Biomechanical analysis of the treatment of intertrochanteric hip fracture with different lengths of dynamic hip screw side plates

Investigation of dynamic hip plate screw systems in different lengths with finite element analysis

Objectives

Dynamic systems aim to create an environment that encourages bone healing while minimizing stress shielding, which is a phenomenon where the bone loses density due to a lack of stress during the healing process. In this study, it was aimed that the stress distributions on plates of different lengths in the dynamic hip plate screw system were investigated.

Materials and methods

In our study, the human proximal femur model (3-D) obtained from computerized tomography was transferred to Finite Element Analysis (FEA) computer simulation. Plates with 2-4-6 holes were placed on the knitted bone model. The models used in this study were mainly determined as five components: cortical-cancellous bone, lateral plate, cortical screws, and compression neck screws. A 1 mm intertrochanteric fracture area was created from the trochanter major region.

Results

When plates of different lengths were applied, there was no significant difference in the stress in the compression screw and the chamber it was located in.It shows that when a 2-hole plate is used, the stress will be high, especially between the lower cortical screw and the cortex. In these three groups, it was observed that the stress points were in at least 6-hole plates.

Conclusion

The results of this study showed that the shorter the plate applied, the greater the stress on the plate and cortical screws in the femur diaphysis.

Analysis of modified surface topographies of titanium-based hip implants using finite element method

BACKGROUND

In order to ensure the proper function of the cementless hip implant, the connection between the femoral bone and the implant has to be as strong as possible. According to experimental studies, implants with a rough surface reduce micro-movements between femoral bone and implant, which helps form a stronger connection between them.

OBJECTIVE

The goal of this study was to analyze how half-cylinder surface topographies of different diameter values affect shear stress values and their distribution on the surface of the hip implant and trabecular femoral bone.

METHODS

Nine models with different half-cylinder diameter values (200 μm, 400 μm, and 500 μm) and distances between half-cylinders were created for the analysis using the finite element method. Each model consisted of three layers: implant, trabecular, and cortical femoral bone.

RESULTS

For all three diameter values, the highest shear stress value, for the implant layer, was located after the first half-cylinder on the side where force was defined. For the trabecular bone, the first half-cylinder was under lower amounts of shear stress.

CONCLUSION

If we only consider shear stress values, we can say that models with 400 μm and 500 μm diameter values are a better choice than models with 100 μm diameter values.

Design considerations for patient-specific bone fixation plates: a literature review

In orthopedic surgery, patient-specific bone plates are used for fixation when conventional bone plates do not fit the specific anatomy of a patient. However, plate failure can occur due to a lack of properly established design parameters that support optimal biomechanical properties of the plate.This review provides an overview of design parameters and biomechanical properties of patient-specific bone plates, which can assist in the design of the optimal plate.A literature search was conducted through PubMed and Embase, resulting in the inclusion of 78 studies, comprising clinical studies using patient-specific bone plates for fracture fixation or experimental studies that evaluated biomechanical properties or design parameters of bone plates. Biomechanical properties of the plates, including elastic stiffness, yield strength, tensile strength, and Poisson's ratio are influenced by various factors, such as material properties, geometry, interface distance, fixation mechanism, screw pattern, working length and manufacturing techniques.Although variations within studies challenge direct translation of experimental results into clinical practice, this review serves as a useful reference guide to determine which parameters must be carefully considered during the design and manufacturing process to achieve the desired biomechanical properties of a plate for fixation of a specific type of fracture.

Trajectory of bolt and length of plate in femoral neck system determine the stability of femur neck fracture and risk of subsequent subtrochanteric fracture : a finite element analysis

BACKGROUND

This study aimed to analyze the differences in the stability of fractures, stress distribution around the distal-most screw according to the length of the plate and the trajectory of the bolt in Pauwels type III femoral neck fracture using the femoral neck system (FNS).

