Geometry of the articular facets of the lateral atlanto-axial joints in the case of occipitalization

This study investigates if atlanto-occipital fusion affects the size and geometrical configuration of the articular facets of the atlanto-axial joint. Morphometric analysis was performed on the male adult skull, the occipital bone of which is assimilated with the first cervical vertebrae (the atlas). The perimeter, Feret’s diameter, surface area, and circularity of the inferior articular fa-cets were measured. However, we did not observe significant bilateral differences in size of the inferior articular facets of the assimilated atlas compared to normal first cervical vertebrae. Geometrical conformation of the articular facets of the atlas and axis was assessed using a coordinate measuring machine (PMM - 12106, Leitz). The results obtained from this machine indicated that the inferior articular facets of the assimilated atlas presented asymmetrical orientation compared to the normal anatomy of the atlas. Hence, in the case of occipitalization, the gap between the articulating facets of the atlas and the axis was measured to be greater than in the normal atlanto-axial joint. Computer assisted tomography was applied to visualise the anatomical relationship between the inferior articular facets of the assimilated atlas and the corresponding facets located on the axis. In this case, radiographic examination revealed that the bilaterally articulating facets (inferior and superior) showed disproportion in their adjustment within the lateral atlanto-axial joints. Thus, we concluded that the fusion of the atlas with the occipital bone altered the geometry of the inferior articular facets of the atlas and influenced the orientation of the superior articular facets of the axis. (Folia Morphol 2010; 69, 3: 147-153

Phenomenon of the lubrication mechanism of human hip joints

W opracowaniu przedstawiono problematykę związaną z wyjaśnieniem doskonałego mechanizmu smarowania stawów człowieka. Mechanizm ten do tej pory nie został w pełni opisany ani odtworzony w Endoprotezach lub innych węzłach łożyskowych. Przeprowadzone rozważania opierają się na identyfikacji warunków tarcia i smarowania w stawach prawidłowych. Obejmują przestrzenne wyznaczenie geometrycznego układu współpracujących powierzchni stawowych, kształtu szpary stawowej, warstwowej budowy struktur chrzęstnych i kostnych, dodatkowych struktur chrzęstnych wspomagających smarowanie. W procesie smarowania ważną rolę przejmuje ciecz maziowa, dla której przeprowadzono badania reologiczne i tribologiczne. Dokonano modelowania i symulacji kontaktu struktur stawowych z wykorzystaniem metody elementów skończonych (MES), które wskazały na odrębny niż w warunkach technicznych mechanizm smarowania – charakterystyczny dla stawów człowieka.The problem concerned with the explanation of a perfect lubrication mechanism is presented in this research. This mechanism has neither been described nor used in any other bearing nodes so far. The major consideration has been based on the identification of friction conditions and lubrication in proper hip joints. The study includes three-dimensional determination of the geometric configuration of cooperating hip joint surfaces, the shape of joint gap, multilayer cartilaginous and bone structures, and additional cartilage structures supporting the lubrication. In the lubrication process, the important role intercepts synovial fluid for which there were made reological and tribological tests. The modelling and simulation of contact using finite element methods (FEM) were made. This simulation shows the mechanism other than in technical condition lubrication. Such a mechanism is characteristic of human hip joints

Identification of the Cause of the Stem Neck Fracture in the Hip Joint Endoprosthesis

Endoprosthesis stem fractures are among the rarest complications that occur after hip joint arthroplasty. The aim of this paper is to evaluate the causes of the fractures of the Aura II stem neck, which is an element of an endoprosthesis implanted in a patient. In order to achieve it, a radiogram was evaluated, the FEM analysis was carried out for the hip joint replaced using the Aura II prosthesis and scanning tests as well as a chemical analysis were performed for the focus of fatigue. The tests performed indicate that the most probable causes leading to the fatigue fracture of the Aura II stem under examination were material defects in the process of casting and forging (forging the material with delamination and the presence of brittle oxides and carbides) that resulted in a significant reduction of strength and resistance to corrosion. In the light of an unprecedented stem neck fracture, this information should be an indication for non-destructive tests of ready-made stems aiming to discover the material and technological defects that may arise in the process of casting and drop forging

The analysis of biomechanical state in a hip joint after complete alloplastics with different variant of cementless endoprosthesis

W opracowaniu wykonano modelowanie i symulacje rozkładów naprężeń i przemieszczeń w aplikacjach z bezcementowymi endoprotezami stawu biodrowego. Analizie poddano biołożyska z panewkami o strukturze warstwowej wykonane z polietylenu wysokocząsteczkowego oraz korundu i polietylenu wysokocząsteczkowego, z zewnętrznymi obejmami z tytanu. We wszystkich endoprotezach głowy były korundowe, a trzpienie tytanowe. Endoprotezy osadzano wirtualnie, w odwzorowanych na podstawie tomografii komputerowej strukturach kostnych. Dla zamodelowanych geometrycznie obiektów badań dokonano analizy wytrzymałościowej z wykorzystaniem metody elementów skończonych. Wyniki badań pozwoliły porównać rozwiązania konstrukcyjne endoprotez oraz ocenić charakter oddziaływania sztucznego stawu na otaczające tkanki kostne w warunkach indywidualnego pacjenta.Modelling and simulation of the stress distribution and displacements in the applications with cementless endoprosthesis of a hip joint were carried out. The analysis subjected biobearings with cups of layered structures made from high molecular polyethylene, corundum, and high molecular polyethylene with external connection clips from titanium. The heads in all endoprosthesis were from corundum and the stems from titanium. The endoprosthesis were seated virtually in natural bone struc- tures that had been obtained from computer tomography. The stress analysis for the geometrically modelled objects of research was made using the finite element method. The results of the analysis allowed us to estimate the stress and displacements distribution in endoprosthesis and the character of the interaction of the artificial joint on the surrounding bone tissue in the conditions of an individual patient