## 2 Materials and Methods
### Non-Linear Finite Element Analysis  
Solid models of the implant, screws, pre-contoured locking plate and remaining right femur were imported into ANSYS to assemble the corresponding bone fracture model. The resulting FE model was meshed using quadratic tetrahedral elements. The number of mesh elements and nodes  
Figure 2: (**a**) Traditional surgical reconstruction methods using morselized bone graft (red circle) alone and strut graft (blue cylinder) with morselized bone graft. This novel implant perfectly matches the fracture site and fills up the defect. Bone graft can be protected within the implant. (**b**) Illustration model of the construct. The patient specific 3D printing titanium implant fit into the bone defect and fixed with host bone with implant screws. Additional lateral site pre-contoured locking plate was applied to secure the construct.  
were chosen based on convergence tests. The remaining femur, implant, screws and pre-contoured locking plate meshes were composed of 175,671, 32,869, 15,565 and 25,495 elements and 272,993, 60,457, 30,439 and 42,194 nodes, respectively (Figure 3). The proximal/distal implant fixation screws and pre-contoured plate locking screws were assumed to have continuous connections with the fixation plates, cortical, and cancellous bones. The bonded condition was used to mimic the screw/plate and screw/bone interfaces. All nodes were constrained at the proximal end as the boundary condition and elastic modulus and Poisson's ratio material properties for cortical, cancellous bone, titanium implant, and locking plates/screws adopted from the literature [9; 10]. The force was applied separately on the medial and lateral condyles. These loads correspond to 3 times the body weight (70 kg) distributed 40% on the lateral condyle (870 N) and 60% on the medial condyle (1160 N) of the stance phase before toe-off (Figure 3) [11; 12].  
Three different simulated conditions for FE analysis were set up to mimic the actual clinical stages. Stage 1 was assumed as the immediate postoperative period, i.e., bone union at the proximal/distal implant-bone interface was not yet complete. Nonlinear contact elements (defined as surface to surface) with friction coefficients of 0.2 were used to simulate the interfacial adaptation between the implant and bone surface. Stage 2 was assumed as the postoperative bone union model with the implant and locking plate in place. Bonded elements, i.e., displacement continuous between different materials, were used to simulate the bone union condition at the implant-bone interface. Stage 3 is assumed as the condition after locking plate removal when postoperative bone union is achieved. The von Mises strain distribution at the implant-bone interface, fracture femur displacements fixed with implant locking plate at different stages, and maximum von Mises stress and distributions were obtained to evaluate the biomechanical behavior.  
Figure 3: FE model consisted of the implant, screws, pre-contoured locking plate, and remaining right femur. Light green area showed the proximal and distal bone-implant contact interface. The force was applied separately on the medial condyle (60%) and the lateral condyle (40%), with correspond to 3 times of body weight.