## 2 Materials and Methods  
3D intact model of the tibia geometry was reconstructed from CT images of a healthy 58-year-old Chinese male. This subject doesn't have any bone tissue or soft tissue disease. The slice thickness of the CT scan image (Light Speed VCT, GE Medical System, General Electric Company, USA) is 1.25 mm, and in-place resolution of 512 \(\times\) 512 pixels. IRB approval of this study is from Show Chwan Memorial Hospital (No. 1021004). The 3D tibia model via the cortical shell and cancellous core were reconstructed by a CAD software, PTC Creo 2.0 (Parametric Technologies Corp., Needham, MA, USA). The cortical thickness was approximately 2.5 mm and 4.5 mm in medial and post wall of this tibial site, respectively. Simulated AO/OTA 43-C1 type fracture was used in this study [10].1 mm gap was simulated between bone fragments (Figure 1) [11].  
Three distal tibial plates were involved in the current study. They are the novel ADLT plate (A Plus Biotechnology Co. Ltd., New Taipei City, Taiwan) and two common implants:  
Figure 1: The AO/OTA 43-C1 type fracture tibia bone model.  
3.5 mm LCP anterolateral distal tibial plate (Synthes 3.5 mm ADT) and 3.5 mm LCP medial distal tibial plate (Synthes 3.5 mm MDT) (Depuy Synthes, Paoli, PA, USA). All plate models were affixed to the tibial shaft with six 3.5-mm locking screws. For the articular fixation, the Aplus ADLT was designed with four distal 2.7-mm locking screws as rafting fixation support, two diagonal 2.7-mm screws for posterior fragment capture, and two 2.7-mm strut screws for construct support (Figure 2). The Synthes 3.5 mm ADT has only four 3.5-mm locking screws in the distal head (Figure 2b) while it accepts six 3.5-mm locking screws in the Synthes 3.5 mm MDT (Figure 2c).  
The ANSYS Workbench 19 (ANSYS Inc., Canonsburg, PA, USA) was used for computational analysis. A convergence test was performed based on total strain energy. For the convergence test, a new tibia FE model with more element and node numbers were calculated and the presented FE model results were compared with those from the new FE model. After convergence test completion, each design model has 511,899 elements on average. Due to the bone plate and threaded screw hole complex geometry, the mesh consists of only tetrahedral elements. The thread on the plates and screws was simplified as a smooth outer surface.  
For load and boundary conditions in each group, the distal end of the tibia was fully constrained in all degrees of freedom. A three-point crutch gait was used for the load condition. Due to the inability of normal walking immediately after operation, the injured leg seldom contacts the ground when a pair of crutches are used. However, muscle forces are generated during the gait swing phase [12]. The adjacent muscles such as the gastrocnemius and soleus generate about 10 percent of the body weight in a tibia when  
Figure 2: Three different type distal tibia plates were implanted on a distal tibia (**a**) Aplus ADLT bone plate, (**b**) Synthes ADT bone plate, and (**c**) Synthes MDT bone plate.  
a leg is in the swing phase in a normal gait cycle [13]. Normal body weight of an adult is 70 kg, and 10 percent of the body weight (70 N) was applied to the tibial plateau [14]. FEA model was assumed as isotropic and linear elastic materials. The material properties of Young's modulus and Poisson's ratio assigned in the FE models are summarized in Table 1[15]. A frictional contact behavior was defined between the fracture fragments with a coefficient of friction of 0.2 for possible contact after loading. Friction coefficient between the bone-plate interactions was 0.42 [16] whereas full constraints were applied between the surrounding bone and screws, and between the screw hole of the plate and the screw head to simulate tightened locking. Each group was compared in terms of the maximum von Mises stress in each plate and the stiffness of the plate-bone construct. The construct stiffness was derived from the load and vertical displacement data.