["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.
Effect of long-term immobilisation on the pattern of bone loss in older dogs.
The time sequence and anatomical locailsation of bone loss in the mid-diaphysis of the forelimb in response to long-term non-traumatic immoblllsation were studied in Beagle dogs aged seven to eight years. The changes in the right forelimb encased in plaster relative to the left one serving as a control were evaluated by means of radiomorphometry and histomorphometry and compared with the responses observed previously in young adult dogs. At the beginning ofthe experiment the older dogs had a bone volume reduced by some eight per cent due to the age-related expansion of the cavity of the bone marrow. After immoblllsation, the bone loss occurred in three stages, as in the young adult dogs althoughless clearly. During the first two months bone volume fell rapklly to a level of 90 to 95 per cent of the volume in the control limbs; a rapid reversal followed to which both periosteal and endosteal surfaces and intracortical porosity contributed. A second slower but longer lasting bone loss began 12 weeks after the hnmoblllsation; it tended to level off towards the end of the experiment. A third stage was characterised by maintenance of the loss which equalled 40 per cent of the original volume. In contradistinction to young adult dogs, in the third metacarpal of the older dogs the endosteal envelope rather than the periosteal was the main contributor to the permanent bone loss, while in the remaining bones the periosteal envelope also contributed substantially. In both age groups the magnitude of bone loss was greatest in the distal bones. The extent of the bone resorption surface on the endosteal envelope paralleled the rate of bone loss. In the older dogs the appositional rate was reduced by 30 per cent in both the control and in the experimental limb relative to young adult dogs, suggesting that the bone loss after long-term immobilisation is mediated by the changes in bone-cell kinetics rather than in the cell function of differentiated existing cells.