mechanical stresses
Functionally the roto-translational system ensures that in deambulatory support phase (Action that during life occurs again to an innumerable cycles of times), in which knee reaches a flexion of 20-25 degrees, there is only a rotary motion which mechanically protects the articular surfaces from usury by rubbing.
In rotation to each point of the femoral condyle corresponds one point on the tibial plateau and the mechanical forces, developed by the burdening of body weight ,are transmitted to compression, without provoking usury.
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In translation contact points slip between them creating friction and usury. The
knee provides this mechanical action in the aircraft phase of deambulation and running so that it will not be performed under load. |
By analyzing these mechanical actions individually, we know that:
rotation, does not provide friction since the load is always transmitted on the same points of contact and is independent from burdening of body weight to which it is subjected;
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translation provides a slip between the parties in contact with surface usury, usury that is more important as the weight of the part that moves.
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In the whole sphere of movement outside of pure deambulatory support phase ( jogging, sprinting, jumping, pedaling, with squat thrusts, impact, bending-ex. In ski-ride, etc..) action of friction is always directly proportional to the degree of bending reached and usury is proportional to the weight of the subject.