Improving bone and implant surface integration

Background and Aims: Cementless joint prosthesis has been a major module in joint replacement since 1980s. However, bone-implant aseptic loosening is still an important complication. This study was performed to assess the effects of implant surface fabrications and coatings on new bone growth on and in implant surface and on mechanical stability. The study also examines the effects of gap on bone healing in bone-implant interface and exogenous mechanical stimuli on bone growth and mechanical stability. And, lastly, the development of a sheep model for implant research was also undertaken.Materials & Methods: Four types of implants were tested: plasma sprayed porous surface titanium implant with electrochemically deposited 20 μm dicalcium phosphate dihydrate (DCPD) and without coating (TiPL); and grit blasted titanium implants with hydroxyapatite (HA) and without coating (TiGB). Implants were inserted into cancellous and cortical bones with gaps and fits in sheep hind limbs. One group of sheep was treated by dynamic motion therapy (DMT) postoperatively. Specimens were retrieved at five timepoints. Bone-implant mechanical stability was assessed by push-out testing. Bone ongrowth, ingrowth and remodelling were investigated by histology, SEM and BSEM images.Results: Thin electrochemical deposited DCPD coating can improve bone ingrowth in porous surface but cannot improve bone-implant interface mechanical strength. Cortical bone has better ingrowth ability than cancellous bone. Plasma sprayed porous surface has higher bone ongrowth rate and mechanical stability than grit blasted surface.Failure mode in TiPL based implants (including TiPL and DCPD) is through newly formed surrounding bone, while that in TiGB based implants (including TiGB and HA) is through bone-implant interface, HA coating or coating-implant interface. HA coating improves bone-implant gap healing better than grit blasted surface. Tighter bone-implant interface leads to earlier healing and remodelling, while a bigger gap results in less bone growth on implant. The current DMT does not enhance bone-implant interface shear strength, but improves toughness and reduces stiffness.Conclusions: The thin DCPD coating can promote osteogenesis in a porous titanium substrate, but did not improve mechanical stability. Plasma sprayed porous surface also demonstrated its superior in mechanical stability, while HA surface had higher osteoconductivity