scholarly journals Design and numerical investigation of an adaptive intramedullary nail with a novel interlocking mechanism

2020 ◽  
Vol 7 (6) ◽  
pp. 722-735
Author(s):  
Mohammad Ali Bagheri ◽  
Gholamreza Rouhi
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Intramedullary Nail ◽  
Adaptive Design ◽  
Stress Shielding ◽  
Element Model ◽  
Fracture Site ◽  
Medullary Canal ◽  
Bone Ash ◽  
Intramedullary Canal

Abstract Malalignment is a common complication in the treatment of distal fractures of the tibia. Numerous efforts have been made to reduce the malalignment ratio. However, the reported cases with this disorder are still high. This study aimed at investigating an adaptive design of an intramedullary nail with a novel interlocking mechanism (AINIM), as an alternative for the customary nailing, in reducing malalignment ratio. A verified finite element model was employed to compare the performance of AINIM with the customary nail. The finite element model of the tibia follows the exact shape of the medullary canal, and nonhomogeneous material properties were assigned to the bone from bone ash density. It was assumed that the nails were implanted and interlocked in the tibia according to surgical protocols, and physiological-like loading was applied to finite element models. The results of this study showed that AINIM reduces the mean shear interfragmentary strains by about 30%, and the axial interfragmentary strain by 55%, also it increases the uniformity in the interfragmentary movements, compared to the customary nail. It was also found that AINIM caused a reduction of the stress on the nail by 60%, and an increase of 25% on the bone, compared to the customary nail. Moreover, average compressive principal strains in the tibia fixed by AINIM increased by 40% from 485 to 678 με, compared to the tibia fixed by the customary nailing method. The results of this work also showed that AINIM causes an increase in the contact area with the intramedullary canal, particularly at the fracture site, and it also escalates the magnitude of contact pressure. Results of this work indicate that, from the biomechanical standpoint, the adaptive nail, i.e. AINIM, with an innovative interlocking mechanism, compared to the customary nailing, can lessen intra- and post-operative malalignment occurrence, and it also mitigates the side effects of stress shielding, and thus better conserves neighboring bone density in a long period.

scholarly journals A validated finite element study of stress shielding in a novel hybrid knee implant

2021 ◽  
Author(s):  
Ziauddin Mahboob
Keyword(s):  
Experimental Study ◽  
Finite Element ◽  
Finite Element Model ◽  
Bone Tissue ◽  
Stress Shielding ◽  
Stress Transfer ◽  
Element Model ◽  
Implant Design ◽  
Polyamide 12 ◽  
Compressive Loads

This study (1) proposes a hybrid knee implant design to improve stress transfer to bone tissue in the distal femur by modifying a conventional femoral implant to include a layer of carbon fibre reinforced polyamide 12, and (2) develops a finite element model of the prosthetic knee joint, validated by comparison with a parallel experimental study. The Duracon knee system was used in the experimental study, and its geometry was modelled using CAD software. Synthetic bone replicas were used instead of cadaveric specimens in the experiments. The strains generated on the femur and implant surfaces were measured under axial compressive loads of 2000 N and 3000 N. A mesh of 105795 nodes was needed to obtain sufficient accuracy in the finite element model, which reproduced the experimental reading within 10-23% in six of the eight test locations. The model of the proposed hybrid design showed considerable improvements in stress transfer to the bone tissue at three test flexion angles of 0°, 20°, and 60°.

Nonlinear Finite Element Model Predicts Vertebral Bone Strength and Fracture Site

Spine ◽  
2006 ◽  
Vol 31 (16) ◽  
pp. 1789-1794 ◽  
Author(s):  
Kazuhiro Imai ◽  
Isao Ohnishi ◽  
Masahiko Bessho ◽  
Kozo Nakamura
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Bone Strength ◽  
Element Model ◽  
Fracture Site ◽  
Nonlinear Finite Element ◽  
Vertebral Bone ◽  
Nonlinear Finite Element Model

scholarly journals A validated finite element study of stress shielding in a novel hybrid knee implant

2021 ◽  
Author(s):  
Ziauddin Mahboob
Keyword(s):  
Experimental Study ◽  
Finite Element ◽  
Finite Element Model ◽  
Bone Tissue ◽  
Stress Shielding ◽  
Stress Transfer ◽  
Element Model ◽  
Implant Design ◽  
Polyamide 12 ◽  
Compressive Loads

This study (1) proposes a hybrid knee implant design to improve stress transfer to bone tissue in the distal femur by modifying a conventional femoral implant to include a layer of carbon fibre reinforced polyamide 12, and (2) develops a finite element model of the prosthetic knee joint, validated by comparison with a parallel experimental study. The Duracon knee system was used in the experimental study, and its geometry was modelled using CAD software. Synthetic bone replicas were used instead of cadaveric specimens in the experiments. The strains generated on the femur and implant surfaces were measured under axial compressive loads of 2000 N and 3000 N. A mesh of 105795 nodes was needed to obtain sufficient accuracy in the finite element model, which reproduced the experimental reading within 10-23% in six of the eight test locations. The model of the proposed hybrid design showed considerable improvements in stress transfer to the bone tissue at three test flexion angles of 0°, 20°, and 60°.

