94 



H. Wagner 



The influence of mechanical factors upon the weight-bearing skeleton has been 

 well known for a long time. The first investigator, who published on this subject, was 

 probably Galileo Galilei in 1638. However, the biomechanic relations seem to be 

 much more complicated, as we already know. 



In the experiment we have studied the reaction of bone tissue to weight-bearing 

 metal implants, especially metal screws, such as we are using in orthopaedic surgery. 

 We have tested screws of a new type, being developed by the AO-Group in Switzer- 

 land (MiJLLER et al., 1963). The fundamental characteristics of these screws are: 



1. the wide and spacious threads, 



2. the fact that the weight-bearing side of the thread is standing at right angles to 

 the direction of force, 



3. the electrolytically polished surface, which gives the implants a high corrosion 

 resistance in the body fluids. 



Histological examination shows a tight embedding of the screws in bone tissue 

 during periods of years without any foreign-body reaction. Also two years after 

 implantation we see a close contact between the metal and the bone tissue without a 

 fibrotic reaction in the marrow. 



But what is going on, when a screw is exposed to mechanical pressure? 



Fig. 1. Screw inserted Into the feni 

 tional ossification on the wcight-bc 



(U'tt) Mde of th. 

 of bone tissue to 



corresponding bone thread, 

 echanical pressure 



ter Implantation apposi- 

 as a biomechanic adap- 



In animal experiments it is difficult to keep a screw under continuous weight- 

 bearing, because fractures and osteotomies in animals heal very quickly. Therefore 

 we inserted the screws into the condyle of the femur across the epiphyseal line, by 



