Finite element analysis of different fixation methods of screws on absorbable plate for rib fractures

Finite element investigation for improving chest wall reconstruction process using ceramic and polymeric implants

Car accidents, infections caused by bacteria or viruses, metastatic lesions, tumors, and malignancies are the most frequent causes of chest wall damage, leading to the removal of the affected area. After excision, artificial bone or synthetic materials are used in chest wall reconstruction to restore the skeletal structure of the chest. Chest implants have traditionally been made from metallic materials like titanium alloys due to their biocompatibility and durability. However, the drawbacks of these materials have prompted researchers to seek alternative materials for use in the reconstruction process. This research aims to explore alternatives to metallic implants in order to overcome their drawbacks and enhance the performance of chest wall reconstruction using the finite element method. In this research, customized implants for the ribs and cartilages are used to repair the defective portion of the chest wall. The implants are made from various materials, including stiff bioceramics (alumina and zirconia), soft polymers (polyether ether ketone (PEEK) and polyethylene (PE)), and polymeric composites (carbon fiber-reinforced PEEK 30 and 60% (CFP 30 and 60%)) as alternatives for titanium. They are tested under normal breathing and impact loading conditions. The null hypothesis suggests that stiff implants will provide optimal results. The results illustrate that when using alumina implants, under normal breathing, the maximum tensile and compressive stresses increased to 11.41 and 15.86 MPa on ribs, while decreasing to 0.32 and 0.324 MPa, and 0.96 and 0.56 Pa on cartilages and lung respectively, compared to titanium. Conversely, when using PE implants, the maximum tensile and compressive stresses decreased to 5.69 and 8.2 MPa on ribs and increased to 0.4 and 0.42 MPa, and 1.71 and 1.1 MPa on cartilages and lung respectively. Under impact force, compared to titanium, the maximum tensile and compressive stresses increased to 47.5 and 49.8 MPa on ribs, and decreased to 1.91 and 6.15 MPa, and 4.56 and 7.7 Pa on cartilages and lung respectively, when using alumina implants. On the other hand, the maximum tensile and compressive stresses decreased to 31 and 23 MPa on ribs and increased to 2.52 and 7.83 MPa, and 5.8 and 9.3 MPa on cartilages and lung respectively, when using PE implants. The highest tensile and compressive strains on ribs were 6,162 and 6,235 µε when using alumina implants under impact force. Additionally, the highest tensile and compressive strains on cartilages and lung were 11,192 and 20,918 µε and 5,836 and 9,335 µε, respectively, when using PE implants. For screws, the peak values of von Mises stress were 61.6 MPa and 433.4 MPa under normal breathing and impact force respectively, when using PE implants. In fatigue analysis, alumina, PEEK, and PE implants failed under impact force as the maximum equivalent alternating stresses exceeded their fatigue limits, resulting in safety factors of less than one. It was concluded that stiff bioceramic implants (alumina and zirconia) produced the lowest stresses and strains on the surrounding cartilages and underlying lung, and the highest stresses and strains on the surrounding ribs, unlike soft PEEK and PE implants. Additionally, CFP 30% and 60% implants distributed stresses on the ribs, cartilages, and lungs similarly to titanium implants. Furthermore, the tensile and compressive stresses and strains on the ribs, cartilages, and lungs did not exceed allowable limits for all used implants. Finally, Zirconia, CFP 30%, and CFP 60% implants can be used as substitutes for titanium in chest wall reconstruction to restore damaged portions of the ribs and cartilage. However, stiff alumina implants and soft PEEK & PE implants were not recommended for use as they were susceptible to fracture under impact force.

Tension band high-strength suture combined with absorbable cannulated screws for treating transverse patellar fractures: finite element analysis and clinical study

Objective: Few reports exist on the treatment of transverse patellar fractures (TPFs) using absorbable cannulated screws and high-strength sutures, and most screws and sutures lack good biomechanics and clinical trials. Therefore, this study aimed to demonstrate the biomechanical stability and clinical efficacy of tension-band high-strength sutures combined with absorbable cannulated screws (TBSAS) in treating TPFs (AO/OTA 34 C1). Methods: Finite element models of five internal fixation schemes were established: tension-band wire with K-wire (TBW), TBW with cerclage wire (TBWC), TBW with headless pressure screws (TBWHS), TBW with full-thread screws (TBWFS), and TBSAS. We comprehensively compared the biomechanical characteristics of the TBSAS treatment scheme during knee flexion and extension. Forty-one patients with TPFs in our hospital between January 2020 and August 2022 were retrospectively enrolled and divided into the TBSAS (n = 22) and TBWC (n = 19) groups. Clinical and follow-up outcomes, including operative time, visual analog scale (VAS) pain score, postoperative complications, Bostman score, and final knee range of motion, were compared between both groups. Results: Finite element analysis (FEA) showed that TBWHS and TBWFS achieved the minimum mean fracture interface relative displacement during knee flexion (45°, 0-500 N bending load) and full extension (0°, 0-500 N axial load). There was no significant difference between TBSAS (0.136 mm) and TBWC (0.146 mm) during knee flexion (500 N); however, TBSAS displacement was smaller (0.075 mm) during full extension (500 N). Furthermore, the stress results for the internal fixation and the patella were generally lower when using TBSAS. Retrospective clinical studies showed that the TBSAS group had a shorter operative time, lower VAS pain score at 1 and 2 months postoperatively, better Bostman knee function score at 3 and 9 months postoperatively, and better final knee joint motion than the TBWC group (all p < 0.05). There were five cases (26.3%) of internal fixation stimulation complications in the TBWC group. Conclusion: TBSAS demonstrated excellent safety and effectiveness in treating TPFs. It is sufficient to meet the needs of TPF fixation and early functional exercise and effectively reduces metal internal fixation-induced complications and secondary surgery-induced trauma.

A biomechanical study of a polymer material bundled rib fracture fixator

BACKGROUND

Rib fractures are one of the most common blunt injuries, accounting for approximately 10% of all trauma patients and 60% of thoracic injuries. Multiple rib fractures, especially flail chest, can cause local chest wall softening due to the loss of rib support, leading to paradoxical breathing, severe pain, and a high likelihood of accompanying lung contusions.

OBJECTIVE

This study investigates the mechanical properties of a new polymer material rib internal fixator to provide theoretical data for its clinical use.

METHODS

We conducted in vitro mechanical tests on 20 fresh caudal fin sheep ribs, using different fracture models across four randomly assigned groups (five ribs per group). The fixators were assessed using non-destructive three-point bending, torsion, and unilateral compression tests, with results averaged. Additionally, finite element analysis compared stress and strain in the polymer fixators and titanium alloy rib plates during bending and torsion tests.

RESULTS

In vitro tests showed that the polymer fixators handled loads effectively up to a maximum without increase beyond a certain displacement. Bending and torsion tests via finite element analysis showed the polymer material sustained lower maximum equivalent stresses (84.455 MPa and 14.426 MPa) compared to titanium alloy plates (219.88 MPa and 46.47 MPa).

CONCLUSION

The polymer rib fixator demonstrated sufficient strength for rib fracture fixation and was superior in stress management compared to titanium alloy plates in both bending and torsion tests, supporting its potential clinical application.

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.