ABSTRACT
OBJETIVO: Las propiedades de los materiales que constituyen el tejido óseo son determinantes en su resistencia mecánica pero los factores que influyen sobre ella son parcialmente desconocidos en la actualidad. MATERIAL Y MÉTODOS: En esta investigación medimos la dureza ósea mediante ensayos de ultra-microindentación con punta tipo Berkovich y una carga de 150 mN en fémures de ratas Sprague-Dawley sometidas a una fractura transversal o a una osteotomía de sustracción, y comparamos los resultados en diferentes localizaciones óseas y grupos experimentales. El estudio comprende los siguientes cuatro grupos experimentales, cada uno de ellos constituido por cuatro ratas: a) fractura diafisiana estándar; b) fractura más osteotomía de 2 mm; c) osteotomía tratada con hormona paratiroidea humana, PTH (1-84); d) osteotomía tratada con ranelato de estroncio. RESULTADOS: Encontramos que la dureza del material era consistentemente mayor en el hueso cortical que en el hueso trabecular. También fue consistentemente más alto en las epífisis femorales superiores que en las epífisis inferiores (diferencia de 1,2 desviaciones estándar). La cirugía redujo la dureza en el fémur operado (diferencia de 0,3 desviaciones estándar, p = 5,5 x 10-2). El tratamiento con PTH indujo un aumento leve pero consistente de la dureza en todos los sitios (p = 1,8 × 10-5) mientras que el efecto del ranelato de estroncio fue inconsistente. CONCLUSIONES: Estos datos muestran que la microdureza tisular está influida por una variedad de factores, incluyendo la anatomía, el tipo de tejido óseo, la lesión esquelética y la terapia farmacológica. Por lo tanto, los estudios futuros sobre la calidad del tejido deberían diseñarse cuidadosamente teniendo en cuenta estos factores
OBJETIVE: The properties of the materials that constitute the bone tissue are decisive in its mechanical strength but the factors that influence it are partially unknown at present. Material and method: In this paper, we gauge bone hardness by means of ultra-microindentation tests with a Berkovich tip and a 150 mN load in femurs of Sprague-Dawley rats subjected to a transverse fracture or a subtraction osteotomy. The results are compared in different bone locations and experimental groups. The study includes the following four experimental groups, each consisting of four rats: a) standard diaphyseal fracture; b) fracture plus osteotomy of 2 mm; c) osteotomy treated with human parathyroid hormone, PTH (1-84); d) osteotomy treated with strontium ranelate. RESULTS: We found the hardness of the material was consistently greater in cortical bone than in trabecular bone. It was also consistently higher in the upper femoral epiphyses than in the lower epiphyses (difference of 1.2 standard deviations). The surgery reduced hardness in the operated femur (difference of 0.3 standard deviations, p = 5.5 x 10-2). PTH treatment induced a slight but consistent increase in hardness at all sites (p = 1.8 x 10-5) while the effect of strontium ranelate was inconsistent. CONCLUSIONS: These data show that tissue micro-hardness is influenced by a variety of factors, including anatomy, type of bone tissue, skeletal injury and drug therapy. Therefore, future studies on tissue quality should be carefully designed with these factors in mind
Subject(s)
Animals , Rats , Tensile Strength , Flexural Strength , Femoral Fractures/physiopathology , Parathyroid Hormone/therapeutic use , Femoral Fractures/drug therapy , Risk Factors , Disease Models, Animal , Rats, Sprague-Dawley , OsteotomyABSTRACT
The aim of the present research is to determine the influence of the calcification of human mitral valves on the mechanical properties of their marginal chordae tendineae. The study was performed on marginal chords obtained from thirteen human mitral valves, explanted at surgery, including six non-calcified, four moderately calcified and three strongly calcified valves. The mechanical response of the chords from the non-calcified and moderately calcified valves was determined by means of quasi-static tensile tests (the poor condition of the strongly calcified valves prevented them from being mechanically characterised). The material parameters that were obtained and analysed (the Young's modulus, the secant modulus, the proportional limit stress, the ultimate strength, the strain at fracture and the density of energy stored up to maximum load) revealed noticeable differences in mechanical behaviour between the two groups of mitral chordae tendineae. Large scatter was obtained in all cases, nevertheless, considering the mean values, it was observed that the normal chords are between three and seven times stiffer or more resistant than the moderately calcified ones. On the contrary, the results obtained for the strain at fracture showed a rather different picture as, in this case, no significant differences were observed between the two families of chords. A scanning electron microscopy study was conducted in order to find out the relevant features of the calcium deposits present in the calcified chordae tendineae. In addition, the general aspects appreciated in the stress vs. strain curves were correlated with the collagen morphological evidences determined microscopically. Finally, the calcium content present in the three groups of chords was quantitatively determined through atomic absorption spectroscopy; then, the relation between the mechanical properties of normal and moderately calcified chords as a function of its calcium content was obtained. This analysis confirmed the existence of a strong correlation between calcium content and stiffness or resistance whereas the influence on the ductility seems to be negligible.
Subject(s)
Calcinosis/metabolism , Chordae Tendineae/metabolism , Materials Testing , Mechanical Phenomena , Mitral Valve/metabolism , Adult , Biomechanical Phenomena , Calcium/metabolism , Chordae Tendineae/physiology , Chordae Tendineae/physiopathology , Female , Humans , Male , Middle Aged , Tensile StrengthABSTRACT
Hereditary spherocytosis is a chronic hemolytic anemia that very infrequently produces severe iron overload. Only 15 cases of hereditary spherocytosis associated with hemochromatosis have been described previously. It was initially thought that hemochromatosis was the result of the increase of iron stores secondary to chronic hemolysis. Afterwards, it became apparent that iron overload could appear in patients splenectomized. This fact suggested that spherocytosis and idiopathic hemochromatosis could be inherited independently. We describe the case of a 45-year-old man, with known hereditary spherocytosis, splenectomized at 5 years of age, who developed iron overload which affected his heart, liver and pancreas.
