Coronoid Fractures

The ulna's coronoid process is the bony prominence on the most proximal portion of the ulna’s volar surface.  In connection with the olecranon process, it forms the greater sigmoid notch which articulates with the distal humerus at the elbow joint.  It serves as a buttress, preventing posterior displacement of the ulna.  It is also the site of attachment for the anterior bundle of the ulnar collateral ligament which inserts on the medial portion of the coronoid, the sublime tubercle, approximately 1.8 centimeters from the tip of the coronoid.  The ulnar collateral ligament serves to limit valgus forces on the elbow joint. More proximally, the elbow joint capsule also attaches about 0.6 centimeters from the intra-articular coronoid tip. Distally, near the base of the coronoid, the brachialis muscle takes a broad insertion; it acts to flex the elbow without effecting forearm rotation. Fractures of the coronoid are highly suggestive of elbow instability; and they often present in association with elbow dislocations and other fractures of the radius, ulna, or humerus.