Cafeteria Diet Can Affect Bone Microarchitecture in Sedentary and Trained Male Rats.

INTRODUCTION: Poor eating habits and a sedentary lifestyle can impair health. Regular physical activity improves the quality of life and is essential for bone health. Therefore, the present study aimed to evaluate the effects of the cafeteria diet on bone quality of sedentary and exercised rats. METHODS: Sixty young male Wistar rats were divided into six groups (n=10) according to diet composition and activity level, being: SD+CON, standard diet and control; SD+SED, standard diet and sedentary; SD+EX, standard diet and exercised; CD+CON, cafeteria diet and control; CD+SED, cafeteria diet and sedentary; CD+EX, cafeteria diet and exercised. The exercise protocol consisted of 10 ladder-climbing sessions/day, 5 days/week, and the sedentary rats were maintained in individual cages with limited mobility. Body mass and food intake were evaluated weekly. After 10 weeks, the animals were euthanized, and white adipose tissue was collected. The bone structure was evaluated by densitometry, mechanical tests, histomorphometric, and micro-computed tomography analyses. RESULTS: The cafeteria diet increased adipose tissue (p<0.001), decreased bone mineral density (p=0.004), and impaired biomechanical properties (p<0.05) and histomorphometry parameters (p=0.044). The sedentarism decreased bone mineral density (p<0.001) and biomechanical properties (p<0.05), and the exercise did not improve bone properties. CONCLUSION: In this experimental model, it was concluded that the cafeteria diet and a sedentary lifestyle negatively affect bone, and ladder-climbing exercise could not prevent the effects of the unhealthy diet.

A high-fat diet can affect bone healing in growing rats.

A high-fat diet (HFD) can have a negative effect on bone quality in young and old people. Although bone healing in children is normally efficient, there is no evidence that children who have a diet rich in fat have compromised bone fracture regeneration compared with children with recommended dietary fat levels. The purpose of the present study was to evaluate the effects of an HFD on bone healing in growing female rats. Twenty-six postweaning female Wistar rats were divided into two groups (13 animals per group): a standard diet (SD) group and an HFD (with 60% of energy from fat) group. The rats received the assigned diets for 5 weeks, and in the third week they were submitted to an osteotomy procedure of the left tibia. Body mass and feed intake were recorded during the experiment. One day before euthanasia, an insulin tolerance test was performed. After euthanasia, the tibiae were removed and analyzed by densitometry, mechanical testing, histomorphometry, stereology and immunohistochemistry. An HFD caused an adaptive response to maintain energetic balance by decreasing feed intake and causing insulin insensitivity. There was no change in bone mineral density, collagen amount and immunostaining for bone formation, but maximal load and stiffness were decreased in the HFD group. In addition, bone volume had a tendency to be higher in the SD group than in the HFD group. Compared with rats receiving an SD, growing rats receiving an HFD for 5 weeks had similar bone mineral density but altered mechanical properties at the osteotomy defect site.

Bridging Plate Development for Treatment of Segmental Bone Defects of the Canine Mandible: Mechanical Tests and Finite Element Method.

With regard to the canine mandible, a mistaken concept of application is to assume that systemic plate-bone resistance is provided by the implant so that biomechanical position could be ignored. Because the alveolar border of the mandible is a tensile zone, the plate would ideally be positioned near this area while avoiding important structures. The aim of this study was to develop 2 bridging plates for the treatment of a segmental bone defect of the canine mandible using monocortical screws to avoid damage to the tooth roots and remaining neurovascular structures. Computed tomography images of the heads of 4 dogs (rottweiler, Doberman, boxer, and miniature poodle breeds) were used as models to develop the project. The images were reconstructed in 3-dimensional (3D) format. For each dog breed, 6 mandible prototypes were produced, each with a segmental bone defect in the right mandible. The mandibular reconstruction was performed with pure titanium bridging plate and locking screws. One plate model was developed for medium- and large-breed dogs and another for small-breed dogs. Mechanical testing showed the platemandible system resists the bite forces in all dog breeds. All safety factors were greater than I in the platemandible system for medium- and large-breed dogs and greater than 10 in the plate-mandible system for small-breed dogs. Thus, bridging plates designed with differentiated geometry and monocortical locking screws showed mechanical resistance to support simulated induced bone model defects and were able to support at least 5 times the value of bite force for each evaluated dog.

