Using artificial neural networks to predict impingement and dislocation in total hip arthroplasty.

Dislocation after total hip arthroplasty (THA) remains a major issue and an important post-surgical complication. Impingement and subsequent dislocation are influenced by the design (head size) and position (anteversion and abduction angles) of the acetabulum and different movements of the patient, with external extension and internal flexion the most critical movements. The aim of this study is to develop a computational tool based on a three-dimensional (3D) parametric finite element (FE) model and an artificial neural network (ANN) to assist clinicians in identifying the optimal prosthesis design and position of the acetabular cup to reduce the probability of impingement and dislocation. A 3D parametric model of a THA was used. The model parameters were the femoral head size and the acetabulum abduction and anteversion angles. Simulations run with this parametric model were used to train an ANN, which predicts the range of movement (ROM) before impingement and dislocation. This study recreates different configurations and obtains absolute errors lower than 5.5° between the ROM obtained from the FE simulations and the ANN predictions. The ROM is also predicted for patients who had already suffered dislocation after THA, and the computational predictions confirm the patient's dislocations. Summarising, the combination of a 3D parametric FE model of a THA and an ANN is a useful computational tool to predict the ROM allowed for different designs of prosthesis heads.

Biomechanical assessment and clinical analysis of different intramedullary nailing systems for oblique fractures.

The aim of this study is to evaluate the fracture union or non-union for a specific patient that presented oblique fractures in tibia and fibula, using a mechanistic-based bone healing model. Normally, this kind of fractures can be treated through an intramedullary nail using two possible configurations that depends on the mechanical stabilisation: static and dynamic. Both cases are simulated under different fracture geometries in order to understand the effect of the mechanical stabilisation on the fracture healing outcome. The results of both simulations are in good agreement with previous clinical experience. From the results, it is demonstrated that the dynamization of the fracture improves healing in comparison with a static or rigid fixation of the fracture. This work shows the versatility and potential of a mechanistic-based bone healing model to predict the final outcome (union, non-union, delayed union) of realistic 3D fractures where even more than one bone is involved.

Fracturas de cadera del anciano / No disponible

No disponible

A comparative FEA of the debonding process in different concepts of cemented hip implants.

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.

Análisis de la rotación del implante femoral en prótesis de rodilla con navegación / Analysis of femoral implant rotation in computerized navigation guided knee arthroplasty

Objetivo. Valorar la línea condílea posterior como referencia, en los 23 casos intervenidos de artroplastia total de rodilla con modelo Natural II durante el año 2003-2004, con sistema de navegación Navitrack (Centerpulse). Material y Métodos: Estudio prospectivo en una serie consecutiva de 23 casos de artrosis de rodilla. Se ha revisado la muestra siguiento el programa Orthocom: sexo, edad, lado, diagnóstico, alineación preoperatoria (eje anatómico), Ahlbäck, técnica quirúrgica. Se han analizado las medidas realizadas con el sistema Navitrack en cuanto a la línea condílea posterior (LCP), línea epicondílea (LE), y línea de Whiteside ó anteroposterior (LAP). Se analiza el ángulo LE-LCP con referencia la LCP (11 casos), en 3 casos fracasa la misma, encontrando una distorsión del ángulo LAP-LE. Tomando como referencia la LAP (12 casos), en 6 casos hay desviación del ángulo LE-LCP. Conclusiones: Con la cirugía protésica de rodilla asistida con navegador vamos a personalizar las referencias anatómicas que van a determinar la rotación femoral. Nos permite colocar la rotación deseada, sin limitaciones de posición propios de la instrumentación manual. Tenemos que pensar que existe una gran variabilidad anatómica. Existe una gran controversia en cuantoa qué referencia anatómica se utiliza para determinar la rotación femoral. Se ha demostrado que la línea AP es la referencia morfológica que menos varía, y tambie´n un buen punto para controlar el centraje rotuliano

Objectives: The purposeof this study was to review the posterior condylar line as a reference, in 23 patients with total knee arthroplasty Natural II between 2003 and 2004, by surgical navigation system Navitrack (Centerpulse). Material and Methods: Prospective analysis of 23 consecutive patients who underwent knee arthroplasty. We reviewed the cases following the Othocom database: sex, age, side, pathology, the preoperative anatomical axis, Ahlbäck, surgical technique. We have studied the references obtained by the Navitrack: posterior condylar line (LCP), transepicondylar line (LE) and the anteroposterior (LAP) or Whiteside line. We measured the LE-LCP angle following the LAP reference and the LAP-LE angle following the LCP reference. Results: Following the LCP reference (11 cases), in 3 cases it is not a reliable reference with a LAP-LE angle distorted. Following the LAP referente (12 cases), in 6 cases the LE-LCP angle was desviated. Conclusions: With the use of surgical navigation in knee arthroplasty we are going to personalize the anatomic references that help us to navigation in knee arthroplasty we are going to personalize the anatomic references that help us to determine the correct rotational alignment of the femoral component. We can choose the rotation that we want without the limitations of the position of manual instrumental alignment. The shape of the distal femur varies among individuals. To choise an anatomical reference to determine the correct femoral component rotational alignment is controversial. The results suggest that the AP line is a more reproducible landmark and a good point to optimise the patellofemoral kinematics

