Three Dimensional Finite Element Analysis Of New Unrestrictive Interphalangeal Joint Prosthesis

Objective:At present,there is a new type of unrestrictive interphalangeal joint(IP)prosthesis in the design and development stage.This study intends to analyze the biomechanical characteristics of its unique sleeve fixation device by using the preliminary design drawing of this prosthesis and the three-dimensional finite element analysis method,so as to test the safety of its design.The clinical feasibility of the new type of prosthesis was evaluated by comparing the stability of the new type of prosthesis with Swanson prosthesis in various states.Methods:The finite element model of the new IP prosthesis was established by using the design drawing of point cloud format;The finite element model of Swanson prosthesis was established by measuring the data of Swanson prosthesis with vernier calipers;The finite element model of the proximal interphalangeal joint of the middle finger was established by CT images of the hands of healthy men.The 3D finite element model of the proximal interphalangeal joint after the replacement of two joint prostheses was established for the subsequent calculation and analysis by using the simulated assembly of Ansys 12.0 software.The base of the proximal phalanx of the middle finger was set as the fixed point,and a load parallel to the axis of the middle phalanx and pointing toward the proximal end of the limb was applied to the distal end of the middle phalanx of the middle finger.The load was gradually increased with a gradient of 50 N from 50 N.The maximum stress value of the new IP prosthesis under different loads at different flexion angles was calculated.A load perpendicular to the middle phalanx and pointing to the dorsal side of the hand was applied to the middle phalanx,and the load was gradually increased with a gradient of 40 N from40N.The maximum displacement of the new IP prosthesis and Swanson prosthesis under different loads at different flexion angles was calculated.Results:The maximum stress value of the new joint prosthesis will increase with the increase of the load applied to the distal part of the middle phalangeal bone,parallel to the axis of the middle phalangeal bone and pointing to the proximal end of the limb.When the flexion angle of the joint increases,the stress value will gradually decrease.In this experiment,the maximum stress peak of the new IP prosthesis onlyoccurs when the prosthesis is subjected to 300 N axial load in neutral position,with the increase of flexion angle,the overall stress distribution of the prosthesis migrated to the joint contact surface,the overall stress gradually decays to both ends of the prosthesis,prosthesis sleeve fixture parts contact with finger will gradually reduce the value of the maximum stress,this suggests that patients with the new prosthesis are more likely to have a safe hand grip in their daily life after surgery.The maximum displacement of the new IP prosthesis and Swanson prosthesis increased with the increase of joint motion angle and joint load.The peak of the maximum displacement of the two prostheses occurred when the interphalangeal joints buckled at 90° and the joints were subjected to a load of 200 N.Under the same condition(the joint moves at the same Angle and receives the same load),the maximum displacement of the new IP prosthesis was significantly smaller than that of Swanson prosthesis,and the difference was statistically significant(p < 0.05).When the new IP prosthesis performed flexion and extension under the maximum load of 200 N,only a small displacement of the prosthesis occurred,showing a good stability.Conclusion:The finite element analysis can make full use of different channels to obtain the data needed to build the finite element model,and the research method is flexible.The new interphalangeal prosthesis sleeve type fixation device is safe and reliable.In daily life,patients can grasp their joints safely within the range of 0°～90°,but excessive hand movements should be avoided.The new interphalangeal prosthesis is stable and allows patients to move their joints more carefully,improving hand function more than Swanson’s prosthesis.In the present three dimensional finite element analysis,no significant defects have been found in the design of the new unconfined interphalangeal joint prosthesis,and its design scheme has the prospect of clinical application.