Biomechanical Effects of a Cross Connector in Sacral Fractures - A Finite Element Analysis

[Diagnostics and treatment of insufficiency fractures of the pelvis]

Insufficiency fractures of the pelvis have increased in recent years, primarily due to the demographic change and the incidence will continue to rise. In addition to conventional X‑rays, the diagnostics always require slice imaging. Unlike high-energy trauma magnetic resonance imaging (MRI) plays an important role in insufficiency fractures. Once the fracture has been diagnosed, in addition to the extent of instability in the anterior and posterior pelvic rings, the pain symptoms are crucial for the decision on surgical treatment. The basic principle is to stabilize as little as possible but as much as necessary. There are currently a variety of procedures that can be applied as a minimally invasive procedure, especially for the often slightly or displaced insufficiency fractures. The decisive factor for treatment is that it enables early mobilization of the patients. All of these measures must be accompanied by thorough diagnostics of osteoporosis and the appropriate treatment.

Pediatric Solid-State 3D Models of Lumbar Vertebrae and Spine

Introduction While various 3D vertebral models have been utilized in numerous studies, there is a notable gap in the representation of pediatric lumbar vertebrae and spine. This study aimed to describe the changing shapes of lumbar vertebrae and spine with age and to develop precise 3D models. Materials and methods Solid-state 3D models of pediatric lumbar vertebrae and spine were created using SOLIDWORKS® Simulation software for five age groups: newborns, infants (ages 0-1), toddlers (ages 1-3), middle childhood (ages 4-7), and preadolescents (ages 8-12). Models were composed of components with varying biomechanical characteristics. Results Created 3D models replicate variations in the dimensions and configurations of vertebrae, taking into account osteometric analyses conducted on actual vertebral specimens. These models also include elements made of cartilage, representing various phases of vertebral growth during ontogeny. Additionally, through 3D parametric design, we developed comprehensive lumbar spine models, incorporating both the vertebrae and intervertebral disks. Conclusion Created pediatric solid-state vertebral 3D models can be utilized in developing virtual or augmented reality applications and for medical research. Users can interact with models, allowing virtual exploration and manipulation, enhancing learning experiences and facilitating a better understanding of spatial relationships. These solid-state 3D models allow finite element analysis and can be used for further research to calculate internal relative deformations and stress distribution under different conditions.

Inter-Specimen Analysis of Diverse Finite Element Models of the Lumbar Spine

Over the past few decades, there has been a growing popularity in utilizing finite element analysis to study the spine. However, most current studies tend to use one specimen for their models. This research aimed to validate multiple finite element models by comparing them with data from in vivo experiments and other existing finite element studies. Additionally, this study sought to analyze the data based on the gender and age of the specimens. For this study, eight lumbar spine (L2-L5) finite element models were developed. These models were then subjected to finite element analysis to simulate the six fundamental motions. CT scans were obtained from a total of eight individuals, four males and four females, ranging in age from forty-four (44) to seventy-three (73) years old. The CT scans were preprocessed and used to construct finite element models that accurately emulated the motions of flexion, extension, lateral bending, and axial rotation. Preloads and moments were applied to the models to replicate physiological loading conditions. This study focused on analyzing various parameters such as vertebral rotation, facet forces, and intradiscal pressure in all loading directions. The obtained data were then compared with the results of other finite element analyses and in vivo experimental measurements found in the existing literature to ensure their validity. This study successfully validated the intervertebral rotation, intradiscal pressure, and facet force results by comparing them with previous research findings. Notably, this study concluded that gender did not have a significant impact on the results. However, the results did highlight the importance of age as a critical variable when modeling the lumbar spine.

Patient-specific bone material modelling can improve the predicted biomechanical outcomes of sacral fracture fixation techniques: A comparative finite element study

OBJECTIVE

To evaluate and compare the biomechanical efficacy of six iliosacral screw fixation techniques for treating unilateral AO Type B2 (Denis Type II) sacral fractures using literature-based and QCT-based bone material properties in finite element (FE) models.

