32 Systems Anatomy

FIGURE 1.21. (continued) E: Proximal radioulnar joint, with radial head removed, showing

annular ligament. F: Proximal ulna, with proximal radius removed to show annular ligament and

radial notch. G: Right elbow, anterior aspect, showing synovial membrane. The capsule has been

removed and the articular cavity distended. H: Right elbow, posterior aspect, showing synovial

membrane. The capsule has been removed and the articular cavity distended.

E F

G H

and 1.21A,E, and F). The notch is narrow, oblong, and

lined with articular cartilage. The notch articulates with the

circumferential rim of the radial head. The anterior and

posterior margins of the radial notch provide the attachment areas for the annular ligament.

Shaft (Body) of the Ulna

The shaft (or body) of the ulna is triangular in cross-section

in the proximal two-thirds, but becomes round in the distal

third. Longitudinally, the proximal half of the shaft is

slightly convex dorsally and concave anteriorly. The distal

half (and sometimes central portion) becomes longitudinally straight. The distal half of the shaft may be slightly

concave laterally and convex medially. In cross-section, the

triangular shape presents an anterior, posterior, and medial

surface, as well as an anterior border, posterior border, and

interosseous border (each of which is located at the apex of

the triangular cross-sectional shape). The interosseous ligament is attached along the interosseous border apex of the

triangle, and there is no true lateral surface in this region of

the bone. More distally, the bone becomes progressively circular in cross-section. The shaft flares slightly distally as it

enlarges into the ulnar head.

The three borders of the ulnar shaft are the anterior,

posterior, and interosseous borders. The anterior border of

the ulna begins proximal at the prominent medial angle of

the coronoid process and extends distally along the

anteromedial aspect of the shaft to terminate anterior and

medial to the styloid process of the head of the ulna. The

anterior border is best defined in its proximal portion, and

becomes rounder, smoother, and less clearly defined in the

central distal portion as the shaft becomes progressively

circular in circumference distally. In this central portion of

the anterior border, the ulna provides a large surface origin for the flexor digitorum profundus muscle (see Fig.

1.17). The distal one-fourth of the anterior border is

referred to as the pronator ridge and provides origin for the

pronator quadratus (4).

The posterior border of the ulna begins proximally at the

apex of the triangular subcutaneous surface of the olecranon

(see Fig. 1.18). The posterior border extends distally along

the mid-posterior portion of the shaft, to terminate posterior to the styloid process. The posterior border is well

defined along its proximal one-third to three-fourths; however, as the ulna becomes more circular in cross-section distally, the distal portion of the posterior border is more

rounded, smooth, and poorly defined. In the well defined

proximal portion, the posterior border of the ulna gives rise

to the attachments of an aponeurosis, which provides a

common origin for the flexor carpi ulnaris, the extensor

carpi ulnaris, and the flexor digitorum profundus (see Fig.

1.18). The posterior border separates the medial and posterior surfaces of the ulna.

The interosseous border of the ulna is well defined and

can be somewhat sharp in its central portion (see Figs 1.17

to 1.20). The interosseous border actually extends along the

lateral margin of the ulna, beginning at the radial notch and

curving slightly anteriorly as it extends distally. A proximal

portion of the interosseous border is referred to as the

supinator crest, providing a ridge for the attachment of a

portion of the supinator muscle. In the distal one-fourth of

the shaft, the interosseous border is less well defined. The

interosseous ligament attaches along the interosseous border and is thickest at its attachment in the central portion

of the interosseous border. The interosseous ligament provides a partition that separates the anterior and posterior

surfaces of the ulna.

 

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

 

ULNA

Derivation and Terminology

The ulna derives its name from the Latin word meaning “the

arm” or “the elbow” (1,3). The plural of ulna is ulnae (1).

