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Introduccion La separacion entre el cemento y el implante femoral se relaciona con los aflojamientos asepticos y con la supervivencia de los implantes. El objetivo del trabajo es el desarrollo de un modelo de dano que simule la degradacion del cemento y el aflojamiento del implante, con dos acabados superficiales del vastago. Material y metodo Aplicamos un modelo axisimetrico de elementos finitos de un vastago rodeado por una capa de cemento. La carga de compresion aplicada al vastago varia de 0 a 7 kN con frecuencia de 1 Hz durante 1,7 millones de ciclos. Una vez que se solto la interfaz se incorporo rozamiento entre ambas superficies. Resultados En los vastagos lisos el dano estimado en el cemento estaba mas distribuido, siendo el dano global menor. En los rugosos hay mayor concentracion del dano y mayor degradacion del cemento en la zona distal, continuandose por la zona proximal. Conclusion La simulacion con elementos finitos permite predecir el comportamiento de los implantes relacionando macrogeometria y superficie. En nuestro modelo se demuestra la influencia del acabado superficial del vastago en la localizacion e intensidad del dano en el cemento y en la interfaz.

Objetivo Nuestro objetivo es analizar los resultados clinicos y radiologicos de forma retrospectiva de 30 recambios de artroplastias de rodilla con vastagos cementados del modelo Natural I y II (Centerpulse ®) en 29 pacientes intervenidos entre los anos 1992 y 2002. Material y metodo Se trata de 29 pacientes (uno intervenido bilateralmente) con una edad media de 71 ± 5 anos (60-83). El 75% eran mujeres. La causa mas importante de recambio protesico ha sido el aflojamiento aseptico (53%), seguido de aflojamiento septico en un 20%, inestabilidad (13%), artrofibrosis (7%) y osteolisis (7%). El tipo mas frecuente de defecto oseo segun la clasificacion del Instituto Anderson fue el tipo 1 en femur (70%) y el tipo 2 en tibia (44%). El seguimiento medio ha sido de 4,3 ± 2,3 anos (2-10). Resultados La puntuacion clinica media segun la Sociedad Americana de la Rodilla al final del seguimiento ha sido 77,4. La puntuacion funcional media ha sido 20. La flexion media ha sido de 79,2° ± 25,2 (r: 10-110) con una extension media de 0,8° ± 3,1 (r: 0-15). La hospitalizacion media fue de 29 ± 22,1 dias (r: 8-85). En 4 casos ha sido necesario un segundo recambio (13%): dos por infeccion, uno por inestabilidad y otro por rotura por fatiga del vastago femoral. Conclusion En este trabajo hemos observado que los pacientes con vastagos cementados en recambio de protesis de rodilla tienen unos resultados clinicos aceptables a medio plazo, con una tasa de segundo recambio de un 13% a 4 anos.

Objetivo Valorar la linea condilea posterior (LCP) como referencia, en 23 casos intervenidos de artroplastia total de rodilla. Material y metodo Estudio prospectivo en una serie consecutiva de 23 casos de artrosis de rodilla. Se analizaron las medidas realizadas con un sistema de navegacion de la LCP, linea epicondilea (LE) y linea de Whiteside o anteroposterior (LAP), y el angulo LE-LCP con referencia LAP y el angulo LAP-LE con referencia LCP. Resultados Tomando como referencia la LCP (11 casos), en tres casos fracaso, encontrando una distorsion del angulo LAP-LE. Tomando como referencia la LAP (12 casos), en 6 casos hubo desviacion del angulo LE-LCP. Conclusiones Con la cirugia protesica de rodilla asistida con navegador vamos a personalizar las referencias anatomicas que van a determinar la rotacion femoral. Nos permite colocar la rotacion deseada, sin limitaciones de posicion propias de la instrumentacion manual. Tenemos que pensar que existe una gran variabilidad anatomica. Existe una gran controversia en cuanto a que referencia anatomica se utiliza para determinar la rotacion femoral. Se ha demostrado que la LAP es la referencia morfologica que menos varia, y tambien un buen punto para controlar el centraje rotuliano.

