A comparative mechanical study of two types of femur bone implant using the finite element method

New Surgical Devices for Closed Reduction of Frontal Sinus Bone Fracture

Traditional surgical interventions for frontal sinus fractures necessitate a cut on the forehead skin, and extant closed reduction techniques aimed at enhancing accessibility continue to grapple with secure tool fixation, stable bone elevation, and screw breakage risk. To address these challenges and augment surgical efficiency, this study introduces novel surgical devices. Design parameters for models with spiral or L-shaped tips are established, considering practical medical requirements and constraints, and subsequently validated through finite element method numerical simulations using commercial software, Ansys. Four spiral-type prototypes are constructed, and three scenarios for each prototype, varying in projection distance from the device handle to the bone-device contact point, are examined via nonlinear simulation analyses. For the L-shaped type, three prototypes are developed, and static analyses are conducted for four scenarios per prototype, differing in traction force locations, based on another simulation result concerning moments of inertia calculation with a force boundary condition unlike pressure. Maximum stress results under a specific force are analyzed, and the maximum permissible force is determined under the most unfavorable force application condition. Simulation outcomes indicate that the spiral type offers greater applicability with less force to lift multiple bones, while the L-shaped type is more suitable under bone hardening conditions.

The Influence Mechanism of Screw Internal Fixation on the Biomechanics of Lateral Malleolus Oblique Fractures

It remains inconclusive about the stability and optimal fixation scheme of screw internal fixation for lateral malleolus oblique fractures in clinical practice. In this study, the effects of different screw internal fixation methods on the biomechanics of lateral malleolus oblique fractures were investigated. These efforts are expected to lay a theoretical foundation for the selection of internal fixation methods and rehabilitation training regimens in the treatment of lateral malleolus fractures. A healthy ankle joint model and a lateral malleolus fracture internal fixation model were established based on CT data with the aid of some software. Besides, the effects of screw internal fixation modalities on the fracture displacement of fibula fractures, fibula Von Mises stress, and screw Von Mises stress under different physiological conditions and loading conditions were investigated using finite element methods (FEMs) and in vitro physical experiments. The double screw vertical fibular axis internal fixation approach had the lowest fracture displacement of fibula fractures and screw Von Mises stress values; while the double screw vertical fracture line internal fixation approach had the lowest fibula Von Mises stress values. Under different physiological conditions, the magnitude of the peak Von Mises stress of the fibula and screw was ranked as plantarflexion 20° > plantarflexion 10° > neutral position > dorsiflexion 10° > dorsiflexion 20°; and the magnitude of the peak displacement of the fibula fracture breaks was ranked as plantarflexion 20° > plantarflexion 10° > neutral position > dorsiflexion 20° > dorsiflexion 10°. The results of in vitro physical experiments and finite element analyses were in good agreement, which validated the validity of finite element analyses. The vertical fracture line screw implantation method displays a better load-sharing ability; while the vertical fibular axis screw implantation method exhibits a better ability to prevent axial shortening of the fibula and also reduces the risk of screw fatigue damage. Overall, the double screw achieves better therapeutic effects than the single screw. Given that the ankle joint has high stability in the dorsiflexion position, it is recommended to prioritize dorsiflexion rehabilitation training, rather than dorsiflexion and plantarflexion rehabilitation training with too large angles, in the treatment of lateral malleolus fractures.

The ratio between the screw distance and femoral neck width on lateral radiography is a reliable predictor of femoral head necrosis: a clinical review and corresponding numerical simulations

BACKGROUND

Fixation instability serves as an initial trigger for femoral head necrosis in patients with femoral neck fractures undergoing internal fixation. The configuration of screw trajectories is critical in determining the stability of the fixation. Our previously published study indicates that abduction of screw trajectories may enhance postoperative angular stability. However, the effectiveness of a wider screw distribution on the sagittal plane in optimizing fixation stability and reducing the risk of femoral head necrosis remains uncertain.