Ossification Centers and Accessory Bones

The ulna has three ossification centers: one in the shaft

(body), one in the proximal portion (proximal extremity),

and one in the distal end (distal extremity). The mid-portion of the shaft is the first ossification center to appear,

becoming visible at approximately the eighth week of fetal

life (Figs. 1.15 and 1.16). The ossification centers then

extend through the major part of the shaft. At birth, the

distal portions and the major part of the olecranon remain

cartilaginous. Between the fifth and sixth years, a center in

the central portion of the ulnar head appears and soon

extends into the styloid process. At approximately the

tenth year, a center appears in the olecranon near its outer

portion. Most of the ossification of the olecranon actually

develops from proximal extension from the center of the

shaft (2,4,5).

Several accessory bones can be associated with the distal

ulna. These accessory bones, if present, usually are the result

of secondary or additional ossification centers that do not

fuse with the distal ulnar or associated carpal bones. Accessory bones associated with the distal ulna include the os triangulare (os intermedium antebrachii, os triquetrum secundarium), the os ulnostyloideum, and the os pisiforme

secundarium (ulnare antebrachii, metapisoid) (see Fig.

1.27B) (44–46). The os triangulare is located distal to the

head of the ulna, between the ulnar head, lunate, and triquetrum. The os ulnostyloideum is located in the vicinity

of the ulnar styloid. The os pisiforme secundarium is

located between the distal ulna and pisiform, close to the

proximal edge of the pisiform.

1 Skeletal Anatomy 27

FIGURE 1.15. Illustration of ulna, showing the three centers of

ossification. There is one center in the shaft (body), one in the

proximal portion (proximal extremity), and one in the distal end

(distal extremity).

FIGURE 1.16. Illustration of proximal and distal ulna in a young

adult, showing epiphyseal lines.

Accessory bones also can occur from other causes such as

trauma (46) or heterotopic ossification of synovial tags (47).

Therefore, anomalous, irregular ossicles or small, rounded

bones of abnormal size or shape may be encountered that

do not fit a specific described accessory bone or location.

Osteology of the Ulna

The ulna is located in the medial aspect of the forearm lying

parallel to the radius when the forearm is supinated. It is a

true long bone with a triangular cross-section proximally

that becomes rounded distally. The ulna consists of a shaft

with thick cortical bone and a long, narrow medullary canal

(Figs. 1.17 to 1.20). The cortex of the ulna is thickest along

the interosseous border and dorsal surface. In the proximal

and distal ends of the ulna, the cortical bone becomes thinner, and the medullary canal is replaced with cancellous

bone. The cortical bone remains relatively thick along the

posterior portion of the olecranon.

The ulna is anatomically divided into three main portions: the proximal end (proximal portion, proximal

extremity), the shaft (body), and the distal end (distal portion, distal extremity) (Fig. 1.21; see Figs. 1.19 and 1.20).

The proximal end contains the hook-shaped olecranon and

the coronoid process to form the medial hinge-like portion

of the elbow. The shaft consists of the major portion of the

body between the proximal and distal portions. The distal

end consists of the head and styloid process. In general, the

ulna becomes progressively smaller and thinner from proximal to distal.

Proximal Ulna

The proximal end of the ulna consists of the olecranon, the

coronoid process, the trochlear notch, and the radial notch

(see Fig. 1.21A–F).

 

Supracondylar Process

In approximately 1% of upper extremities, there is a downward-curved, hook-shaped process of bone that emanates

from the medial cortex approximately 5 cm proximal to the

medial epicondyle. It can be associated with a connecting

fibrous band (ligament of Struthers), which can be a proximal extension of the pronator teres. The median nerve may

pass deep to the supracondylar process and ligament, and

may be subject to compression, resulting in median neuropathy. The brachial artery also may pass deep to the ligament (28,40–43).

Lateral Epicondylitis

Lateral epicondylitis commonly is referred to as tennis

elbow. It is thought to consist of either chronic inflammation, partial tear, or “overuse injury” of the common extensor origin. Chronic or repetitive wrist or digital extension

often is associated with the onset of symptoms. The extensor carpi radialis brevis often is implicated as the main muscle involved. Although management usually is conservative

(activity modification, antiinflammatory medications,

splinting, cortisone injections), severe and refractory cases

can be managed with operative exploration and release,

debridement, or repair of the extensor carpi radialis brevis

origin or other involved muscle.

