Biomechanics Of Absorbable Sheath Of Nail In Preventing Stress Shielding Of Interlocking Intramedullary Nail

Objective Through universal electronic mechanical testing machine and finite element analysis to measure of the mechanical strength of fracture healing at different healing times or the stress condition of bone callus of self-developed Absorbable Sheath(AS)interlocking intramedullary nail(IMN)and common metal nails with interlocking intramedullary nail for goat femoral shaft fractures.Methods 1.Sixteen goats were randomly divided into experimental group and control group.Locking nails and common locking nails were used to lock the intramedullary nails.At 4 weeks,12 weeks,24 weeks,and 36 weeks after surgery,the corresponding goats were sacrificed,and the goat’s right femur was removed;Compression and three-point bending test were used to compare the biomechanical strength of fracture healing in both groups.The effectiveness and mechanism of absorbable locking screw sheath to prevent stress shielding of interlocking intramedullary nails were analyzed.2.The three-dimensional solid model was imported into SolidWorks,the goat femur interlocking intramedullary nail main nails,AS lock nails,and general metal locking nails were established.Finally,goat femur model was re-expanded and assembled according to the requirement of locking intramedullary nails.Each models were then integrated into the ANSYS to analyze the stress conditions and the differences in stress shielding.Results 1.At 4th week after surgery,the difference in compressive stress of the experimental group was 1381.2 N,and control group was 4174.3N;experimental group at 12 weeks after surgery was 806.5N,control group was 3258.7 N;experimental group was 302.8 N at 24 weeks after operation,and 3258.7 N in control group;The difference between experimental group and control group was-689.55 N and 366.8N after 36 weeks.At 4 weeks after surgery,the difference in bending stress between experimental group and control group was 708.4 N and 1596.6 N.The difference between the experimental group and the experimental group was 12 weeks after surgery.The value was 373.35 N,control group was 934.3 N.The difference between experimental group and control group was 160.55 N and 416.7 N at 24 weeks after operation.The difference between experimental group and control group was-329.3 N and 36.45 N after 36 weeks.2.The results showed that the AS locking nail group decreased about 4% in the initial period,about 8% in the middle period and about 23% in the later period.Conclusions 1.At the same time,the fracture healing strength of the AS locking nail group was higher than that of the ordinary locking nail group;2.In vertical compression test,right femur fracture in the control group was at or near the femoral fracture,experimental group,the fracture site near the base of the femoral neck at 36 weeks postoperatively,all goat femur specimens were fractured at the three-point bending test or near the fracture;3.According to the results of finite element analysis,the growth,stress,and stress occlusion of bone fractures in the AS locking group were all superior to those of the ordinary locking group;4.The results were basically consistent and proved that AS locking nails with interlocking intramedullary nails can shorten fracture healing time,increase fracture healing strength,and reduce stress shielding caused by traditional interlocking intramedullary nails;5.The number of specimens performed in this experiment was relatively small,and statistically significant samples should be continued to prove this conclusion.