Biomechanical Study Of Artificial Metacarpophalangeal Joint Replacement

Objective:The domestic expert team designed a new type of metacarpophalangeal joint prosthesis,which adopts the design of articular surface contact and threaded shank fixation,in order to reduce the risk of the fracture of the prosthesis and the surrounding fracture and ensure the stable fixation of the prosthesis.This experiment intends to analyze the biomechanical properties of the prosthesis by means of three-dimensional finite element analysis,and to verify the effectiveness of the design scheme by comparing the biomechanical properties of the new prosthesis and Swanson prosthesis.Methods:1.Establish the 3d finite element model of the third metacarpophalangeal joint:A functional high-resolution CT scan of the right hand of a healthy adult male,import the acquired CT data into the Mimics software,the 3d model of the third metacarpophalangeal joint was established.The model was imported into Geomogic Studio2013 for fine processing,and the results were imported into Ansys12.0 software.The 3d finite element model of the third metacarpoparangeal joint was established after material assignment and other operations.2.Three-dimensional finite element model of two kinds of prostheses was established:The design data of the new metacarpophalangeal joint prosthesis was imported into Geomogic Studio2013.After a series of fine processing,the obtained data results were imported into Ansys12.0.After grid division and other operations,the 3d finite element model of the new metacarpophalangeal joint prosthesis was established.The Swanson prosthesis was accurately measured,and the measurement results were input into Ansys12.0.The three-dimensional finite element model of Swanson prosthesis was established through the Workbench module of the software.3.The three-dimensional finite element model of the two prostheses was analyzed as follows:The new metacarpophalangeal joint prosthesis and Swanson prosthesis were matched with the 3d finite element model of the third metacarpophalangeal joint according to the surgical method of each prosthesis joint replacement.With the base of the third metacarpal bone as the fixed point,a 200 Nload parallel to the long axis of the phalanx was applied to the distal end of the proximal phalanx of the middle finger.The stress values of the metacarpophalangeal joint at the rotation center of the prosthesis at different flexion and extension angles were calculated.The shear force and relative displacement of the metacarpophalangeal joint after the replacement of the two prostheses were calculated under different loading conditions.Results:(1)By using Mimics,Geomogic Studio2013,Ansys12.0 software and high-resolution CT data,a high-precision three-dimensional finite element model of the third metacarpoparangeal joint was established.The design data of the new metacarpophalangeal joint prosthesis were imported into Geomogic Studio2013,and the data were imported into Ansys12.0 software after refined processing,and the finite element model of the new metacarpophalangeal joint prosthesis was established.The finite element model of Swanson prosthesis was built in the Workbench module using the accurately measured Swanson prosthesis data.(2)Under the load of 200 N,the stress centers of Swanson prosthesis shifted from 90° flexion to 50° dorsiflexion,while the stress concentration of the new metacarpophalangeal joint prosthesis always appeared at the joint surface.The stress at the center of rotation of the new metacarpophalangeal prosthesis was consistently lower than that of the Swanson prosthesis in the range of 90° flexion to 50°dorsiflexion.Under the same vector load,Swanson prosthesis showed significant sliding displacement in the medullary cavity,while the new metacarpophalangeal joint prosthesis did not show significant sliding displacement in the medullary cavity.Conclusion:The new metacarpophalangeal joint prosthesis has better biomechanical properties than Swanson prosthesis.It can move freely in the normal range of joint flexion and extension.In the range of motion,the stress concentration area mainly occurs at the joint surface,and the threaded design of the prosthesis allows the prosthesis to be firmly fixed in the medullary cavity.New threaded shank metacarpophalangeal prosthesis can provide a new option for metacarpophalangeal joint replacement.