| Objective In this study,the performance and effects of the modular intercalary diaphyseal endoprosthesis with the tenon and mortise joint were evaluted by animal experiments,and the differences in imaging and biomechanics were compared between the different fixations of modular intercalary diaphyseal endoprosthesis.This study on the stability of the cementless diaphyseal endoprosthesis with 3D-printing technology provides an experimental and theoretical basis for the clinical application of the diaphyseal endoprosthesis.Methods Based on the data of CT scanning of the right canine femurs,a three-dimensional model of the right femoral diaphyseal defect was established by using computer aided design,reverse engineering and rapid prototyping technology.According to the 3D model of the canine femoral diaphyseal defect,two different fixations of the modular intercalary diaphyseal endoprosthesis with the tenon and mortise joint were designed and fabricated.One of them was the cementless diaphyseal endoprosthesis using the 3D-printing technology.The other was the cement diaphyseal endoprosthesis with anti-rotation groove using the traditional method.When the 2.0cm osteotomy in the middle of the canine right femur was completed in surgery,the canine femoral diaphyseal defects were reconstructed with the different fixations of the modular intercalary diaphyseal endoprosthesis.At different times after the operation,the canines were killed and their right femoral specimens were harvested.The specimens were observed and evaluated in radiology,histology,biomechanical test and bone histomorphometry,and analyzed the experimental results of them.Results 1.General observation: The function of the affected limbs in two groups recovered well postoperatively,and all of them could bear weight early.However,the weight-bearing time of the affected limbs in 3D-printing Group was significantly later than that in Cement Group.2.Gross observation: The femoral reconstruction force line is normal in two groups,and the endoprosthesis had no dislocation,loosening,deformation and so on.3.X-ray film: All the endoprosthesis were firm postoperatively in two groups without dislocation,loosening,subsidence,deformation and so on.However,the stable cases evaluated by X-ray increased in 3D-printing Group and decreased in Cement Group with the increase of the endoprosthesis fixation time.4.Micro-CT scanning: In 3D-printing Group,the newly formed bones in the pores of the endoprosthesis and their density increased with the increase of the endoprosthesis fixation time,and they interlocked with the endoprosthesis gradually.5.Biomechanical test: In non-destructive test(torsional,bending and tensile test),the torque,bending moment and tension in 3D-printing Group were significantly lower than those in Cement Group at the same time respectively within 4 weeks ~ 20 weeks(P<0.01).With the increase of the endoprosthesis fixation time,the torque,bending moment and tension significantly increased in 3D-printing Group(P<0.01)and decreased in Cement Group.They had high positive correlations in 3D-printing Group(P<0.01)and had moderate negative correlations in Cement Group(P<0.05)with the endoprosthesis fixation time.In destructive tensile test(pull-out test),the maximum shear strength in 3D-printing Group was significantly lower than that in Cement Group at the same time respectively within 4 weeks ~ 20 weeks(P<0.01).With the increase of the endoprosthesis fixation time,the maximum shear strength significantly increased in 3D-printing Group(P<0.01)and decreased in Cement Group.It had a high positive correlation in 3D-printing Group(P<0.01)and had a moderate negative correlation in Cement Group(P<0.05)with the endoprosthesis fixation time.It shows that the torsional,bending,tensile and shearing strength in 3D-printing Group were much lower than those in Cement Group respectively at the same time.With the increase of the endoprosthesis fixation time,they significantly increased in 3D-printing Group and decreased in Cement Group,and the gaps of those between the two groups were gradually reduced.6.Histological observation: Within 4 weeks ~ 20 weeks,the boundaries of the different fluorescent markers in 3D-Printing Group become wider and clearer,and the gaps between them gradually widened with the increase of the endoprosthesis fixation time.The osteoblast in the pores of the endoprosthesis increased and enlarged gradually,and their nucleus increased.7.Bone histomorphometry: Within 4 weeks ~ 20 weeks,the bone volume fraction,mineral apposition rate,bone formation rate and osseointegration rate in 3D-printing Group increased with the increase of the endoprosthesis fixation time(P<0.05),and they had high positive correlations with the endoprosthesis fixation time(P<0.01).They increased more within 4 weeks ~ 12 weeks than within 12 weeks ~ 20 weeks.Conclusion 1.In this study,it is scientific and reasonable to choose canines as the experimental object,and the preparation of bone defect model accorded with the requirements of the large bone defect.Postoperatively the function of the affected limb recovered well and can carry weight earlier,the stability of the endoprosthesis is better without complications.This demonstrates that the modular intercalary diaphyseal endoprosthesis with the tenon and mortise joint have better performance and treatment effects,and it has a good improvement on the intercalary diaphyseal endoprosthesis.2.The weight-bearing time of the affected limbs in 3D-printing Group was significantly later than that in Cement Group,and the biomechanical strength in 3D-printing Group was significantly lower than that in Cement Group at the same time.However,with the increase of the endoprosthesis fixation time,the X-ray stable cases and the biomechanical strength increased in 3D-printing Group and the gaps of the biomechanical strength between the two groups narrowed gradually.This indicates that the stability of the 3D-printing cementless diaphyseal endoprosthesis was weaker than that of the cement diaphyseal endoprosthesis in early stage.With the increase of the fixation time,the stability of the 3D-printing cementless diaphyseal endoprosthesis turned stronger and the gap between the two groups was gradually narrowing.3.The results of bone histomorphometry in 3D-printing Group increased with the increase of the endoprosthesis fixation time.The increases in early stage(within 4 weeks ~ 12 weeks)was more than those in late stage(within 12 weeks ~ 20 weeks).It shows that the 3D-printing cementless endoprosthesis has good bone induction which is beneficial to the bone ingrowth,and the more the bone ingrowth,the more the osseointegration.The osteogenesis and osteointegrationis are stronger in early stage than in late stage.4.The results of bone histomorphometry and the biomechanical test both had high positively correlations with the endoprosthesis fixation time.The results of bone histomorphometry were in good agreement with those of the biomechanical test.This highlights that the stability of 3D-printing cementless diaphyseal endoprosthesis is closely related with the osteogenesis and osseointegration.The better the osteogenesis and osseointegration,the stronger the stability of 3D-printing cementless diaphyseal endoprosthesis. |
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