METHODS

Two FE models of the intact pelvis were constructed: the literature-based model (LBM) with bone material properties taken from the literature, and the patient-specific model (PSM) with QCT-derived bone material properties. Unilateral transforaminal sacral fracture was modelled to assess different fixation techniques: iliosacral screw (ISS) at the first sacral vertebra (S1) (ISS1), ISS at the second sacral vertebra (S2) (ISS2), ISS at S1 and S2 (ISS12), transverse iliosacral screws (TISS) at S1 (TISS1), TISS at S2 (TISS2), and TISS at S1 and S2 (TISS12). A 600 N vertical load with both acetabula fixed was applied. Vertical stiffness (VS), relative interfragmentary displacement (RID), and the von Mises stress values in the screws and fracture interface were analysed.

RESULTS

The lowest and highest normalised VS was given by ISS1 and TISS12 techniques for LBM and PSM, with 137 % and 149 %, and 375 % and 472 %, respectively. In comparison with the LBM, the patient-specific bone modelling increased the maximum screw stress values by 19.3, 16.3, 27.8, 2.3, 24.4 and 7.8 % for ISS1, ISS2, ISS12, TISS1, TISS2 and TISS12, respectively. The maximum RID values were between 0.10 mm and 0.47 mm for all fixation techniques in both models. The maximum von Mises stress results on the fracture interface show a substantial difference between the two models, as PSM (mean ± SD of 15.76 ± 8.26 MPa) gave lower stress values for all fixation techniques than LBM (mean ± SD of 28.95 ± 6.91 MPa).

CONCLUSION

The differences in stress distribution underline the importance of considering locally defined bone material properties when investigating internal mechanical parameters. Based on the results, all techniques demonstrated clinically sufficient stability, with TISS12 being superior from a biomechanical standpoint. Both LBM and PSM models indicated a consistent trend in ranking the fixation techniques based on stability. However, long-term clinical trials are recommended to confirm the findings of the study.

Different internal fixation methods for Hoffa-like fractures of the tibial plateau: a finite element analysis

Due to the low incidence of posteromedial tibial plateau fractures and limited clinical data available, the optimal treatment for this type of fracture remains to be established. This type of fracture, also known as Hoffa-like fracture of the tibial plateau, shares a similar mechanism of injury with the Hoffa fracture of the femoral condyle. In the field of orthopedics, finite element analysis is considered a valuable method to guide clinical decision-making. In this study, four methods used for internal fixation of Hoffa-like fractures of the tibial plateau were compared using computer simulation and applying a finite element method (FEM). The methods compared were lateral L-plate fixation alone (Model A); lateral L-plate combined with posterior anti-slip plate (reconstruction plate/T-plate) fixation (Model B); lateral L-plate combined with posterior hollow nail fixation of the fracture block (Model C); and lateral L-plate combined with anterior hollow nail fixation of the fracture (Model D). The maximum displacement of the model and the maximum stress of the internal fixation material were analyzed by applying an axial load of 2,500 N. The results showed that, in the normal bone model, the maximum displacement of the fracture in Model A was 0.60032 mm, with improved stability through the addition of posterior lateral plate fixation in Model B and reduction of the displacement to 0.38882 mm. The maximum displacement in Model C and Model D was comparable, amounting to 0.42345 mm and 0.42273 mm, respectively. Maximum stress was 1235.6 MPa for Model A, 84.724 MPa for Model B, 99.805 MPa for Model C, and 103.19 MPa for Model D. In the internal fixation analysis of the osteoporotic fracture model, we observed patterns similar to the results of the normal bone model. The results indicated that Model B yielded the overall best results in the treatment of Hoffa-like fractures of the tibial plateau. The orthopedic surgeon may wish to implement these insights into the perioperative algorithm, thereby refining and optimizing clinical patient care. In addition, our findings pave the way for future research efforts.