Associated Joints

The scapula articulates with the acromial end of the clavicle

at the acromioclavicular articulation (see earlier, under

Clavicle), and articulates with the proximal humerus at the

glenoid articulation. The scapula slides and rotates on the

thorax, stabilized by muscular attachments, and forms the

soft tissue scapulothoracic articulation.

Muscle Origins and Insertions

Muscle attachments include the trapezius, deltoid (deltoideus), supraspinatus, infraspinatus, levator scapulae,

minor and major rhomboids (rhomboideus), serratus anterior, teres major, teres minor, subscapularis, triceps, long

and short heads of the biceps, coracobrachialis, pectoralis

minor, and the omohyoid (see Figs. 1.6 and 1.7). The costal

(anterior) surface provides the origin for the subscapularis.

The dorsal (posterior) surface provides the origins for the

supraspinatus (from the supraspinatus fossa) and infraspinatus (from the infraspinatus fossa). The spine contains

part of the insertion of the trapezius as well as a portion of

the origin of the deltoid. The dorsal portion of the

acromion contains additional areas for the origin of the deltoid. The coracoid process contains the origins of the coracobrachialis and the short head of the biceps as well as the

insertion of the pectoralis minor. The dorsal rim of the

medial (vertebral) border receives the insertions of the levator scapulae and the minor and major rhomboid muscles.

The levator scapulae insertion is located superior to the

level of the spine, the rhomboideus minor insertion is

located at the level of the spine, and the superior rhomboideus major insertion is located inferior to the level of the

spine. The serratus anterior inserts along the anterior

(costal) surface of the medial border. The teres minor and

the teres major originate along the dorsal rim of the lateral

border. The teres minor origin lies superior to the teres

major. The origin of the long head of the triceps is located

inferior to the glenoid. The long head of the biceps originates superior to the glenoid. The omohyoid inserts on the

upper rim of body, superior to the supraspinatus fossa.

Clinical Correlations: Scapula

Failure of Bony Union

Congenital failure of bony union between the acromion

and spine may occur. The junction may be stabilized by

fibrous tissue or may exist as a defect in the scapula. This

may be mistaken for a fracture of the acromion, when in

reality it represents a chronic fibrous union.

Os Acromiale

The base of the acromion is formed from three or four ossification centers. Persistence of one of the individual ossification centers of the acromion that does not fuse with the

others or with the scapula can present as an accessory bone,

the os acromiale. The os acromiale can be mistaken for a

fracture of the acromion or humerus, or can resemble calcific tendinitis of the supraspinatus tendon. The os acromiale usually can be detected because it usually is located at

the lateral margin of the acromion; it is of variable size and

shape but usually is rounded and bilateral (25). It may exist

as a small accessory ossicle directly above the greater

tuberosity of the humerus, separated from the acromion by

approximately 1 cm, and usually is somewhat circular (25).

The Acromion as a Bony Landmark

The lateral border of the acromion usually is palpable. It

allows orientation for operative procedures in the vicinity of

the subdeltoid bursa or rotator cuff.