Varization open-wedge osteotomy of the distal femur: comparison between locking plate and angle blade plate constructs.

PURPOSE: Biomechanical properties of locking plate and angle blade plate constructs in opening-wedge distal femur osteotomy were compared, with special attention to the impact of opposite cortex breakage and buttressing. METHODS: Forty-eight synthetic femora underwent a lateral opening-wedge distal femur osteotomy, which was fixed either with a locking plate or with an angle blade plate. Two main groups were constituted based on the integrity of the opposite medial cortex-intact medial cortex and fractured medial cortex (FMC). Axial compression and torsion tests were performed comparing stiffness of all bone-implant constructs. In the group FMC, a special subgroup has been tested taking into consideration the effect of placing an additional 6.5-mm cancellous screw buttressing the medial cortex. Statistical level of significance was fixed in 0.05 using a confidence interval of 95 %. RESULTS: Intact medial cortex significantly increased the stiffness for both implants tested in this study. In the FMC group, angle blade plate constructs reached higher stiffness mean values for both torsion and axial compression. The insertion of a buttressing screw on the medial cortex increased the stiffness of all tested bone-plate constructs. This additional screw favoured mostly locking plate constructs implementing their stiffness to torsion to mean values comparable to those reached by angle blade plate constructs. CONCLUSIONS: Angle blade plate constructs reached higher stiffness mean values than locking plates for both axial compression and torsion loads. The addition of a buttressing screw on the opposite cortex increased the stability of all bone-implant constructs to levels similar to those showed with an intact medial cortex. The present study findings support the clinical use of angle blade plates, alone or associated with a medial buttressing screw, as an alternative fixation method for supracondylar open-wedge osteotomies of the femur.

Analysis of the influence of implant shape on primary stability using the correlation of multiple methods.

OBJECTIVES: The purpose of this study was to analyze the influence of the shape of various implants and the density of substrate on primary stability using a combination of methods. MATERIALS AND METHODS: Fifty-four Neodent® brand cylindrical and conical implants with different prosthetic platforms were used. Implants were inserted into a pork rib bone and polyurethane blocks. Primary stability was assessed by insertion torque (IT), resonance frequency analysis (RFA), and pullout strength. Screws were also analyzed by scanning electron microscopy (SEM) before insertion and after removal to justify their use for inserting in different substrates. RESULTS: The conical cone morse implant had the highest average for all of the assays performed and was significantly different (p < 0.05) from the cylindrical implants for IT in the bone, pullout strength in the 40 per cubic foot (PCF) polyurethane, and the bone. The internal hex cylindrical implant had the lowest averages, which were significantly different (p < 0.05) from the conical implants for IT and RFA in the bone, pullout strength in the 40 PCF polyurethane, and the bone. The IT, RFA, and pullout strength assays were moderately correlated, and the photomicrographs did not reveal changes in the implants. CONCLUSIONS: The analysis of different implants showed a better primary stability of tapered implants; the density of the substrate influences the primary stability and the 15 PCF polyurethane was not adequate to evaluate primary stability; correlation was obtained between the different methodologies of analysis of primary stability. CLINICAL RELEVANCE: The study shows the influence of different implant macro-geometries and densities of substrates on primary stability.

Influence of torsional strength on different types of dental implant platforms.

AIM: The study assessed deformation of implant components submitted to torsion tests of 80 and 120 N · cm using an optical stereomicroscope. MATERIAL AND METHODS: The following 3 types of Titaniumfix conical implant connections (n = 5) measuring Ø 4.0 × 11.5 mm were used: external, internal hexagon and Morse taper connections. The diagonal and lateral measurements of the hexagon implant platform were measured before and after the torsion test. RESULTS: The torsion test using torque of 80 and 120 N · cm altered the implant dental platforms. All groups presented deformation of implant component after torque of 80 N · cm with no statistical difference among them. During torque of 120 N · cm, a difference in the Morse taper connection in relation to the internal and external hexagon connection was observed. The Morse taper connection implant, followed by the internal hex implant, underwent less deformation. Greater deformation occurred in the external hex implants. CONCLUSION: For all the implants, high insertion torques deformed the implant platform preventing long-term maintenance and stability of implants.

