Experimental Research And Early Clinical Outcomes Of Severely Acetabular Bone Defect Reconstructed By 3D Printed Porous Ti6A14V Augment

Objectives:1.To establish an animal model of acetabular bone defect,to design and implant the 3D printed porous Ti6A14V augment according to the individual anatomy of the modeled bone defect and then to evaluate bone ingrowth and biomechanics.2.To establish the finite element model of acetabular bone defect reconstructed by 3D printed porous Ti6A14V augment and further to analyze the stress distribution and clinical safety of augment,screws and bone.3.To report the early clinical outcomes of patients with severely acetabular bone defect reconstructed by 3D printed porous Ti6A14V augment.Methods:1.The inner structural parameters of 3D printed porous Ti6A14V augment were measured by scanning electron microscope(SEM),including porosity,pore size and trabecular diameter.The matching degree between postoperative augment and designed augment was measured by CT scan and 3D reconstruction.2.The stiffness,compressive strength,elastic modulus and biomechanics of 3D printed porous Ti6A14V augment were measured by mechanical testing machine.3.The bone ingrowth and implant osseointegration were evaluated by Micro-CT scan and histological examination.4.The finite element model of acetabular bone defect reconstructed by 3D printed porous Ti6A14V augment was established by the CT data of a patient with Paprosky IIIA defect.The von Mises stress of augment,screws and bone were analyzed by a vertical load applied in 3 increments(500 N,2000 N and 3000 N).5.Eleven patients with severely acetabular bone defect reconstructed by 3D printed porous Ti6A14V augment were retrospectively analyzed the general information,intra-operative data,imaging data,functional scores and complications.Results:1.The inner structural parameters of porous Ti6A14V augment were 55.48 ±0.6%porosity,pore size 319.2 ± 25.1 um and trabecular diameter 240.1 ± 23.5 um.The stiffness,compressive strength and elastic modulus were 21465 ± 1092 N/mm,231 ± 12 MPa and 5.35 ± 0.23 GPa,respectively.The matching degree between postoperative augment and designed augment was 91.4 ± 2.8%.2.The image of Micro-CT shows the bone growth into porous coating of the 3D printed porous Ti6A14V augment.Bone histomorphometry analyses show that the mineral apposition rate is 3.77 ± 0.93 um/day and that the percentage of bone tissue volume is 22.3 ± 4.5%.3.The maximal shear strength of 3D printed porous Ti6A14V augment implanted immediately and 12 weeks after surgery were 929.5 ± 296.0 N and 1521.9 ± 98.4 N(p=0.0302),respectively(p<0.05).4.The peak von Mises stresses under 500 N load in the porous augment,screws and cortical bone were 10.13 MPa、12.424 MPa and 10.439 MPa.And they were 40.706 MP、50.25 MPa and 42.627 MPa under 2000 N load.And they were 61.213 MPa、75.86 MPa and 64.554 MPa under 3000 N load.5.The average limb-length discrepancy(LLD)was 36.1± 22.6(16-92)mm preoperatively,7.7 ± 6.6(1-21)mm(p=0.0027)postoperatively and 7.0 ± 5.7(0-18)mm at latest follow-up.The mean vertical position of hip center of rotation(HCOR)from the interteardrop line changed from 51.0 ± 19.3(23.6-92)mm preoperatively to 22.6 ± 10.4(6.2-40.3)mm(p=0.0060)postoperatively and 22.8 ± 10.2(6.3-40.5)mm at latest follow-up.Radiolucencies and radiological loosening of the acetabular components and augments were found in no hip at follow-up.The Bone ingrowth was observed by CT scans at follow-up and the matching degree between postoperative augment and designed augment was 92.3 ± 2.5%.The average HHS improved from 44.0 ± 14.9(range,26-71)preoperatively to 84.3 ± 9.7(range,68-97)at the last follow-up(p<0.0001).Follow-up data shows no hip dislocation,PJI,fracture,re-revision and no other complications.Conclusions:1.The 3D printed porous Ti6A14V augment designed in this current study has good bone tissue biocompatibility and biomechanical property.2.The finite element analysis shows that all the components will be intact under 500 N(single-legged standing).However,partial cancellous bone contacted with porous augment and screws will be failed under 2000 N(normal walking)and 3000 N(jogging).So we recommend that patients can stand under full bearing,but can not walk or jog immediately after surgery.3.Surgical technique of 3D printed porous Ti6A14V augment to reconstruct severely acetabular bone defect is easy to master and the porous augment is well matched with the defect bone surface and the acetabular component.Imaging and functional outcomes are apparently improved at latest follow-up.