Medial Epicondylitis

Medial epicondylitis commonly is referred to as golfer’s

elbow. Similar to lateral epicondylitis, it is though to consist

of either chronic inflammation, partial tear, or overuse

injury of the common flexor pronator muscle origin.

26 Systems Anatomy

Chronic or repetitive wrist or digital flexion often is associated with symptoms.

Osteochondrosis

Osteochondrosis (osteochondritis dissecans, osteonecrosis)

of the capitellum of the humerus is referred to as Panner’s

disease.

 

Hill-Sacks Lesion

This is a defect in the posterolateral aspect of the humeral

head resulting from anterior dislocation (often associated

with recurrent injuries). The lesion occurs when the dislocated humeral head strikes the inferior margin of the glenoid, producing a “hatchet” compression fracture defect of

the humeral head. It usually is demonstrated on the antero1 Skeletal Anatomy 25

posterior view radiograph of the shoulder with the humerus

internally rotated. The presence of this lesion is virtually

diagnostic of previous anterior dislocation (17).

Bankart Lesion

Injury to the anterior-inferior cartilaginous labrum, which

is usually associated with an avulsion of the inferior glenohumeral ligament from the anterior-inferior glenoid rim.

Associated from anterior dislocation of the glenohumeral

joint. It may affect only fibrocartilaginous portion of the

glenoid, but is commonly noted in association with a fracture of the anterior aspect of the inferior osseous rim of the

glenoid. The Bankart lesion is less commonly seen than the

Hill-Sacks lesion. The presence of this lesion is virtually

diagnostic of previous anterior dislocation (17).

Posterior Dislocation of the Shoulder

This accounts for 2% to 3% of shoulder dislocations. It can

occur from direct force or a blow to the anterior shoulder,

from indirect force applied to the arm combining adduction,

flexion, and internal rotation, or it can be associated with

severe muscle contraction from electric shock or convulsive

seizures. The humeral head is located posterior to the glenoid

fossa, and usually impacts on the posterior rim of the glenoid.

The shoulder usually is positioned or locked in adduction

and internal rotation. Standard radiographs may not demonstrate the lesion (because the humeral head lies directly posteriorly, and radiographs may appear unremarkable on standard anteroposterior views). Injury can be demonstrated by

either an axillary view (often difficult to obtain because of the

arm locked in adduction) or by a special anteroposterior view

with the patient rotated 40 degrees toward the affected side.

With this view, the normal clear space of the glenohumeral

joint is obliterated by the overlap of the humeral head located

posterior and slightly medial to the surface of the glenoid.

Fractures of the Shaft Proximal to the

Insertion of the Deltoid Muscle

If a fracture of the humeral shaft occurs just proximal to the

insertion of the deltoid, the proximal fragment of the

humerus usually is adducted or pulled medially by the pectoralis major, latissimus dorsi, and teres major. The distal

fragment usually is displaced or angulated laterally (apex

medially, or fracture in valgus) because of the deltoid.

Fractures of the Humeral Shaft Distal to the

Insertion of the Deltoid Muscle

If a fracture of the humeral shaft occurs just distal to the

insertion of the deltoid, the proximal fragment usually is

displaced laterally by the deltoid and supraspinatus muscle.

The distal fragment usually is pulled medially and upward

by the triceps, biceps, and the coracobrachialis muscles.

Fractures of the Humeral Shaft Associated

with Radial Nerve Palsy

Up to 18% of humeral shaft fractures have an associated

radial nerve injury (33–36). Most nerve injuries represent a

neurapraxia or axonotmesis, and 90% resolve in 3 to 4

months (37–39). This injury often is referred to as the Holstein-Lewis fracture, which describes an oblique fracture of

the distal third of the humerus. However, radial nerve palsy

is associated most commonly with fractures of the middle

third of the humerus (34,38).

