Computational Mechanical Analysis of AO 44A1, 44B1, and 44C1 Fractures with Finite Element Modeling: Evaluation of Screw, Plate, and Kirschner Wire Fixation.

BACKGROUND: The aim of this study was to create AO 44A1, 44B1, and 44C1 fractures using finite element analysis to determine the stability of Kirschner wire, intramedullary screw, and plate-screw fixation methods in fracture. METHODS: Using finite element analysis, the postreduction behavior of AO 44A1, 44B1, and 44C1 fractures with Kirschner wire, intramedullary screw, and plate-screw fixation methods was analyzed and compared in terms of displacement and stress. RESULTS: The lowest amount of displacement was provided with the intramedullary screw method in AO 44A1 and 44B1 fractures and with the 4-mm Kirschner wire method in AO 44C1 fractures. The total displacement of the intramedullary screw system used for fixation in AO 44A1, 44B1, and 44C1 fractures was lower. CONCLUSIONS: According to finite element analysis results, the lowest amount of displacement was obtained with intramedullary screw fixation in AO 44A1 and 44B1 fractures, and 4-mm Kirschner wire fixation was achieved in AO 44C1 fractures.

Biomechanical effect of ankle ligament injury in AO 44B2.1 lateral malleolus fractures after lateral plate fixation: A finite element analysis.

BACKGROUND: Distal fibula fractures at the ankle level are common and are usually accompanied by ligament injuries. This study aims to evaluate the effects of ankle ligament ruptures on ankle joints, fracture instability, and plate stress after distal fibula fracture fixed with plate created by finite element analysis (FEA) modeling and loading applied to ligament rupture models that may accompany this fracture. METHODS: A finite element model consisting of 3-D (3D) fibula, tibia, foot bones, and ankle ligaments was designed to investigate the effects of ligament injuries accompanying plate-detected Arbeitsgemeinschaft für Osteosynthesefragen (AO 44B2.1)-type fractures on fracture detection, fixation material, and ankle joints. Then, the results were evaluated by modeling ligament rupture in 6 different ways. RESULTS: In the modeling where the deltoid and the talofibular ligament are broken together, instability is the highest in the ankle (2.31 mm) and fracture line (0.15 mm). In our study, the rupture of the tibiofibular anterior and posterior ligaments associated with syndesmosis caused less instability in the fracture and ankle than the single rupture models of both the deltoid and the talofibular ligament. CONCLUSIONS: In the finite element modeling of AO 44B2.1-type fractures detected with plate, the importance and potential effects of often overlooked ankle ligaments are pointed out shown. It is important to keep in mind that when treating ankle injuries, the ankle should be treated as a whole, with both bone and soft tissue. In some cases, the fracture may represent the visible tip of the iceberg.

Can a coracoclavicular screw added to the clavicular hook plate reduce subacromial stress? A finite element analysis.

OBJECTIVES: The aim of this study was to investigate the stresses on the plate and the clavicle in the standard clavicular hook plate model and the clavicular hook plate models with a coracoclavicular (CC) screw by finite element analysis (FEA). MATERIALS AND METHODS: The FEA models were created with the combination of acromion, clavicle, coracoid process, 8-hole clavicular hook plate and screw components. Model 1 was created as a standard clavicular hook plate model and plates were implanted to the clavicle and the acromion by six locking screws. Model 2 was created by a cortical screw placed in the coracoid process through the third hole of the plate (CC screw) and fixation of hook plate by five locking screws. The upward-pull force was applied to clavicle at the insertion of sternocleidomastoid muscle with three axes. The stress exerted by acromion on the hook of the plate, stresses on the plate, clavicle, and CC screw were analyzed. RESULTS: When the screw holes were compared, in Model 1, the highest stress was found in the last hole of the plate. In Model 2, the highest stress was detected on the CC screw. The stress on the clavicle was found to be 0.14 Mpa in Model 1 and 0.21 Mpa in Model 2. In Model 1 and Model 2, the stress exerted by acromion on the subacromial part of the plate was found to be 2.05 KPa and 1.66x10-6 KPa, respectively. CONCLUSION: The results of this study show that addition of CC screw to the standard clavicular hook plate shares the loading and reduces the stress on the hook of the plate.

Computational wear of knee implant polyethylene insert surface under continuous dynamic loading and posterior tibial slope variation based on cadaver experiments with comparative verification.

BACKGROUND: The effect of posterior tibial slope on the maximum contact pressure and wear volume of polyethylene (PE) insert were not given special attention. The effects of flexion angle, Anterior-Posterior (AP) Translation, and Tibial slope on the max contact pressure and wear of PE insert of TKR were investigated under loadings which were obtained in cadaver experiments by using Archard's wear law. This study uses not only loads obtained from cadaver experiments but also dynamic flexion starting from 0 to 90 degrees. METHOD: Wear on knee implant PE insert was investigated using a 2.5 size 3 dimensional (3D) cruciate sacrificing total knee replacement model and Finite Element Method (FEM) under loadings and AP Translation data ranging from 0 to 90 flexion angles validated by cadaver experiments. Two types of analyses were done to measure the wear effect on knee implant PE insert. The first set of analyses included the flexion angles dynamically changing with the knee rotating from 0 to 90 angles according to the femur axis and the transient analyses for loadings changing with a certain angle and duration. RESULTS: It is seen that the contact pressure on the PE insert decreases as the cycle increases for both Flexion and Flexion+AP Translation. It is clear that as the cycle increases, the wear obtained for both cases increases. The loadings acting on the PE insert cannot create sufficient pressure due to the AP Translation effect at low speeds and have an effect to reduce the wear, while the effect increases with the wear as the cycle increases, and the AP Translation now contributes to the wear at high speeds. It is seen that as the posterior tibial slope angle increases, the maximum contact pressure values slightly decrease for the same cycle. CONCLUSIONS: This study indicated that AP Translation, which changes direction during flexion, had a significant effect on both contact pressure and wear. Unlike previous similar studies, it was seen that the amount of wear continues to increase as the cycle increases. This situation strengthens the argument that loading and AP Translation values that change with flexion shape the wear effects on PE Insert.

