3 The Waldenburg Circle
Studies of osteosynthesis in large animals The experimental work on horse bones in the Straumann laboratories began immediately after the key meeting between Drs Björn von Salis and Fritz Straumann. The primary questions to be answered were: (1) what type of fractures actually occur in horses; (2) how could such fractures be stabilized with already existing AO implants, and what specific implants and instruments needed to be developed; (3) would such fixations remain stable under the heavy weight-bearing load of an adult horse; and (4) would the fracture eventually heal with the help of internal fixation, and would the attainable stability suffice? For this work von Salis collected horse bones from animals that had to be slaughtered because they had suffered a fracture. X-rays of the bones were taken with the mobile x-ray unit from his Equine Ambulance. Very soon it became clear that on the large bones, such as the adult femur and humerus, osteosynthesis would be almost impossible from a biomechanical point of view. For the other bones of the limbs there seemed to be possibilities for internal fixation, given the fractures were not too complicated. With the largest type of existing AO plates and screws, some of the actual fractures could be well stabilized. Interestingly, the mechanical loading tests that followed demonstrated that it was extremely important to apply the compression plates and screws in a biomechanically optimal way as taught by the AO principles for human surgery. Also the most precise anatomical fracture reduction was necessary to achieve sufficient postoperative stability and immediately allow full weight bearing on the fractured leg. Some of the instruments had to be modified because of the big diameters of the horse bones. The first explorations were encouraging and suggested that there might be certain types of common fracture configurations that could be treated surgically. It appeared that the largest, the 4.5 mm cortex screw and plate system, would be suitable for the major applications and other already available implants seemed useful too. But some new implants and instruments would have to be developed and others adapted to the dimensions of the horse bones (Fig 12). Later on, a 5.5 mm large animal cortex screw was developed by Pohler with improved strength and good holding resistance in cortical and cancellous bone [49]. However, the major question remained: would such
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