Biomedical Engineering Reference
In-Depth Information
12.2 Normal Anatomy of the Rotator Cuff
and its Insertion Site
The rotator cuff muscles and tendons of the shoulder are a complex group of
muscles that play a critical role in maintaining strength and stability in what is
otherwise a biomechanically challenging joint. The shoulder is comprised of a
shallow socket (the glenoid), an osseous component of the scapula, and a relatively
large humeral head. The osseous structures result in a relatively unstable joint, thus
the soft tissue stabilizers of the shoulder are important for normal function of the
upper extremity. The static stabilizers of the shoulder include a ring of labral
cartilage located circumferentially around the glenoid, which serves to deepen the
socket, and the capsuloligamentous structures, which individually tighten at various
shoulder positions. The rotator cuff provides dynamic stability and is active in
nearly all phases of shoulder motion [
6
]. The contraction of the rotator cuff
effectively centers the humeral head on the glenoid, counteracting the upward
vector of the deltoid (Fig.
12.1
).
The rotator cuff is comprised of four separate muscles (supraspinatus,
infraspinatus, teres minor, and subscapularis), all of which originate from the
scapula. The supraspinatus, infraspinatus, and teres minor muscles form the supe-
rior and posterior portions of the rotator cuff, and as they course laterally, they
merge and join to form a single tendinous structure that inserts on the greater
tuberosity (an osseous protuberance on the humeral head). The subscapularis arises
from the anterior portion of the scapula and attaches to the lesser tuberosity,
forming the anterior musculature of the shoulder.
Mature tendon has a highly organized and aligned structure. It is composed
primarily of collagen type I and is relatively acellular [
7
]. Tendon exhibits high
strength in response to tensile force and provides the mode of bony attachment for
most muscles in the skeletal system. The rotator cuff has a relatively hypovascular
area within what is known as the rotator cuff cable (Fig.
12.2
). This hypovascular
Fig. 12.1
(
a
) The rotator cuff is made up of four muscles that arise from the scapula and insert
onto the humeral head. They are active during all phases of shoulder motion, centering the humeral
head on the glenoid. (
b
) The rotator cuff insertion site is comprised of tendon, unmineralized
fibrocartilage, mineralized fibrocartilage, and bone
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