METHODS

This retrospective study reviewed imaging data from patients with femoral neck fractures who were treated with inverse triangle cannulated screw fixation. Postoperative lateral radiographs were used to evaluate the screw configuration strategy. The distance between the two cranial screws and the femoral neck width at its narrowest point were measured. The ratio of these two measurements was calculated to represent the screw spread grade. Demographic and imaging parameters were compared between patients who developed femoral head necrosis and those who did not. Regression analysis was conducted to identify potential risk factors associated with femoral head necrosis. Additionally, numerical models were employed to simulate the biomechanical impact of variations in screw spread grade.

RESULTS

The clinical analysis revealed that a lower screw distance-to-femoral width ratio was associated with a higher incidence of femoral head necrosis. This ratio was also identified as an independent risk factor for femoral head necrosis. Biomechanical simulations corroborated these findings, demonstrating that models with a lower screw-to-femoral width ratio exhibited reduced fixation stability and increased stress distribution.

CONCLUSIONS

Wider distribution of screws along the sagittal plane may significantly mitigate the risk of femoral head necrosis by enhancing fixation stability. The optimization of screw trajectories, particularly through broader screw spacing facilitated by a navigation system, emerges as a promising strategy for improving the local biomechanical environment and reducing the likelihood of femoral head necrosis.

Impact of blade direction on postoperative femoral head varus in PFNA fixed patients: a clinical review and biomechanical research

Intertrochanteric femur fracture is a common type of osteoporotic fracture in elderly patients, and postoperative femoral head varus following proximal femoral nail anti-rotation (PFNA) fixation is a crucial factor contributing to the deterioration of clinical outcomes. The cross-angle between the implant and bone might influence fixation stability. Although there is a wide range of adjustment in the direction of anti-rotation blades within the femoral neck, the impact of this direct variation on the risk of femoral head varus and its biomechanical mechanisms remain unexplored. In this study, we conducted a retrospective analysis of clinical data from 69 patients with PFNA fixation in our institution. We judge the direction of blade on the femoral neck in on the immediate postoperative lateral X-rays or intraoperative C-arm fluoroscopy, investigating its influence on the early postoperative risk of femoral head varus. p < 0.05 indicates significant results in both correlation and regression analyses. Simultaneously, a three-dimensional finite element model was constructed based on the Syn-Bone standard proximal femur outline, exploring the biomechanical mechanisms of the femoral neck-anti-rotation blade direction variation on the risk of this complication. The results indicated that ventral direction insertion of the anti-rotation blade is an independent risk factor for increased femoral head varus. Complementary biomechanical studies further confirmed that ventral angulation leads to loss of fixation stability and a decrease in fixation failure strength. Therefore, based on this study, it is recommended to avoid ventral directional insertion of the anti-rotation blade in PFNA operation or to adjust it in order to reduce the risk of femoral head varus biomechanically, especially in unstable fractures. This adjustment will help enhance clinical outcomes for patients.

The significance of reduction of valgus-intercalated femoral neck fracture with valgus angle > 15°and the selection of internal fixation by finite element analysis

BACKGROUND

Currently, consensus is lacking on the necessity of internal fixation after reducing valgus-intercalated femoral neck fractures with abduction > 15°. This study employs finite element analysis to compare the biomechanical differences between the femoral neck dynamic cross nail system (FNS) and inverted cannulated screw (ICS), aiming to provide a foundation for clinical procedures.

METHODS

Human femur CT scan data were processed using MimICS21.0 and Geomagic 2021 software, imported into Solidworks2021 to create fracture models, based on Garden I abduction and Valgus-intercalated femoral neck fractures. The internal fixation model was divided into two groups: A-Anatomic reduction group; B-Valgus-intercalated femoral neck fracture group. ANSYS software facilitated meshing, material assignment, and data calculation for stress and displacement comparisons when ICS and FNS were applied in reduction or non-reduction scenarios.

