Is decreased tissue elasticity more important than histopathological changes in ruptures of ascending aortic aneurysms?

Background: In this study, we aimed to investigate the natural properties of ascending aortic aneurysms and to compare dilated aortic tissues of patients with ascending aortic aneurysms and the non-pathological aortic tissues of cadavers. Methods: Between January 2017 and January 2020, a total of 14 patients (12 males, 2 females; mean age: 66.6±8.4 years; range, 54 to 77 years) who underwent elective ascending aortic surgery without genetic disease or family history in the etiology were included in the study. Aortic tissues taken from the patients with ascending aortic aneurysms and cadavers without any aortic pathology were compared histopathologically and biomechanically. An experienced pathologist performed a histological evaluation with appropriate staining and scoring. In the biomechanical examination, stress-strain curves were created with the uniaxial tensile test. The instantaneous elastic modulus was calculated based on the first regions of the curves (Ei) and the slopes of the linear region close to rupturing (Es). Results: In the pathological examination, there was no statistically significant difference in the parameters of both the patient and control groups (p>0.05). In the biomechanical examination, Ei values were significantly higher in the patients with ascending aortic aneurysms, while Es values were comparable between the groups (p=0.028 and p=0.609, respectively). Conclusion: Our study results showed that the tissues of the ascending aortic aneurysm were much more rigid, although no significant histopathological changes were detected. These findings are meaningful in understanding the structure of normal and pathological aortic tissue.

A comparison of stress, contact pressure, and contact area on menisci in re-injury mechanisms after reconstruction of the anterior cruciate ligament with autograft and synthetic graft: a finite element study.

PURPOSE: The anterior cruciate ligament (ACL) is crucial in maintaining knee stability. Some motion mechanisms, which are common in sports, cause excessive load to be passed on the ACL. In non-contact ACL injuries, the ACL cannot sustain the high stress and becomes injured or ruptures in the valgus-external rotation mechanism (VERM) and varus-internal rotation mechanism (VIRM). The mechanical strength of the grafts used to repair the torn ligament varies. The purpose of this study is to look at the alterations in the menisci after anterior cruciate ligament repair with autografts and synthetic grafts in cases of non-contact re-injury mechanisms. METHODS: In the finite element analysis, VERM and VIRM motions of the injury were simulated with different ACL graft materials. During the simulations of these mechanism motions with polyethylene terephthalate (PET) and patellar tendon (PT), the contact pressures, contact areas, and von mises stress values created in the medial and lateral meniscus were compared. RESULTS: The peak contact pressures on the menisci during the VERM are higher than the peak contact pressures during the VIRM, except for one variation. The peak contact pressure of the medial meniscus is almost the same for both graft materials and mechanisms. Furthermore, the peak contact pressures in the menisci are higher than in the VERM. For all injury mechanisms, the peak contact stresses on the lateral meniscus are higher than on the medial meniscus. CONCLUSIONS: The findings suggest that VERM can induce further knee joint injury. It was found that the PET will lessen the pressure on the menisci even more. It is also advantageous since it does not damage the anterior extremities and transmits less pressure to the menisci. In conclusion, using a high-strength ACL is healthier for the menisci. Even though synthetic grafts are not clinically preferred, the study demonstrates that enhancing the material properties of synthetic grafts will increase the chance of their use in the future, based on the current results.

Biomechanical Comparison of Headless Compression Screws, Kirschner Wires and Bioabsorbable Pins in Distal Oblique Metatarsal Osteotomy for Correction of Hallux Valgus.

