| BACKGROUNDExternal fixator is an important method for first aid and treatment of diaphyseal fractures of long bones of limbs;especially when the patient is accompanied by multiple injuries,severe soft tissue injury,bone infection,and bone defect.However,the existing external fixator usually does not have the function of assisting fracture reduction,and it is difficult to achieve high-quality reduction when used,which may easily lead to malunion,delayed union and other complications.OBJECTIVEIn order to address the above problems,our team designed and manufactured a novel external fixator with both reduction and fixation functions through computer virtual fracture reduction and 3D printing technology.We call it 3D-Printed Self-reducing External Fixator(3DP-SEF).In this study,we will introduce the reduction principle and manufacturing method of the external fixator in detail,and test and analyze its reduction effect,mechanical properties and preliminary clinical application,so as to provide theoretical basis and practical guidance for the optimization and promotion of this technology.MATERIALS & METHODS1.The working principle and manufacturing process of the 3DP-SEF external fixatorThe fractured long bones were temporarily fixed by a simple external fixator,and then computed tomography was performed.The obtained DICOM files were imported into Mimics software for 3-D reconstruction of the limb contour,bone fragments,and external fixation pins,and virtual fracture reduction.Then,the data after fracture reduction was imported into Solidworks software for 3DP-SEF external fixator design and 3D printing by selective laser sintering technology.Fracture reduction can be automatically completed through the precise assembly of pins and the specific hole of the 3DP-SEF external fixator.The weight,appearance,manufacturing accuracy and fracture reduction effect of 3DP-SEF external fixator were tested.2.Validation experiment of the reduction effect of 3DP-SEF external fixatorThirty closed fracture models were made by polyurethane foam encapsulation,10 of which were 42-A2.1,42-B2.1,and 42-C2.1(AO classification),and then equally distributed to the experimental group and the control group.The experimental group used3DP-SEF external fixator for reduction,and the control group used traditional fluoroscopy-assisted reduction.The reduction time,the number of reduction attempts,the number of fluoroscopy,and the residual deformity parameters before and after reduction were recorded and compared in each group.3.Finite Element Analysis of Fixation Effect of 3DP-SEF external fixatorThe 3DP-SEF external fixator and Hoffmann Ⅱ external fixator were modeled using Solid Works software,and assembled with the tibial fracture model.Then import the assembled model into Abaqus software,apply 500 N axial compression load,20N·m torsional load and 200 N four-point bending load respectively,and perform finite element static analysis.Export and compare the stress cloud map,displacement cloud map,maximum stress,maximum displacement,etc.of the two external fixators and each bone fragment of the tibia under various loads.4.Biomechanical test of the fixation effect of 3DP-SEF external fixatorEighteen artificial tibia models were made into fracture models with a 20 mm defect in the middle,and then they were evenly distributed to the experimental group and the control group.The experimental group was fixed with a 3DP-SEF external fixator,and the control group was fixed with a Hoffmann II external fixator;each group was divided into 3 groups,respectively,for axial compression test,axial torsion test,and four-point bending test.Three-dimensional digital image correlation method was used to measure and compare the displacement of fracture ends after loading.And the axial compression stiffness and axial torsional stiffness of the two external fixators were calculated respectively,and then statistically compared.5.Preliminary clinical application evaluation of 3DP-SEF external fixatorPatients who visited the emergency room from July 2016 to June 2020 and met the inclusion and exclusion criteria were treated with 3DP-SEF external fixator and followed up regularly.The gender,age,cause of injury,fracture type,combined injury and other general information of the patients were collected,as well as the time from injury to initial surgery,the design and manufacture time of the 3DP-SEF external fixator,the assembly time of the 3DP-SEF external fixator,the postoperative time to full weight bearing,the time to complete fracture healing,efficacy evaluation,complications and other treatment-related information.And the residual deformity parameters of the affected limb before and after reduction were measured and compared.RESULTS1.The working principle and manufacturing process of the 3DP-SEF external fixator(1)The 3DP-SEF external fixator is mainly composed of reduction fixator,auxiliary fixator,pin pressure pads,fastening screws and other components.The pin holes in the reduction fixator records the position information of the pins after virtual fracture reduction,and is mainly used for fracture reduction;the auxiliary fixator is combined with the reduction fixator to form a ring structure by fastening screws,which is mainly used to enhance the fixation effect.(2)The surfaces of the four manufactured 3DP-SEF external fixators were regular and free of defects such as depressions,protrusions and cracks.The average total weight of the external fixators was 716.2g(±19.5),of which the average weight of 3D-printed parts was651.5g(±23.5),and the average weight of metal parts was 64.7g(±5.4).The distribution of manufacturing error values was relatively concentrated,mainly within the range of±0.5mm,and the maximum manufacturing error values were all within ±1.0mm.(3)The reduction process of the 4 fracture models was smooth.After reduction,the axial residual displacement was 1.10±0.34 mm,the lateral residual displacement was0.72±0.44 mm,the axial residual angle was 1.69±0.66°,and the axial residual rotation was1.50±0.68°.2.Validation experiment of the reduction effect of 3DP-SEF external fixator(1)For 42-A2.1 fracture,the reduction time,the number of reduction attempts,and the number of fluoroscopy in the experimental group were less than those in the control group,but the difference in reduction time between the two groups was not statistically significant(P=0.201),and all other differences were statistically significant.For 42-B2.1and 42-C2.1 fractures,the reduction time,the number of reduction attempts,and the number of fluoroscopy in the experimental group were also less than those in the control group,and the differences were all statistically significant.