Relationship between the surface chemical composition of implants and contact with the substrate.

The purpose of the study was to use scanning electron microscopy and energy dispersive x-ray spectrometry to assess possible morphologic and chemical changes after performing double-insertion and pullout tests of implants of different shapes and surface treatments. Four different types of implants were used-cylindrical machined-surface implants, cylindrical double-surface-treated porous implants, cylindrical surface-treated porous implants, and tapered surface-treated porous implants-representing a total of 32 screws. The implants were inserted into synthetic bone femurs, totaling 8 samples, before performing each insertion with standardized torque. After each pullout the implants were analyzed by scanning electron microscopy and energy dispersive x-ray spectrometry using a universal testing machine and magnified 35 times. No structural changes were detected on morphological surface characterization, only substrate accumulation. As for composition, there were concentration differences in the titanium, oxygen, and carbon elements. Implants with surface acid treatment undergo greater superficial changes in chemical composition than machined implants, that is, the greater the contact area of the implant with the substrate, the greater the oxide layer change. In addition, prior manipulation can alter the chemical composition of implants, typically to a greater degree in surface-treated implants.

Effect of pilot hole on biomechanical and in vivo pedicle screw-bone interface.

PURPOSE: To experimentally study the influence of pilot hole diameter (smaller than or equal to the internal (core) diameter of the screw) on biomechanical (insertion torque and pullout strength) and histomorphometric parameters of screw-bone interface in the acute phase and 8 weeks after pedicle screw insertion. METHODS: Fifteen sheep were operated upon and pedicle screws inserted in the L1-L3 pedicles bilaterally. The pilot hole was smaller (2.0 mm) than the internal diameter (core) of the screw on the left side pedicle and equal (2.8 mm) to the internal diameter (core) of the screw on the right side pedicle. Ten animals were sacrificed immediately (five animals were assigned to pullout strength tests and five animals were used for histomorphometric bone-screw interface evaluation). Five animals were sacrificed 8 weeks after pedicle screw insertion for histomorphometric bone-screw interface evaluation. RESULTS: The insertion torque and pullout strength were significantly greater in pedicle screws inserted into pilot holes smaller than internal (core) diameter of the screw. Histomorphometric evaluation of bone-screw interface showed that the percentage of bone-implant contact, the area of bone inside the screw thread and the area of bone outside the screw thread were significantly higher for pilot holes smaller than the internal (core) diameter of the screw immediately after insertion and after 8 weeks. CONCLUSION: A pilot diameter smaller than the internal (core) diameter of the screw improved the insertion torque and pullout strength immediately after screw insertion as well the pedicle screw-bone interface contact immediately and 8 weeks after screw placement in sheep with good bone mineral density.

Collagen membrane from bovine pericardium for treatment of long bone defect.

The treatment of bone regeneration failures has been constantly improved with the study of new biomaterials. Techgraft® is a collagen membrane derived from bovine pericardium, which has been shown to have biocompatibility and effectiveness in tissue repair. However, its use in orthopedics has not yet been evaluated. Therefore, the purpose of this study was to characterize a bovine pericardium collagen membrane and evaluate the effects of its use in the regeneration of a bone defect in rat tibia. Scanning electron microscopy, atomic force microscopy, weight lost and water uptake tests, and mechanical test were performed. Afterwards, the membrane was tested in an experimental study, using 12 male Sprague Dawley rats. A bone defect was surgically made in tibiae of animals, which were assigned to two groups (n = 6): bone defect treated with collagen membrane (TG) and bone defect without treatment (CONT). Then, tibiae were submitted to micro-CT. The membranes preserved their natural collagen characteristics, presenting great strength, high water absorption, hydrophilicity, and almost complete dissolution in 30 days. In the experimental study, the membrane enhanced the growth of bone tissue in contact with its surface. A higher bone volume and trabeculae number and less trabecular space was observed in bone defects of the membrane group compared to the control group at 21 days. In conclusion, the Techgraft membrane seems to have favorable characteristics for treatment of long bone repair.

