Valoración evolutiva de fracturas de calcáneo mediante el análisis biomecánico de la marcha. Análisis de resultados / Follow-up assessment of calcaneus fractures by means of biomechanical gait analysis. Results

Introducción: En el vol. 10, n. °4 de esta revista presentamos la metodología del proyecto realizado en colaboración con la Clínica FREMAP de Rehabilitación de Valencia sobre la valoración de la marcha en pacientes con fractura de calcáneo. En este artículo se presentan y discuten los resultados obtenidos. Material y métodos: Con una muestra inicial de 16 pacientes y a partir de magnitudes biomecánicas se definieron y calcularon indicadores objetivos de calidad de la marcha mediante análisis estadístico avanzado. Resultados y discusión: Parámetros relacionados con la distribución asimétrica de presiones plantares, velocidad de progresión, longitud de zancada, asimetrías temporales, descarga asimétrica y discrepancia respecto al patrón de fuerzas en población sana son variables capaces de capturar de forma fiable y objetiva las variaciones que se operan en el patrón de marcha durante la rehabilitación. La distribución asimétrica de presiones en el antepié medida antes del alta clínica, permite predecir en la mayoría de los casos el resultado del sujeto desde el punto de vista biomecánico. Conclusiones: Se sugiere la posibilidad de utilizar plantillas instrumentadas principalmente, y plataformas dinamométricas de forma auxiliar, para predecir la evolución de fracturas de calcáneo y para asistir en la toma de decisiones en estadios tempranos de su rehabilitación (AU)

Quantitative assessment of gait deviation: contribution to the objective measurement of disability.

Three biomechanical parameters based on force plate measurements were defined as indicators of gait deviation. Symmetry was specified as the relative difference in stance time and vertical impulse loading between both feet, constancy as the mean S.D. of the force curves for one subject under a specified gait condition and discrepancy as the average difference between the individual gait pattern and the expected force curves, normalised by the value of the S.D. in a control group. One hundred and forty four patients with osteoarthritis (OA) of the lower extremity and 144 control subjects were studied. There were 45 patients with OA of the hip, 54 of the knee and 45 of the ankle and their function was determined using the Harris Hip score, the hospital for special surgery knee score and the Mazur ankle score, respectively. The temporal asymmetry indicator was more sensitive to unilateral joint affliction, whereas the discrepancy indicators were sensitive to the presence of OA. Both correlated with the patient's function as measured by the relevant clinical score. A significant increase of gait discrepancy was detected in the arthritis group when patients were asked to walk at faster speeds; whilst walking barefoot led to an unexpected reduction of intra-subject kinetic variability. Our results confirm the validity and usefulness of the gait deviation concept in patients with OA.

Application of fuzzy logic techniques for the qualitative interpretation of preferences in a collective questionnaire for users of wheelchairs.

Active participation of users in the evaluation of technical aids is essential, since they are part of the interface with the system and constitute a fundamental source of design criteria. In this study, 88 active users of wheelchairs were interviewed by means of a written questionnaire about their opinion concerning the adaptation of his/her wheelchair to the office workplace. A conceptual framework was introduced linking objective measurements of the user-wheelchair interface to the subjective preferences expressed by the user. Discriminant analysis was used in order to select and quantify the importance of the most significant factors influencing the user's opinions. Fuzzy logic was introduced for the qualitative interpretation of the relationship between those significant factors, based on an inductive algorithm for generating fuzzy rules. Fuzzy logic enables a person to model the uncertainty within the subjective formulation of knowledge or opinions. From the results, a mismatch between actual performance of conventional wheelchairs and requirements of office work became evident. The proposed methods make it possible to determine reliable rules explaining subjective preferences; thus, they provide a flexible means of interpreting user questionnaires and obtaining new design criteria.

Design and test of neural networks and statistical classifiers in computer-aided movement analysis: a case study on gait analysis.

OBJECTIVE: To describe the methods for designing and testing diagnostic systems in movement analysis and to verify the clinical usefulness of neural networks and statistical classifiers in a case study. DESIGN: Connectionist and statistical models trained and tested with measured data. BACKGROUND: A basic need in rehabilitation and related fields is to efficiently manage the vast information obtained from a movement analysis laboratory. Many studies have dealt with the interpretation of measured variables in order to correlate objective descriptors to the presence and/or severity of specific neuromusculoskeletal disorders or their consequences. This traditional analytical approach has been complemented in the last decade by new non-linear classification tools called neural networks. METHODS: A gait analysis study on 148 lower limb arthrosis patients and 88 age-matched control subjects. Pathological and healthy gait patterns obtained from force plates wer discriminated by means of multilayer perceptrons and statistical classifiers. RESULTS: Ten input features were enough to train a multilayer perceptron with six hidden neurons. The discrimination rate of the neural net was 80% after cross-validation, significantly higher (P<0.05) than the performance of a Bayes quadratic classifier (about 75%). A great variance due to a small cross-validation set could be demonstrated. CONCLUSIONS: Strict statistical requirements must be observed for designing a neural network. Although these models attain a better performance than conventional statistical approaches, the benefits they bring are sometimes not sufficient to justify their use. Furthermore, clinicians routinely involved in critical decisions may not consider such diagnostic systems reliable enough.

Optimisation of the prescription for trans-tibial (TT) amputees.

The great diversity of prosthetic mechanisms available nowadays leads to the question of which type of artificial foot would be the most advisable for a particular person. To answer correctly, it is necessary to establish, in an objective way, the performance of each type of prosthetic mechanism. This knowledge is obtained by means of the study of the subject-prosthesis interaction, both in static and dynamic conditions. This paper, based on the analysis of 8 trans-tibial (TT) amputees, presents a quantitative method for the study of human gait which allows the determination of the influence of four different prosthetic ankle-foot mechanisms (SACH, Single-axis, Greissinger and Dynamic) on gait. To do this, 1341 gait trials at different cadences were analysed (383 with normal subjects and 958 with amputees, using the four prosthetic feet under study). From all the variables available for study only those which offered interpretable clinical information were chosen for analysis. A total of 18 variables (kinetic, kinematic and time-related) were selected. A covariance analysis (ANOVA) of these variables was made, which showed that the factors influencing TT amputee gait were, in order of importance, cadence and leg studied (sound or prosthetic), inter-individual variability and, finally, the prosthetic mechanism used. When looking at the performance during gait of the 4 prosthetic mechanisms studied it can be observed that there are similarities in the kinetic study between SACH and Dynamic feet on one hand and Single-axis and Greissinger feet on the other. These results seem to support the classification criteria of articulated and non-articulated prosthetic mechanisms.

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.

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.