Mechanical properties of the California sea lion (Zalophus californianus) and northern elephant seal (Mirounga angustirostris) lower jaws explain trophic plasticity.

The fossil record of pinnipeds documents a suite of morphological changes that facilitate their ecological transition from a terrestrial to an aquatic lifestyle. Among these is the loss of the tribosphenic molar and the behavior typically associated with it in mammals: mastication. Instead, modern pinnipeds exhibit a broad range of feeding strategies that facilitate their distinct aquatic ecologies. Here, we examine the feeding morphology of two species of pinnipeds with disparate feeding ecologies: Zalophus californianus, a specialized raptorial biter, and Mirounga angustirostris, a suction specialist. Specifically, we test whether the morphology of the lower jaws facilitates trophic plasticity in feeding for either of these species. We used finite element analysis (FEA) to simulate the stresses during the opening and closing of the lower jaws in these species to explore the mechanical limits of their feeding ecology. Our simulations demonstrate that both jaws are highly resistant to the tensile stresses experienced during feeding. The lower jaws of Z. californianus experienced the maximum stress at the articular condyle and the base of the coronoid process. The lower jaws of M. angustirostris experienced the maximum stress at the angular process and were more evenly distributed throughout the body of the mandible. Surprisingly, the lower jaws of M. angustirostris were even more resistant to the stresses experienced during feeding than those of Z. californianus. Thus, we conclude that the superlative trophic plasticity of Z. californianus is driven by other factors unrelated to the mandible's tensile resistance to stress during feeding.

Sistema auxiliar para colocar el marco estereotactico en el craneo / Auxiliary system for positioning the stereotactic frame to the skull

En neurocirugía funcional y radioneurocirugía estereotáctica, la fijación de un marco en el cráneo, permite el establecimiento de un sistema tridimensional de coordenadas, para localizar y definir con precisión los objetivos en el cerebro. El montaje se basa en la experiencia y la percepción visual del médico, pero los resultados son subjetivos y la calibración de las coordenadas del marco con respecto al cráneo no siempre es la óptima para el desarrollo del procedimiento quirúrgico. Este estudio evalúa la eficacia y la funcionalidad de un sistema auxiliar diseñado para colocar el marco estereotáctico en el cráneo. La evaluación se realiza por medio de un estudio comparativo de dos grupos de 7 pacientes cada uno sometidos a tratamiento de radioneurocirugía. En el primer grupo no es utilizado el sistema, solo en el segundo, se tomaron 165 imágenes (IRM) en promedio por cada estudio. El empleo del sistema auxiliar disminuye la variación de la inclinación y la rotación del marco con respecto al cráneo hasta un 64%, la apreciación subjetiva del médico es sustituida por una medición objetiva, obteniéndose certidumbre al posicionar el marco sobre el cráneo. Los resultados muestran que el sistema auxiliar diseñado es eficaz y funcional.

In functional neurosurgery and stereotactic radioneurosurgery, the fixation of a frame to the skull allows the establishment of a three-dimensional coordinate system, to locate and precisely defined objectives in the brain. The montage is based on experience and visual perception the doctor, the results obtained and the calibration of the coordinates of the frame with respect to the skull is not always the optimal for developing the surgical procedure. This study evaluates the effectiveness and functionality of an auxiliary system designed to collocate the stereotactic frame to the skull. The evaluation is done by means of a comparative study of two groups of 7 patients each underwent radioneurosurgery treatment. The first group is not using the system, only in the second, were performed on average 165 images (MRI) for each study. The use of auxiliary system reduces the variation of the inclination and rotation of the frame with respect to the skull by 64%, the subjective appreciation the doctor is substituted by an objective measure, thus obtaining certainty to position the frame on the skull. The results show that the auxiliary system designed is effective and functional.

Numerical-experimental study of internal fixation system "Dufoo" for vertebral fractures.

BACKGROUND: We describe a numerical experimental study of the stress generated by the internal fixation system "Dufoo" used in the treatment of vertebral fractures with the purpose of validating the numerical model of human lumbar vertebrae under the main physiological loads that the human body is exposed to in this area. The objective is to model and numerically simulate the elements of the musculoskeletal system to collect the stresses generated and other parameters that are difficult to measure experimentally in the thoracic lumbar vertebrae. METHODS: We used an internal fixator "Dufoo" and vertebrae L2-L3-L4 specimens from pig and human. The system uses a total L3 corpectomy. The fixator acts as a mechanical bridge implant from L2 to L4. Numerical analysis was performed using the finite element method (FEM). For the experimental study, reflective photoelasticity and extensometry were used. RESULTS: Torsion and combined loads generate the main displacements and stresses in the study system, determining that the internal fixation carries out part of the function of the damaged organ structure when absorbing the stresses presented by applied loads. CONCLUSIONS: Numerical analysis allows great freedom in the management of the variables involved in the developed models using radiological images. Geometric models are obtained and are entered into FEM programs that allow testing using parameters that, under actual conditions, may not be easily carried out, allowing to comprehensively determine the biomechanical behavior of the coupled system of study.

Laparoscopic Nissen solo surgery using PMAT (first experience).

This article describes the use of a Postural Mechatronic Assistant Trainer (PMAT) in pediatric Nissen surgery. This mechatronic system enables users to establish the logistical considerations for solo surgery and determine the advantages this new tool offers for the autonomous handling of optics.