Experimental Study On Mechanical Stability Comparison Of Double Screw Cross Fixation In Percutaneous Subtalar Arthrodesis

Objective: By means of cadaver specimen experiment,the subtalar joints were subjected to percutaneous fusion,cannulated nail fixation,and mechanical experiment to simulate the subtalar joint movement,so as to verify the reliability of the internal fixation method.The ratio of the area of subtalar arthrodesis was calculated,and the feasibility of this method was discussed,providing experimental data basis for clinical percutaneous subtalar arthrodesis.Methods: Sixteen adult cadavers were randomly divided into group A and group B.In both groups,a 2cm incision was made near the Achilles tendon,and the subtalar joint was fused by trephine with a diameter of 12 mm and fixed with a hollow screw of 7.1mm.Group A: under the calcaneal tubercle,screw about 55-70 mm in the direction of the talus body in the posterior third of the heel,and try to ensure that the Angle is perpendicular to the posterior articular surface on the lateral position of the calcaneus;After another in the fifth metatarsal base 2 cm,1 cm away from the foot edge,and the horizontal plane to 40 °,with Chopart on coronary axis line(fu horizontal joints of attachment)parallel,nailing.Group B: the first screw is the same as above;In addition,from the back of the calcaneus,the guide wire was driven in the direction of the talus neck,and the position was suitable for c-arm fluoroscopy,and the cannulated nail was driven.X-ray examination was performed postoperatively in both groups,and biomechanical experiments were conducted after the positions were satisfied.The displacement and torsion stiffness generated in the axial compression test after subtalar joint fusion were obtained,and the stability of the two groups was compared.After the completion of the biomechanical experiment,the specimen was dissected,the screw was removed,and the joint surface area and fusion area were measured by Computed Tomography.Results:1.Group A(beat from the back of the fifth metatarsal base 2cm in the direction of the talus neck,and the other from the back of the calcaneus in the direction of the talus body)and group B(double screw cross drive from the back of the calcaneus into the talus body and talus neck respectively)were subjected to gravity compression experiment.The data obtained were as follows: when n=100N,the displacement of group A was less than that of group B [(0.51 0.09)mm vs(0.92 0.17)mm,P <0.01].When n=200N,the displacement of group A was smaller than that of group B [0.86(0.14)mm vs1.27(0.19)mm,P <0.01].When n=300N,the displacement of group A was less than that of group B [1.1(0.82)mm vs1.55(0.23)mm,P <0.01].When n=400N,the displacement of group A was less than that of group B [1.32(0.15)mm vs1.76(0.18)mm,P <0.01].When n=500N,the displacement of group A was smaller than that of group B [1.51(0.15)mm vs1.9(0.22)mm,P <0.01].When n=600N,the displacement of group A is smaller than that of group B [1.74(0.19)mm vs2.12(0.22)mm,P <0.01].When n=700N,the displacement of group A was less than that of group B [1.82(0.26)mm vs2.30(0.24)mm,P <0.05].Analysis of experimental data of positive and negative rotary loading: the stiffness of group B was less than that of group A [(0.42 0.16)mm vs(0.45 0.63)mm,P > 0.05].Negative rotation group: the stiffness of group B was less than that of group A [(0.51 0.04)mm vs(0.60 0.10)mm,P < 0.05];2.In the anti-torsion load capacity experiment,in the case of negative torsion,the stiffness of group A was greater than that of group B,and the difference was statistically significant;In the case of positive torsion,the stiffness of group A was greater than that of group B,and there was no statistical difference between the two groups.2.Computed Tomography calculation of fusion area ratio: the average ratio of group A and group B of calcaneal surface was 57% and 56%,respectively,and the difference was not statistically significant.The average ratio of group A and group B was 56% and 55%,respectively,with no statistical significance.Conclusions:1.According to the biomechanical data of the two groups of cadaver specimens,in the gravity compression experiment,the data of group A(beating toward the talus neck from the back of the fifth metatarsal base 2cm,and the other from the back of the calcaneus toward the talus body)was less than that of group B(driving into the talus body and talus neck from the back of the calcaneus with double screws).In terms of torsion experimental data,group A is superior to group B,so group A has smaller displacement and stronger stability after weight bearing,which is more conducive to the early weight bearing of diseased feet after surgery.2.Percutaneous subtalar arthrodesis of the two groups of cadaver specimens was performed,and the area ratio of subtalar joint fusion measured by postoperative Computed Tomography was both higher than 50%,which ensured the fusion rate of subtalar joint fusion and had good clinical practicability.