Biomechanics of internal fixation in Hoffa fractures - A comparison of four different constructs.

OBJECTIVE: Compare the biomechanical effectiveness of four different bone-implant constructs in preventing fracture displacement under axial loading. METHODS: Twenty artificial femora had a standardized coronally oriented fracture of the lateral femoral condyle, representing a Hoffa fracture classified as a Letenneur type I. Four different fixation constructs were applied to the synthetic bones for biomechanical testing. The constructs consisted of a posterolateral (PL) buttressing locking plate in conjunction with two cannulated lag screws inserted from posterior to anterior (PA) - Group 1; Two cannulated screws inserted from anterior to posterior (AP) without plating- Group 2; A posterolateral (PL) buttressing locking plate in isolation - Group 3; and a combination of two lag screws from anterior to posterior (AP) in addition to a horizontal one-third tubular locking plate - Group 4. An axial load was applied to the fracture site with a constant displacement speed of 20 mm/min, and the test was interrupted when a secondary displacement was detected determining a fixation failure. We recorded the maximum applied force and the maximum fracture displacement values. RESULTS: Group 1 demonstrated the highest overall bone-implant axial stiffness with the lowest secondary displacement under loading. Groups 3 and 4 showed equivalent mechanical behavior. Group 2 presented the lowest mechanical stiffness to axial loading. The combination of the one-third tubular locking plate with anterior-to-posterior lag screws (Group 4) resulted in 302 % increase in fixation stiffness when compared to anterior-to-posterior lag screws only (Group 2). CONCLUSIONS: This study confirms the mechanical superiority of having a plate applied parallel to the main fracture plane in the setting of coronally oriented femoral condyle fractures. The addition of a horizontal plate, perpendicular to the main fracture plane, significantly increased the resistance to shearing forces at the fracture site when compared to constructs adopting just cannulated screws. LEVEL OF EVIDENCE: Biomechanical study.

Busch-Hoffa fracture: A systematic review.

BACKGROUND: Accomplish a thorough review on the existing biomechanical and clinical studies about coronal plane fractures of the distal femur. METHODS: We performed an electronic search of PubMed/MEDLINE database from April to June, 2023. The terms for the database search included "Hoffa fractures," OR "Busch-Hoffa fractures" OR "coronal plane fractures of the distal femur." RESULTS: The search identified 277 potentially eligible studies. After application of inclusion and exclusion criteria, 113 articles were analyzed in terms of the most important topics related to coronal plane fractures of the distal femur. CONCLUSION: Lateral coronal plane fractures of the distal femur are more frequent than medial, present a more vertical fracture line, and usually concentrate on the weight bearing zone of the condyle. The Letenneur system is the most used classification method for this fracture pattern. Posterior-to-anterior fixation using isolated lag screws (for osteochondral fragments-Letenneur type 2) or associated with a posterior buttressing plate (when the fracture pattern is amenable for plate fixation-Letenneur types 1 and 3) is biomechanically more efficient than anterior-to-posterior fixation. Anterior-to-posterior fixation using lag screws complemented or not by a plate remains a widely used treatment option due to the surgeons' familiarity with the anterior approaches and lower risk of iatrogenic neurovascular injuries. There is no consensus in the literature regarding diameter and number of screws for fixation of coronal plane fractures of the distal femur.

Experimental and Numerical Comparison of Impact Behavior between Thermoplastic and Thermoset Composite for Wind Turbine Blades.

Damage generated due to low velocity impact in composite plates was evaluated focusing on the design and structural integrity of wind turbine blades. Impact properties of composite plates manufactured with thermoplastic and thermoset resins for different energy levels were measured and compared. Specimens were fabricated using VARTM (vacuum assisted resin transfer molding), using both matrix systems in conjunction with carbon, glass and carbon/glass hybrid fibers in the NCF (non-crimp fabric) architecture. Resin systems used were ELIUM 188O (thermoplastic) from Arkema Co., Ltd. and a standard epoxy reference, EPR-L20 from Hexion Co., Ltd. (thermoset). Auxiliary numerical finite element analyses were performed to better understand the tests physics. These models were then compared with the experimental results to verify their predictive capacity, given the intrinsic limitations due to their simplicity. Based in the presented results, it is possible to observe that ELIUM is capable to replace a conventional thermoset matrix. The thermoplastic panels presented similar results compared to its thermoset counterparts, with even a trend of less impact damage. Additionally, for both thermoplastic and thermoset resin systems, glass layups showed the lowest levels of damage while carbon panels presented the highest damage levels. Hybrid laminates can be applied as a compromise solution.

The effect of prosthesis length and implant diameter on the stress distribution in tooth-implant-supported prostheses: a finite element analysis.

