| Objective(s): Based on the anatomical data of adult metacarpal and proximal phalanx measured previously,a new metacarpophalangeal joint prosthesis made of Ni-Ti memory alloy was designed and produced based on the improvement of the first-generation metacarpophalangeal joint prosthesis,and the biomechanical properties of the prosthesis were tested to provide biomechanical basis for the improvement and later clinical application of the prosthesis.Methods: 1.On the basis of summarizing and analyzing the finite element data of the first-generation metacarpophalangeal joint prosthesis and consulting relevant literature,the first-generation prosthesis was improved:(1)Four rows of inverted fixed tooth structure were cut from the sagittal plane of the tail of the metacarpal side prosthesis and the coronal plane of the tail of the phalangeal side prosthesis,and then the inverted fixed tooth structure was rotated 90°to solve the problems of shallow depth and unstable fixation of the inverted fixed tooth structure of the first generation prosthesis.(2)In order to solve the problem of poor rotation resistance of the first generation prosthesis,an arc hugging structure was added to each of the four fixed feet in the extramedullary part of the metacarpal side prosthesis.(3)The intramedullary part of metacarpal side and phalangeal side prosthesis was extended to 25 mm,and the intramedullary part was designed as an arc structure of 3°outward,so as to better fit the medullary cavity of metacarpal and phalangeal bone,so as to solve the problem of poor stability of the first-generation prosthesis.2.Ni-Ti memory alloy plate with thickness of 2 mm was selected as the main material of the prosthesis,and polymer polyethylene was selected as the gasket material of the phalange-side prosthesis.The prosthesis was processed according to CAD engineering drawings,and biomechanical tests were conducted on the resulting prosthesis:(1)Axial compression test: Ten fresh adult hand specimens were randomly divided into experimental group(metacarpophalangeal joint prosthesis implant)and control group(sham operation treatment)according to the digital table method,with five sides in each group and the left and right sides randomly.Then,the second to fifth metacarpophalangeal joints were dissected,and the specimens were fixed on the BOSE material testing machine in the extended position,30° flexion position and 60°flexion position,respectively.The load-displacement of specimens at different positions was measured,and the axial compression stiffness was calculated,and the two groups of data were statistically analyzed.(2)Strain change test: Ten fresh adult specimens of the second metacarpophalangeal joint were randomly divided into experimental group(implant metacarpophalangeal joint prosthesis)and control group(no treatment),5 sides in each group,and then the muscles,joint capsule,collateral ligament and other soft tissues around the joint of the two groups of specimens were removed,only the bone part,namely the metacarpal and the proximal phalanx part,and then the two groups of specimens were sprayed with black and white speckle treatment.Subsequently,the specimens were fixed in the extended position on the BOSE material test machine.The stress changes of the four surfaces of the specimens,namely,the palmar side,the dorsal side,the ulnar side and the radial side,were tested using the GOM non-contact optical strain measurement system,and the data were analyzed statistically.(3)Fatigue wear test: Ten pieces of Ni-Ti memory alloy metacarpophalephalanx prosthesis produced in the same batch were randomly selected,and 5 of them were randomly selected as the experimental group.The ETK5510 material testing machine was used for mechanical wear test,and then the mass loss,volume wear and volume wear rate of the prosthesis were calculated before and after the test,and the data were analyzed statistically.Then,the other 5 prostheses without fatigue wear test were set as the control group,and the pull-out force experiment was carried out on the polymer polyethylene gasket part of the prostheses in the experimental group and the control group,and the data were statistically analyzed.Results: In the axial compression experiment,compared with the experimental group and the control group,there was no statistical significance in the axial compression stiffness of the metacarpophalangeal joints of the second to fifth digits at 0° extension(all P values > 0.05).At 30° and 60° flexion,the axial compression stiffness of the prosthesis group was greater than that of the control group,the differences were statistically significant(all P < 0.05).Compared between the experimental group and the control group,there was no statistical significance in the axial compression stiffness of different metacarpophalangeal joints in the same group at the extension and 30° and 60° flexion positions(all P > 0.05).In the test of strain change,there was no statistical significance between the experimental group and the normal group(P >0.05).In the fatigue wear test,the average mass loss and volume wear of the experimental group were 17.2mg,17.619 mm3 and 0.12%.There was no significant difference in the maximum pull-out capacity between the experimental group and the control group(P > 0.05).Conclusion(s): The new Ni-Ti memory alloy metacarpal and phalangeal joint prosthesis is in line with the biomechanical characteristics of normal metacarpal and phalangeal joints.After implantation of the prosthesis,different metacarpal and phalangeal joints have good stability under different flexion angles,and the prosthesis has excellent anti-fatigue performance.After implantation of the prosthesis,metacarpal and phalangeal joints can fully meet the needs of daily joint activities. |
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