Assessment of bone ingrowth around beaded coated tibial implant for total ankle replacement using mechanoregulatory algorithm.

The long-term performance of porous coated tibial implants for total ankle replacement (TAR) primarily depends on the extent of bone ingrowth at the bone-implant interface. Although attempts were made for primary fixation for immediate post-operative stability, no investigation was conducted on secondary fixation. The aim of this study is to assess bone ingrowth around the porous beaded coated tibial implant for TAR using a mechanoregulatory algorithm. A realistic macroscale finite element (FE) model of the implanted tibia was developed based on computer tomography (CT) data to assess implant-bone micromotions and coupled with microscale FE models of the implant-bone interface to predict bone ingrowth around tibial implant for TAR. The macroscale FE model was subjected to three near physiological loading conditions to evaluate the site-specific implant-bone micromotion, which were then incorporated into the corresponding microscale model to mimic the near physiological loading conditions. Results of the study demonstrated that the implant experienced tangential micromotion ranged from 0 to 71 µm with a mean of 3.871 µm. Tissue differentiation results revealed that bone ingrowth across the implant ranged from 44 to 96 %, with a mean of around 70 %. The average Young's modulus of the inter-bead tissue layer varied from 1444 to 4180 MPa around the different regions of the implant. The analysis postulates that when peak micromotion touches 30 µm around different regions of the implant, it leads to pronounced fibrous tissues on the implant surface. The highest amount of bone ingrowth was observed in the central regions, and poor bone ingrowth was seen in the anterior parts of the implant, which indicate improper osseointegration around this region. This macro-micro mechanical FE framework can be extended to improve the implant design to enhance the bone ingrowth and in future to develop porous lattice-structured implants to predict and enhance osseointegration around the implant.

Reemplazo protésico en artrosis de tobillo / Prosthetic replacement in ankle osteoarthriti

CONTEXTO CLÍNICO: La osteoartrosis se define como la presencia de lesiones degenerativas, desgaste y pérdida o reducción del espesor del cartílago articular. Esta puede ser primaria (no tiene una causa específica) o secundaria a traumatismos a repetición, inestabilidad crónica, fracturas, processos inflamatorios autoinmunes (como la artritis reumatoide), artropatía hemofílica, gotosa o neuropática. A nivel del tobillo, los traumatismos y la inestabilidad crónica secundaria a esguinces son las causas más frecuentes de artrosis avanzada representando el 70% de los casos, mientras que el 12% aproximadamente es secundario a artritis reumatoide. Si bien no se dispone de estos datos en la Argentina, en los Estados Unidos, se diagnostican 50.000 casos nuevos por año. Los síntomas principales son dolor, movilidad articular disminuida, dificultad para caminar y para realizar actividades como subir escaleras, manejar automóviles y arrodillarse. Las limitaciones físicas de esta patología son percibidas por los pacientes,según las escalas globales de salud, junto a condiciones tales como la enfermedad coronaria, hemodiálisis y artrosis de cadera o de coluna cervical. TECNOLOGÍA: El reemplazo total de tobillo (RTT) es una cirugía ortopédica que se realiza bajo anestesia peridural o general y consiste en realizar incisiones en la articulación del tobillo, preservando estructuras tendinosas, nerviosas y vasculares, y mediante el abordaje de la cápsula articular se accede a la articulación tibioperóneo-astragalina. Se resecan las superficies óseas dañadas de la tibia istal, peroné y astrágalo para reemplazarlas por los componentes de la prótesis que se fijan a las superficies óseas. Luego, por un período de tres semanas aproximadamente, el paciente no puede descargar peso en el miembro operado. OBJETIVO: El objetivo del presente informe es evaluar la evidencia disponible acerca de la eficacia, seguridade y aspectos relacionados a las políticas de cobertura del uso del reemplazo total de tobillo em pacientes con artrosis avanzada de tobillo. MÉTODOS: Se realizó una búsqueda en las principales bases de datos bibliográficas, en buscadores genéricos de internet, y financiadores de salud. Se priorizó la inclusión de revisiones sistemáticas (RS), ensayos clínicos controlados aleatorizados (ECAs), evaluaciones de tecnologías sanitarias (ETS), evaluaciones económicas, guías de práctica clínica (GPC) y políticas de cobertura de diferentes sistemas de salud. RESULTADOS: Se incluyeron un MA, una RS, tres estudios de cohorte, un documento de una sociedad científica, una ETS, y siete informes de políticas de cobertura para la prótesis total de tobillo en artroses avanzada de tobillo. CONCLUSIONES: Evidencia de baja calidad sugiere que, en pacientes con artrosis avanzada de tobillo, la mejoría del dolor y función del miembro inferior es similar luego del reemplazo total de tobillo o la artrodesis tibioperoneo-astragalina. Así mismo, los pacientes con prótesis de tobillo tendrían un mejor patrón de marcha respecto a los pacientes con artrodesis. La heterogeneidad de resultados no permite concluir que un tratamiento se asocie a mayor riesgo de re-operación o complicaciones. No se encontraron guías de práctica clínica para esta patología. Una sociedad científica de estadounidense recomienda el reemplazo total de tobillo como alternativa a la artrodesis en casos de artrosis avanzada, y frente a la presencia de artrodesis del tobillo contralateral y/o artrosis em las articulaciones adyacentes. Financiadores públicos de México, Canadá, Australia y los Estados Unidos brindan cobertura para esta tecnología.

