CHAPTER 8 Structure and Function of the Shoulder Complex
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Upper trapezius
Middle trapezius
Lower trapezius
Levator scapulae
Rhomboid minor
Rhomboid major
Lower trapezius
Latissimus dorsi
A
Pectoralis minor
Figure 8.24 In a reversal of action, the latissimus dorsi and lower trapezius muscles elevate the pelvis against a stabilized scapula. In this example, a client sitting in a wheelchair places the arms on the armrest and contracts the lower trapezius and latissimus dorsi to elevate the pelvis up toward the fixed scapula. This maneuver lifts the ischial tuberosities off the seat and decreases contact pressure on the tissues between the bony prominences and the seat.
also assist with scapular retraction. These muscles are recruited during pulling activities involving the arms, as they retract the scapulae and stabilize them on the thorax. Because of the superior diagonal orientation of the rhomboid fi bers and the inferior orientation of the lower trapezius fi bers, these opposing directions cancel each other, resulting in retraction (Fig. 8.25B).
B Anterior
Figure 8.23 (A) Posterior view of the scapulothoracic muscles. (B) Anterior view of the scapular depressor pectoralis minor.
the serratus can protract the scapulae and lift the thorax further up from the support surface (Fig. 8.25A). The middle trapezius fi bers are aligned in a near- horizontal direction and function as the primary scapular retractors. The rhomboids and lower trapezius muscles
Upward and Downward Rotators
Scapular upward rotation is accomplished by the synergis- tic contractions of the serratus anterior and the upper and lower trapezius muscles. These contractions are essential to keep the glenoid fossa aligned with the humeral head and maintain an effi cient length of the deltoid muscle during arm elevation. Without upward rotation of the scapula, the length of the deltoid muscle could not produce adequate tension to elevate the humerus.
