The Development And Biomechanical Study Of NITI Shape Memory Alloy STT Arthrodesis Concentrator

Objective:The anatomic parameters of the the three bones(scaphoid,trapezoid and trapezium)were measured with vernier caliper.According to the measured results of the three bones and the characteristics of Nitinol,a special internal fixator for STT arthrodesis,NiTi shape memory alloy STT arthrodesis concentrator(NT—STTAC) was designed.In order to provide the biomechanical proofs for clinical application, the biomechanical characteristics of NT—STTAC were tested with 858-Material Test System(858-MTS).Methods:Firstly,32 cases of adult forearm specimens were anatomized.Distance from scaphoid to trapezium,distance from scaphoid to trapezoid and distance from trapezium to trapezoid were measured.Then Scaphoid,trapezoid and trapezium were observed and their lengths,widths and depths were measured.Secondly,According to the measured datum and anatomic features of the three bones(scaphoid,trapezoid and trapezium),a special internal fixator—NITI shape memory alloy STT arthrodesis concentrator(NT-STTAC)was designed with Nitinol.Thirdly,the STT arthrodesises were carried out in 24 carpal specimens of the three bones(scaphoid,trapezoid and trapezium)in vitro,12 specimens of the three bones(scaphoid,trapezoid and trapezium)were fixed with NT-STTAC,and the others were fixed with K-wires. Finally,The fixed strength of the NT-STTAC groups and the K-wires groups were tested with 858-MTS.Six NT—STTACs were fatigued with 19.6～196N cycling pulling load(1 HZ)delivered by MTS-858 and the deformation of them were carefully observed.Finally,the biomechanical feature of NT-STTAC were evaluated according to the tested data.The biomechanical characteristics of NT—STTAC were evaluated according to analyze the datum. Result:Scaphoid,trapezoid and trapezium have their bone marks.The distance from scaphoid to trapezium is(38.60±1.70)mm,distance from scaphoid to trapezoid is (32.14±2.22)mm and distance from trapezium to trapezoid is(30.73±1.95)mm. The trapezium is the thickest bone,its depth is(10.36±0.83)mm.The implanted cancellous bones in the intercarpal joint could be hold in place by the body of NT—STTAC because they were held by the body of NT—STTAC The fixed strength was stronger in NT—STTAC group than Kirschner wires group(P＜0.05).When the six NT—STTAC were deformed to 6%by pulling load,they had resisted the pulling load for 3012,3228,3356,3678,3424 and 3986 respectively.The three bones could be concentrated by the restored force that was made generated by the fixed arms of NT—STTAC.Conclusion:(1)The standard established by bone marks can be used to measure irregular scaphoid,trapezoid and trapezium.(2)According to the measurement data, adjacent joint injury can be avoided,operation complications will decrease and arthrodesis rate improve.(3)Related data are the key index to design new internal fixation device of STT arthrodesis.(4)The design of NT-STTAC is in accordance with the anatomical features of the three bones.Its biomechanical strength allows early movement.The range of fatigue strength covers the period for bony fusion.