Determining the Cost-Savings Threshold and Alignment Accuracy of Patient-Specific Instrumentation in Total Ankle Replacements.

BACKGROUND: Traditional intraoperative referencing for total ankle replacements (TARs) involves multiple steps and fluoroscopic guidance to determine mechanical alignment. Recent adoption of patient-specific instrumentation (PSI) allows for referencing to be determined preoperatively, resulting in less steps and potentially decreased operative time. We hypothesized that usage of PSI would result in decreased operating room time that would offset the additional cost of PSI compared with standard referencing (SR). In addition, we aimed to compare postoperative radiographic alignment between PSI and SR. METHODS: Between August 2014 and September 2015, 87 patients undergoing TAR were enrolled in a prospectively collected TAR database. Patients were divided into cohorts based on PSI vs SR, and operative times were reviewed. Radiographic alignment parameters were retrospectively measured at 6 weeks postoperatively. Time-driven activity-based costing (TDABC) was used to derive direct costs. Cost vs operative time-savings were examined via 2-way sensitivity analysis to determine cost-saving thresholds for PSI applicable to a range of institution types. Cost-saving thresholds defined the price of PSI below which PSI would be cost-saving. A total of 35 PSI and 52 SR cases were evaluated with no significant differences identified in patient characteristics. RESULTS: Operative time from incision to completion of casting in cases without adjunct procedures was 127 minutes with PSI and 161 minutes with SR ( P < .05). PSI demonstrated similar postoperative accuracy to SR in coronal tibial-plafond alignment (1.1 vs 0.3 degrees varus, P = .06), tibial-plafond alignment (0.3 ± 2.1 vs 1.1 ± 2.1 degrees varus, P = .06), and tibial component sagittal alignment (0.7 vs 0.9 degrees plantarflexion, P = .14). The TDABC method estimated a PSI cost-savings threshold range at our institution of $863 below which PSI pricing would provide net cost-savings. Two-way sensitivity analysis generated a globally applicable cost-savings threshold model based on institution-specific costs and surgeon-specific time-savings. CONCLUSIONS: This study demonstrated equivalent postoperative TAR alignment with PSI and SR referencing systems but with a significant decrease in operative time with PSI. Based on TDABC and associated sensitivity analysis, a cost-savings threshold of $863 was identified for PSI pricing at our institution below which PSI was less costly than SR. Similar internal cost accounting may benefit health care systems for identifying cost drivers and obtaining leverage during price negotiations. LEVEL OF EVIDENCE: Level III, therapeutic study.