Ligaments give the spirals in each bone continuity across joints; from one bone to another. A given bone may spiral more than once while it is growing, but the second spiral will be in the same direction.
A good example of this is the clavicle (collar bone).Â You can see that there is a spiral on the left side of the picture where it would attach to the scapula and the rest of the arm.Â That spiral rotation is contiguous with the spiral further to the right where the bone would attach to the sternum.Â Each of those spirals are actually the same spiral but the one on the arm side grew first, the one on the sternum side happened later.
So if you are trying to figure out how the spiral in you humerus (upper arm) continues through to your sternum, find the first part of the spiral rotating your arm forward/inward, then find the second part of the spiral by bringing your sternum up.
The spirals in our bones are there all the time.Â If you know which way each bone spirals,Â you can figure out which ways force will transfer through the body most easily.
Internal arts are all designed with these spirals in mind.
Here is a cool website which says something different about human structure, but interesting none-the-less.