Evaluation of dentinal fluid flow behaviours: a fluid-structure interaction simulation

Biomechanical comparison between low profile 2.7 mm distal locking hook plate and 3.5 mm distal locking hook plate for acromioclavicular joint injury: A finite element analysis

PURPOSE

Although hook plate fixation is popularly used, concerns exist regarding periprosthetic fractures and the necessity to remove the plate to prevent subacromial erosion and subsequent acromion fracture, due to its non-anatomical design. We hypothesized that a low profile 2.7 mm distal locking hook plate would provide comparable stability to a properly used 3.5 mm distal locking hook plate MATERIALS AND METHODS: A 3.5 mm distal locking plate (type 1) and a low profile 2.7 mm plate (type 2) were assessed by finite element analysis. Peak von Mises stress (PVMS) was calculated on the acromion's undersurface, clavicle shaft, and hook, focusing on how these stresses varied with the number and placement of distal locking screws.

RESULTS

Increased distal screws in both types led to lower PVMS on the acromion's undersurface and the hook, with the lowest acromion PVMS observed in type 2 with three distal screws, and on the hook in type 1 with two distal screws. Increasing the number of distal screws similarly reduced PVMS on the clavicle shaft, with the lowest in type 1 with two distal screws. In both plate types, the most posterior distal locking screw played a crucial role in distributing stress across the acromion and the hook.

CONCLUSION

The low profile 2.7 mm distal locking hook plate showed comparable biomechanical results to the 3.5 mm distal locking hook plate. Increasing the number of distal locking screws showed less stress concentration on the bone and hook in both models. The most posterior distal locking screw showed an essential role in stress distribution.

BIOMECHANICAL EFFECT OF DIFFERENT LAG SCREW LENGTHS WITH DIFFERENT BARREL LENGTHS IN DYNAMIC HIP SCREW SYSTEM: A FINITE ELEMENT ANALYSIS STUDY

The dynamic hip screw (DHS) system is commonly used to treat intertrochanteric fracture of the hip joint. Breakage of the lag screw was noted in clinical practice and the length of lag screw as well as the length of the side plate in the DHS system appeared to play a role in the risk of breakage. Thus, the aim of this study was to investigate the biomechanical effect of different lag screw lengths and barrel plate lengths in the DHS implant system by finite element analysis (FEA). Four FEA simulation models were created according to different lengths of lag screw (79[Formula: see text]mm and 63[Formula: see text]mm) and different lengths of barrel side plate (43[Formula: see text]mm and 37[Formula: see text]mm). The von Mises stress was used as the observation indicator. The results showed that the maximum tensile stress on the long lag screw was slightly greater than that of the shorter lag screw. Use of a shorter barrel side plate may also cause high stress between the lag screw and the barrel side plate. This finding provides biomechanical reference data that may be of value to orthopedic surgeons with respect to choice of implant size and length in the treatment of intertrochanteric fracture with a DHS system to prevent complications such as implant failure caused by broken lag screws.

INFLUENCE OF THREE DIFFERENT CURVATURES FLEX-FOOT PROSTHESIS WHILE SINGLE-LEG STANDING OR RUNNING: A FINITE ELEMENT ANALYSIS STUDY

Flex foot device was one of the most common prosthesis for the athletes with the transtibial amputation on the recent market. Thus, the results of investigation with biomechanics on the flex foot would be a considerable impact on the performance of disabled athletes wearing the flex foots. This study was designed to investigate the biomechanical condition of the flex foot prosthesis with different curvatures while standing and running by finite element analysis. This study demonstrated finite element models of flex foot established with three different curvatures 20[Formula: see text] (small bending), 35[Formula: see text] (medium bending) and 50[Formula: see text] (big bending). Besides, it simulates and investigates the condition of flex foot while a person is wearing it with single-leg standing or running. The evaluation indices were selected as von Mises stress and displacements at top of socket surface. The results show that the big-bending flex foot generated the higher stress and the larger deformed displacement. Without exceeding the material tolerance of the flex foot, the larger displacement of big-bending flex foot could generate more energy, which possessed larger resilient potential energy and enabled the athletes to have better performance after using the flex foot. As a result, due to its beneficial property of energy storage and return, the large-bending flex foot user could have better effect. In the future, more innovative designs of the flex foot prosthesis can be laid out with the reference of the result in this study.

Biomechanical analysis of clavicle hook plate implantation with different hook angles in the acromioclavicular joint

PURPOSE

A clavicle hook plate is a simple and effective method for treating acromioclavicular dislocation and distal clavicle fractures. However, subacromial osteolysis and peri-implant fractures are complicated for surgeons to manage. This study uses finite element analysis (FEA) to investigate the post-implantation biomechanics of clavicle hook plates with different hook angles.

METHODS

This FEA study constructed a model with a clavicle, acromion, clavicle hook plate, and screws to simulate the implantation of clavicle hook plates at different hook angles (90°, 95°, 100°, 105°, and 110°) for treating acromioclavicular joint dislocations. This study investigated the biomechanics of the acromion, clavicle, hook plate, and screws.

RESULTS

A smaller hook angle increases the stress on the middle third of the clavicle. A larger hook angle increases the force exerted by the clavicle hook plate on the acromion. The screw at the most medial position on the plate generated the highest stress. The highest stress on the implanted clavicle hook plate was on the turning corner of the hook.