BACKGROUND: Distal osteotomy of the first metatarsal is a widely used method for the correction of mild-to-moderate hallux valgus deformities. The objective of this study was to compare the stability of headless compression screws, kirschner wires and absorbable pins in terms of stiffness and maximum load in distal oblique metatarsal osteotomy. METHODS: A total of 30 4th generation first metatarsal synthetic bone models were divided into three groups according to the fixation techniques. The stiffness of the first metatarsal was calculated as the slope of the linear curve that fit with the first linear part of the force displacement curve. The failure strength was recorded as the maximum load. The stiffness and maximum load values in the axillary and transverse configurations were compared between the three fixation groups. RESULTS: The stiffness was statistically higher in Group K and Group C compared to Group B in both axial and transverse loading. Similarly, the maximum load was significantly higher in both Group K and Group C compared to Group B in both loading conditions. No significant difference was found between Group K and Group C in stability. The higher failure strength was obtained with headless compression screws (113.34±35.88 N) in the axial loading. The lowest failure strength was found in the absorbable pins technique (16.17±7.72 N) in the transverse loading. CONCLUSION: No significant difference was found between the Kirschner wires and headless compression screws techniques, although the highest strength was obtained with headless compression screws that are increasingly used in orthopedic practice.

Is the magnesium screw as stable as the titanium screw in the fixation of first metatarsal distal chevron osteotomy? A comparative biomechanical study on sawbones models.

Background: Distal chevron osteotomy (DCO) is commonly performed in hallux valgus surgery. The fixation of the osteotomy is provided by various implants. The usage of biodegradable implants such as magnesium is gradually increasing due to the advantages they provide. In this study, we aimed to compare the fixation of DCO with magnesium or titanium screw biomechanically. Methods: Twenty sawbones were used. The samples were divided into two equal groups, including ten sawbones for fixation with single headless titanium (group-1) or magnesium screw (group-2). DCO and screw fixations were performed on all samples using the same technique. Biomechanical testing was applied to five samples in each group in cantilever and the other five in a physiological configuration using a computer connected to the electromechanical test machine. The obtained data were evaluated using the Shapiro-Wilk test, Student's t-test and Mann-Whitney U test on the IBM® SPSS (Statistical Package for the Social Sciences) V22.0 software. Significance was accepted at the p < 0.05 level. Results: There was no statistically significant difference between the magnesium screw and the titanium screw in terms of maximum force, maximum displacement and stiffness measurements in cantilever and physiological loadings (p > 0.05 for all). Conclusion: This study found no significant difference in biomechanical stability between the magnesium and titanium screws in DCO fixation on sawbones. Further studies with real bones are needed.

Suture anchor fixation may be an alternative to tension band wiring in olecranon fractures: Finite element analysis.

OBJECTIVES: This study aims to analyze and compare total deformations with tension band wiring (TBW), intramedullary screw (IS) and novel suture anchor (SA) fixation methods, and to investigate practicality of SA fixation in olecranon fractures using finite element analysis (FEA). MATERIALS AND METHODS: This finite element analysis study was conducted between May 2019 and October 2019. TBW, IS and SA fixation methods were compared in order to analyze fracture behavior in the ulna and humerus using FEA, which is among the mathematical methods of stress analysis. Boundary conditions were applied to the created model and total deformation amounts were compared among the methods in terms of displacement. RESULTS: The lowest amount of displacement was obtained with TBW method (1.2095 mm), while IS method (2.7703 mm) showed the highest amount of total displacement. Total displacement was lower with SA system (2.0397 mm) compared to IS fixation. In addition, no problem was observed with SA system in terms of failure occurrence. CONCLUSION: According to the results of FEA, although the lowest amount of displacement was obtained with TBW, it is concluded that anchor fixation method may be an alternative with practicality and mechanical properties. However, further studies are needed to obtain more precise data.

Biomechanical comparison of a new handy tension band with malleolar screw, bicortical screw and conventional tension band for the fixation of transverse medial malleolar fractures.

OBJECTIVES: This study aims to compare the biomechanical features of a new handy tension band with the malleolar screw, bicortical screw and conventional tension band for the fixation of transverse medial malleolar fractures. MATERIALS AND METHODS: This study used 20 Kirschner wires, five cerclage wires, six double-hole U pins, six cortical screws, six malleolar screws, three malleolar clamps and one osteotomy set. A total of 24 tibias of two-year-old cows were obtained and stripped from soft tissue. Each tibia was cut with an electric saw at 15 cm proximal to the tibiotalar joint surface and the proximal tibia sections were discarded. A transverse fracture line was created with an osteotome on the medial malleolus. The tibias were separated into four groups with six tibias in each group. The distal tibia medial malleolar transverse fragments were fixed under guidance of fluoroscopy with the malleolar screw, bicortical screw, conventional tension band and the new handy tension band. RESULTS: In the application of both transverse and axial force, the new handy tension band resisted higher forces in respect of catastrophic damage force being more resistant compared to the bicortical screw, malleolar screw, and conventional tension band. However, in respect of the 2 mm displacement force of the forces applied in the axial and transverse sections, no difference was determined between the handy tension band and the other three implants. CONCLUSION: The new handy tension band seems to be more successful when biomechanically compared with the other implants.

