RESUMEN
Thirty-three X-press cementless stems (Depuy) manufactured according to standardized X-rays were inserted from 1992 to 1994. The patients' mean age was 49 (range 15-79) years with a mean follow-up of 32 (+/-6) months. A characteristic radiographic pattern of aseptic loosening with erosion of the medial cortex by the tip of the stem occurred in 28 patients and a valgus shift of the implant in 14 cases. A radiolucent line with increased sclerosis below the tip (zone Gruen 4) was observed in 17 cases. Four stems were revised due to histologically confirmed aseptic loosening. Biomechanical investigation of one of the revised stems with the typical pattern of valgus angulation and medial cortex erosion included photoelasticity and finite-element analysis. The intertrochanteric fit and fill obviously resulted in an unfavorable distribution of contact areas, including peaks of high stress on the medial tip of the stem. These experimental findings are even evident for a postulated rotational stability. The clinical and radiographic results of the cementless X-press stems do not seem to support the fixation concept of intertrochanteric fit and fill of femoral components.
Asunto(s)
Análisis de Elementos Finitos , Prótesis de Cadera , Falla de Prótesis , Adolescente , Adulto , Anciano , Elasticidad , Humanos , Persona de Mediana Edad , Estrés MecánicoAsunto(s)
Clavos Ortopédicos , Simulación por Computador , Fijadores Externos , Análisis de Elementos Finitos , Procesamiento de Imagen Asistido por Computador/instrumentación , Soporte de Peso/fisiología , Fenómenos Biomecánicos , Matriz Ósea , Gráficos por Computador , Análisis de Falla de Equipo/instrumentación , Humanos , Programas Informáticos , Resistencia a la TracciónRESUMEN
Optical tension experiments for model statistics were conducted for more elucidation of lifting osteotomy of tibial tuberosity and mechanisms of its impact upon the femoropatellar joint. The following two qualitative conclusions were primarily drawn: Growing pre-displacement caused reduction in the maximum number of isochromates. Stepwise pre-displacement caused dislocation of the contact point. While full translation of the above results to natural conditions is considered impermissible, displacement of femoropatellar pressures is felt to be an important mechanism of action.
Asunto(s)
Articulación de la Rodilla/fisiopatología , Osteotomía/métodos , Rótula/fisiopatología , Tibia/cirugía , Fenómenos Biomecánicos , Fémur/fisiopatología , Humanos , Modelos Anatómicos , Tibia/fisiopatologíaRESUMEN
In the connection with the pathogenesis and therapy of the diseases of the temporo- mandibulare joint it is of interest, if and in what kind of extent the joint is pressure burden. For examining this problem photoelastic investigations on a lower jaw model were performed. According to the opening angle, burden height and attack point of the burden, pressure strengths of 90-270 N were ascertained on the proc. condylaris , when a pure rotation-movement was performed.
Asunto(s)
Articulación Temporomandibular/fisiología , Fenómenos Biomecánicos , Humanos , Mandíbula/fisiología , Masticación , Músculos Masticadores/fisiología , PresiónRESUMEN
Three different methods of measurement are used to objectify the maximum load-carrying capacity of individual pairs of teeth. For these, use is made of a mechanical, electric, and elastooptic measuring instrument. The measurement results obtained using the mechanical and electric instruments are largely identical. They are in the neighborhood of 20 kgf and 50 kgf for incisors and molars, respectively, of male subjects. The results obtained for female test subjects were lower by an average of 10 kgf. The mechanical and electric measuring instruments may be used for the examination of a larger number of test subjects as well as under pathological conditions.