| By the method of experimental biomechanics and computed biomechanics, the biomechanical foundation of Proximal Humerus Memory Connector(PHMC) was studied,which are made of nitinol and used for treating fractrure, nonunion and malunion of proximal humerus. The clinical significance of three-dimensional fixation, dynamically memorial stress for treating fractures, nonunion,malunion of proximal humeral was discuss.Methods: By electrometric mothod and three-dimensional finite element analysis, the study was perfermed. Electrometric method: By pasting gauge, standardization , load-strain curve was got, then dynamically memorial holding force of PHMC for fixing proximal humerus was calculated. Three-dimensional finite element analysis: The PHMC and proximal humerus was analyzed by ANSYS. And the procedure of PHMC fixating the proximal humerus was imitated. The finite element model of PHMC was divided into57231 elements, the number of nodes was33174 , the element was three-dimensional brick unit with 20 nodes, 4faces. The finite element model of proximal humerus was divided into52524 elements, the number of nodes was 77234 , the element was three-dimensional unit with 10 nodes. Clinically, the PHMC was applied in 22 cases, including fractures, nonunion and malunion of proximal humerus. The mean following-up time was 18.5 months.Results: Electrometric method:The continuously memorial holding force of PHMC was 12.51kg; Three-dimensional finite element analysis: The PHMC was come in for tension force on its internal face , and pressure force on its external face when it fixated the proximal humerus. The first structrue maximum stress value was 136.2Mpa and -16Mpa, which was much less than its ultimate stress and fatigue limit. The dynamically memorial holding force for maintaining axial direction was 127.75N ,which was coincident with the results of electrometric method, and the longitudinally dynamically compressive force was 184N. The stress distributed on the surface of the proximal humerus was even, and the stress of every node was positive chiefly. The clinical results indicated that the bone healing time was even 3.6 months for the fracture cases and 4.5 months for the nonunion cases. The healing style was characterized by plate bone substitution, no disordering callus was observed. After internally fixated by PHMC, no external fixation was needed, and the patients began to do active exercises 7 to 12 days after operation. The function of the shoulder was scored average 88.5 points according to the criteria of Michael Reese rating system. Conclusion: 1) PHMC is safe to use and has good repeatability. 2) The multiple points fixation of PHMC when it connects the nonstandard "tubular bone" is good for the blood supply, and the overall stress distribution is helpful to the fixation and stability of graft bones. 3) Each part of PHMC joints each other, harmonizes with each other, takes charge of each function. Thus overcomes the disadvantages of plates and screws which are non-integrity effecting components, and forms three-dimensitonal fixation stress fields, which provides enough stability. Therefore, no external fixation is needed after operation and early functional execise is feasible. 4) The unique body compressive part of PHMC produces compressive force at the fracture site, which will not disappear with the absorption of fracture line. This continuous compressive force prompts fracture healing. The stress field at the fracture site which is dynamic, memorial, and compressive, and the positive in chief character of stress may be the biomechanical basis of "anatomic" plate substitute characterized by "no callus, no stress shielding effects".5)The PHMC can provide enough stability for the fractures of proximal humerus.6) PHMC was an efficacious method to treat every type fractures and nonunion of the region from anatomical neck to the diaphysis part of humerus, and a new way was explored to reduce the rate of prostheses displacement of this part.
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