In vitro mechanical analysis of X-shaped femoroplasty with polymethyl methacrylate boundary a fall on the greater trochanter.

To evaluate with mechanical testing (MT) using synthetic femurs, an X-shaped femoroplasty technique with polymethyl methacrylate (PMMA), analyzing the results applied to the prophylaxis of proximal femur (PF) fractures caused by low-energy trauma. MT was performed simulating a fall on the greater trochanter, using fifteen Sawbones™ models. They were divided into three experimental groups (n = 5): control (DP) group, drilled without augmentation (DWA) group, and X-shaped augmentation (DX) group. Maximum load, stiffness, absorbed energy and displacement were analyzed primarily in all groups; and secondarily then, morphology and fracture type were verified in all groups while PMMA volume, temperature and time polymerization were analyzed only in the DX group. The MT results obtained for synthetic models respectively in the DP, DWA, and DX groups were: mean maximum load (5562.0 ±â€¯464.8) N, (4798.0 ±â€¯121.2) N, and (7132.0 ±â€¯206.9) N; mean stiffness values (673 ±â€¯64.34) N/mm, (636 ±â€¯8.7) N/mm, and (738 ±â€¯17.13) N/mm, and mean absorbed energy values (36,203 ±â€¯3819) N.mm, (27,617 ±â€¯3011) N.mm, (44,762 ±â€¯3219) N.mm; mean displacement values (13.6 ±â€¯1.45) N, (11.1 ±â€¯0.5) N, and (13.2 ±â€¯0.69) N. The mean volume, temperature reached during filling in the DX group were 9.8 mL, 42.54ºC with 1' 56" of polymerization. The fracture types were similar between the DP and DWA groups, affecting the trochanteric region, as distinctly to those in the DX group, which were restricted to the femoral neck. The values obtained in MT showed statistical significance when analyzed by one-way ANOVA (5%) for maximum load, stiffness, and absorbed energy between groups. In conclusion, X-shaped PMMA augmentation presents a protective biomechanical characteristic against PF fractures generated in synthetic models by boundary a fall on the greater trochanter.

Systemic effects of oral tolerance in bone healing.

Bone fractures cause acute inflammation that, despite being important for initial repair, may delay the healing of the damaged bone. Parenteral injection of dietary protein has been shown to decrease inflammation and accelerate the repair of skin wounds and other inflammatory pathologies. Thus, our aim was to evaluate whether the intraperitoneal (i.p.) immunization with zein, an abundant protein in rodent chow, would favor bone healing. Wistar rats received i.p. immunization: saline (SG), adjuvant (AG) and zein associated with adjuvant (ZG). Then, a 2 mm of defect bone was performed on the right tibia, and on days 7, 14, 28 and 45 thereafter, analyses were performed. The results showed that the injection of zein reduced inflammation without impairing bone mineralization. Moreover, biomechanical tests demonstrated higher levels of maximum force (N) in ZG, indicating better mechanical resistance in relation to the others. The computerized tomography also indicated lower levels of medullary content in the ZG than in the SG, suggesting the absence of trabeculae in the medullary region in the ZG. These findings suggest that the injection of zein in previously tolerated animals may improve bone repair, leading to mechanically functional bone formation.

Bone strength is reduced in a neonatal androgenized rat model.

