Biomedical subjects
Publications and source records attributed to F Holzweissig.
The simple mechanical models and experimental spinal examinations could be established that the double curved scoliosis operated with two Harrington rods and dorsal spondylodesis is better than the use of one Harrington rod.
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The present paper deals with biomechanical investigations applying static pressures to endoprosthetic hip shafts implanted into cadaveric femora with bone cement. The purpose of the investigations was to observe the maximal breakload of the femora or endoprosthesis. We did experiments with 27 femora and implanted 4 different endoprostheses (3 metallic shafts and 1 ceramic shaft). The investigations showed a significant difference between metallic and ceramic shafts in maximal breakload. The metallic shafts showed a favourable load distribution from the prostheses shafts to the femora. That means a higher breakload when the angle between prosthesis-collar and shaft is more than 140 degrees.
The skull has a system of vibration with characteristic Eigen-frequencies and oscillation modes. Macereted and non-macereted skulls showed lines of nodes of a typical manner which is specific for the hominides. Specially the mod of vibration of the 2. Eigen-frequency is strongly correlated with the state of the skull. Defined fractures of the base causes the Eigen-frequency shifting in rostral direction. Patterns of fracture, diaphanoscopic and x-ray investigation showed no correlations to the mod of vibration of all the Eigen-frequencies. In the clinical practice this findings give a diagnostic possibility in immediate identification of the fractures and infractures.
Using a computer program for the evaluating of free eligible rotation-symmetrical cylinder shells the number of magnitude of the natural-frequencies were estimated. Assuming the skull of being annulary fixed the calculated values doe in the same range as those got from deat bodies or macerated skulls respectively. Modeling the vibration conditions for the non-fixed border of the skull, the mode shifts into a singulaer point on the rotations axis. In fact the mode in exactly known basis fractures tends to go to the vertex.
The skull as a biosystem capable vibration shows characteristic oscillation modes with specific Eigen-frequencies. For the calculation of the these values we used a test method. The 4 lowest Eigen-frequencies are in the range of 1-3 KHz(f1 = 1,03 +/- 0,35KHz;f2 = 1,71 +/- 0,13KHz;f3 = 2,16 +/- 0,12 KHz and f4 = 2,57 +/- 0,11 KHz;n = 13). The shifting of the vibration mode is of diagnostic value in estimating of skull-basis-fractures.
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By biomechanic examinations of the vertebrae of human dead bodies the ultimate stress due to shearing (Schubbruchspannung) of the spongy substance could be found out with 1.80 N/mm2 and the ultimate stress due to compression (Druckbruchspannung) of the cortical-belonging to the thick of cortical--with 280 N/mm2. Both measuring results are important for the ultimate strength of the connection (Verankerungsfestigkeit) of screws in vertebae.
The firmness of the bone structure of vertebrae of human cadavers was investigated by turning screws of four different types into vertebrae T6 to L5 and subjecting them to axial tension up to the point of extraction. It was found that the cancellous bone screws (rather than the Zielke screw) had the best anchoring characteristics in bone tissue. The shearing fracture stress of the vertebral bone tissue was found to be approx. 1.80 N/mm2; the relation between the extraction forces and the individual vertebrae was also examined. In addition, the extraction forces were determined for screws inserted into vertebrae T6 to L4, as performed in Zielke's ventral spondylodesis procedure, as well as the lower tolerance limit for each vertebra in this segment of the vertebral column.