Thoracic Limb
Forearm (Antebrachium)
Ulna: The proximal extremity is the olecranon, which includes the olecranon tuber and the anconeal process. It serves as a lever arm for the extensor muscles of the elbow. The trochlear notch is a smooth, vertical, half-moon-shaped concavity facing cranially. The whole trochlear notch articulates with the trochlea of the Humerus. At its proximal end a sharp-edged, slightly hooked anconeal process fits into the olecranon fossa of the Humerus when the elbow is extended forward. Found at the distal most end of the notch are medial and lateral coronoid processes, which articulate with the Humerus and radius. The body of the ulna is compressed laterally and gradually loses its borders distally and becomes irregular. The ulnar tuberosity is a small, elongated eminence on the medial surface of the bone at its proximal end, just distal to the medial coronoid process. Another feature of the ulna is the interosseous border; this is the place of articulation with the radius by means of a heavy ligament. The most distal extremity represents the head of the ulna that articulates with the radius at the articular circumference. It has a prominent styloid process.
Clinical correlation: All the various types of fractures can be seen involving either or both the radius and ulna. Distal to the proximal third of the radius these bones usually fractures as a unit, but proximal to this region independent fractures of both bones are commonly seen. The development of angulation and rotation at the fracture site; delayed union; and nonunion are not uncommon sequelae in distal third fractures. Measures to prevent them should be kept in mind constantly.