Background: Whether polycystic ovary syndrome (PCOS) affects bone health during a woman's lifespan remains controversial. An androgenized rodent model replicated many metabolic and reproductive features of women with PCOS, and we aimed to use it to investigate the impact of androgens on microarchitecture (by micro-CT), bone mechanical strength, bone formation and resorption markers in rats with intact ovaries (SHAM) who underwent oophorectomy. Methods: Wistar rats (Rattus norvegicus albinus) were employed for the experiments in this study. The protocol of androgenization consisted of the application of 1.25 mg s.c. testosterone propionate beteween days 2-5 of life, while the controls received the same amount of corn oil s.c. as previously established. Androgenized SHAM rats exhibited chronic anovulation identified by vaginal cytology and a reduction in the proportion of corpus luteum in the ovary in comparison to control SHAM rats. The realization of the ovariectomy or SHAM procedure occurred on Day 100 of life. All groups (n = 8) were followed-up for 180 days to address the study endpoints. Results: Micro-CT from androgenized female rats (SHAM) showed a divergence between the trabecular and cortical bone profiles. Compared to SHAM controls, these rats had an increase in trabecular bone mass with a diminution in bone resorption C-terminal telopeptide of type 1 collagen (CTX) (p < 0.05), a concomitant decrease in cortical area and thickness in the femur, and a reduction in the strength of the femur on the mechanical test (p < 0.01). Conclusions: Our results suggest that a reduction in the cortical thickness and cortical area observed in PCOS model rats was associated with a reduced strength of the femur, despite increased trabecular formation. Ovariectomy in the androgenized OVX group limited the progression rate of cortical bone loss, resulting in bone resistance and cortical thickness comparable to those observed in the control OVX group.

Experimental in vivo acute and chronic biomechanical and histomorphometrical comparison of self-drilling and self-tapping anterior cervical screws.

PURPOSE: Self-drilling screws (SDS) and self-tapping screws (STS) allow for quicker bone insertion and are associated with increased anchorage. This is an experimental in vivo comparison of anterior cervical SDS and STS in the post-insertion acute and chronic phases. METHODS: Thirty C2-C6 vertebrae from six Santa Inês hair sheep were used. Each screw design was randomly assigned to five of each spinal level. Insertion torque was measured using a torque device. Three animals were killed in each phase. Vertebrae were randomly assigned to pullout tests and histomorphometrical bone-screw interface evaluation (percent screw-bone contact and bone density inside and outside the threaded area). Statistical significance was set at P < 0.05. RESULTS: SDS insertion torque was greater than STS (P = 0.0001). SDS pullout strength was significantly greater than STS in the acute and chronic phases (P = 0.0001, 0.0003, respectively). SDS percent screw-bone contact and inside area bone density were significantly greater in both phases. No outside area bone density differences were observed in either phase. CONCLUSIONS: SDS had higher insertion torque and better anchorage than STS in both phases. SDS percent bone-screw contact and inside area bone density were higher in both phases.

The Influence of Thread Tap Mismatch on Pedicle Screw Pullout Strength.

Objective We aimed to study the "in vitro" pullout strength of SpineGuard/Zavation Dynamic Surgical Guidance Z-Direct Screw (DSG Screw, SpineGuard Inc, Boulder, Colorado, USA), a screw designed to be inserted using a direct insertion technique. Methods Dynamic Surgical Guidance Screws of 5.5 and 6.5 mm were introduced into polyurethane blocks with a density of 10 PCF (0,16g/cm 3 ). According to the experimental group, screws were inserted without pilot hole, with pilot without tapping, undertapping and line-to-line tapping. Screw pullout tests were performed using a universal test machine after screw insertion into polyurethane blocks. Results Screws inserted directly into the polyurethane blocks without pilot hole and tapping showed a statistically higher pullout strength. Insertion of the screw without tapping or with undertapping increases the pullout screw strength compared with line-to-line tapping. Conclusion Dynamic Surgical Guidance Screw showed the highest pullout strength after its insertion without pilot hole and tapping.

Mechanical Analysis after Proximal Femoral Reinforcement with Polymethylmethacrylate in Alternated Double Holes.

Objective To evaluate, through a biomechanical assay, the maximum load, energy, and displacement necessary for the occurrence of fractures in synthetic models of femurs after the removal of cannulated screws and the performance of a reinforcement technique with polymethylmethacrylate (PMMA) in different combined positions. Methods In total, 25 synthetic bones were used, and they were divided into 4 groups: the control group (CG), with 10 models without perforation, and the test groups (A, B and C), with 5 models each. The test groups were fixed with cannulated screws using the Asnis technique, and they had the synthesis removed, and two of the holes formed by the reinforcement technique with PMMA were filled. The biomechanical analysis was performed simulating a fall on the large trochanter using a servo-hydraulic machine. Results All specimens of the CG and of groups A, B and C presented basal-cervical fracture of the femoral neck, except for a single model in group B, which presented a longitudinal fracture. An average of 5.4 mL of PMMA were used to reinforce the groups with filling. According to the analysis of variance (ANOVA) and the Tukey multiple comparison test, at the level of 5%, we observed that the CG presented significant differences in relation to groups A and C in the following parameters: maximum load, energy up to the fracture, and displacement. Conclusion We observed that groups A and C, when compared to the CG, showed significant differences in the observation of displacement, maximum load, and energy until the fracture.

