Development And Finite Element Analysis Of The Anatomic Nano Hydroxyapatite / Polyamide 66 Cage For Lumbar XLIF/OLIF Approach

ObjectiveTo develop an anatomic nano hydroxyapatite / polyamide 66(n-HA/PA66) intervertebral fusion cage for specific application in the extreme lateral interbody fusion(XLIF) and oblique lumbar interbody fusion(OLIF).To study the biomechanical attributes of the anatomical n-HA/PA66 cage in XLIF/OLIF surgery by three dimensional finite element analysis.Methods1.Different models of cage were designed according to the anatomical characteristics of the human lumbar and n-HA/PA66 material properties.2.Cages were did pre operative experiments on cadavers to validate the applicability in different lumbar segments.3.A three dimensional finite element model of normal human L3 ~ 5was established, and the validity of the model was verified.4.Based on the intact model,the new anatomic cage and the bullet-liked cage were fitted to the L4-5 vertebral body in order to simulate the XLIF/OLIF operation process and analysed the maximum stress,stress distribution of the two kinds of cage and the ROM of the L4-L5.Results1.A new lumbar anatomic n-HA/PA66 cage was designed and developed Successfully,its unique front high rear low tilt angle(2° to8 °) and the "drumhead " design of the adhering part of superior endplates, can better meet the lumbar lordosis and intervertebral disc structure.2.Through the pre operation experiments on the cadaver specimens,the cage of different sizes could be verified to meet the intervertebral implant of different lumbar segments.3.The normal finite element model of L3-L5 mobility Under various load conditions was reported in the literature.4.In thel finite element analysis of simulated XLIF/OLIF operation in L4-L5 segment,under the motion of flexion, extension, bending and rotation, the maximum stress of the anatomic cage was 56.91、61.78、35.82、52.28、31.76、32.45 MPa,the bullet-liked cage was 134.83、79.17、71.31、114.96、76.85、78.77 MPa,the maximum stress of the anatomic cage was significantly smaller than that of the bullet-liked cage and the stress distribution of anatomic cage was smaller and more dispersed than that of the bullet-liked cage;under six different motion,the L4-L5 vertebral activities of the anatomic cage group were 0.51、0.42、0.34、0.31、0.27、0.24 and the bullet-liked cage group were 0.67、0.48、0.37、0.37、0.28、0.24,but the normal human activities were 3.83、2.74、2.14、2.13 、 2.01 、 1.98.The L4-L5 vertebral activities of two groups were significantly less than normal activity degrees, and the anatomic cage group activities were less than the bullet-liked cage group.Conclusion1.The new lumbar anatomic n-HA/PA66 cage, with larger area and volume in shape,can meet the need of XLIF/OLIF surgically implanted.2.The normal L3-L5 finite element model is verified to be valid and can be used in the following three dimensional finite element analysis.3.The application of new lumbar anatomic n-HA/PA66 cage in the XLIF/OLIF surgery can decrease the maximum stress,avoid stress concentration and reduce vertebral activity.