(2)In terms of the reduction effect of 42-A2.1 fracture,the residual deformity parameters of the experimental group were all smaller than those of the control group,but only the difference between the medial-lateral residual displacement was statistically significant,and the other residual deformity parameters had no statistical significance.In terms of the reduction effect of 42-B2.1 fractures,the residual deformity parameters of the experimental group were all smaller than those of the control group,only the difference between the axial residual displacements was not statistically significant,and the differences of other residual deformity parameters were all statistically significant.In terms of the reduction effect of 42-C2.1 fractures,the residual deformity parameters of the experimental group were also smaller than those of the control group,and the differences between all residual deformity parameters were statistically significant.3.Finite Element Analysis of Fixation Effect of 3DP-SEF external fixator(1)After 500 N axial compressive load was applied,the maximum bone displacement in the Hoffmann II external fixator group was as high as 62.871 mm,and the fracture end was displaced significantly(20.960-27.940 mm);the maximum stress on the external fixator was 636.147 MPa.The maximum bone displacement of the 3DP-SEF external fixator group was 15.195mm(only 24.2% of the Hoffmann II external fixator group),and the displacement of the fracture end was small(1.688-3.377mm);the maximum stress on the external fixator was 278.97 MPa,of which the maximum stress on the 3D-printed parts was 27.616 MPa.(2)After 20N·m torque loading,the maximum bone displacement in the Hoffmann II external fixator group was as high as 27.208 mm,and the fracture end was displaced significantly(9.066-18.140mm);the maximum stress on the external fixator was364.499 MPa.The maximum bone displacement of the 3DP-SEF external fixator group was 15.597mm(only 57.6% of the Hoffmann II external fixator group).The fractured end was also displaced(3.466-8.665mm);the maximum stress on the external fixator was319.786 MPa,of which the maximum stress on the 3D-printed parts was 38.740 MPa.(3)After loading with 200 N four-point bending load,the maximum displacement of the fractured end in the Hoffmann II external fixator group was 0.412 mm,and the maximum stress on the external fixator was 23.814 MPa.The maximum displacement of the bone fractured end in the 3DP-SEF external fixator group was 0.354mm(slightly smaller than that of the Hoffmann II external fixator group),and the maximum stress on the external fixator was 35.007 MPa,of which the maximum stress on the 3D-printed parts was 3.093 MPa.4.Biomechanical test of the fixation effect of 3DP-SEF external fixator(1)The axial compression stiffness of the Hoffmann II external fixator is16.83±1.24N/mm,and the axial compression stiffness of the 3DP-SEF external fixator is300.10±14.94N/mm,which is about 18 times that of the Hoffmann II external fixator.(2)The axial torsional stiffness of the Hoffmann II external fixator is1.10±0.06N·m/°,and the axial torsional stiffness of the 3DP-SEF external fixator is5.43±0.9N·m/°,which is about 5 times that of Hoffmann II external fixator.(3)Under the four-point bending loads of 20 N,40N,60 N,80N,and 100 N,the displacement of the fractured end in the Hoffmann Ⅱ external fixator group in the X direction was greater than that in the 3DP-SEF external fixator group,and the differences were statistically significant.In the Z direction,the displacement of the Hoffmann II external fixator group was also greater than that of the 3DP-SEF external fixator group,but under 20 N load,the difference between the two groups was not statistically significant(P=0.107),and other differences were statistically significant.5.Preliminary clinical application evaluation of 3DP-SEF external fixatorA total of 26 patients were treated with the 3DP-SEF external fixator,of which 9patients had polytrauma,14 patients had severe soft tissue injuries around the fracture,and3 patients had both injuries.Fifteen patients underwent reduction under anesthesia in the operating room.The reduction took an average of 9.3 minutes and the average fluoroscopy was 3.3 times.Eleven patients underwent reduction under simple analgesia at the bedside,which took an average of 7.5 minutes;the entire procedure did not require fluoroscopy.Among them,25 patients(96.2%)obtained high-quality fracture reduction,and all deformity parameters were decreased compared with those before reduction,and the difference was statistically significant(all P < 0.0001).The mean follow-up was 7.2(6-12)months;the mean time from injury to initial surgery for all patients was 6.9 hours;the mean time required for 3DP-SEF external fixator design and manufacture was 5.4 days;the mean postoperative time to full weight bearing of the affected limb was 3.8 months;the mean fracture healing time was 5.7 months.The excellent and good rate of limb function was 92.3%.Except for malunion in 1 patient,there were no other serious complications.CONCLUSIONS(1)The 3DP-SEF external fixator designed by the our team is not only light in weight and high in manufacturing precision,but also easy in operation,convenient in use and satisfactory in fracture reduction.(2)Compared with the traditional fluoroscopy reduction technique,the 3DP-SEF external fixator reduction technique can not only effectively improve the quality of reduction,but also reduce the number of reduction attempts,reduce the radiation exposure of doctors and patients,and does not prolong the reduction time.(3)The finite element analysis results show that the mechanical properties of the3DP-SEF external fixator under axial compression and axial torsional loads are significantly better than those of the Hoffmann Ⅱ external fixator commonly used in clinical practice.Under the four-point bending load,the mechanical properties of the two external fixator are equivalent..(4)Biomechanical test results show that the 3DP-SEF external fixator is superior to the Hoffmann Ⅱ external fixator commonly used in clinic in terms of axial compression stiffness,axial torsional stiffness and bending resistance.(5)Preliminary clinical research results show that the 3DP-SEF external fixator not only exerts an excellent reduction function,but also can achieve effective fixation.And the success rate,excellent and good rate,complication rate and other indicators of treatment with this technology are all satisfactory.These indicate that the 3DP-SEF external fixator is a promising new strategy for fracture treatment. |
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