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)