14 Dance Anatomy and Kinesiology
synovial membrane and synovial fluid that gives rise
to the name of this type of joint, “synovial” joint.
Synovial joints are generally reinforced by liga-
ments. Ligaments (L. ligamentum, a band) are strong
bands of fibrous tissue that bind the articulating
bones together. They contain abundant collagen
fibers arranged in a lengthwise manner (dense
regular connective tissue), which provide them with
good tensile strength. Ligaments serve as passive
constraints to prevent dislocations and add greater
stability to joints. They also tend to limit the direc-
tion and extent of motion allowed at a given joint.
These ligaments can be deep to (intracapsular),
part of (capsular), or outside of (extracapsular) the
joint capsule. The cruciate ligaments of the knee
are examples of intracapsular ligaments; and the
collateral ligaments of the knee (figure 5.3 on p. 240)
are examples of extracapsular ligaments. The gle-
nohumeral ligaments of the shoulder (figure 7.7 on
p. 380) are examples of capsular ligaments.
Some synovial joints contain another specialized
structure called a fibrocartilage disc (alternately
termed articular disc). As the name suggests, this
structure is composed of fibrous cartilage. Fibrous
cartilage has more collagen fibers in its extracellular
matrix and hence is stronger than hyaline cartilage.
In some joints this fibrocartilage structure is shaped
more like a circumferential ring than a disc and is
called a labrum. These fibrocartilage structures are
located within the joint and function to enhance
joint congruency, joint stability, and joint shock
absorbency. They are present only in select synovial
joints such as the knee (meniscus), shoulder (glenoid
labrum), and hip (acetabular labrum). Two examples
are shown in figure 1.6.
Many synovial joints have other associated struc-
tures that aid in their function, such as fat pads,
bursae, tendon sheaths, and retinacula. As their
name suggests, fat pads are an accumulation of
somewhat encapsulated fatty tissue (adipose tissue).
They aid with cushioning and shock absorption and
can be found at various places such as the hip, knee,
and under the heel. A bursa (L. a purse) is a con-
nective tissue sac lined with synovial membrane and
containing a thin film of synovial fluid that functions
to help reduce friction. Bursae often protect soft
tissue such as tendons or skin from underlying hard
bone, and there are approximately 150 present in the
human body (McCarthy, 1989). For example, there is
a bursa between the back of your heel bone and the
overlying tendon, and one between the patella and
the overlying skin. Synovial tissue can also be used to
protect tendons via a double-layered sac-like covering
called a tendon sheath. These tendon sheaths areoften found surrounding tendons that come into
close association with bones such as the long tendons
of the hand and foot. A retinaculum (L. a band, a
halter) is a thickened band of connective tissue that
helps hold tendons in place. Retinacula are also
prevalent around the ankle and foot. Examples of
these structures associated with the foot are shown
in figure 1.7.Subclassification of Synovial Joints
Despite sharing the common structure just described,
synovial joints vary considerably in their shape and
the movements they allow. Table 1.4 illustrates one
commonly used classification system for basic types
of synovial joints and their associated movements.
Here, the six types of synovial joints are described
only in terms of their shape. However, their shape
has important implications for movement capacity
(noted in parentheses in table 1.4) and will be dis-
cussed after the necessary terminology is covered in
the next two sections of this chapter.FIGURE 1.6 Fibrocartilage structures associated with
synovial joints. (A) Menisci of the knee (right knee,
superior view) and (B) glenoid labrum of shoulder (right
scapula, anterior view).