Vástagos cementados en recambio de prótesis de rodilla. Nuestra experiencia / Cemented stems for revision knee arthroplasty. Our experience

Objetivo: Nuestro objetivo es analizar los resultados clínicos y radiológicos de los vástagos de revisión cementados del modelo Natural I y II (Centerpulse) intervenidos en el servicio desde 1992 hasta 2002. Material y Métodos: Para ello se hace una valoración clínica y radiológica de la última consulta realizada en el hospital utilizando la base de datos Orthocom (Centerpulse) y una encuesta telefónica para determinar el estado de salud (SF-12) así como el grado de satisfacción del paciente. Un 75% de la muestra eran mujeres. LA edad media era 71+/- 5 años (60-83). El seguimiento medio ha sido de 3,5 +/- 2 años (1,3-9). Resultados: La causa más frecuente de recambio ha sido el aflojamiento aséptico de los componentes (15 casos) predominando el aflojamiento el componente tibial con delaminación de la bandeja de polietileno, seguido de infección en 5 casos, inestabilidades en varo: 2 casos y en valgo: 2 casos, y 1 caso de artrofibrosis. En un caso la prótesis fracasó con una inestabilidad en valgo, por lo que fue necesario un segundo recambio. Discusión: Existen pocas series publicadas, con un seguimiento muy limitado. En este trabajo hemos encontrado que los pacientes con vástagos cementados en recambio de prótesis de rodilla tienen unos resultados clínicos aceptables a medio plazo, pero con una tasa de segundo recambio de un 13% a casi 4 años, hecho que nos preocupa

Objective: The purpose of the study was to review the clinical and radiographic outcome of revision total knee arthroplasty using cemented component fixation with Natural I and II stems between 1992 and 2002 (Centerpulse). Material and Methods: We study the clinical and radiographic outcome of the last visit in our office and use the Orthocom database (Centerpulse). We do a questions list by phone to determine the SF-12 and the satisfaction of the patient. A 75% of the patients were females. The mean age was 71+/-5 years (range 60-83). Patients were followed for a mena of 3,5+/-2 years (range: 1,3-9). Results: The majority of the revisions (15 patients) were for aseptic loosening of components, mainly tibial component with polyethylene delamination. Infection occurred in 5 cases, instability in varus: 2 cases and in valgus: 2 cases, and 1 case of arthrofibrosis. A case of instability in valgus was re-vised. Discussion: There are few studies, most with limited follow-up that have been published regarding uncemented and cemented intramedullary stems in revision total knee arthroplatsy. This study found that patients with cemented components in revision knew arthroplasty has acceptable midterm clinical results, but the rate of re-revision, 13% at almost 4 years, is a concern

Vástagos cementados en recambios de prótesis totales de rodilla / Cemented femoral stems in revision total knee replacement

Objetivo. Nuestro objetivo es analizar los resultados clínicos y radiológicos de forma retrospectiva de 30 recambios de artroplastias de rodilla con vástagos cementados del modelo Natural I y II (Centerpulse ®) en 29 pacientes intervenidos entre los años 1992 y 2002. Material y método. Se trata de 29 pacientes (uno intervenido bilateralmente) con una edad media de 71 ± 5 años (60-83). El 75% eran mujeres. La causa más importante de recambio protésico ha sido el aflojamiento aséptico (53%), seguido de aflojamiento séptico en un 20%, inestabilidad (13%), artrofibrosis (7%) y osteolisis (7%). El tipo más frecuente de defecto óseo según la clasificación del Instituto Anderson fue el tipo 1 en fémur (70%) y el tipo 2 en tibia (44%). El seguimiento medio ha sido de 4,3 ± 2,3 años (2-10). Resultados. La puntuación clínica media según la Sociedad Americana de la Rodilla al final del seguimiento ha sido 77,4. La puntuación funcional media ha sido 20. La flexión media ha sido de 79,2° ± 25,2 (r: 10-110) con una extensión media de 0,8° ± 3,1 (r: 0-15). La hospitalización media fue de 29 ± 22,1 días (r: 8-85). En 4 casos ha sido necesario un segundo recambio (13%): dos por infección, uno por inestabilidad y otro por rotura por fatiga del vástago femoral. Conclusión. En este trabajo hemos observado que los pacientes con vástagos cementados en recambio de prótesis de rodilla tienen unos resultados clínicos aceptables a medio plazo, con una tasa de segundo recambio de un 13% a 4 años

