Biomechanical consequences of callus development in Hoffmann, Wagner, Orthofix and Ilizarov external fixators.

A theoretical analysis by a finite elements model (FEM) of some external fixators (Hoffmann, Wagner, Orthofix and Ilizarov) was carried out. This study considered a logarithmic progress of callus elastic characteristics. A standard configuration of each fixator was defined where design and application characteristics were modified. A comparison among standard configurations and influence of every variation was made with regard to displacement and load transmission at the fracture site. An experimental evaluation of standard configurations was performed with a testing machine. After experimental validation of the theoretical model was achieved, an application of physiological loads which act on a fractured limb during normal gait was analysed. A minimal contribution from an external fixator to the total rigidity of the bone-callus-fixator system was assessed when a callus showing minimum elastic characteristics had just been established. Insufficient rigidity from the fixation devices to assure an adequate immobilization during the early stages of fracture healing was verified. However, regardless of the external fixator, callus development was the overriding element for the rigidity of the fixator-bone system.

Load transmission through the callus site with external fixation systems: theoretical and experimental analysis.

The fracture callus contribution to the total rigidity of external fixator-fractured bone element was analysed. This study was achieved from both theoretical and experimental perspectives. The theoretical study was done using the finite element method with a three-dimensional model. In this model, both the callus and the development of its elastic characteristics were considered. A series of 38 New Zealand-California white rabbits with tibial fractures treated with some external fixation system was used in this study. Such devices could reproduce either rigid or elastic features. The frame dynamization can be obtained at different fracture healing stages. Animals were classified into four series: (1) rigid fixators, (2) dynamized fixators two weeks after surgery, (3) three weeks after surgery and (4) four weeks after surgery. Tension tests were performed to evaluate callus strength. Theoretical results showed significant levels of callus load transmission (85.5%) when the callus elastic modulus is 1/100 of the elastic modulus of intact bone in an external fixator with rigid features. Experimental analysis of the callus obtained with different external fixator systems did not show differences among them. This fact implies that the immature callus theoretically modelled (E = 100 N mm-2) appears early in the rabbit fracture model (before two weeks, when first dynamization was made), for this reason no differences were found between the two types of treatment (rigid and dynamized systems). This fact questions the reliability of the dynamization process in external fixation of fractures and it implies accurate investigations in the clinical field.

Design and development of a new general purpose stereotaxic device.

This paper describes the design and development of a new device which allows the surgeon to locate an internal point following two X-ray views with an image intensifier. Three dimensional coordinates of the target point are directly estimated by means of two ring-and-bead sights and no computer calculations are necessary. After the location of the target point it is possible to choose any track to it by means of the rotation of an arc and the circumferential sliding of the arc. The system reduces radiation doses and it can be used for many purposes such as percutaneous discectomies and chemonucleolysis, biopsies and screw insertion of interlocking nails.

Desarrollo de una nueva metodología para la valoración de la movilidad cervical basada en técnicas de fotogrametría / Development of a new methodology for the assessment of cervical mobility based on photogrammetry techniques

Introducción. La inexistencia de métodos objetivos, fiables y precisos de valoración funcional de la movilidad de la columna cervical dificulta la elección de un adecuado tratamiento rehabilitador y posterior control de su evolución en pacientes afectados de dolor cervical. Todo esto ha planteado la necesidad de desarrollar una nueva metodología de valoración de la movilidad cervical a partir de técnicas de vídeo-fotogrametría y de definición de los patrones de movilidad en función de las variables edad y género. Material y métodos. Para la realización del estudio se ha seleccionado una muestra de 50 personas de edades comprendidas entre 20 y 79 años, con ausencia de patología cervical. También se ha realizado un estudio piloto con 14 personas afectadas de dolor cervical. El equipo de medida está basado en un sistema de video-fotogrametría. Los movimientos que se registraron fueron el de flexo-extensión, inclinación lateral y el de rotación de la cabeza. Resultados. Cabe destacar la alta influencia de las variables edad y sexo en los rangos de movimiento, además de la disminución de los rangos de movilidad en los pacientes aquejados de latigazo cervical cuya significación también es muy alta. Discusión. Se ha demostrado que la metodología presentada en el siguiente trabajo resulta una herramienta muy útil para la valoración funcional de la movilidad de la columna cervical, mejorando la precisión y la fiabilidad de los resultados obtenidos y permitiendo realizar un tratamiento rehabilitador de un modo más eficaz y controlado

Introduction. The non-existence of objective, reliable and precise methods of functional valuation of the cervical spine mobility makes difficult the election of a suitable rehabilitation treatment and subsequent control of its evolution in affected patients of cervical pain. All this has raised the need of developing a new methodology of cervical mobility valuation based on video-photogrammetry techniques and to define the patterns of mobility based on the parameters age and gender. Material and methods. For the accomplishment of the study a sample of 50 people aged between 20 and 79 years with absence of cervical pathology has been selected. Besides, a pilot study was made with 14 affected people of cervical pain. The measuring equipment is based on a video-photogrammetry system. The movements that were registered were flexo-extension, lateral flexion and rotation of the head. Results. It is possible to emphasize the high influence of the variables age and sex in the movement ranges, in addition to the diminution of the ranges of mobility in patients affected of whiplash injury whose meaning also is very high. Discusion. The methodology presented in the present work has been demonstrated as a useful tool for the functional valuation of the cervical spine mobility, improving the accuracy and the reliability of the obtained results and allowing making a rehabilitation treatment in a more effective and controlled way