Design and finite-element evaluation of a partially bioabsorbable interbody fusion cage / 第二军医大学学报

ABSTRACT

Objective To design a partially bioabsorbable interbody fusion cage (PBIFC) and to analyze its biomechanics using finite-element evaluation method. Methods A new type of PBIFC was designed and made from nano-hydroxyapatite/polyamide 66 (n-HA/PA66) and multi-(amino acid) copolymer-calcium sulfate; a 3D finite-element model of L3-L4 segment was constructed and validated. A PBIFC or a non-absorbable cage of identical shape (n-HA/PA66 cage) was implanted via anterior approach on the model, and four models were established, including the immediate implantation model and 4-week implantation model of each cage. An axial compressive preload of 400 N and a torque of 10 Nm were applied to the L3 segment to simulate spinal compression, flexion, extension, rotation, and lateral bending. The stress and stress contour of different loading conditions were calculated. Results Immediately after implantation, stresses of the bone graft in PBIFC model were higher than those in n-HA/PA66 cage model, while stresses of the cage and endplate in PBIFC model were lower; and no significant difference in stress contours on endplate was found between the two models. Four weeks after implantation, stresses of the bone graft in PBIFC were higher than those in n-HA/PA66 cage, and stresses of the cage and endplate in PBIFC model were lower, with the stress differences being greater than those of immediately after implantation. The stress contours on endplate in PBIFC model was larger than that in the n-HA/PA66 cage model. Conclusion PBIFC is probably more suitable than a non-absorbable cage of identical shape for lumbar interbody fusion.