Osseointegration and fixation opportunities of sacroiliac instrumentation: a preclinical evaluation in a large animal model.

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

Methods: We evaluated the performance of three titanium alloy implants: (A) iFuse-TORQ implant; (B) Fenestrated Sacroiliac Device; and (C) Standard Cancellous Bone Screw in the cancellous bone of the distal femur and proximal tibia in 8 sheep. Group A was produced using additive manufacturing [three-dimensional (3D) printing] while Groups B and C were made with traditional methods. The responses of the implants at the implant-bone interface were examined using mechanical testing (push out and removal torque), polymethyl methacrylate (PMMA) histology combined with fluorochrome labels and quantitative histomorphometry of bone ongrowth, ingrowth and through growth at 3 and 6 weeks.

Results: 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. Implant designs that provide osseointegration via ongrowth, ingrowth and through growth improve implant fixation in torsion. The 3D printed surface in group A was rougher and outperformed traditional manufacturing surfaces of groups B and C in torsion. The porous domains and fenestrations in the design of group A allowed for bone ingrowth and through growth, which accounted for the superior torsional properties.

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