METHODS

Finite element models of Pauwels type III femoral neck fractures were established with surgical variations in the trajectory of the bolt (central, inferior, valgus, and varus) and length of the lateral plate (1- and 2-hole plate). The models were subsequently subjected to normal walking and stair-climbing loads.

RESULTS

The screw-holding cortical bone in subtrochanter in the model with a 2-hole plate and the bolt in the inferior trajectory and the models with 1-hole or 2-hole plate and the bolt in valgus trajectory had shown greater maximum principal strain than the models with central or varus trajectories. The gap and sliding distance on the fracture surface were larger with inferior or varus trajectories of the bolt and smaller with the valgus trajectory of the bolt under both loads, compared to those of the central trajectory.

CONCLUSION

For the fixation of Pauwels type III femoral neck fracture, the trajectory of the FNS bolt and the length of the plate affect the mechanical stability of the fracture and the strain of cortical bone around the distal-most screw. The surgical target should stay on the central trajectory of the bolt and the 2-hole plate's mechanical benefits did not exceed the risk.

Trochanteric Nails for the Reduction of Intertrochanteric Fractures: A Biomechanical Analysis Based on Finite Element Analysis and DIC System

Purpose

Intertrochanteric fractures are common among femoral fractures in the elderly population. The trochanteric nail is a standard internal fixator used in treating femoral intertrochanteric fractures. The technique of femoral fracture reduction affects the postoperative outcome. Here, we applied finite element analysis (FEA) to study mechanical effects of different reduction approaches using the trochanteric nail in treating both stable and unstable intertrochanteric fractures.

Methods

We combined FEA and in vitro experiments using a digital imaging correlation (DIC) technique to study effects of different alignment conditions after treating 4 cases of intertrochanteric fractures using the trochanteric nail system. A downward force of 2250 N was applied to the femoral head, and the distal end of the femur was fixed. The observed indicators were the femur displacement, together with the stress on the femur and trochanteric nail system. In addition, the displacement distribution was analyzed using DIC.

Results

In the case of space reduction, the force was transmitted by the trochanteric nail system, resulting in greater stress imposed on the femur or the trochanteric nail system. In the case of closed reduction, the stress was much smaller. In the case of unstable fracture reduction, closed reduction was associated with a smaller contact area at the fracture site, resulting in greater stress on both trochanter and the trochanteric nail system.

Conclusion

When the trochanteric nail system was used for fixation, the fracture site was well aligned, reducing the stress on the femur or the trochanteric nail.

Novel Design of Minimal Incision Double Oblique Device for Osteosynthesis (DODO) of Hip: Results of an In-silico Study Based on the Femur Morphometrics of the Northeast (NE) Indian population

BACKGROUND

Hip fractures account for a large proportion of hospitalization among the trauma cases. Low cost, simple technique, easy removal, and high rate of the bone union makes extramedullary (EM) fixation techniques a preferred choice. A close-fit bone and plate are essential for the success of such implantation. Various studies have found femur morphometry being related to regional features and social differences. Most of the available commercial implants are developed based on the data of the Caucasian population.

METHODS

In the herein study, a novel design, Double Oblique Device for Osteosynthesis of hip (DODO), is proposed while considering the regional morphometry of the Northeast (NE) population of India. This study employs finite element (FE) analysis to compare the biomechanical outcome of the new device with that of proximal femoral locking plate (PFLP) and variable angle dynamic hip screw (VA-DHS) on a femur having an Evans type-I intertrochanteric fracture.

RESULTS

The stress shielding was substantially high for the PFLP and VA-DHS in the distal bone fragment (lateral aspect) and for DODO in the femoral head. The difference in axial displacement between the post-implanted DODO-fixed femur and its respective intact femur was predicted to be almost the same as that of PFLP-fixed femur and its respective intact femur.

CONCLUSION

The computational results found the new device to be a viable alternative to the conventional plating techniques, especially for the NE population of India, and predicted better to comparable biomechanical characteristics.