No as the Neck – A narrow area of bone, which lies between the radial head and radial tuberosity is considered part of the distal end of the ulna not the shaft.
| Shaft of the ulna | Borders: anterior border, posterior border, interosseous border
Surfaces: anterior surface, posterior surface, medial surface |
| Distal end of the ulna | Head - articular surface that joints with the triangular articular disc and the ulnar notch of the radius
Styloid process - attachment to the ulnar collateral ligament of the wrist joint |
Distal ulnar fractures are divided into two groups:
- isolated:
- associated with distal radius fractures: Frykman classification of distal radial fractures
Shaft of the Ulna
The ulnar shaft is
triangular in shape, with three borders and three surfaces. As it moves distally, it decreases in width.
The three surfaces:
- Anterior – site of attachment for the pronator quadratus muscle distally.
The volar surface (
facies volaris; anterior surface), much broader above than below, is concave in its upper three-fourths, and gives origin to the
flexor digitorum profundus; its lower fourth, also concave, is covered by the
pronator quadratus. The lower fourth is separated from the remaining portion by a ridge, directed obliquely downward and medialward, which marks the extent of origin of the pronator quadratus. At the junction of the upper with the middle third of the bone is the
nutrient canal, directed obliquely upward.
- Posterior – site of attachment for many muscles.
The dorsal surface (
facies dorsalis; posterior surface) directed backward and lateralward, is broad and concave above; convex and somewhat narrower in the middle; narrow, smooth, and rounded below. On its upper part is an oblique ridge, which runs from the dorsal end of the radial notch, downward to the dorsal border; the triangular surface above this ridge receives the insertion of the
Anconæus, while the upper part of the ridge affords attachment to the
supinator. Below this the surface is subdivided by a longitudinal ridge, sometimes called the perpendicular line, into two parts: the medial part is smooth, and covered by the
extensor carpi ulnaris; the lateral portion, wider and rougher, gives origin from above downward to the
Supinator, the
abductor pollicis longus, the
extensor pollicis longus, and the
extensor indicis proprius.
The medial surface (
facies medialis; internal surface) is broad and concave above, narrow and convex below. Its upper three-fourths give origin to the
Flexor digitorum profundus; its lower fourth is subcutaneous.
The three borders:
- Posterior – palpable along the entire length of the forearm posteriorly
The dorsal border (
margo dorsalis; posterior border) begins above at the apex of the triangular subcutaneous surface at the back part of the
olecranon, and ends below at the back of the
styloid process; it is well-marked in the upper three-fourths, and gives attachment to an
aponeurosis which affords a common origin to the
flexor carpi ulnaris, the
extensor carpi ulnaris, and the
flexor digitorum profundus; its lower fourth is smooth and rounded. This border separates the medial from the dorsal surface.
- Interosseous – site of attachment for the interosseous membrane, which spans the distance between the two forearm bones.
The interosseous crest (
crista interossea; external or interosseous border) begins above by the union of two lines, which converge from the extremities of the
radial notch and enclose between them a triangular space for the origin of part of the
Supinator; it ends below at the head of the ulna. Its upper part is sharp, its lower fourth smooth and rounded. This crest gives attachment to the
interosseous membrane, and separates the volar from the dorsal surface.
The volar border (
margo volaris; anterior border) begins above at the prominent medial angle of the
coronoid process, and ends below in front of the
styloid process. Its upper part, well-defined, and its middle portion, smooth and rounded, give origin to the
flexor digitorum profundus; its lower fourth serves for the origin of the
pronator quadratus. This border separates the volar from the medial surface.