Evaluating a NiTi Implant Under Realistic Loads: A Simulation Study

2016 ◽  
Author(s):  
Amirhesam Amerinatanzi ◽  
Narges Shayesteh Moghaddam ◽  
Hamdy Ibrahim ◽  
Mohammad Elahinia
Keyword(s):  
Finite Element ◽  
Additive Manufacturing ◽  
Finite Element Model ◽  
Cortical Bone ◽  
Reconstructive Surgery ◽  
Stress Shielding ◽  
Element Model ◽  
Patient Specific ◽  
Porous Niti ◽  
Biocompatible Alloys

Additive manufacturing (i.e. 3D printing) has only recently be shown as a well-established technology to create complex shapes and porous structures from different biocompatible metal powder such as titanium, nitinol, and stainless steel alloys. This allows for manufacturing bone fixation hardware with patient-specific geometry and properties (e.g. density and mechanical properties) directly from CAD files. Superelastic NiTi is one of the most biocompatible alloys with high shock absorption and biomimetic hysteresis behavior. More importantly, NiTi has the lowest stiffness (36–68 GPa) among all biocompatible alloys [1]. The stiffness of NiTi can further be reduced, to the level of the cortical bone (10–31.2 GPa), by introducing engineered porosity using additive manufacturing [2–4]. The low level of fixation stiffness allows for bone to receive a stress profile close to that of healthy bone during the healing period. This enhances the bone remodeling process (Wolf’s Law) which primarily driven by the pattern of stress. Also, this match in the stiffness of bone and fixation mitigates the problem of stress shielding and detrimental stress concentrations. Stress shielding is a known problem for the currently in-use Ti-6Al-4V fixation hardware. The high stiffness of Ti-6Al-4V (112 GPa) compared to bone results in the absence of mechanical loading on the adjacent bone that causes loss of bone mass and density and subsequently bone/implant failure. We have proposed additively manufactured porous NiTi fixation hardware with a patient-specific stiffness to be used for the mandibular reconstructive surgery (MRS). In MRS, the use of metallic fixation hardware and double barrel fibula graft is the standard methodology to restore the mandible functionality and aesthetic. A validated finite element model was developed from a dried cadaveric mandible using CT scan data. The model simulated a patient’s mandible after mandibular reconstructive surgery to compare the performance of the conventional Ti-6Al-4V fixation hardware with the proposed one (porous superelastic NiTi fixation plates). An optimized level of porosity was determined to match the NiTi equivalent stiffness to that of a resected bone, then it was imposed to the simulated fixation plates. Moreover, the material property of superelastic NiTi was simulated by using a validated customized code. The code was calibrated by using DSC analysis and mechanical tests on several prepared bulk samples of Ni-rich NiTi. The model was run under common activities such as chewing by considering different levels of the applied fastening torques on screws. The results show a higher level of stress distribution on mandible cortical bone in the case of using NiTi fixation plates. Based on wolf’s law it can lead to a lower level of stress shielding on the grafted bone and over time bone can remodel itself. Moreover, the results suggest an optimum fastening torque for fastening the screws for the superelastic fixations causes more normal distribution of stress on the bone similar to that for the healthy mandible. Finally, we successfully fabricated the stiffness-matched porous NiTi fixation plates using selective laser melting technique, and they were mounted on the dried cadaveric mandible used to create the finite element model.

scholarly journals Biomechanical Evaluation Of Periprosthetic Femoral Fracture Fixation

2021 ◽  
Author(s):  
Seung Y.R. Kim
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Stress Shielding ◽  
Element Model ◽  
The Other ◽  
Bone Plate ◽  
Shielding Effect ◽  
Fixation Method ◽  
Periprosthetic Femoral Fracture ◽  
The Finite Element Model

This study proposes a bone plate fixation method to reduce the stress shielding effect on the fractured periprosthetic femur fixed with a metallic bone plate. The goal of this study is to design the finite element models of 5 bone plate attachment configurations applied to the periprosthetic femur fractured at 2 different levels (one with simple transverse fracture at mid-shaft with 1mm gap, and the other with 5mm gap at the fracture site simulating bone loss), and to validate the results by comparing with the experimental study. The average stiffness of the intact femur construct was 2502 N/mm which decreased to 1803 N/mm and 801 N/mm for a 1mm and 5mm gap construct, respectively. The finite element model predicted the stiffness results of the experiments within 10% for the 1mm gap fracture case. The finite element model was less reliable when used to predict the stiffness values in the 5mm gap fracture case. The construct fixed only with cables in the proximal femur resulted in the least amount of stress shielding while maintaining a similar level of stiffness compared to the other configurations.

scholarly journals Biomechanical Evaluation Of Periprosthetic Femoral Fracture Fixation

2021 ◽  
Author(s):  
Seung Y.R. Kim
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Stress Shielding ◽  
Element Model ◽  
The Other ◽  
Bone Plate ◽  
Shielding Effect ◽  
Fixation Method ◽  
Periprosthetic Femoral Fracture ◽  
The Finite Element Model

This study proposes a bone plate fixation method to reduce the stress shielding effect on the fractured periprosthetic femur fixed with a metallic bone plate. The goal of this study is to design the finite element models of 5 bone plate attachment configurations applied to the periprosthetic femur fractured at 2 different levels (one with simple transverse fracture at mid-shaft with 1mm gap, and the other with 5mm gap at the fracture site simulating bone loss), and to validate the results by comparing with the experimental study. The average stiffness of the intact femur construct was 2502 N/mm which decreased to 1803 N/mm and 801 N/mm for a 1mm and 5mm gap construct, respectively. The finite element model predicted the stiffness results of the experiments within 10% for the 1mm gap fracture case. The finite element model was less reliable when used to predict the stiffness values in the 5mm gap fracture case. The construct fixed only with cables in the proximal femur resulted in the least amount of stress shielding while maintaining a similar level of stiffness compared to the other configurations.

Sign in / Sign up

Export Citation Format

Share Document