The coronoid process or processus coronoideus in Latin (‘coronoid’ meaning crown shaped) is an eminence that projects anteriorly from the proximal end of the ulna. Its articular superolateral surface, together with the olecranon process, form the trochlear notch that articulates with the humerus. On its lateral surface lies a shallow smooth radial notch that articulates with the peripheral head of the radius.
The coronoid process projects anterior and distal to the more proximal and beak-like olecranon eminence. Its upper portion forms the distal aspect of the trochlear notch, and its lateral surface marks the oval shaped radial notch. Just inferior to this notch, is a distal hollowed out fossa made to accommodate the radial tuberosity into changing position during both supination and pronation movement. The supinator crest is formed by the broadened posterior margin of said fossa.
The anterior surface of the coronoid tuberosity is triangular in shape. Its apex faces downwards, and has many roughenings for muscle attachments. The largest of which is the ulnar tuberosity that serves as an attachment for the brachial muscle belonging to the anterior compartment of the arm (the remaining two are: the coracobrachialis and biceps brachii muscles). The oblique and anterior bands of the ulnar collateral ligament, as well as the distal part of the humero-ulnar slip of the flexor digitorum superficialis, attach to a small tubercle that lies in the sharp medial border of the proximal end of the coronoid process. Distal to this area lies a ridge that gives attachment for the ulnar part of the pronator teres. In some cases, the ulnar part of the flexor pollicis longus may attach to the lateral or even more rarely the medial border of the coronoid process. Some fibers from the flexor digitorum profundus muscle attaches to the medial border of the coronoid process as well.
The coronoid process of the ulna should not be confused with the coronoid process of the mandible or the similar sounding coracoid process of the scapula.
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