The Design, Manufacture And Biomechanical Study Of Individulized Metacarpophalangeal Prothesis Made Of Titannium Alloy

Many diseases such as rheumatoid arthritis, retrogression osteoarthritis, and suppuration osteoarthritis, and injuries could cause pain, abnormity and rigor of hand joints which leading to the lose of hand function. The therapeutic methods to the impaired hand joints in advanced stage include arthroplasty, joint transplantation and prosthetic joint replacement et al. Each method has its indication, the site and the degree of the damage severity of the joint, the age, profession and the financial state of the patient all should be considered.Prosthetic joint replacement has developed for nearly half century. An ideal prosthetic joint can keep the stability and recover the movement of the joint. The abnormity and appearance can also be improved and the pain be relieved at the same time. In the early stage, the effect of prothetic joint replacement was not ideal because of the limitation of the design and the material, and the complications were common.At present, there are 4 models of prothetic joint: linked and constrained, non- constrained, spacer and anatomical shape designs. They all have advantages and disadvantages. As the study of the anatomy and biomechanic of the joint and the design of the prothetic improves and the new bio-material appears, a combination of the three recent developments may open up a new direction in the design of finger joint prosthesis.Objective: To design and manufacture a new individualized prothetic MP joint made of titanium alloy by utilizing CT data and CAD technique. The metacarpophalangeal (MP) prothesis has intramedullary stem that matched individual metacarpal cavity size. The biomechanic characters of the new prothesis will also be tested.Methods: (1) A cadaver hand were scanned with spiral Siemens CT machine.The transaxial 2D image data of digitus metacarpophalangeal joint were reconstructed into 3D digitized contour data by 3DMSR software. Then the individulized metacarpophalangeal prothesis which matched intramedullary cavity size was designed by using Surface9.0 software. (2) The resina model was constructed by FS-320QZ rapid prototyping machine. Combining the resina model and the advanced casting technology, an individulized titannium alloy metacarpophalangeal prothesis was made by fusing model, making corona, calcinating, embedding, spraying and casting. (3) Biomechanic study: The experimental specimens were divided into three groups. Group A included the cavaders of which the MP joints were replaced by individulized titannium alloy prothesis; Group B was the same except the MP joints were replaced by Swanson prothesis; Group C was normal comparative group. Every group included 5 hands. The load was exerted to each specimen by CSS-44020 machine with vertical loading of 50N, 100N, 150N, 50N, 300N, 350N, the straining changes of metacarpal and phalanx bone were oberserved. The loading-straining curves were also drawn. The biomechanics behavior of individulized Titannium alloy prothesis, Swanson prothesis and normal metacapophalangeal joints were analysized and compared.Results: (1) Clear 2D image data after CT scanning were obtained. Then 3D image was reconstructed by 3DMSR. Surface9.0 software was utilized to design individualized intramedullary stem that was matched size of intramedullary cavity. Those were inverted STL data that could be input to rapid prototyping machine. (2) After STL data were inverted into rapid prototyping machine, we gained resina model of individualized metacarpophalangeal prothesis. Individualized titannium alloy metacarpophalangeal prothesis after a series of casting methods were got. (3) The straining changes were increased of metacarpal and proximal phalanx bones as soon as loadings on them were increased. The straining changes of metacarpal bones were larger than proximal phalanx bones of different loading. They all had"platform"period. When the straining changes of B group were contrasted to A, C group, significant difference (P<0.01) was observed as soon as the straining was larger than 100N. The straining changes of A group contrast toC group had no difference (P>0.05).Conclusion: (1) Individulized metacarpophalangeal prothesis that matched anatomical shape conveniently and rapidly based on CT and CAD can be designed. Meanwhile, these data can be inverted STL data that can be input into rapid prototyping machine. (2) Individulized titannium alloy metacarpophalangeal prothesis with material titannium alloy through rapid prototyping and casting technique can be casted. (3) Biomechanics methods by mechanics machine to simulate individulized titannium alloy metacarpophalangeal prothesis, Swanson prothesis and metacarpophalangeal joints to metacarpal and phalanges bones are used. So we can prove superiority of individulized titannium alloy metacarpophal-angeal prothesis that matched anatomical shape of metacarpophalangeal joints.