Finite Element Analysis of Short- Versus Long-Segment Posterior Fixation for Thoracolumbar Burst Fracture.

OBJECTIVE: The thoracolumbar (TL) area marks the transition of the rigid thoracic spine into the mobile lumbar spine, and it is considered to be the weakest part of the spine. This study was designed to develop a finite element (FE) model of the TL junction (T9-L3) to provide data that could help the clinician and researcher to answer the question of whether short-segment posterior fixation is sufficient for biomechanical performance. In addition, the aim was to examine whether long-segment posterior fixation carries a greater risk of the development of adjacent segment disease. METHODS: This was a biomechanical finite element model analysis. FE analysis of the spine was conducted with posterior instrumentation under multidirectional loading conditions in order to evaluate the kinematics of the instrumented lumbar spine, as well as stresses in the posterior spinal instrumentation. We analyzed the following: 1) the range of motion of the T9-L3 region; and 2) the von Mises stress nephograms of the pedicle screws, rods, vertebrae, endplates, and intervertebral discs of 2 fixation FE models. RESULTS: Long-segment stabilization was found to be beneficial in terms of reducing total stress on the spine. However, it is possible to reduce the stress on the system by incorporating the spinal fracture into the stabilization system. Therefore, short-segment stabilization is sufficient to create a safe and robust stabilization system and to maintain neighboring intact vertebrae. CONCLUSIONS: Short-segment posterior fixation is sufficient to stabilize fractures at the TL junction, where the spinal fracture is included in the stabilization system.

Medial malleolus fractures: A biomechanical comparison of tension band wiring fixation methods.

BACKGROUND: This study compared the biomechanical properties of three different fixation methods of tension band wirings, used in the treatment of medial malleolus fractures. The first method used an innovative "handmade bent pin" for cerclage fixation. The second method used a U-shaped K-wire to attach the cerclage to the medial tibial cortex. These two novel fixation techniques were compared with the traditional tension band wiring technique which is fixated to the bone by a screw. HYPOTHESIS: Novel fixation techniques of tension band wiring provide stable fixation. MATERIAL AND METHODS: In this study 27 artificial bone models, which medial malleolus fractures were simulated on, were used. Using an electromechanical test device, the force required to pull out each implant was assessed and compared. RESULTS: This study found that; while handmade bent pinning resulted averagely 840.25N (range: 647-1066±118.72) and U-shaped K-wire fixation was 381.71N (range: 176-651±150.2) pull out strength, traditional tension band wiring indicated 871.33N (range: 549-1008±137.74) pull out strength. DISCUSSION: Handmade bent pinning method provide similar results with traditional tension band wiring. Therefore, in suitable cases, it may be an acceptable alternative to traditional tension band wiring techniques when treating malleolar fractures. Although the outcomes of U-shaped K-wire fixation indicated lower than other two groups, the outcomes were comparable with the literature. So while performing tension band wiring, both handmade fixation systems may be used in certain cases. For Orthopaedic surgeons, it is better to know and think about these alternative handmade pinning systems created from simple K-wires during the surgery if needed. LEVEL OF EVIDENCE: IV, Biomechanical trial.

The effect of cement on hip stem fixation: a biomechanical study.

