The olecranon is the large, thick curved portion of the

proximal ulna. The most proximal portion of the olecranon

is angled slightly forward or distally to form a prominent lip

that passes into the olecranon fossa of the humerus when

the elbow is extended. The base of the olecranon is slightly

constricted where it joins the shaft of the ulna, forming the

narrowest part of the proximal ulna. The posterior surface

of the olecranon is triangular and smooth. This prominent

area, easily palpable through the skin, is covered by the olecranon bursa. The superior (or most proximal) surface of

the olecranon is somewhat quadrilateral in shape and has a

rough surface for the insertion of the triceps tendon. The

anterior surface of the olecranon is concave and smooth,

and is lined with articular cartilage to form the proximal

portion of the trochlear notch. There usually is a nonarticular zone in the mid-portion of the articular surface (see

later discussion of trochlear notch). The elbow joint capsule

attaches to the anterior aspect of the superior surface of the

olecranon. The medial portion of the olecranon provides

attachment for the oblique and posterior parts of the ulnar

collateral ligament. The medial aspect of the olecranon also

provides an area for the origin of a portion of the flexor

carpi ulnaris muscle. The posteromedial portion also provides a part of the origin of the flexor digitorum superficialis. The lateral portion of the olecranon provides the

insertion of the anconeus muscle (see Fig. 1.18).

28 Systems Anatomy

FIGURE 1.17. Right ulna and radius, anterior aspect, showing

muscle origins (red) and insertions (blue).

The coronoid process is a triangular eminence that projects from the anterior surface of the ulna, roughly at the

junction of the shaft with the proximal portion (see Fig.

1.19). Its base arises from the proximal and anterior part

of the shaft. The superior surface of the coronoid process

is smooth and concave, and forms the inferior portion of

the trochlear notch. Its inferior surface is concave and

rough. At the junction of the coronoid with the shaft of

the ulna is a thickened, rough eminence, the tuberosity of

the ulna. This tuberosity provides the attachment area for

the brachialis as well as the oblique cord of the radius. The

lateral surface of the coronoid contains the radial notch,

1 Skeletal Anatomy 29

FIGURE 1.18. Right ulna and radius, posterior aspect, showing

muscle origins (red) and insertions (blue).

FIGURE 1.19. Right ulna and radius, anterior aspect.

which is a narrow, rounded, oblong depression lined with

articular cartilage. The radial notch articulates with the

rim of the radial head during forearm supination and

pronation. The medial surface of the coronoid process

provides the area of attachment of the anterior and

oblique portions of the ulnar collateral ligament. At the

anterior portion of the medial surface of the coronoid is a

small, rounded eminence for the origin of three humeroulnar heads of the flexor digitorum superficialis. Posterior to this eminence, a slight ridge extends from the

medial aspect of the coronoid distally. Along this ridge

arise the proximal portions of the insertions of the flexor

digitorum profundus, along with the ulnar head of the

pronator teres. In addition, a small ulnar head of the

flexor pollicis longus may arise from the distal part of the

coronoid process (see Fig. 1.of attachment of the anterior and

oblique portions of the ulnar collateral ligament. At the

anterior portion of the medial surface of the coronoid is a

small, rounded eminence for the origin of three humeroulnar heads of the flexor digitorum superficialis. Posterior to this eminence, a slight ridge extends from the

medial aspect of the coronoid distally. Along this ridge

arise the proximal portions of the insertions of the flexor

digitorum profundus, along with the ulnar head of the

pronator teres. In addition, a small ulnar head of the

flexor pollicis longus may arise from the distal part of the

coronoid process (see Fig. 1.17).

30 Systems Anatomy

FIGURE 1.20. Right ulna and radius, posterior aspect.

The trochlear notch of the ulna is a large concave depression that is semilunar in shape and formed by the coronoid

process and the olecranon (see Figs. 1.19 and 1.21A,E, and

F). The trochlear notch, covered anteriorly by articular cartilage, provides the articular surface for the trochlea of the

humerus. The articular surface of the trochlear notch has an

area near its mid-portion that contains a central transverse

area that usually is deficient in articular cartilage. This area

subdivides the articular surface into a proximal portion (on

the anterior surface of the olecranon) and a distal portion

(on the anterosuperior surface of the coronoid). At this

mid-portion of the trochlear notch, the borders are slightly

indented near its middle, creating a narrow portion in the

proximal ulna.

The radial notch of the ulna is the articular depression

on the lateral aspect of the coronoid process (see Figs. 1.19,

1 Skeletal Anatomy 31

FIGURE 1.21. A: Proximal right ulna, lateral aspect. B: Right elbow, medial aspect, showing capsular attachment and medial ligaments. C: Right elbow, lateral aspect, showing capsular attachment and lateral ligaments. D: Right elbow, sagittal section. E: Proximal radioulnar joint, with

radial head removed, showing annular ligament.

(continued on next page)

A B

C D