RESULTS

Without internal fixation, peak femur stress in both groups was 142.93 MPa and 183.62 MPa. Post FNS fixation, peak stress was 254.11 MPa and 424.81 MPa; peak stresses for the two FNS models were 141.26 MPa and 248.33 MPa. Maximum displacements for the two FNS groups were 1.91 mm and 1.26 mm, with peak fracture-end stress at 50.751 MPa and 124.47 MPa. After ICS fixation, femur peak stress was 204.76 MPa and 274.08 MPa; maximum displacements were 1.53 mm and 1.15 mm. ICS peak stress was 123.88 MPa and 174.61 MPa; maximum displacements were 1.17 mm and 1.09 mm, with peak fracture-end stress at 61.732 MPa and 104.02 MPa, respectively.

CONCLUSIONS

Our finite element study indicates superior mechanical stability with internal fixation after reducing valgus-intercalated femoral neck fractures (> 15°) compared to in situ fixation. Additionally, ICS biomechanical properties are more suitable for this fracture type than FNS.

Prediction of the biomechanical behaviour of the lumbar spine under multi-axis whole-body vibration using a whole-body finite element model

Low back pain has been reported to have a high prevalence among occupational drivers. Whole-body vibration during the driving environment has been found to be a possible factor leading to low back pain. Vibration loads might lead to degeneration and herniation of the intervertebral disc, which would increase incidence of low back problems among drivers. Some previous studies have reported the effects of whole-body vibration on the human body, but studies on the internal dynamic responses of the lumbar spine under multi-axis vibration are limited. In this study, the internal biomechanical response of the intervertebral disc was extracted to investigate the biomechanical behaviour of the lumbar spine under a multi-axial vibration in a whole-body environment. A whole-body finite element model, including skin, soft tissues, the bone skeleton, internal organs and a detailed ligamentous lumbar spine, was used to provide a whole-body condition for analyses. The results showed that both vibrations close to vertical and fore-and-aft resonance frequencies would increase the transmission of vibrations in the intervertebral disc, and vertical vibration might have a greater effect on the lumbar spine than fore-and-aft vibration. The larger deformation of the posterior region of the intervertebral disc in a multi-axis vibration environment might contribute to the higher susceptibility of the posterior region of the intervertebral disc to injury. The findings of this study revealed the dynamic behaviours of the lumbar spine in multi-axis vehicle vibration conditions, and suggested that both vertical and fore-and-aft vibration should be considered for protecting the lumbar health of occupational drivers.

Lateral cortical notching facilitates dynamization of proximal femoral nailing - A finite element analysis

INTRODUCTION

Dynamization of proximal femoral nailing by removal of distal interlocking is one of the recommended treatment options for nonunions of femur fractures. However, in certain inter-/subtrochanteric fractures, gliding of the nail along the femoral shaft is blocked by lateral femoral cortical support of the lag screw. For these cases, Biber et al. proposed lateral cortical notching (LCN), in which the supporting lateral bone is removed. This study investigates the biomechanical effect of LCN on gliding of proximal femoral nailing and stress distribution at the bone/implant interface.

MATERIALS AND METHODS

In this finite element analysis a three-dimensional model of an unstable intertrochanteric fracture with proximal femoral nailing without distal interlocking was simulated using the FebioStudio software suite. To simulate LCN, the lag screw hole was lengthened to 15.34 mm at the lateral cortex. Displacement of the nail along the femoral shaft axis and von Mises stress distribution were compared between LCN model and standard implantation model.

RESULTS

Displacement of the nail along the femoral shaft axis was higher in the LCN model than in the standard implantation model (0.48 mm vs. 0.07 mm). Highest von Mises stresses of 176-178 MPa at the implant and of 52-81 MPa at the proximal femur were detected. Maximum von Mises stresses of the implant were comparable at all sides, except for a reduced von Mises stress at the lateral inferior side in the LCN model (80 vs. 102 MPa). At the inferior lateral screw hole and the anterior/posterior lateral screw hole maximum von Mises stress was reduced in the LCN model (2 vs. 49 MPa and 52 vs. 81 MPa), whereas the maximum von Mises stress at the inferior medial screw hole was higher in the LCN model than in the standard implantation model (53 vs. 27 MPa).