PURPOSE: The goal of this study was to compare the stress distribution of tooth-implant-supported prostheses (TISPs) and solely implant-supported prostheses (ISPs) with two different pontic spans (three units versus four units). MATERIALS AND METHODS: Two-dimensional finite element models were constructed from the radiographs of polyester resin casts to mimic TISPs and ISPs. In all, eight models were analyzed. Occlusal loads of 15 N and 30 N were applied to the premolars and molars, respectively. The lateral and inferior borders of the models were constrained, with all degrees of freedom equal to zero. Eight-node elements with plane strain assumption were used for simulation. RESULTS: The authors found that TISPs with a short span and wider-diameter implants resulted in more homogenous stress distribution and less stress concentration on the implants. The long span yielded higher stress concentrations on the implants and between the pontics. CONCLUSIONS: In all models analyzed, stress concentrations were present in the implants.

Evaluation of pitch up of two-axle solid waste collection compactor trucks in the static condition.

The study of pitch up limit for solid waste collection compactor trucks in tilted public roads is of great relevance both for the planning of waste collection, mainly in cities with very uneven street gradient, or for use as a design parameter in projects involving public roads. Considering the typical construction and use of rear loader waste compactor equipment, the centre of gravity moves towards the rear of the vehicle as it is loaded, resulting in overload in the rear axle at the end of the waste collection period. In the city of Belo Horizonte (Brazil), several cases of pitch up have been reported for this type of vehicle, in streets with different inclinations and with loading situations in which the load box was not completely full. The present study investigated the variation of the imminence pitch up angles of the two-axle, rear-loading, solid waste collection compactor truck in a static condition, determined by the variation of its centre of gravity coordinates, which were obtained experimentally by means of a testing programme for different loading situations. The critical inclination angle was 0.347 rad (19.89°), which corresponds to a ramp inclination of 36.17%, for the condition of total weight of 157.06 kN (16 027 kgf) with payload of 63.42 kN (6472 kgf).

3D finite element analysis on esthetic indirect dental restorations under thermal and mechanical loading.

Thermo-mechanical finite element analyses in 3-D models are described for determination of the stress levels due to thermal and mechanical loads in a healthy and restored tooth. Transient thermo-mechanical analysis simulating the ingestion of cold and hot drinks was performed to determine the temperature distribution in the models of the teeth, followed by linear elastic stress analyses. The thermal loads were applied on the occlusal and lingual surfaces. Subsequently, coupled variation of the temperature and mastication loading was considered. The vertical loading was distributed at occlusal points, adding up to 180 N. Maximum stresses were verified in resin restoration under thermal loads. When studying coupled effect of mechanical loading with that arising from thermal effects, higher tensile stress values occurred in porcelain restorations, especially at the restoration-dentin interface. Regions of high tensile stress were detected and their possible clinical significance with respect to restoration damage and microleakage were discussed.

Comparative 3D finite element stress analysis of straight and angled wedge-shaped implant designs.

PURPOSE: The goal of this work was to analyze the stress distribution in 2 wedge-shaped implant designs, straight and angled, by means of a 3-dimensional finite element method (FEM) stress analysis. MATERIALS AND METHODS: A model was generated from computerized tomography of a human edentulous mandible with the implants placed in the left first molar region. The model included boundary conditions representing the muscles of mastication and the temporomandibular joint. An axial load of 100 N and a horizontal load of 20 N were separately applied at the tops of the implant abutments, and system equilibrium equations were used to find each muscle intensity force based on its position and direction. The mandibular boundary conditions were modeled considering the anatomy of the supporting muscle system. Cortical and medullary bones were assumed to be homogeneous, isotropic, and linearly elastic. RESULTS: The stress analysis provided results in terms of normal maximum tensile (sigma1) and compressive (sigma3) stress fields. The stress distribution was quite similar for both designs, indicating a good performance of the angled design. CONCLUSIONS: Stresses in the angled implant were in general lower than in the straight implant, and the differences between the 2 designs studied were more relevant for the vertical load. No indication was found that angled implants of the type described generate stress-induced problems compared to straight implants.

Abfraction and anisotropy--effects of prism orientation on stress distribution.

This work discusses the effect of enamel anisotropy in the stress concentration at the cement-enamel junction (CEJ), a probable cause of fracture in enamel leading to abfraction. Usual simplifications when developing computer models in dentistry are to consider enamel isotropic, or that the direction of the prisms is orthogonal to either the dentine-enamel interface or the tooth outer surface. In this paper, a more refined model for the material behavior is described, based on laboratory observation and on the work of Fernandes and Chevitarese. The material description is used in a two-dimensional (2D) finite element model of the first upper premolar, and the analysis is performed for two different situations: vertical loads, typical of normal mastication and horizontal loads, dominant in bruxism. The analyses were performed using a unit load, which under the hypothesis of linear response of the tooth, allows the combinations described in the text to simulate different functional and parafunctional loads. The results indicate that a realistic enamel description in terms of mechanical properties and spatial distribution of its prisms alters significantly the resulting stress distribution. For all cases included in this study, the detailed description of prism orientation and resulting anisotropy led to improved response in terms of stress distribution, even when loading was horizontal.