This study presents the numerical analysis of stem fixation in hip surgery using with/without cement methods since the use of cement is still controversial based on the clinical studies in the literature. Many different factors such as stress shielding, aseptic loosening, material properties of the stem, surgeon experiences etc. play an important role in the failure of the stem fixations. The stem fixation methods, cemented and uncemented, were evaluated in terms of mechanical failure aspects using computerized finite element method. For the modeling processes, three dimensional (3D) femur model was generated from computerized tomography (CT) images taken from a patient using the MIMICS Software. The design of the stem was also generated as 3D CAD model using the design parameters taken from the manufacturer catalogue. These 3D CAD models were generated and combined with/without cement considering the surgical procedure using SolidWorks program and then imported into ANSYS Workbench Software. Two different material properties, CoCrMo and Ti6Al4V, for the stem model and Poly Methyl Methacrylate (PMMA) for the cement were assigned. The material properties of the femur were described according to a density calculated from the CT images. Body weight and muscle forces were applied on the femur and the distal femur was fixed for the boundary conditions. The calculations of the stress distributions of the models including cement and relative movements of the contacts examined to evaluate the effects of the cement and different stem material usage on the failure of stem fixation. According to the results, the use of cement for the stem fixation reduces the stress shielding but increases the aseptic loosening depending on the cement crack formations. Additionally, using the stiffer material for the stem reduces the cement stress but increases the stress shielding. Based on the results obtained in the study, even when taking the disadvantages into account, the cement usage is more suitable for the hip fixations.

Comparison of the Lag Screw Placements for the Treatment of Stable and Unstable Intertrochanteric Femoral Fractures regarding Trabecular Bone Failure.

Background. In this study, the cut-out risk of Dynamic Hip Screw (DHS) was investigated in nine different positions of the lag screw for two fracture types by using Finite Element Analysis (FEA). Methods. Two types of fractures (31-A1.1 and A2.1 in AO classification) were generated in the femur model obtained from Computerized Tomography images. The DHS model was placed into the fractured femur model in nine different positions. Tip-Apex Distances were measured using SolidWorks. In FEA, the force applied to the femoral head was determined according to the maximum value being observed during walking. Results. The highest volume percentage exceeding the yield strength of trabecular bone was obtained in posterior-inferior region in both fracture types. The best placement region for the lag screw was found in the middle of both fracture types. There are compatible results between Tip-Apex Distances and the cut-out risk except for posterior-superior and superior region of 31-A2.1 fracture type. Conclusion. The position of the lag screw affects the risk of cut-out significantly. Also, Tip-Apex Distance is a good predictor of the cut-out risk. All in all, we can supposedly say that the density distribution of the trabecular bone is a more efficient factor compared to the positions of lag screw in the cut-out risk.

Evaluation of prebent miniplates in fixation of Le Fort I advancement osteotomy with the finite element method.

The stability of segments after Le Fort I osteotomy first attracted the researcher's interest when the surgical concept was conceived. Prebent plates are the ultimate modification of plate systems in craniofacial surgery; they have two right angles and are available in different lengths for use in maxillary advancement surgery. For this research, cone-beam computed tomography (CBCT) images of a male patient were obtained and scanned, and a 3D maxillary bone was created. Conventional Le Fort I osteotomies with 5 and 10 mm advancements were performed on both the cortical and trabecular bone using the Surgical Simulation Module of Mimics software; 1.7 mm Leibinger standard orthognathic 5-hole L plates and 1.7 mm Leibinger orthognathic advancement 11-hole prebent plates were adapted to the fragments. Displacement of the segment, the von Mises (VM) stresses (on the titanium miniplates) and the maximum principal (MP) stresses (on the bone) were evaluated for each configuration. Prebent plates offer a good alternative to the conventional two plate system, except in operations where maxillary advancement exceeds 5 mm. Surgical procedures that include advancement exceeding 5 mm or vertical position changes remain controversial and further studies are needed.

Use of cone-beam computed tomography and three-dimensional modeling for assessment of anomalous pulp canal configuration: a case report.

