Influence of a threaded implant design and manufacturing on osseointegration

Introduction: Implant fixation is often the cornerstone of musculoskeletal surgical procedures performed to provide bony fixation and/or fusion. The purpose of this study was to evaluate how different design features and manufacturing methods influence implant osseointegration and mechanical properties associated with fixation in the cancellous bone of adult sheep.

Methods: This study evaluated the in vivo performance of 3 titanium alloy implants: A) iFuse-TORQ B) Fenestrated Sacroiliac Device C) Machined Screw in the distal femur and proximal tibia in 8 sheep using an established model. Group A was produced using additive manufacturing (3D printing) while groups B and C were made with traditional methods. The vivo responses of the implants at the implant-bone interface were examined using mechanical testing (push out and removal torque), PMMA histology combined with fluorochrome labels and quantitative histomorphometry of bone ongrowth, ingrowth and through growth at 3 and 6 weeks.

Results: Removal torque at 3 and 6 weeks statistically improved with time and group A was statistically greater compared to the other groups which did not increase with time. Shear stress push out data did not differ between groups. New bone formed directly on all groups and no adverse reactions were noted. Osseointegration via ongrowth, ingrowth and through growth was a function of implant design. The 3D printed surface in group A was rougher and outperformed traditional manufacturing surfaces of groups B and C. The porous domains and fenestrations in the design of group A allowed for bone ingrowth and through growth which accounted for the superior mechanical properties.

Conclusion : Implant designs that provide osseointegration via ongrowth, ingrowth and through growth improve implant fixation.