CONCLUSIONS

A clavicle hook plate with different hook angles may induce different biomechanical behaviors in the clavicle and acromion. Orthopedic surgeons must select a suitable clavicle hook plate based on the anatomical structure of each patient.

Biomechanical Analysis of Implanted Clavicle Hook Plates With Different Implant Depths and Materials in the Acromioclavicular Joint: A Finite Element Analysis Study

Clinical implantation of clavicle hook plates is often used as a treatment for acromioclavicular joint dislocation. However, it is not uncommon to find patients that have developed acromion osteolysis or had peri-implant fracture after hook plate fixation. With the aim of preventing complications or fixation failure caused by implantation of inappropriate clavicle hook plates, the present study investigated the biomechanics of clavicle hook plates made of different materials and with different hook depths in treating acromioclavicular joint dislocation, using finite element analysis (FEA). This study established four parts using computer models: the clavicle, acromion, clavicle hook plate, and screws, and these established models were used for FEA. Moreover, implantations of clavicle hook plates made of different materials (stainless steel and titanium alloy) and with different depths (12, 15, and 18 mm) in patients with acromioclavicular joint dislocation were simulated in the biomechanical analysis. The results indicate that deeper implantation of the clavicle hook plate reduces stress on the clavicle, and also reduces the force applied to the acromion by the clavicle hook plate. Even though a clavicle hook plate made of titanium alloy (a material with a lower Young's modulus) reduces the force applied to the acromion by the clavicle hook plate, slightly higher stress on the clavicle may occur. The results obtained in this study provide a better reference for orthopedic surgeons in choosing different clavicle hook plates for surgery.

Role of the compression screw in the dynamic hip-screw system: A finite-element study

The dynamic hip-screw (DHS) system is a common implant for fixation of proximal femur fractures. During assembly, it has been recommended to remove the compression screw after initial compression has been obtained; however, related complications had been reported. So far, the role of compression screw in the reconstructed stability of hip fractures as well as the mechanical strength of the DHS system has rarely been mentioned. This study investigated the function of this screw in the DHS system during fracture healing. Based on the FE method, six numerical models of proximal femur were employed to analyze the mechanical response of a DHS implant with various fracture types and different fixation strategies (with or without a compression screw). The displacement of the femur head and peak von Mises stress were selected as indices of the stability of a fractured femur stabilized by a DHS device and of the risk of implant failure, respectively. Our results showed that a retained compression screw increased reconstructed structural stiffness, reducing the displacement of the femur head. This screw also helped to lessen mechanical failure of side plate by reducing the peak von Mises stress around the connection between the barrel and side plate. Both findings were evident in the proximal femur fracture involving the intertrochanteric part, and even more obvious in the setting of bony defects. Thus, we recommend the maintenance of compression screw in the DHS system while treating the intertrochanteric fracture, particularly in cases with bony defects.

Biomechanical analysis of acromioclavicular joint dislocation treated with clavicle hook plates in different lengths

PURPOSE

Clavicle hook plates are frequently used in clinical orthopaedics to treat acromioclavicular joint dislocation. However, patients often exhibit acromion osteolysis and per-implant fracture after undergoing hook plate fixation. With the intent of avoiding future complications or fixation failure after clavicle hook plate fixation, we used finite element analysis (FEA) to investigate the biomechanics of clavicle hook plates of different materials and sizes when used in treating acromioclavicular joint dislocation.

METHODS

Using finite element analysis, this study constructed a model comprising four parts: clavicle, acromion, clavicle hook plate and screws, and used the model to simulate implanting different types of clavicle hook plates in patients with acromioclavicular joint dislocation. Then, the biomechanics of stainless steel and titanium alloy clavicle hook plates containing either six or eight screw holes were investigated.

RESULTS

The results indicated that using a longer clavicle hook plate decreased the stress value in the clavicle, and mitigated the force that clavicle hook plates exert on the acromion. Using a clavicle hook plate material characterized by a smaller Young's modulus caused a slight increase in the stress on the clavicle. However, the external force the material imposed on the acromion was less than the force exerted on the clavicle.

CONCLUSIONS

The findings of this study can serve as a reference to help orthopaedic surgeons select clavicle hook plates.

An investigation of dentinal fluid flow in dental pulp during food mastication: simulation of fluid-structure interaction

This study uses fluid-structure interaction (FSI) simulation to investigate the relationship between the dentinal fluid flow in the dental pulp of a tooth and the elastic modulus of masticated food particles and to investigate the effects of chewing rate on fluid flow in the dental pulp. Three-dimensional simulation models of a premolar tooth (enamel, dentine, pulp, periodontal ligament, cortical bone, and cancellous bone) and food particle were created. Food particles with elastic modulus of 2,000 and 10,000 MPa were used, respectively. The external displacement loading (5 μm) was gradually directed to the food particle surface for 1 and 0.1 s, respectively, to simulate the chewing of food particles. The displacement and stress on tooth structure and fluid flow in the dental pulp were selected as evaluation indices. The results show that masticating food with a high elastic modulus results in high stress and deformation in the tooth structure, causing faster dentinal fluid flow in the pulp in comparison with that obtained with soft food. In addition, fast chewing of hard food particles can induce faster fluid flow in the pulp, which may result in dental pain. FSI analysis is shown to be a useful tool for investigating dental biomechanics during food mastication. FSI simulation can be used to predict intrapulpal fluid flow in dental pulp; this information may provide the clinician with important concept in dental biomechanics during food mastication.