Purpose. To review in a retrospective study clinical and radiological results of 30 total knee revision arthroplasties, for a failed previous prosthesis, using Centerpulse ® cemented prostheses Natural I and II in 29 patients (one patient had a bilateral replacement) carried out from 1992 to 2002. Materials and methods. We studied a total of 29 patients (one patient had a bilateral replacement) with a mean age of 71 ± 5 (60-83), 75% of the patients were female. The most important reasons for replacing a prosthesis were: aseptic loosening (53%), septic loosening (20%), instability (13%), intra-articular fibrosis (7%), and osteolysis (7%). The most frequent bone disorder according to the Anderson Institute Classification was: type 1 (70%) in the femur and type 2 (44%) in the tibia. The average follow-up was 4.3 ± 2.3 years (2-10). Results. By the end of follow-up the clinical score according to the American Knee Society was 77.4. The final average score was 20. Mean flexion was 79.2° ± 25.2 (range 10-110) with an average extension of 0.8° ± 3.1 (range 0-15). Average hospitalisation was 29 ± 22.1 days (range 8-85). In 4 cases a second prosthesis replacement was necessary (13%): in 2 cases due to infection, in 1 due to instability, and in the remaining case due to a fatigue fracture of the femoral prosthesis. Conclusion. In this study we saw acceptable medium-term clinical results in patients that required revision of a failed cemented knee prosthesis, with a rate of second surgical revision procedures of 13% over 4 years

Análisis de la rotación del implante femoral en prótesis de rodilla con navegación / Analysis of femoral implant rotation in computerized navigation-guided knee arthroplasty

Objetivo. Valorar la línea condílea posterior (LCP) como referencia, en 23 casos intervenidos de artroplastia total de rodilla. Material y método. Estudio prospectivo en una serie consecutiva de 23 casos de artrosis de rodilla. Se analizaron las medidas realizadas con un sistema de navegación de la LCP, línea epicondílea (LE) y línea de Whiteside o anteroposterior (LAP), y el ángulo LE-LCP con referencia LAP y el ángulo LAP-LE con referencia LCP. Resultados. Tomando como referencia la LCP (11 casos), en tres casos fracasó, encontrando una distorsión del ángulo LAP-LE. Tomando como referencia la LAP (12 casos), en 6 casos hubo desviación del ángulo LE-LCP. Conclusiones. Con la cirugía protésica de rodilla asistida con navegador vamos a personalizar las referencias anatómicas que van a determinar la rotación femoral. Nos permite colocar la rotación deseada, sin limitaciones de posición propias de la instrumentación manual. Tenemos que pensar que existe una gran variabilidad anatómica. Existe una gran controversia en cuanto a qué referencia anatómica se utiliza para determinar la rotación femoral. Se ha demostrado que la LAP es la referencia morfológica que menos varía, y también un buen punto para controlar el centraje rotuliano

Aim. To assess the posterior condylar line as an anatomic reference in 23 patients who underwent total knee arthroplasty. Materials and methods. Prospective study of a consecutive series of 23 patients with knee osteoarthritis. Measurements made with a computerized navigation system of the posterior condylar line (PCL), epicondylar line (EL), Whiteside or anteroposterior line (APL), EL-PCL angle with reference to APL, and APL-EL angle with reference to PCL were analyzed. Results. With reference to the PCL (11 patients), arthroplasty failed in three patients, resulting in distortion of the APL-EL angle. With reference to APL (12 cases), 6 patients showed deviation of the EL-PCL angle. Conclusions. Computerized navigation-assisted knee arthroplasty makes it possible to personalize the anatomic references determining femoral rotation. It allowed us to position the target rotation with none of the positioning limitations typical of manual instrumentation. We must take into consideration the importance of anatomic variability. The anatomic reference to be used to determine femoral rotation is under debate. It has been shown that APL is the morphologic reference with the least variation, and a good reference for controlling patellar centering

Periprosthetic bone remodeling. A finite elementstudy of the influence of the implant design.

Remodeling periprosthetic femoral bone after total hip arthroplasty has been studied extensively. Finite element (FE) analysis, together with mathematical remodeling theories, has predicted that femoral bone-mineral density decreases proximally after total hip arthroplasty. There is significant controversy concerning the clinical consequences of bone remodeling such as the reduction in bone strength, the possibility of a cement mantle fracture, the aseptic loosening of the implant, or the appearance of a periprosthetic fracture, which could threaten the survival of the hip prosthesis. The status of periprosthetic bone stock is an important concern when total hip arthroplasty revision is undertaken. This study was conducted to evaluate the periprosthetic bone-mineral density evolution following primary total hip arthroplasty by FE analysis. We compared two cemented stems with different designs: the Exeter and the SHP to study the phenomenon of femoral stress shielding and bone cement deterioration. We found that with the best mechanical conditions and with the same materials, the prosthesis design determines a different periprosthetic bone remodeling.

