["Elastic osteosynthesis" with autocompression plates of carbon fiber reinforced thermoplastic material].
The problem of atrophic bone that occurs in osteosynthesis employing rigid plates is first depicted. Attempts at fabricating "simirigid" plates, which, however, have so far failed to gain any practical importance are then discussed. The reason for this seems to be that made of duroplastics cannot be molded during the operation and the thermoplastics do not have sufficient strength. The production of semirigid plates made of thermoplastic Polyethersulfon (PES), reinforced with 20% short carbon fibres, results in plates which are made moldable by heating in a small oven, white retaining sufficient static strength, although only limited fatigue strength. Biomechanical examinations revealed that with appropriate dimensioning of the plates, "elastic osteosynthesis" results in less loss of mechanical function of the stabilized bones, so that less atrophy of the bone may be expected. During more pronounced exercise loading, a reversible "springiness" of the fracture results, which might stimulate callus formation and improved stability.
Verträglichkeit implantatgeeigneter alloplastischer Werkstoffe im Organismus
Die Bedeutung von Implantaten zur Wiederherstellung von Korperfunktionen, die durch Krankheit, naturliche Abnutzung oder Unfall verlorengegangen sind, nimmt stetig zu und last sich am einfachsten anhand des grosen Bedarfs ermessen. Jahrlich werden mehr als 1 500 000 Personen mit Gefasprothesen versorgt, in 100 000 Fallen werden kunstliche Herzklappen eingesetzt, etwa 220 000 Patienten erhalten einen implantierbaren Herzschrittmacher. Fur die extrakorporale Zirkulation bei Operationen am Herzen werden jahrlich etwa 600 000 Oxygenatoren benotigt. Der Jahresbedarf an kunstlichen Nieren nahert sich der Zahl 1 000 000. Beim Gelenkersatz steht die Huftprothese mit ca. 350 000 Implantationen an erster Stelle vor dem Ersatz des Finger-, Knie-, Schulter- und Ellenbogengelenks. Implantierbare Materialien fur die rekonstruktive Chirurgie haben den Umfang vieler Tonnen erreicht. Einen Eindruck von den vielfaltigen Einsatzgebieten moderner Kunststoffe vermittelt Tabelle 1.
The biocompatibility of materials for internal fixation of fractures.
Surgically produced fractures of rabbit tibiae were internally stabilized with intramedullary rods of stainless steel (316LVM), titanium (6A1,4V), polyacetal (Delrin), and polyamide (Nylon 101). Periodic radiographs were taken until sacrifice at 16 weeks after fracture. Structural properties of the tibiae were determined in torsion with the rods in situ, and then the tissue was prepared for histology or microradiography. The results demonstrated that fracture remodeling was adversely affected by the metal rods. New bone was seen to have formed over the ends of the metal rods, and cortical bone resorption was observed in the fracture region, suggestive of transfer of mechanical stress to the rods, resulting in stress shielding of the diaphysis. Negligible osseous response to the polymeric rods was observed; fracture callus remodeling was extensive. The torsional test results demonstrated that fractures with polymeric rods were significantly stronger and tougher than those with metallic rods. With the exception of titanium, the strength of healed fractures was inversely related to the elastic moduli of the implant materials.