Establishment of design guidelines for patient-specific 3D-printed reconstruction implants for large distal femoral defects

The aim of this study was to establish design guidelines for large distal femoral defects with anterior (AD), posterior (PD), medial (MD) and lateral (LD) reconstruction implants based on titanium 3D-printing technology. The AD/PD/MD/LD defect regions with weakest structure (worst case) were defined and validated through clinical CT imaging of osteosarcoma cases. Finite element analysis and topology optimization were used to determine guidelines with worst-structure defect sizes. Biomechanical analysis and fatigue testing of 3D-printed implants assembled to bones were performed at immediately post-surgery (bone not-healed) and a period after surgery (bone healed) stages. Results showed that 70 % of patients met defined defect rules and the design guidelines proposed that featured a 2-mm thick shell, excavated areas with 5*5 mm2 rhombic mesh on the implant surface, and lattice designed at the implant back bone/implant interface. Simulated and fatigue testing results showed that displacement differences between the medial/lateral sides were smaller in the bone healed stage due to stress transfer continue and all implants withstood cyclic loads without damage. The proposed 3D-printed implant design guidelines can be adapted to individual femoral dimensions and ensure mechanical stability in large femoral defect reconstruction as long as the defect size is within the defined range.