A comparative analysis of different treatments for distal femur fractures using the finite element method.

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.

Finite element study of intramedullary osteosynthesis in the treatment of trochanteric fractures of the hip: Gamma and PFN.

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.

3D finite element analysis of the gamma nail and dhs plate in trochanteric hip fractures.

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!

Extramedullary versus intramedullary osteosynthesis in trochanteric hip fractures. Three-dimensional finite-element analysis.

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Estudio biomecánico de la osteosíntesis intramedular en el tratamiento de las fracturas trocantéreas de cadera: Gamma y PFN / Biomechanical study of intramedullary osteosynthesis in the treatment of trochanteric fractures of the hip: Gamma y PFN

El tratamiento quirúrgico de las fracturas trocantéreas de cadera, y sobre todo las fracturas inestables, constituye un tema controvertido en la actualidad, lo que conlleva que se esté produciendo un cambio de los diseños de nuevos implantes. Nuestro objetivo ha sido comparar biomecánicamente mediante elementos finitos los dos implantes centromedulares más utilizados en nuestro medio (clavo Gamma® estándar, Howmedica vs clavo PFN®, Stratec) y estudiar: a) los desplazamientos del foco de fractura y b) la distribución de tensiones en el fémur y en el implante. Se ha podido observar que con ambos implantes se produce una redistribución importante de tensiones en el fémur, transmitiéndose mayor concentración de las mismas con PFN®. El grado de desplazamiento del foco de fractura tratada con el PFN® es menor. Además, el trabajo al que está sometido dicho clavo es menor que el del clavo Gamma® (AU)

Estudio clínico de la osteosíntesis intra y extramedular en las fracturas trocantéreas de cadera / Clinical study of intramedullary and extramedullary osteosynthesis in trochanteric fractures of the hip

Se ha realizado un estudio comparativo de las fracturas trocantéreas tratadas con sistema extramedular modelo placa con tornillo-deslizante DHS de AO (Synthes®) y sistema intramedular modelo clavo Gamma de 2ª generación (Howmedica®) desde 1996 hasta julio de 1998. Se trata de un estudio retrospectivo de 95 pacientes tratados con ambos sistemas (56 pacientes con Gamma y 39 con DHS), sobre un total de 250 historias clínicas revisadas. El objeto de este estudio clínico ha sido el corroborar en la clínica los resultados biomecánicos observados en el estudio de ambas técnicas mediante elementos finitos. Con relación al sistema DHS, el clavo Gamma consigue resultados similares en las fracturas estables. En las fracturas inestables, el clavo Gamma permite una reanudación más precoz de la marcha. Las dificultades y los errores técnicos determinan con el clavo Gamma estático una mayor incidencia de complicaciones en la evolución del tornillo cefálico (AU)

Osteosíntesis extramedular vs. intramedular en las fracturas trocantéreas de cadera. Análisis 3D con elementos finitos / Extramedullary vs. intramedullary osteosynthesis in trochanteric hip fractures. Three-dimensional finite-element analysis

El estudio mediante elementos finitos se ha convertido en un instrumento ampliamente aceptado y divulgado para el estudio del comportamiento biomecánico del hueso y el sistema hueso-implante. Desde su introducción en los años setenta, y en orden a resolver problemas complejos como la geometría, el patrón de cargas y el comportamiento de los materiales, se ha convertido en un método fundamental de investigación en biomecánica. La investigación en esta materia supone la realización de experimentos muy costosos con especímenes reales. De ahí el interés por encontrar modelos numéricos que simulen de forma suficientemente aproximada el comportamiento del fémur. Se ha realizado un estudio biomecánico del tratamiento de las fracturas trocantéreas de fémur, comparando dos sistemas, Gamma® (Howmedica) y DHS® (Synthes) mediante elementos finitos. Se han encontrado diferencias entre ambos sistemas en cuanto a los desplazamientos del foco de fractura, la distribución de cargas y la distribución de tensiones en los implantes. Tanto con el modelo extramedular como con el intramedular se producen distorsiones importantes en la transmisión de cargas con relación al patrón anatómico, por lo que desde un punto de vista biomecánico ambos sistemas tienen evidentes limitaciones (AU)

Three-dimensional finite element analysis of several internal and external pelvis fixations.

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.

Baker's pseudocyst in the prosthetic knee affected with aggressive granulomatosis caused by polyethylene wear.

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.