Anatom3DRadial head & annular ligament
Caput radii et ligamentum anulare radii · Hlavička kosti vřetenní a prstencový vaz
Joints & cartilage
Looks like
The round disc on top of the radius, turning inside a tight ring of ligament (the annular ligament) at the outer elbow.
What it does
Spins as the forearm turns the palm up and down.
Keeping it well
In toddlers a sudden pull on the hand slips it out of the ring ('pulled elbow') — easily put back by a clinician. In adults it breaks in falls.