The ongoing debate surrounding the surgical treatment of trochanteric hip fractures, particularly unstable fractures, has led to continuous changes in the design of well-established implants and to the development of new ones. The goal of this paper was to use a finite element simulation to compare the biomechanical behaviour of two intramedullary implants most often used at the University Hospital of Zaragoza: the standard Gamma® nail (Howmedica) and the proximal femoral nail (PFN®, Stratec). The main focus was on the displacements of the fracture focus and the stress distributions along the femur and the implant. Both nails produced an important redistribution of stress in the bone tissue, but the redistribution of peak stress was higher for the Gamma® nail. On the other hand, with PFN® there were smaller displacements at the fracture site. Finally, under the same workload, the Gamma® nail supported higher stresses than the PFN®.

Objetivo Los quistes meniscales suelen asociarse a la rotura del menisco, no obstante pueden presentarse en ausencia de lesion meniscal. Se reviso la etiologia y el posible tratamiento en los casos de quiste del menisco lateral no asociados a roturas del mismo. Caso clinico Se presenta un caso clinico de quiste del cuerno anterior del menisco lateral no asociado a lesion del mismo en un paciente joven. Resultados Se realiza tratamiento artroscopico con buen resultado clinico a los 6 meses de la intervencion, que se confirma mediante estudio con resonancia magnetica (RM). Conclusiones En los casos en los que los quistes meniscales no se asocian a rotura meniscal, la cirugia artroscopica consistente en la descompresion del quiste asociado a reparacion de la union meniscocapsular proporciona un buen resultado clinico.

Objetivos Se ha desarrollado un modelo tridimensional mediante elementos finitos de la articulacion femorotibial para determinar las areas de contacto y distribucion de presiones entre el menisco y el cartilago articular e investigar los efectos de la meniscectomia. Material y metodo Partiendo de imagenes de una rodilla sana, obtenidas por resonancia magnetica nuclear (RMN), se ha elaborado un modelo geometrico de elementos finitos sobre el que se han desarrollado diferentes tipos de meniscectomias, estudiando el comportamiento del modelo en diferentes situaciones: con menisco sano, con lesion meniscal, tras meniscectomia parcial y tras meniscectomia total, para analizar los efectos sobre el cartilago articular. Resultados En el modelo de lesion meniscal del tipo longitudinal la aparicion de tensiones de traccion en el borde de la fisura meniscal podria explicar la inestabilidad de estas lesiones y su propagacion. En el modelo de meniscectomia parcial, se origina un incremento de la compresion sobre el cartilago articular en zonas inicialmente descargadas. Finalmente, en el modelo con meniscectomia total, el menisco externo es el que absorbio la totalidad del contacto apareciendo importantes cambios sobre el cartilago del condilo femoral lateral. Conclusiones Consideramos, analizando los resultados obtenidos, que influyen tanto la zona meniscal resecada como la cantidad de menisco que se reseca. Ademas, las roturas de los meniscos son inestables a largo plazo. Asimismo, hemos comprobado que la meniscectomia parcial altera el comportamiento normal de la articulacion, y en especial del cartilago articular, aumentando hasta un 126% las tensiones de compresion, lo que podria justificar su deterioro.

El analisis mediante elementos finitos (AEF) viene aplicandose en la bibliografia al estudio biomecanico de las protesis de rodilla. Material y metodo En nuestro trabajo hemos realizado un modelo de articulacion de rodilla y otro de artroplastia de rodilla mediante AEF, estudiando el efecto de las cargas sobre ambos modelos en la fase de soporte unilateral a 0° y 15° de flexion. Se han comparado los desplazamientos, las tensiones en direccion vertical para el tejido oseo y las tensiones de Von Mises para los implantes protesicos. Resultados En extension los desplazamientos obtenidos con la rodilla anatomica son mayores que con artroplastia. En la rodilla con artroplastia se produce una mayor concentracion de tensiones a nivel de la cabeza femoral, mientras que en el modelo de rodilla anatomica la distribucion es mas uniforme. El componente tibial es el que mas trabaja, sobre todo en la zona del vastago pero tambien en la bandeja metalica. Conclusiones A pesar de las limitaciones del modelo, podemos afirmar que el AEF permite realizar un estudio biomecanico del comportamiento estructural de la articulacion de la rodilla y la rodilla con artroplastia.

