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.
Highlights
The distal femur fracture is a rare but severe injury
About 10% of distal femur fractures are complicated with open wound injuries
Traditional methods provide inferior immediate postoperative stability. This is because the chosen bone grafts are often ill-matched with the bone defect, as the bone wound site dimensions and geometry are always irregular and uneven
Summary
The distal femur fracture is a rare but severe injury. Its reported incidence is 3–6% of all femur fractures [1]. About 10% of distal femur fractures are complicated with open wound injuries. Traditional methods provide inferior immediate postoperative stability This is because the chosen bone grafts are often ill-matched with the bone defect, as the bone wound site dimensions and geometry are always irregular and uneven. The customizability of 3D printing with regard to size and shape make it a potential alternative for complex posttraumatic limb reconstructions such as distal femur fractures with segmental large bone defects. From a biomechanical point of view, patient-specific 3D implant designs for severe distal femur defect reconstruction must achieve original geometry restoration and macro-comprehensive structures with light optimal structures that can withstand physiological loads. This study proposes a novel titanium 3D printing PSI for a distal femur fracture with segmental large bone defect design. This implant is being tested for its biomechanical performance using nonlinear finite element (FE) analysis
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