Dance Anatomy & Kinesiology

The Upper Extremity 385

muscles rather than as a prime mover (Moseley et al., 1992). Posturally, it can pull the medial border

and particularly the inferior angle of the scapula away from the rib cage (winged scapula). However, if

the scapula is adequately stabilized, contraction of the pectoralis minor will instead act to elevate the

upper ribs and contribute to a desired lifted posture of the chest (Hamilton and Luttgens, 2002), often

used in dance as part of presentation.

Rotator Cuff

The rotator cuff is composed of the four muscles that span between the scapula and the proximal

humerus—the supraspinatus, infraspinatus, teres minor, and subscapularis. These muscles form a

hood or cuff about the head of the humerus, and their tendons actually merge into the capsule of the

shoulder joint and provide a net compression force that helps stabilize the head of the humerus in the

glenoid cavity. In addition to helping keep the humerus in contact with the glenoid cavity, these muscles

produce rotation that is often used to position the head of the humerus or the arm to facilitate optimal

mechanics. Some of these muscles also have other actions at the shoulder joint.

Supraspinatus

The supraspinatus is a small but important muscle

located under the upper portion of the trapezius.

As its name implies, the supraspinatus (supra,

above + spin, spine) originates above the spine of

the scapula, in the supraspinous fossa, and runs

laterally to attach to the top of the humerus (figure

7.12). Near the tip of the shoulder, the muscle

fibers of the supraspinatus converge to form a short

tendon that courses underneath the acromion and

adheres to the capsule. This tendon is a common

site of injury. The superior line of pull of this muscle

allows the supraspinatus to be an effective abduc-

tor of the shoulder, and it appears to be particularly

important for initiation of abduction when the arms

are down by the sides (Hall-Craggs, 1985). Despite

its relatively small size, the supraspinatus has been

shown to be able to effect full abduction of the arm

when the deltoid is not operative and is estimated

to normally contribute about 50% of the torque for

abduction when the deltoid is operative (Smith,

Weiss, and Lehmkuhl, 1996). Its line of pull also

allows this muscle to help pull the humerus into

the glenoid cavity and help prevent downward dislocation of the shoulder.

Palpation: Place the fingertips of your left hand just above the spine of the right scapula. The supra-

spinatus can be felt contracting under the trapezius when you quickly and repetitively raise your arm

just about 8 inches (20 centimeters) to the side (shoulder abduction).

Attachments and Primary Actions of Supraspinatus

Muscle Proximal attachment(s) Distal attachment(s) Primary action(s)

Supraspinatus

(soo-prah-spi-NAH-tus)

Inner portion of

supraspinous fossa of

scapula

Top of greater tubercle of

humerus

Shoulder abduction

Stabilization of shoulder

FIGURE 7.12 Posterior view of rotator cuff muscles:

supraspinatus, infraspinatus, and teres minor (left

shoulder, deep view).

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