化骨科；组织工程

Key words: proximal humerus fracture, medial column reconstruction, Philos plate, double plate, finite element analysis