Radius and Ulna

The lower arm consists of two bones, the radius and the ulna.  The ulna articulates with the humerus to form a hinge joint.  The radius articulates with the ulna at the radial notch and forms a pivot joint, allowing for the rotation of the wrist. This type of movement where the radius crosses over the ulna is called pronation.  At the distal end of the radius is a projection of bone called the styloid process.   A break in the styloid process is called a Chauffer’s fracture, which is caused when the scaphoid bone (carpal of the wrist) is forcefully pushed against the styloid process.   It was a common break for early chauffer’s who had to hand-crank to start a car and a backfire would force the crank into the hand.

radius and ulna

A=styloid process B=radial tuberosity C = head of radius D=coronoid process E=olecranon process