Designing a 3D-printed medical implant with mechanically macrostructural topology and microbionic lattices: A novel wedgeshaped spacer for high tibial osteotomy and biomechanical study

Metal three-dimensional (3D) printing has become an important manufacturing process in medical implant development. Nevertheless, the metal 3D-printed implant needs to be considered with structural optimization to reduce the stress-shielding effects and to be incorporated with a lattice design to generate better bone ingrowth environment. This study combines topology optimization (TO) and lattice design to acquire an optimal wedge-shaped spacer (OWS) for high tibial osteotomy (HTO) fixation. The OWS was manufactured using titanium alloy 3D printing to conduct biomechanical fatigue testing for mechanical performance validation. A solid wedge-shaped spacer (SWS) with three embedded screws was designed using the HTO model. An OWS was obtained under physiological loads through finite element (FE) analysis and TO. A deformed YM lattice with a porosity of 60% and pore size of 700 µm was filled at the OWS posterior region. The HTO mechanical performance was simulated for SWS, OWS, and commercial T-shaped plate (TP) fixations using FE analysis. The displacement/fracture patterns under OWS and TP fixations were verified using fatigue testing. The manufacturing errors for all 3D-printed OWS features were found to be less than 1%. The FE results revealed that the OWS fixation demonstrated reductions of 56.46%, 11.98%, and 64.31% in displacement, stress in the implant and bone, respectively, compared to the TP fixation. The fatigue test indicated that the OWS fixation exhibited smaller displacement for the HTO, as well as a higher load capacity, minor bone fracture collapse, and a greater number of cycles than the TP system. This study concluded that medical implants can be designed by integrating macro TO and microlattice design to provide enough mechanical strength and an environment for bone ingrowth after surgery. Both FE analysis and biomechanical fatigue tests confirmed that OWS mechanical performance with lattice design was more stable than the HTO TP fixations.