The Finite Element Method (FEM) can be used to analyze very complex geometries, such as the pelvis, and complicated constitutive behaviors, such as the heterogeneous, nonlinear, and anisotropic behavior of bone tissue or the noncompression, nonbending character of ligaments. Here, FEM was used to simulate the mechanical ability of several external and internal fixations that stabilize pelvic ring disruptions. A customized pelvic fracture analysis was performed by computer simulation to determine the best fixation method for each individual treatment. The stability of open-book fractures with external fixations at either the iliac crests or the pelvic equator was similar, and increased greatly when they were used in combination. However, external fixations did not effectively stabilize rotationally and vertically unstable fractures. Adequate stabilization was only achieved using an internal pubis fixation with two sacroiliac screws. [S0148-0731(00)00905-5]

Debonding of the stem-cement interface and damage accumulation in the cement mantle are basic events that contribute to the long-term failure of cemented hip reconstructions. In this work, a numerical study with these two processes coupled is presented. On the one hand, debonding of the stem-cement interface was simulated by means of a cohesive surface theory that was implemented into an interface finite element. This interface model includes a tensile-shear behavior law, the fatigue failure of the interface, and the friction evolution between both surfaces. On the other hand, damage accumulation in the cement was formulated through the theory of continuum damage mechanics, considering cement damage due to tension, creep under compression, crack closure effects, non-linear damage accumulation and cement residual stresses appearing during polymerisation. This methodology was applied to simulate and compare the degradation process of the cement and stem-cement interface in four different concepts of design: Exeter, Charnley, Elite Plus and ABG II stems. As the actual mechanical properties of the surface of each specific prosthesis are not known, we assumed the same for all of them, distinguishing between polished and matt surfaces. With this assumption, the predicted results showed that the debonding process is very different for each implant depending on the stem geometry. Lower cement deterioration was obtained for the Exeter and ABG II stems, while the lowest stem-cement interface debonding was produced in the Exeter and the Elite Plus stems.

The main objective of this work is the evaluation, by means of the finite element method (FEM) of the mechanical stability and long-term microstructural modifications in bone induced to three different kinds of fractures of the distal femur by three types of implants: the Condyle Plate, the less invasive stabilization system plate (LISS) and the distal femur nail (DFN). The displacement and the stress distributions both in bone and implants and the internal bone remodelling process after fracture and fixation are obtained and analysed by computational simulation. The main conclusions of this work are that distal femoral fractures can be treated correctly with the Condyle Plate, the LISS plate and the DFN. The stresses both in LISS and DFN implant are high especially around the screws. When respect to remodelling, the LISS produces an important resorption in the fractured region, while the other two implants do not strongly modify bone tissue microstructure.

Among 79 patients candidates to hip (53) and knee (26) replacement an evaluation was made of the influence of a two-week program with LMWH on the evolution of hypercoagulability markers: D-D, TAT, and F1 + 2. Measurements were performed by ELISA preoperatively and on days 1, 7 and about 45 postoperatively; in the latter, two extraction intervals were considered:or = 45 days and45 days. With both surgical modalities, D-D and F1 + 2 peaked at 7th day postoperatively, whereas TAT peaked on day 1. Among D-D and F1 + 2 values quantitated on day 7th and the extraction intervalor = 45 days, no significant differences were obtained (Z2.64). The hypercoagulative chronicity exhibited by D-D and F1 + 2 during the first month and a half after this surgery, might require in some cases a more prolonged thromboprophylaxis.

