The application of bone cement to partial head screws or metaphyseal defects to enhance the fixation system's stability is effective in treating proximal humeral fractures. In addition, relevant studies have shown that bone cement material will not cause damage to bone or cartilage. This paper presents an anatomic intramedullary supporting bone cement placeholder designed according to the intramedullary geometry of the proximal humerus to support the humerus head and compensate for the absence of the medial column. It can be simulated and fabricated before surgery, inserted into the marrow cavity through the fracture window, attached to the medial cortex, and supported by the medial column. Based on previous clinical trials, we speculated that cement intramedullary support spacers could provide more substantial medial column support than intramedullary fibula support, and their mechanical properties were more similar to those of anteromedial plates. At the same time, they would not increase the risk of intraoperative nerve and vascular injury due to excessive stripping of medial soft tissue.

To compare the biomechanical characteristics of fibula, columnar cement, and anatomic cement spacer combined with locking plate in treating proximal humerus fractures with disrupted medial column instability by finite element analysis.

After establishing a three-dimensional finite element model of proximal humerus fracture with disrupted medial column instability, lateral locking plate (LLP) , lateral locking plate combined with fibular shaft allograft (LLP-FS) , and lateral locking plate combined with column cement spacer (LLP-CC) , lateral locking plate combined with anatomic cement spacer (LLP-AC) , and lateral locking plate combined with medial reconstruction plate (LLP-MRP) different internal fixation systems were implanted for assembly. Under normal and osteoporotic conditions, abductive, adductive, flexion, axial compression, and rotational loads were applied to the models. The biomechanical properties were evaluated and compared by comparing the structural strength, the maximum stress and stress distribution of the internal fixators, and the vertical displacement in the fracture region.

Compared with the LLP group, the biomechanical properties of the LLP-FS, LLP-CC, and LLP-AC were improved to different degrees. Compared with the other two methods of intramedullary support, the overall structural stiffness of the LLP-AC group was significantly higher under various loads, the maximum stress in the plant was smaller, the stress distribution was more uniform, and the vertical displacement in the fracture region was minimal. Its biomechanical properties are closer to or even better than the LLP-MRP group.

From the perspective of finite element, an anatomic cement intramedullary support spacer can provide a solid and practical medial column support, which can better disperse the stress on the lateral locking plate and enhance the biomechanical properties of the lateral locking plate fixation system. Anatomic cement intramedullary support spacer combined with a lateral locking plate can effectively treat proximal humerus fractures with disrupted medial column instability.