Three-dimensional (3D) reconstruction of cone-beam computed tomography (CBCT) scans appears to be a valuable method for assessing pulp canal configuration. The aim of this report is to describe endodontic treatment of a mandibular second premolar with aberrant pulp canal morphology detected by CBCT and confirmed by 3D modeling. An accessory canal was suspected during endodontic treatment of the mandibular left second premolar in a 21 year old woman with a chief complaint of pulsating pain. Axial cross-sectional CBCT scans revealed that the pulp canal divided into mesiobuccal, lingual, and buccal canals in the middle third and ended as four separate foramina. 3D modeling confirmed the anomalous configuration of the fused root with a deep lingual groove. Endodontic treatment of the tooth was completed in two appointments. The root canals were obturated using lateral compaction of gutta-percha and root canal sealer. The tooth remained asymptomatic and did not develop periapical pathology until 12 months postoperatively. CBCT and 3D modeling enable preoperative evaluation of aberrant root canal systems and facilitate endodontic treatment.

Evaluation of contact characteristics of a patient-specific artificial dysplastic hip joint.

This study addresses the results of the experimental measurements for the contact surface areas and contact pressure distributions of a dysplastic hip joint. The hip joint consists of pelvis, proximal femur and artificial cartilages for both acetabulum and femoral head. The dysplastic hip joint is modeled in three dimensional (3D) form using the computerized tomography (CT) images obtained in vivo of an adult female patient. The modeled hip joint components are manufactured as a non-natural dysplastic hip joint using different materials and manufacturing processes. The dysplastic hip joint produced is subjected to compression forces experimentally to measure the contact surface area and contact pressure distributions between the femoral head and acetabulum using the pressure sensitive Fuji film. Different types of specific fixtures and molds are designed and manufactured to produce the dysplastic hip joint components and perform the experimental studies. The measured results using a non-natural dysplastic hip joint are compared with relevant results reported in current literature considering the peak and mean contact pressure values. Therefore, the obtained results showed that the non-natural dysplastic hip models can be generated and replaced to determine the contact characteristics for an elusive cadaveric model. In conclusion, the artificial models might be useful to understand the contact pressure distributions and potential changes in surface pressure contours and their effects on the stress distributions.

Effects of the hyperbaric oxygen on de novo bone formation during periosteal distraction.

OBJECTIVE: The purpose of this study was to investigate the effect of hyperbaric oxygen (HBO) therapy on de novo bone formation during periosteal distraction (PD). MATERIALS AND METHODS: Periosteal distraction was performed in 24 mature male New Zealand rabbits using a custom-designed device placed on the lateral surface of the mandibular corpus. Twelve rabbits (group H) were given adjunctive HBO treatment, whereas 12 rabbits (group N) were kept in a normal environment (normobaric oxygen). After a 7-day latency period, the same distraction protocol was applied to both groups. However, the rabbits in group H were treated with pure oxygen at 2.4 atm absolute for 25 times. Both groups were further divided into 2 subgroups and killed after consolidation periods of 4 and 8 weeks. Photodensitometric and histologic analyses were performed to evaluate the newly formed bone. RESULTS: There was no significant difference between the 4-week consolidated HBO group and the 8-week consolidated normobaric oxygen subgroup (P = 0.229). Moreover, there was better bone formation in the 8-week HBO group than in the 8-week control group. CONCLUSION: The results of this study indicate that PD with HBO could be used to increase the quality and the quantity of the bone newly formed by PD.

Effect of platelet rich fibrin and beta tricalcium phosphate on bone healing. A histological study in pigs.

PURPOSE: To investigate the effect of platelet rich fibrin (PRF) and beta tricalcium phosphate (ß-TCP), alone or in combination, on bone regeneration in pig tibial defects. METHODS: Four standardized defects were prepared in both tibias of three adult male pigs. The first defect was left unfilled as a control; the others were grafted with either PRF, ß-TCP or PRF mixed with ß-TCP. All animals were sacrificed on the 12th postoperative week and the tibial bones were removed, histologic sections were prepared and the experimental sites were examined microscopically and stereologically. RESULTS: Histologic and stereologic examination revealed more new bone formation in the defects filled with PRF mixed ß-TCP than in the defects grafted with either ß-TCP or PRF alone. CONCLUSION: The platelet rich fibrin and beta tricalcium phosphate combination effectively induces new bone formation.

