In this study, a fixation plate for ulnar olecranon fracture has been proposed and its performance is analyzed using the finite element method. Four screws are used to stabilize the fracture and the response of intact and fractured bone fixed with the implant plate under physiological loading is investigated. It was observed that the use of the proposed plate can stabilize the olecranon fracture and the stress experienced by the fractured bone, will have a milder distribution when using this plate. In addition, various components of the model, including the ulna bone, screw and fixation plate under the investigated load, showed a stress much lower than the yield stress magnitude. Therefore, the proposed plate demonstrated its effective application in fracture fixation and in the future, the results of this study can be compared with a range of experimental data to ensure the medical application of the plate.

Objective: This study aimed to compare the outcomes of fixing scapholunate with pins and screws in parallel,convergent, and divergent orientations.Methods: In this computer simulation study, the CT scan images of a healthy subject wereused to construct a 3D model of the wrist joint using MIMICS software. The imposed force to scaphoid and3D model lunate bones, as well as the scapholunate angle and distance, were compared in different surgicaltechniques using parallel, divergent, and convergent pins and screws.Results: In the absence of external force, the imposed stress applied to the scaphoid and lunate bones in casesof parallel pins and screws were 7.5MPa, 5.08MPa (pins), 1.134MPa, and 1.151MPa (screws), and 10.90MPa,10.90MPa (pins), 9.7MPa, and 34.1MPa (screws) for 50N flexion force. The imposed stress in this approach issignificantly lower compared to other interventions. Better outcomes were seen regarding scapholunate angleand scapholunate distance in using parallel pins or screws as well.Conclusion: In conclusion, implementing parallel pins and screws for scapholunate fixation had better resultsin terms of achieving carpal stability in scapholunate dissociation. However, fixation with pins and screwsshowed a statistically significant difference. Furthermore, a wide range of motion exercises with no additionalforces can be used in the rehabilitation of patients undergoing this surgery.

Background: The finite element method is a used computational technique in obtaining detailed displacement of the fractured mandible with a fixation system. Objectives: The aim of the study was the evaluation of the biomechanical performance of different rigid fixation methods in mandibular angle fractures. Methods: Computed Tomography (CT) scans applied to prepare a model of the mandible with a mandibular fracture angle. The fracture line was fixed with 7 different fixation plates. The CT scans were transferred and converted to the finite element model. The commercial ANSYS software was applied to analyze the Von Mises stresses and the amount of displacement on bones, plates, and screws. 150-newton vertical force was applied to central incisors in order to simulate the most critical loading. Results: The maximum Von Mises stress values were found in the Champy technique with 474 Mpa in bones and 579 Mpa in screws, whereas the lowest Von Mises stress values observed in the square plate which was 180 Mpa. The minimum displacement observed in the Reconstructive plate & mini-plate which was 0. 25 millimeters. Conclusion: The application of Reconstructive Plate & Mini-Plate, Dual straight mini-plates, Square Mini-Plate led to lower stress and displacement than other techniques in the bone, Plate, and screw. Reconstructive Plate & Mini-Plate, Dual straight mini-plates, Square mini-plate offers more resistance and stability at the fracture site than other techniques used in the current study. This study was done based on the analysis of computer data. Clinical evidence showed that other procedures were used for many years with success. There are many other factors in the clinical application that have a critical role in stability.

Background: Orthopedic fixation devices are widely used in treatment of spinal diseases. It is expected that application of dynamic stabilization confers valuable movement possibility besides its main role of load bearing. Comparative investigation between rigid and 2 dynamic fixation systems may elucidate the efficacy of each design. The goal of the present study is to evaluate the efficacy of three fixation systems mounted on L4-L5 motion segment.Materials and Methods: In this numerical study, a 3D precious model of L4, L5 and their intervertebral disc has been employed based on CT images. Three fixation devices have been also implanted internally to the motion segment. Finite element method was used to evaluate stress distribution in the disc and determine the overall displacement of the segment as a measure of movement possibility.Results: Maximum stress in the disc has been observed in dynamic systems but within the safe range. The greater movement of the motion segment has been also appeared in dynamic fixations. Existence of the fixation systems reduced 58% of the load on intervertebral disc which might be exerted in intact cases.Conclusions: Use of the fixation devices can considerably reduce the load on the discs and prepare conditions for healing of the injured ones. Furthermore, dynamic modes of fixation confer possibility of movement to the motion segments in order to facilitate the spinal activities.

Background: Sacral stress fracture is a rare but severe fracture that can be fixed by screw insertion. However, location and number of screws have been remained controversial. The goal of the present paper is to examine the efficiency of three fixation systems (1S-sup, 1S-inf and 2S) which vary in number and insertion location.Materials and Methods: A 3D precious model of sacrum based on CT images, fractured from zone 2, was undergone to L5-S1 joint forces after the screws inserted in three fixation systems. Finite element method was used for the present research to evaluate stress distribution within the models and find the interfragmentary motion at the sacral fracture line.Results: Stress is concentrated in vicinity to the fracture gap on the screws. Maximum stress was determined for 1S-inf system, considerably greater than two other systems. Although 1S-sup and 2S systems received similar maximum stress values, the relative displacement between the fragments was more limited in 2S system.Conclusion: Screw fixation can be an efficient technique to fix the sacral fracture. By considering one screw to be inserted, superior location to the first foramina is more effective. Two-screw fixation system (2S) noticeably reduced the relative displacement between the fragments and prepared proper situation for fracture healing.