Patient-Specific 3-Dimensional Printing Titanium Implant Biomechanical Evaluation for Complex Distal Femoral Open Fracture Reconstruction with Segmental Large Bone Defect: A Nonlinear Finite Element Analysis

Abstract

This study proposes a novel titanium 3D printing patient-specific implant: a lightweight structure with enough biomechanical strength for a distal femur fracture with segmental large defect using nonlinear finite element (FE) analysis. CT scanning images were processed to identify the size and shape of a large bone defect in the right distal femur of a young patient. A novel titanium implant was designed with a proximal cylinder tube for increasing mechanical stability, proximal/distal shells for increasing bone ingrowth contact areas, and lattice mesh at the outer surface to provide space for morselized cancellous bone grafting. The implant was fixed by transverse screws at the proximal/distal host bone. A pre-contoured locking plate was applied at the lateral site to secure the whole construct. A FE model with nonlinear contact element implant-bone interfaces was constructed to perform simulations for three clinical stages under single leg standing load conditions. The three stages were the initial postoperative period, fracture healing, and post fracture healing and locking plate removal. The results showed that the maximum implant von Mises stress reached 1318 MPa at the sharp angles of the outer mesh structure, exceeding the titanium destruction value (1000 MPa) and requiring round mesh angles to decrease the stress in the initial postoperative period. Bone stress values were found decreasing all the way from the postoperative period to fracture healing and locking plate removal. The overall construct deformation value reached 4.8 mm in the postoperative period, 2.5 mm with fracture healing assisted by the locking plate, and 2.1 mm after locking plate removal. The strain value at the proximal/distal implant-bone interfaces were valuable in inducing bone grafting in the initial postoperative period. The proposed patient-specific 3D printed implant is biomechanically stable for treating distal femoral fractures with large defect. It provides excellent lightweight structure, proximal/distal bone ingrowth contact areas, and implant rounded outer lattice mesh for morselized cancellous bone grafting.

Biomechanical Analysis and Design Method for Patient-Specific Reconstructive Implants for Large Bone Defects of the Distal Lateral Femur

“…Previous studies have combined CT imaging, CAD, FE analysis, and 3D printing to design implants for large defects in the supra-iliac spine [ 18 ], proximal tibia [ 19 ], and mandible [ 3 ], and for distal femur repair after traumatic injury [ 13 ]. However, these studies focused only on the implant design for a single case and did not generalize the design method or set rigorous design parameters to allow for applicability to other patients.…”

“…The CAD model of the femur/solid-core implant/implant screw/bone screw and bone plate system was imported into the computer-aided engineering analysis software (ANSYS, v19.0, ANSYS Inc., Canonsburg, PA, USA) for FE analysis. The properties of the materials used in the model, including cortical bone, cancellous bone, Ti6Al4V implant, and bone nail/bone plate system, were assumed to have linear elastic property with homogeneous and isotropy and corresponding Young’s modulus and Poisson’s ratio of different materials were assigned in the FE model ( Table 1 ) [ 13 ]. The free mesh method using a tetrahedron element was adopted to generate the FE mesh model.…”

“…However, metal implants are heavy, and the higher elastic modulus of a metal implant can limit the load transferred to bone, causing stress shielding that can result in the cessation of bone growth [ 11 ]. Thus, the optimal implant structure must be lightweight and stabilized to allow for osteointegration and protected weight bearing [ 12 , 13 , 14 , 15 ].…”

Effectiveness Assessment of CAD Simulation in Complex Orthopedic Surgery Practices

“…A valid option is to use dedicated medical software: in "Application of computer simulation in the treatment of traumatic cubitus varus deformity in children" [11] MIMICS is used for the simulation of osteotomy, in "Accuracy of the preoperative planning for cementless total hip arthroplasty" [12] use is made of the Hip-PlanTM software (Symbios, Yverdon, Switzerland), which deals only with hip arthroplasty planning, while in "Integration of CAD/CAM planning into computer assisted orthopaedic surgery" [13] the model is transformed into three dimensions and customized bone prostheses are created for the patient via MIMICS software. Another interesting study is the one presented in the script of Wong et al (2020) [14], where a novel titanium 3D-printed patient-specific implant, starting from a model made with parametric software, is presented. Additionally, there is the paper of Milojevic et al (2010) [15] that performs a three-dimensional approximation of a femur from X-ray images to verify the exact position and measurements of the screws which are built-in in the human femur.…”

Finite element analysis of patient-specific additive-manufactured implants

“…While various finite element (FE) models have been developed to simulate human bones, particularly by extracting bone geometry from CT scans and correlating associated Hounsfield Unit (HU) values to bone material properties ( Bessho et al, 2007 ; Poelert et al, 2012 ; Basafa et al, 2013 ; Schermann et al, 2020 ), only a limited number of studies have employed finite element analysis to simulate the stiffness and behavior of bones implanted with 3D printed implants ( Wong et al, 2020 ; Yan et al, 2020 ; Liu et al, 2022 ). Notably, none of these studies have validated their simulation results with experimental data for implanted bones.…”