Effect of platelet rich fibrin and beta tricalcium phosphate on bone healing. A histological study in pigs

To investigate the effect of platelet rich fibrin (PRF) and beta tricalcium phosphate (β-TCP), alone or in combination, on bone regeneration in pig tibial defects. METHODS: Four standardized defects were prepared in both tibias of three adult male pigs. The first defect was left unfilled as a control; the others were grafted with either PRF, β-TCP or PRF mixed with β-TCP. All animals were sacrificed on the 12th postoperative week and the tibial bones were removed, histologic sections were prepared and the experimental sites were examined microscopically and stereologically. RESULTS: Histologic and stereologic examination revealed more new bone formation in the defects filled with PRF mixed β-TCP than in the defects grafted with either β-TCP or PRF alone. CONCLUSION: The platelet rich fibrin and beta tricalcium phosphate combination effectively induces new bone formation.

The effect of proximal tibial corrective osteotomy on menisci, tibia and tarsal bones: a finite element model study of tibia vara.

BACKGROUND: Proximal tibial open wedge osteotomy (PTO) is a corrective operation used in the surgery of lower extremities and is applied to patients with varus deformities for sufficient correction. The aim of the study was to evaluate whether the PTO can achieve decreased stress-bearing on the tibia and tarsal bones in addition to correcting the mechanical axis of the lower limb in patients with tibia vara. METHODS: Three-dimensional (3D) solid modelling of the lower extremity was carried out using computed tomography (CT) and magnetic resonance (MR)-containing images of all of the bony elements and non-bony structures. PTO was applied to the obtained deformed model in the computer environment and the correction was carried out. RESULTS: Stress distributions in menisci, tibia and tarsal bones were calculated. With respect to loading on the tarsal bones, the maximum equivalent stresses on all bones decreased except for the navicula in the PTO-simulated model in the current study. CONCLUSION: These results clearly indicate that PTO can achieve decreased stresses on the tarsal bones in patients with tibia vara.

Narcotic prescribing habits and other methods of pain control by oral and maxillofacial surgeons after impacted third molar removal.

PURPOSE: It has been suggested that a source of narcotics used for nonmedical purposes by young adults is the unused opioids prescribed for the management of pain after the removal of impacted third molars. The purpose of the present study was to determine whether oral and maxillofacial surgeons routinely prescribe larger amounts of a narcotic than would generally be needed for adequate postoperative pain control. A secondary goal was to determine whether they use methods other than analgesic drugs to minimize postoperative pain and thereby reduce the amount of narcotic that might be needed. PATIENTS AND METHODS: An 8-question survey was sent to 100 randomly selected oral and maxillofacial surgeon members of the American Association of Oral and Maxillofacial Surgeons in each of the 6 association districts. The questions asked were related to whether a narcotic was routinely prescribed for patients who have had impacted teeth removed, the most common drug used, and the dosage and number of tablets prescribed. The participants were also asked whether they had pretreated patients with a nonsteroidal anti-inflammatory drug or had prescribed one along with the narcotic, had injected a steroid, or had used a long-lasting local anesthetic postoperatively. RESULTS: Only 2 of the 384 respondents stated that they did not prescribe a narcotic for patients who had had impacted teeth removed. Hydrocodone (5 mg) was the most frequently prescribed narcotic. The number of tablets varied from 10 to 40, but the most common number was 20 tablets. However, 80 respondents (22%) prescribed more, with 40 prescribing 30 tablets. Also, 80% of the respondents injected their patients with a steroid, and 62% injected a long-lasting local anesthetic postoperatively. Only 34% pretreated their patients with a nonsteroidal anti-inflammatory drug, but 66% recommended such use postoperatively. CONCLUSIONS: Most oral and maxillofacial surgeons prescribe analgesic drugs of an appropriate type and dosage and use proper adjunctive pain control measures to supplement these drugs. However, our findings also indicated that more than 20% prescribe more tablets than would generally be necessary to control the postoperative pain after the removal of impacted third molars. This could be a source of drug diversion and nonmedical use by young adults and should be avoided.