Distal radius fracture fixation using volar plate: A comparative study evaluating the biomechanical behavior of uni and bicortical distal screws.

Extensor tendon ruptures caused by bicortical screws impingement following distal radius fracture fixation with volar plates are extensively reported in the literature. Thus, a biomechanical study comparing unicortical and bicortical fixations in intra-articular distal radius fracture models is critical in decision-making regarding distal radius fracture management. Forty-two synthetic radius models were fixed using a variable angle volar distal locking plate with seven screws. They were divided into 6 groups (n = 7): G1/G3/G4 unicortical fixation (75% of anteroposterior distal radius lenght); G2/G4/G6 bicortical fixation. Each group underwent a different mechanical test: axial compression (G1/G2), dorsal flexion (G3/G4), and volar flexion (G5/G6). The load application rate was 5 mm/min and 1000 cycles of 50 to 250 N at 1 Hz were performed between both static tests. Comparative results in the first static test, in the second static test, and in failure generally showed a very similar behavior. Models depicted similar behavior in the second static test when cyclic load was performed. Therefore, one can realize that stiffness differed during dorsal flexion only in the first static test. Maximum force to break the model in axial compression was greater in bicortical than in unicortical construct. Since biomechanical properties are similar, we recommend using unicortical distal locking screws in distal radius fracture fixation with volar plates to prevent extensor tendon ruptures.

DIRECT PEDICLE SCREW INSERTION PULLOUT STRENGTH.

OBJECTIVE: Study the in vitro pullout strength of SpineGuard/Zavation Dynamic Surgical Guidance Z-Direct Screw (DSG Screw), a screw pedicle designed to be inserted using a direct insertion technique. METHODS: DSG Screws of 5.5 mm and 6.5 mm were introduced into polyurethane blocks with a density of 10 PCF (0,16 g/cm3). According to the experimental group, screws were inserted without pilot hole, with pilot without tapping, undertapping and line-to-line tapping. Screw pullout tests were performed using a universal test machine after screw insertion into polyurethane blocks. RESULTS: Screws inserted directly into the polyurethane blocks without pilot hole and tapping showed a statistically higher pullout strength. Insertion of the screw without tapping or with undertapping increases the pullout screw strength compared to line-to-line tapping. CONCLUSION: DSG Screw showed the highest pullout strength after its insertion without pilot hole and tapping. Level of Evidence V, Expert Opinion.

OBJETIVO: Estudar a resistência ao arrancamento in vitro do parafuso de inserção direta da SpineGuard/Zavation (parafuso DSG), um parafuso pedicular projetado para ser inserido usando a técnica de inserção direta. MÉTODOS: Parafusos DSG de 5,5 mm e 6,5 mm foram introduzidos em blocos de poliuretano com densidade de 10 PCF (0,16 g/cm3). De acordo com o grupo experimental, os parafusos foram inseridos sem orifício piloto, com orifício e sem macheamento e macheamento diâmetro inferior com mesma geometria. Os testes de resistência dos parafusos foram realizados usando uma máquina de teste universal após a inserção dos parafusos nos blocos de poliuretano. RESULTADOS: Os parafusos inseridos diretamente nos blocos de poliuretano sem orifício piloto e sem macheamento apresentaram uma resistência de arrancamento com significância estatística maior. A inserção do parafuso sem macheamento ou com macheamento com diâmetro inferior apresenta maior resistência ao arrancamento em comparação com o macheamento do mesmo diâmetro. CONCLUSÃO: O parafuso DSG apresentou a maior resistência ao arrancamento após sua inserção sem orifício piloto e sem macheamento. Nível de Evidência V, Opinião do Especialista.

