Abnormal olecranon morphology Elbow fracture Olecranon fracture 2023-12-11T15:55:33Z A partial or complete break in the olecranon,which is the proximal articular portion of the ulna and makes up part of the elbow. The olecranon is the proximal articular portion of the ulna. Along with the coronoid process, it forms the greater sigmoid (semilunar) notch which articulates with the humerus to provide flexion and extension of the elbow.