Supracondylar Fractures

The area of bone at the supracondylar level is relatively thin,

and fractures through this area are common, especially in

children. Structures at risk for injury in supracondylar fractures include the brachial artery and median nerve anteriorly and the radial nerve laterally. Brachial artery injury

subsequently is associated with compartment syndrome of

the forearm.

 

n Stage I: Local edema or hemorrhage; reversible condition. Usual age group: young, active individuals involved

in sports requiring excessive overhead use of arm.

n Stage II: Fibrosis, thickening of subacromial soft tissue,

rotator cuff tendinitis, and possible partial tear of rotator

cuff; manifested by recurrent pain. Usual age group: 25

to 40 years.

n Stage III: Complete rupture of rotator cuff, progressive

disability. Usual age group: over 40 years.

Fractures of the Proximal Humerus

Neer has classified fractures of the proximal humerus as to

the number of segments (18):

n One-part fractures of the proximal humerus are fractures

with minimal or no displacement or angulation.

n Two-part fractures consist of two major displaced fragments. This can include a displaced fracture of either the

greater or lesser tuberosity, fracture of the surgical neck,

or fracture of the anatomic neck.

n Three-part fractures consist of three major displaced

fragments. This can include fractures of both the greater

and lesser tuberosities, or a combination of fracture of

one of the tuberosities and fracture of the surgical neck.

n Four-part fractures consist of four displaced fragments,

such as those involving both tuberosities as well as the

surgical neck.

Anterior Dislocation of the Shoulder

In this injury, the humeral head dislocates anterior to the

glenoid; it accounts for 97% of shoulder dislocations. It

usually is diagnosed on anteroposterior radiographs. Definitive radiographic diagnosis is by the transscapular (“Y”

view) or axillary view.

 

 and with the radius at the radiocapitellar joint.

24 Systems Anatomy

Muscle Origins and Insertions

Muscle attachments include 24 muscles (see Figs. 1.13A–B).

The greater tuberosity provides the insertion of the

supraspinatus, the infraspinatus, and the teres minor. The

lesser tuberosity affords the insertion of the subscapularis.

The pectoralis major inserts to the anterior bicipital groove,

the teres major inserts to the posterior bicipital groove, and

the latissimus dorsi inserts to the central portion or crest of

the bicipital groove. The shaft of the humerus provides the

insertion of the deltoid and coracobrachialis, and the origins

of the brachialis and the triceps (medial and lateral heads).

The lateral shaft and epicondyle is the area of origin of the

brachioradialis; the medial epicondyle provides the origin of

the pronator teres, the flexor carpi radialis, the palmaris

longus, the flexor digitorum superficialis, the flexor digitorum profundus, the flexor carpi ulnaris, and the anconeus.

The lateral epicondyle provides origin for the extensor carpi

radialis longus and brevis, the extensor digitorum communis,

extensor digiti minimi, extensor carpi ulnaris, and anconeus.

Clinical Correlations: Humerus

The Surgical Neck

The surgical neck, located at the junction of the head (and

tuberosities) with the shaft, is an area of frequent fracture,

hence its name. Fractures of the surgical neck are much

more common than in the anatomic neck, and usually are

the result of a direct impact or a fall onto the elbow with the

arm abducted. Deformity of fractures of the surgical neck

usually include adduction or medial displacement of the

shaft due to the pull of the pectoralis major, teres major, and

latissimus dorsi. The proximal fragment may be abducted

by the pull of the supraspinatus muscle.

The Anatomic Neck

Fractures rarely occur along the anatomic neck. When fractures do occur in this location, it usually is in an older

patient and often is the result of a fall onto the shoulder.

Because the shoulder capsule attaches to the bone distal to

the anatomic neck, fractures of the anatomic neck usually

are intracapsular.

