BIOMECHANICAL PRINCIPLES FOR DIATHROSES AND SYNARTHROSES .1. BASIC CONCEPTIONS FOR DIARTHROSES

The incongruity of the articulating surfaces is one of the main constr uctional characteristics of human joints. Unfortunately, this has virt ually been neglected in studying of the mechanism of joints. Only in i nconcruent articulating surfaces does the force locking, which is perm anently produced by gravity and/or compressively acting muscular force s (muscular tonus), engender mechanically stable states of balance of the connected limbs. From the incongruity one can conclude that the di meric link chain represents the most simple constructional element of the human joints. They are force locked, constrained gear systems comp osed by dimeric link chains. In this context the overlapped dimeric li nk chain deserves special attention since it is the only mechanically stable device in the presence of compressive forces. We present fundam ental terms and characteristics of the gear mechanisms of human joints .