Experimental Study On Modified Threaded Kirschner Wires Treating Ulna Coronoid Process Fractures

Objective: This project designed and prepared a type of modified threaded Kirschner wires,did mechanical experiments to test if modified threaded Kirschner wires can meet clinical requirments,and did animal experiments to study modified threaded Kirschner wires’ treating effect on ulna coronoid process fractures.Method: Experiment 1: Designed the thread segment length of modified Kirschner wires to be 60 mm,the major diameter to be 1.5mm(d=1.5mm),the minor diameter to be 1.2mm(d1=1.2mm),the pitch to be 0.35mm(P=0.35mm),the thread angle to be 60°(α=60°),and the lead angle to be 5°(γ=5°).Chose the generic Kirschner wires as raw materials and standard fine pitch threading dies as molds to make modified threaded Kirschner wires.Experiment 2:(1)Mechanical experiments: Performed tensile tests,bending tests and twisting tests of modified Kirschner wires(d=1.5mm,Group A),generic Kirschner wires(d=1.5mm,Group B)and generic Kirschner wires(d=1.2mm,Group C)on the universal testing machine,recorded experiments results and made statistical analyses.(2)Biomechanics experiments: Chose 6 anticorrosion-treated human ulna specimens(12 cases)and established ulna coronoid process Type-Ⅱ Regan-Morrey fractures models.Every specimen fixed internally with modified Kirschner wires(d=1.5mm,Group A)and generic Kirschner wires(d=1.5mm,Group B).Did the pull-out experiments of internal fixations on universal testing machine,recorded experiments results and made statistical analyses.Experiment 3:(1)Chose 16 adult Beagles(16 cases)with similar weight and randomly divided dogs into experimental group and control group,8 dogs(8 cases)in each group.Established right ulna coronoid process Type-Ⅱ fracture models on Beagles according to Regan-Morrey classification.Experimental group fixed internally with modified threaded Kirschner wires,control group fixed with generic ones.X-rayed the limbs(same day,oneweek,two weeks,four weeks,eight weeks,and twelve weeks after surgery)and observed healing condition of ulna coronoid processes and internal fixations’ positions.(2)Removed fixations at the twelfth week after internal fixation surgery,observed the integrity of internal fixations,and X-rayed again one week after removal to observe healing condition of ulna coronoid processes.Results: 1.Mechanical tests: From the aspects of average maximum tensile load,maximum bending load and maximum twisting load,Group A was compared with Group B and Group C separately.The differences were statistically significant(P<0.05).Group A was better than Group C,Group B was better than Group A.From the aspects of average maximum tensile displacement and maximum twisting angle,Group A was compared with Group B and Group C separately.The differences were statistically significant(P<0.05).Group A was better than Group C,Group B was better than Group A.From the aspect of average maximum displacement under average maximum bending load,Group A was compared with Group B and Group C separately.The differences were not statistically significant(P>0.05).2.Biomechanics tests: From the aspects of average maximum pullout load and the average maximum displacement under the maximum pullout load,Group was compared with Group B.The difference was statistically significant(P<0.05).Group A was better than Group B.2.General observation: Beagles in both groups were observed until the 13 th week after surgery.Skin wounds all healed primarily.1~6 days after internal fixation surgery of right ulna coronoid process fractures,injured limbs dangled.7~17 days after surgery,injured limbs gradually bore load.18~21 days after surgery,injured limbs completely bore load.4.Radiograph observation:(1)8 cases in experimental group all healed properly;5 cases in control group healed properly,1 case had malunion and 2 cases had nonunion.The right ulna coronoid process fractures healing condition of the experimental group was better than that of the control group.The difference between two groups was statisticallysignificant(P<0.05).(2)In experimental group,8 cases’ internal fixations did not loosen.In control group,5 cases’ internal fixations did not loosen,3 cases’ internal fixations loosed.The internal fixations’ looseness of the experimental group was better than that of the control group.The difference between two groups was statistically significant(P<0.05).(3)In experimental group,8 cases’ fracture fragments did not displace.In control group,5cases’ fracture fragments did not displace,3 cases’ fracture fragments displaced.The fracture fragments displacement of the experimental group was better than that of the control group.The difference between two groups was statistically significant(P<0.05).5.Removed internal fixations observation: Removal processes of internal fixations in both group were smooth,with good completeness and no wires breaking.Conclusions: 1.Modified threaded Kirschner wires have reliable strength and can meetclinical requirements.2.Treating dogs’ ulna coronoid process fractures,modified threadedKirschner wires can fix tightly and securely and are not easy to looseand convenient to remove,so modified threaded Kirschner wires is apreferable internal fixation material.