Impingement Syndrome

Impingement syndrome of the shoulder refers to a condition in which the supraspinatus tendon and subacromial

bursa are chronically or repetitively entrapped between the

humeral head inferiorly and either the anterior acromion

itself, spurs of the anterior acromion or acromioclavicular

joint, or the coracoacromial ligament superiorly (17).

Osseous findings seen radiographically can include thickening or proliferation of the acromion, spurring at the

anteroinferior aspect of the acromion, degenerative changes

of the humeral tuberosities at the insertion of the rotator

cuff, or a humeral head that is slightly superiorly located or

mildly superiorly subluxated. Magnetic resonance imaging

(MRI) can demonstrate soft tissue changes such as bursal

inflammation, thickening and effusion, and inflammatory

changes or partial tearing of the rotator cuff before osseous

changes seen by standard radiographs (17).

Neer Classification of Impingement Syndrome

(32)

 

Distal Portion of the Humerus

The distal portion of the humerus is often referred anatomically as the distal extremity of the humerus (see Figs. 1.11

to 1.14). The distal portion is flat, widened, and ends distally in a broad, articular surface. The distal portion contains the two condyles, medial and lateral (see Fig. 1.14).

The lateral portion of the distal articular part consists of a

smooth, somewhat semi-spherical shaped capitulum of the

humerus. The capitulum is covered with articular cartilage

on its anterior surface and articulates with the fovea of the

head of the radius. Proximal to the capitulum, there is a

slight depression in the humerus, the radial fossa. The radial

fossa provides a space for the anterior border of the head of

the radius when the elbow is fully flexed. Just medial to the

capitulum is a slight shallow groove, in which the medial

margin of the head of the radius articulates. Just proximal

to the capitulum on the anterior surface of the humerus are

several small foramina for nutrient vessels.

The medial side of the articular surface of the distal

humerus is comprised of the spool-shaped trochlea (see

Fig. 1.14). The trochlea occupies the anterior, inferior,

and posterior surfaces of the condyle. The trochlea has a

deep groove between two well demarcated borders. The

lateral border is separated from the capitulum by the shallow groove. The medial border of the trochlea is thicker,

wider, and more prominent, and projects more distally

than the lateral border. The grooved portion of the articular surface of the trochlea is shaped well to fit the articular surface of the trochlear notch of the ulna. The trochlea

is wider and deeper on the dorsal surface than on the anterior surface. Proximal to the anterior portion of the

trochlea is a small depression, the coronoid fossa. The

coronoid fossa provides a space for the coronoid process of

the ulna during flexion of the elbow. Proximal to the posterior part of the trochlea is a deep, triangular depression,

the olecranon fossa. The olecranon fossa provides a space

to accept the most proximal portion of the olecranon

when the elbow is extended. The olecranon fossa and the

coronoid fossa are separated from each other by a thin,

sometimes translucent partition of bone. The partition

may be perforated to produce a supratrochlear foramen.

The fossae are lined by a synovial membrane that extends

from the elbow joint. The margins of the fossae provide

attachment for the anterior and posterior ligaments and

joint capsule of the elbow.

Above the medial and lateral condyles are the epicondyles. These projections provide the attachment for several muscles. The medial epicondyle is larger and more

prominent than the lateral epicondyle. The medial epicondyle contains the origin of the extrinsic flexor pronator

muscles of the forearm and flexor muscles of the hand and

wrist. These include the pronator teres, flexor carpi radialis,

palmaris longus, flexor digitorum superficialis, flexor digitorum profundus, and flexor carpi ulnaris. The ulnar collateral ligaments of the elbow joint also originate from the

medial epicondyle. On the posterior surface of the medial

epicondyle is a shallow groove in which the ulnar nerve traverses.