Proposal for a New Fixation Method for Pauwels Type III Femoral Neck Fracture-Metaphyseal Stem: A Finite-Element Analysis.

OBJECTIVE: To evaluate the biomechanical behavior of a metaphyseal stem specifically designed for the fixation of Pauwels type-III femoral neck fractures using finite-element analysis. METHODS: Three different constructions were studied: the dynamic hip screw with a superior anti-rotation screw (DHS + ARS), multiple cannulated screws in an inverted triangle configuration (ASNIS), and the Metaphyseal Nailing System (MNS), a new implant developed by the authors. Vertical and total displacement, localized and total maximum and minimum principal, and the Von Mises peak stresses were evaluated. RESULTS: Results are shown for the DHS + ARS, ASNIS, and MNS models, respectively. Vertical displacement (mm) was 1.49, 3.63, and 1.90; total displacement (mm) was: 5.33, 6.02, and 6.30; localized maximum principal (Mpa) was: 2.77, 4.5, and 1.7; Total maximum principal (Mpa) was: 126, 223, and 531; localized minimum principal (Mpa) was: -1.8, -3.15, and -0.39; total minimum (Mpa) was: -121, -449, and -245; and Von Mises peak stress (MPA) was: 315.5, 326.1, and 286.0. CONCLUSION: The present FEM study showed that the MNS device increases general stresses and reduces localized stresses, when compared to the DHS + ARS and ASNIS constructions used to fix Pauwels type-III femoral neck fracture in synthetic models. In this sense, the MNS showed a low fracture focus shift, conducive to the consolidation environment. The significant reduction in the maximum principal stress, allows to affirm that the main deforming force, the shear, in this fracture pattern, was considerably reduced and the low value of Von Mises obtained, consistent with an implant capable of making an effective load sharing.

Biomechanical evaluation of a new femoral stem design for total hip replacement in a canine model.

PURPOSE: To evaluate the biomechanical properties of a novel total hip replacement femoral stem. METHODS: Eight pairs of femurs from dog cadavers were used. The femurs were separated into different groups. A novel femoral stem with a convex proximal portion (Stem B) was biomechanically evaluated and compared to awell-known veterinary collared stem (Stem A). Femoral stems were inserted into the contralateral femurs from the same dog, forming 16 constructs. A flexo-compression load was applied on the axial axis of each sample. Maximum strength, deflection, stiffness, and energy absorption were analysed. RESULTS: Group B constructs showed significantly higher values (p ? 0.05) for the variables, except stiffness. The mean maximum strength was 1,347 ± 357 N for Group A and 1,805 ± 123 N for Group B (p ? 0.0069). The mean deflection was5.54 ± 2.63 mm for Group A and 10.03 ± 3.99 mm for Group B (p ? 0.0056). For the energy variable, the force was 6,203 ± 3,488 N/mm for Group A and 12,885 ± 5,056 N/mm for Group B (p ? 0.0054). Stem B had greater maximum strength, deflection, and energy. CONCLUSIONS: The new stem was effective in neutralizing the impact of axial flexion-compression stresses during biomechanical tests in cadaveric models.

Finite element modeling for development and optimization of a bone plate for mandibular fracture in dogs.

This study aimed to develop a plate to treat fractures of the mandibular body in dogs and to validate the project using finite elements and biomechanical essays. Mandible prototypes were produced with 10 oblique ventrorostral fractures (favorable) and 10 oblique ventrocaudal fractures (unfavorable). Three groups were established for each fracture type. Osteosynthesis with a pure titanium plate of double-arch geometry and blocked monocortical screws of free angulation were used. The mechanical resistance of the prototype with unfavorable fracture was lower than that of the favorable fracture. In both fractures, the deflection increased and the relative stiffness decreased proportionally to the diminishing screw number The finite element analysis validated this plate study, since the maximum tension concentration observed on the plate was lower than the resistance limit tension admitted by the titanium. In conclusion, the double-arch geometry plate fixed with blocked monocortical screws has sufficient resistance to stabilize oblique fractures, without compromising mandibular dental or neurovascular structures.