The ulna is one of the two bones in the forearm. It is categorized as a long bone and its major features include the trochlear notch, olecranon, radial notch, head, and styloid process.

Biomechanically, the ulna enables a variety of different activities involving different movements, including throwing, lifting, and writing. The ulna is the second major component in the kinematic chain of the arm. It is larger on the proximal end than the radius and therefore contributes more to elbow function, including movement and transfer of forces at the joint.   

The ulna is part of two major body joints, the elbow and the wrist. The trochlear notch is at the proximal end and joins with the trochlea of the humerus to form one of the two articulations that make up the elbow joint. The elbow is a hinge joint that functions primarily on the sagittal plane to allow flexion and extension. The surfaces of both the trochlea and trochlear notch are covered by articular cartilage. Ligaments keep the bones from separating during activity. Together with the distal end of the radius, eight carpal bones, and the proximal portions of the five metacarpal bones of the palm, it forms the wrist joint.