The lateral epicondyle is smaller and less prominent than

the medial epicondyle. The lateral epicondyle contains the

origin of several muscles, including the wrist and digit

extrinsic extensor muscles and the supinator. Muscle attachments to the lateral epicondyle include the supinator, extensor carpi radialis longus, extensor carpi radialis brevis,

extensor digitorum communis, extensor carpi ulnaris, extensor digiti minimi, and anconeus. The lateral epicondyle also

provides attachment for the radial collateral ligament of the

elbow joint

Associated Joints

The humerus articulates with the scapula at the glenohumeral joint, with the ulna at the ulnohumeral joint

(trochleoulnar joint),

 

FIGURE 1.14. Distal humerus, inferior surface, showing

articular surface and contours of trochlea and capitulum.

radial sulcus. The anterior portion of the distal third provides the origin area for the brachialis muscle (see above

under shaft of the humerus). The posterior portion of the

distal third and medial border of the medial and distal

thirds of the shaft provide the wide origin area of the medial

head of the triceps. The distal third of the medial border is

raised into a ridge, the medial supracondylar ridge. This

ridge becomes more prominent distally. The medial supracondylar ridge provides an anterior lip for a portion of the

origin of the brachialis muscle. The ridge also provides a

posterior lip for a portion of the medial head of the triceps

brachii. The medial intermuscular septum attaches in an

intermediate portion of the medial supracondylar ridge.

The lateral border of the humerus extends from the dorsal part of the greater tuberosity to the lateral epicondyle.

The lateral border separates the anterolateral surface of the

humerus from the posterior surface. The proximal half of

the lateral border is rounded and indistinctly marked, serving for the attachment of part of the insertion of the teres

minor, and the origin of the lateral head of the triceps

brachii. The sulcus or groove for the radial nerve (see above)

crosses the central portion of the lateral border of the

humerus. The distal part of the lateral border forms a

rough, prominent margin, the lateral supracondylar ridge.

The lateral supracondylar ridge provides the attachment

area for several structures. Superiorly, there is an anterior lip

for the origin of the brachioradialis muscle. Distal to this

area, the lateral supracondylar ridge provides an area for the

origin for the extensor carpi radialis longus. Distally, there

is a posterior lip for a portion of the origin of the medial

head of the triceps brachii. The intermediate portion of the

lateral supracondylar ridge provides the attachment site for

the lateral intermuscular septum.

 

The anteromedial surface of the humeral shaft contains

a portion of the bicipital groove proximally. The tendon of

the latissimus dorsi inserts into or along the medial crest of

the intertubercular groove in the area just distal to that traversed by the bicipital tendon. Distal and medial to this area

near the medial border, is the insertion area of the teres

major. In the midportion of the anteromedial shaft, near

the medial border of the humerus is the insertion area of the

coracobrachialis. In the distal portion of the anteromedial

surface of the humerus, the bone is flat and smooth, and

provides for the large origin of the brachialis muscle.

The dorsal surface of the humerus slightly rotates from

proximal to distal, so that the proximal portion is directed

slightly medially, and the distal portion is directed posteriorly and slightly laterally. The surface of the posterior surface of the humerus is nearly completely covered by the lateral and medial heads of the triceps brachii. The lateral head

arises from the proximal portion, on the lateral half of the

bone, just lateral to the radial sulcus. The origin of the

medial head of the triceps begins on the proximal third of

the posterior surface of the humerus, along the medial border of the bone and the medial distal border of the radial

sulcus. This large origin area extends the length of the posterior humerus, covering the major portion of the posterior

half of the humerus. The triceps origin extends distally to

end as far as distal as the posterior portion of the lateral epicondyle, just proximal to the origin of the anconeus muscle.

The medial and lateral borders run the entire length of

the humerus. The medial border of the humerus extends

from the lesser tuberosity to the medial epicondyle. The

proximal third of the medial border consists of a prominent

crest, the crest of the lesser tuberosity. The crest of the lesser

tuberosity provides the insertion area of the tendon of the

teres major. More distally, in the mid-portion of the shaft

and located on the medial border is a rough impression for

the insertion of the coracobrachialis. Distal to this area is

the entrance of the nutrient canal into the humerus. A second nutrient canal may exist at the starting point of the

1 Skeletal Anatomy 23