Curettage and filling with acrylic cement in the treatment of para-articular giant cell tumor (GCT) has multiple advantages as compared to other methods; nonetheless, the possibility of progression in arthrosis is still a drawback. The literature does not report long-term functional results when this method was used. Four cases are presented with a mean long-term follow-up of 13.5 years (minimum 11, maximum 18). Clinical results, evaluated by the Enneking system (18), were excellent, and there were no radiological modifications, so that we believe that this is the method to choose for Campanacci stage I and II GCT (1), and in some stage III cases, as joint function is not compromised in time.

We have carried out an experimental investigation of lesions of the intervertebral disc produced by flexion, lateral bending and rotational forces in an attempt to produce disc herniations. Adult Wistar rats were divided into 4 groups: control and posterior, lateral and rotational herniation. There were 10 rats in each group. The tail between the 5th and 8th vertebral segments was used. A Kirschner wire was inserted into each of 2 adjacent vertebrae and the movement produced had an apex which was anterior or lateral depending on the group involved. Variables such as rupture of the annulus, the cellularity of the nucleus pulposus and the site of the lesion in the disc were studied histologically. The height of the disc, the protrusion, the thickness, and the surfaces of the annulus fibrosus and the nucleus pulposus were measured. In every case we found a nuclear displacement which did not become a protrusion. The surface parameters and the cellularity of the nucleus pulposus are most useful indicators and should be included in any study examining the disc after the injection of substances for treatment.

A case of giant cell tumor localized in the proximal end of the right tibia, initially treated by simple curettage is described. After 11 years there was local recurrence, confirmed anatomopathologically, observed during wide resection and reconstruction by arthroplasty plus homoplastic grafting. After a few months there were metastatic lesions in the left parietooccipital and right retroorbitary area. Biopsy of the parietooccipital lesion showed giant cells in a sarcomatous stroma. The patient died after several attempts at chemotherapy. Even if only sporadic cases have been described of late recurrences and of extrapulmonary metastases for giant cell tumors, the case presented here is exceptionally rare. The factors that influence recurrence of these tumors and their ability to metastasize is discussed.

It is our belief that this is the first histologically documented case of popliteal cyst secondary to early failure of a cementless knee prosthesis, that occurred after 4 years. The walls of the cyst presented with granulomatous reaction to polyethylene particles. In prosthetic reimplantation successive to excision of the cyst we observed a recurrence of cysts and osteointegration of the prosthetic components, that made reimplantation difficult. Histological assessment of the synovial tissue, periprosthetic tissue and underlying bone showed granulomatous reaction to polyethylene debris. A "tumor" in a patient that has a knee prosthesis can be caused by implant failure. In cases of early failure wear forms large particles and their migration at the bone-prosthesis interface may be obstructed and thus cause a different biological response. If reimplantation is necessary osteointegration of the implants may make surgery difficult.

Although total knee arthroplasty is a valuable surgical technique, complications and problems do occur. Associated stress fracture of the femoral neck is relatively rare and we have only found eleven relevant reports. In this paper we present a case of bilateral total knee arthroplasty where three months after the second replacement, and without significant injury, the patient suffered a femoral neck fracture in the limb which had received the first new knee joint.

Synovial chondromatosis is an uncommon lesion, characterised by cartilaginous and osseous metaplasia of the joint synovium. It usually involves a large joint and rarely occurs in the hand. A case of tenosynovial chondromatosis of the third finger is reported.

A new case of these rare entity is described. Histopathology and ultrastructure of cartilage is studied pointing out some pathogenics aspects.

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Objective The finite element method (FEM) was used to evaluate the short-term mechanical stability of trochanteric fractures treated by two types of implants: the Gamma" nail (Howmedica) and the Dynamic Hip Screw, DHS" (Synthes). Methods The displacement and stress distributions of bone and implants were computed using a complete 3D FE model. Results The main conclusion is that proximal stable femoral fractures can be treated correctly with the Gamma Nail and DHS. For unstable fractures, the Gamma Nail achieves good stabilization but DHS is insufficient and requires a static screw due to the lack of torsional stiffness. Both extramedullary and intramedullary systems were found to distort the load transmission with respect to the anatomic pattern, so they both have biomechanical limitations in the long-term. (Hip International 2004; 14: 18-23)NO PDF AVAILABLE!