Mechanisms of synovial joint and articular cartilage development.

Articular cartilage is formed at the end of epiphyses in the synovial joint cavity and permanently contributes to the smooth movement of synovial joints. Most skeletal elements develop from transient cartilage by a biological process known as endochondral ossification. Accumulating evidence indicates that articular and growth plate cartilage are derived from different cell sources and that different molecules and signaling pathways regulate these two kinds of cartilage. As the first sign of joint development, the interzone emerges at the presumptive joint site within a pre-cartilage tissue. After that, joint cavitation occurs in the center of the interzone, and the cells in the interzone and its surroundings gradually form articular cartilage and the synovial joint. During joint development, the interzone cells continuously migrate out to the epiphyseal cartilage and the surrounding cells influx into the joint region. These complicated phenomena are regulated by various molecules and signaling pathways, including GDF5, Wnt, IHH, PTHrP, BMP, TGF-ß, and FGF. Here, we summarize current literature and discuss the molecular mechanisms underlying joint formation and articular development.

Time-dependent processes in stem cell-based tissue engineering of articular cartilage.

Articular cartilage (AC), situated in diarthrodial joints at the end of the long bones, is composed of a single cell type (chondrocytes) embedded in dense extracellular matrix comprised of collagens and proteoglycans. AC is avascular and alymphatic and is not innervated. At first glance, such a seemingly simple tissue appears to be an easy target for the rapidly developing field of tissue engineering. However, cartilage engineering has proven to be very challenging. We focus on time-dependent processes associated with the development of native cartilage starting from stem cells, and the modalities for utilizing these processes for tissue engineering of articular cartilage.

Modeling capsule tissue growth around disk-shaped implants: a numerical and in vivo study.

We propose a new mathematical model that describes the growth of fibrous tissue around rigid, disk-shaped implants. A solution methodology based on an efficient regularized iterative method is presented to calibrate the model from some measurements of the capsule tissue concentration. Numerical results obtained with synthetic data are presented to demonstrate the ability of the proposed solution methodology to determine the model parameters corresponding to a given implant. In addition, numerical results obtained with experimental data are presented to illustrate the validity of the proposed model.

Avaliação ultra-sonográfica da articulação temporomandibular em adolescentes / Ultrasonographic evaluation of the temporomandibular joint in adolescents

Objetivo: O objetivo deste estudo foi avaliar imagens da articulação temporomandibular (ATM) de indivíduos portadores e não portadores de DTM, através da ultra-sonografia estática. Métodos: Foram avaliados 217 adolescentes entre 12 e 18 anos de idade através do Craniomandibular Index (CMI) e do questionário de sintomas subjetivos. Foram selicionados 40, que apresentaram escores extremos, distribuídos em: GrupoI- 20 adolescentes sem DTM e GrupoII- 20 adolescentes com Disfunção Temporomandibular (DTM). Utilizou-se o ultra-som digital Just Vision 200 (Toshiba Corporation, USA), com transdutor linear de 10 MHz, mensurando-se nas imagens a distância entre a cápsula articular e a superfície lateral do côndilo mandibular, na posição de repouso. Os dados foram analisados pelo teste T de Student, correlação de Pearson. Resultados: Os sintomas subjetivos mais prevalentes no Grupo II foram os ruídos articulares, a dor na face e/ou mandíbula e a dor de cabeça. As médias de espaços na ultra-sonografia foram de 1,90mm para o grupo I e 1,85mm para o grupo II, não se correlacionando com os escores do CMI (p>0,05). Conclusão: A avaliação da ATM pela ultra-sonografia não se correlacionou com o diagnóstico de DTM. Concluímos que a ultra-sonografia, segundo a metodologia utilizada não é eficaz para o diagnóstico de DTM

Changes in the content of the fibrillar collagens and the expression of their mRNAs in the menisci of the rabbit knee joint during development and ageing.

The menisci are first seen as triangular aggregations of cells in the 20-day rabbit fetus. At 25-days, a matrix that contains types I, III and V collagens has formed. These collagens are also found in the 1-week neonatal meniscus, but by 3 weeks, type II collagen is present in some regions. By 12 to 14 weeks, typically cartilaginous areas with large cells in lacunae are found and by 2 years, these occupy the central regions of the inner two-thirds of the meniscus. The surface layers of the meniscus contain predominantly type I collagen. From 12 to 14 weeks onwards, there is little overlap between the regions with types I or II collagens, that is, these are discrete regions of type I-containing fibrocartilage and type II-containing cartilage. Types III and V collagens are found throughout the menisci, particularly in the pericellular regions. All the cells in the fetal and early neonatal menisci express the mRNA for type I collagen. At 3 weeks postnatal, cells that express type I collagen mRNA are found throughout the meniscus, but type II collagen mRNA is expressed only in the regions of developing cartilage. At 12- to 14-weeks, only type II collagen mRNA is expressed, except at the periphery next to the ligament where a few cells still express type I collagen mRNA. Rabbit menisci, therefore, undergo profound changes in their content and arrangement of collagens during postnatal development.

Changes in temporomandibular joint after mandibular subcondylar osteotomy: an experimental study in rats.

The objective of this study was to analyze the changes in the different components of the temporomandibular joint and their relation with age after subcondylar osteotomy. For this purpose 149 Wistar rats were divided into three groups: osteotomy, sham operation, and control. Two experimental ages (30 and 70 days) and radiologic, morphometric, macroscopic, and histologic methods of analysis were used. Different changes were observed in young and adult animals. Subcondylar mandibular osteotomy in growing rats caused anteroinferior displacement of the temporal and mandibular component of the joint. At the end of the experimental period only condylar displacement was maintained. Other changes were flattening of the mandibular condyle, which was transient, and lateral thickening of the articular disc. Subcondylar mandibular osteotomy in adult rats caused slight anterior displacement of the joint components at the end of the experimental period. At this age, although changes similar to those in growing animals were observed in some cases, in other cases the presence of pathologic findings, such as deformation of the condylar cartilage, thickening of the disc, intra-articular adherences, and osteolysis of the temporal fossa, were observed. Changes in the joint components were more marked in growing rats than in adults. In growing rats they affected the form of the condylar process to a greater extent, but the majority of these changes were transient. In adult rats, alterations in the joints were less pronounced, but they affected a greater number of joint components and were permanent.