CONCLUSIONS

Lateral cortical notching facilitates gliding of a distally dynamized proximal femoral nail along the femoral shaft axis in intertrochanteric fractures. Additionally, the lack of lateral cortical bone support at the lag screw reduces von Mises stress at the bone/implant interface and thus could lower the risk for implant breakage and peri‑implant fractures.

Finite element comparative analysis of three different internal fixation methods in the treatment of Pauwels type III femoral neck fractures

BACKGROUND

Comparison of 4 cannulated lag screws (3 inverted triangular cannulated screws + anti-rotating screws;4 CLS), dynamic hip screws + derotational screws (DHS + DS), and femoral neck fixation system (FNS) in the treatment of Biomechanical properties of middle-aged Pauwels type III femoral neck fractures.

METHODS

The femur CT data of a healthy young volunteer was selected and imported into Mimics software to construct a three-dimensional model of a normal femur. Pauwels type III femoral neck fractures were simulated according to the 70° fracture line. Use Geomagic and SolidWorks software to optimize and build CLS, DHS + DS, and FNS fracture internal fixation models. Finally, Ansys software was used to analyze the stress distribution, peak value, and maximum displacement of the proximal fracture fragment and internal fixation; the displacement distribution, and peak value of the fracture surface at the fracture end.

RESULTS

① The stress peaks of the proximal fracture fragments in the three groups were concentrated near the femoral calcar. The peak stress of the FNS group was the largest, and the DHS + DS group was the smallest. ②The displacement of the fracture fragments was all located at the top of the femur. The peak displacement of the FNS group was the largest, and the DHS + DS group was the smallest. ③ The internal fixation stress of the three groups is concentrated in the middle part of the device. The stress distribution of the first two groups of models is more uniform than that of FNS. The peak stress of FNS is the largest and the CLS is the smallest. ④ The internal fixed displacements are all located at the top of the model. The peak displacement of the CLS is the largest, and the DHS + DS is the smallest. ⑤ The displacement of the fracture surface is in the upper part of the fractured end. The peak displacement of the FNS group was the largest, and the DHS + DS group was the smallest.

CONCLUSION

Compared with the other two internal fixation methods, dynamic hip screw + derotational screw (DHS + DS) showed good biomechanical stability. When Pauwels type III femoral neck fracture occurs in young adults, DHS + DS can be given priority as the preferred treatment for this type of fracture.

Analysis and validation of a 3D finite element model for human forearm fracture

Most researchers have performed finite element (FE) analysis of the human forearm fracture by exploring the strength and load transmission of the bones. However, few studies concentrated a complete simulation of the whole forearm complex including ligaments. This paper aims to investigate the load transmission through the bones, contact stress at the joints and strain in the ligaments by using an elaborate FE model, further validating the fracture condition for human forearm. The interosseous ligament was separated into three regions based on the distance to the proximal and distal ends. The FE simulation results were slightly more or less than a previous experimental data in the literature, but generally provided a close approximation of the bone and ligament behaviors. Compared with the experiment results under different loading conditions, maximum contact stress at the proximal radio ulnar joint (PRUJ) and distal radio ulnar joint (DRUJ) of the simulations was higher with an average of 13.4%, and peak strain in the interosseous ligament (IOL) was lower with an average of 11.0%. Under 10 kg load, the maximum stress in the radius (2.25 MPa) was less than double the value in the ulna (1.43 MPa). Finally, the FE model has been validated with the onset and location of the Colles' fracture in the literature. This study will provide a great benefit in terms of surgical and medical applications related to forearm fracture that require an extensive knowledge of the behavior of the bones and ligaments under various loading conditions.