Why do we have kneecaps on our legs but no “armcaps” on our arms?
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Our forearms, the area between the elbow and the wrist, need to be able to rotate, like when we are turning a door knob. Another way to think of this motion is pronation (making your palm face downwards) vs supination (making your palm face upwards). An “armcap” or elbow cap would get in the way of pronation/supination.
The feet and shins do not need to rotate in this way, we are unable to make our toes point behind us for example, therefore it makes sense to have a more stable and rigid joint where the knee cap can act as a fulcrum or lever for more powerful movement.
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