Our forearms do amazing jobs for a variety of functional motions. Our palms can face up or down to work on different objects, like turning doorknobs. We always act on it unconsciously. Have you ever wondered how we can practically flip your hands to turn doorknobs?
Supination and pronation are movements that define the orientation of the palm and forearm. Supination refers to palms facing upwards, while pronation refers to palms facing downwards. The joints involved are proximal and distal radioulnar joints formed between the upper and lower ends of the radius and ulna.
When we are pronating or supinating, it is easy to think that the two forearm bones would rotate around each other, just like ropes. However, the ulna is locked to the humerus with its hinge joint, which would not allow any rotation. Hence, the radius is the only bone moving for pronation and supination. In supination, the radius is parallel to the ulna. In pronation, the radius rotates around the hinge with a 180 deg amplitude. It would go across the ulna, and thus palms facing down. At the elbow joint, the annular ligament encircles the radius head which allows it to pivot during these movements.
Fun fact, we can actually turn our palms facing down to up without flipping our hands. Starting with the arm extended with palm facing down at shoulder level. Now, you need to move your forearm across the body, then rotate your upper arms till the fingers are pointed to the sky. After that, straighten up your arms so that the fingers point to the front. Repeat the 3 steps once again, now the palm should be facing up! This trick helps rotate the arms without turning the hands.
Besides our forearms, there is also supination and pronation in the lower limbs. Stay tuned for our posts next week!