Effects of immediately static loading on osteointegration and osteogenesis around 3D-printed porous implant: A histological and biomechanical study

The 3D-printed porous implant is capable of achieving favorable osteointegration and osteogenesis in the absence of mechanical stimulation during the early healing period. The purpose of this study is to evaluate the impact of immediately static loading on bone osteointegration and osteogenesis around the 3D-printed porous implant. Thirty porous implants with optimal configuration were installed bilaterally into femurs of 15 rabbits. The Load group on the left side was applied the maximal initial load of 10 N offered by a diminutive and built-in loading device and the Non-load group was on the contralateral side. At 2, 4, and 8 weeks post-operatively, the explants were harvested for push-out test to measure the biological fixation strength. The quantity and quality of new bone were evaluated by the means of histological examination, Micro-CT and bone density analysis. Moreover, the animal data were integrated into finite element models to assess the biomechanics of peri-implant bone. The results indicated that the quantity, quality and biomechanical properties of the new bone increased and optimized along with the healing time. It also demonstrated that the immediately static loading increased the volume of new bone with inferior quality in 2 weeks after implantation and the adverse influence emerged gradually as time extended. Moreover, finite element results demonstrated that the early structures of new bone around porous implant were not suitable for functional loading. This study indicated the mineralization modes of distance osteogenesis and contact osteogenesis around the porous implant. Accordingly, the delay and progressive loading protocol was recommended.