Comparative finite element analysis of four different internal fixation implants for Pauwels type III femoral neck fractures in various fracture angles in the sagittal plane.

OBJECTIVES: This study aimed to evaluate the performance of four different fixation techniques for Pauwels type III femoral neck fractures considering the fracture morphology in the sagittal plane. MATERIALS AND METHODS: We constructed three different fracture morphologies in the sagittal plane in Pauwels type III femoral neck fractures: posteriorly angled at 20°, neutral, and anteriorly angled at 20°. We set up four fixation devices, including three cannulated screws (3CS), a dynamic hip screw with an antirotational screw (DHS+CS), a proximal femoral locking plate (PFLP), and three cannulated screws with a medial buttress plate (3CS+MBP). The twelve models were created and analyzed using the finite element analysis. RESULTS: The finite element analysis revealed that 3CS+MBP yields better results in total vertical and rotational displacements, regardless of the fracture angle in the sagittal plane. For the anterior and posterior angled fractures in the sagittal plane, the PFLP was superior to the DHS+CS. However, the DHS+CS exhibited less displacement than the PFLP in the neutral fracture line in the sagittal plane. The 3CS group demonstrated poor mechanical stability for Pauwels type III fractures. CONCLUSION: Regardless of the fracture line in the sagittal plane, the 3CS+MBP showed better biomechanical behaviors than the 3CS, DHS+CS, and PFLP. In addition, in contrast to the DHS+CS, the PFLP displayed less vertical and rotational displacement in the anterior and posterior fracture lines in the sagittal plane.

Is the fracture morphology in the sagittal plane important in determining the ideal placement of the lag screw in intertrochanteric femoral fractures?: Ideal lag screw placement in intertrochanteric fractures in the sagittal plane.

OBJECTIVE: The aim of this study was to determine the ideal placement of the lag screw taking into account the fracture morphology in the sagittal plane. MATERIALS AND METHODS: Three different morphology of fractures were created on the sagittal plane in femur models obtained in 3D CT scanning: posteriorly angled (Type A), transverse (Type B) and anteriorly angled (Type C). The lag screw was applied in each of the three fracture morphology as neutral, anteverted and retroverted in the sagittal plane. The nine models created were transferred to the Ansys Workbench program and analyzes were performed. RESULTS: In Type A fracture, the stress value at the lag screw apex increase as the lag screw placement changes from the anteverted position to the retroverted position. It decreases in the Type B and Type C fractures. As the lag screw placement is changed towards the anteverted position, the stress at the lag screw-nail junction decreases in the Type A fracture and increases in the Type C fracture . There is no significant change in the Type B fracture. As the lag screw placement is changed towards the anteverted position, the stress in the calcar region increases in Type A fractures and decreases in Type C fractures. There is no significant change in type B fractures. CONCLUSION: While the ideal lag screw placement in a type A fracture in the sagittal plane is the retroverted placement, the anteverted placement is ideal placement in type C fractures. Fracture morphology in the sagittal plane should be taken into account in the lag screw placement.

A new proximal femoral nail antirotation design: Is it effective in preventing varus collapse and cut-out?

OBJECTIVES: This study aims to compare the mechanical features of the existing proximal femoral nail antirotation (PFNA) system and the new PFNA system that we designed using three-dimensional (3D) finite element analysis. MATERIALS AND METHODS: This experimental study was conducted between 2019 and 2020. We constructed two femur models with Arbeitsgemeinschaft für Osteosynthesefragen (AO) type A1 fractures using 3D computed tomography scans. The new and standard PFNA designs were inserted into the femur models and subsequently transferred to the program. We investigated the distribution of stress on the tip of the lag screw, the calcar region, lag screw-nail junction, and the additional screw inserted through the greater trochanter (only present in the new PFNA design) using 3D finite element analysis. RESULTS: When the von Mises stress distributions in our models were examined, the maximum stress at the lag screw-nail junction was 18 mpa in the new design PFNA, while it was 20 mpa in the classic PFNA model. The maximum stress at the junction of the additional screw that had greater trochanter inlet with the nail was found as 42.5 mpa. The maximum stress on the calcar region was found to be 10 mpa at the new design PFNA, while it was 13 mpa with 30% increase in the classic PFNA. The stress on the tip of the lag screw was found to be 49 mpa in the classic PFNA design, while in the new design PFNA it was found as 28 mpa with a decrease of more than 40%. CONCLUSION: As per our findings, the new PFNA design leads to reduced stress on the lag screw-nail junction, the calcar region, and the tip of the lag screw.