After completing this chapter, you will
be able to:
- Categorize joints based on structure and movement capabilities.
- Explain the functions of articular cartilage and fibrocartilage.
- Describe the material properties of articular connective tissues.
- Explain advantages and disadvantages of different approaches
to increasing or maintaining joint flexibility.
- Describe the biomechanical contributions to common joint injuries
The joints of the human body largely govern
the directional motion capabilities of body segments. The anatomical
structure of a given joint, such as the uninjured knee, varies little from
person to person; as do the directions in which the attached body
segments, such as the thigh and lower leg, are permitted to move
at the joint. However, differences in the relative tightness or laxity
of the surrounding soft tissues result in differences in joint ranges
of movement. This chapter discusses the biomechanical aspects of
joint function, including the concepts of joint stability and joint
flexibility, and related implications for injury potential.
Anatomists have categorized joints in several ways, based on
joint complexity, the number of axes present, joint geometry, or
movement capabilities (53). Since this book focuses on human movement,
a joint classification system based on motion capabilities is presented.
1. Synarthroses (immovable)
(syn = together; arthron = joint): These fibrous
joints can attenuate force (absorb shock) but permit little or no
movement of the articulating bones.
a. Sutures: In these joints,
the irregularly grooved articulating bone sheets mate closely and
are tightly connected by fibers that are continuous with the periosteum.
The fibers begin to ossify in early adulthood and are eventually
replaced completely by bone. The only example in the human body
is the sutures of the skull.
b. Syndesmoses (syndesmosis = held by bands):
In these joints, dense fibrous tissue binds the bones together,
permitting extremely limited movement. Examples include the coracoacromial,
mid-radioulnar, mid-tibiofibular, and inferior tibiofibular joints.
2. Amphiarthroses (slightly
movable) (amphi = on both
sides): These cartilaginous joints attenuate applied forces and
permit more motion of the adjacent bones than synarthrodial joints.
Sutures between the occipital and parietal
bones of the skull represent synarthroses (immovable joints). From Shier, Butler, and Lewis. Hole’s Human Anatomy and Physiology, © 1996. Reprinted by permission
of The McGraw-Hill Companies, Inc.
3. Diarthroses or synovial (freely movable) (diarthrosis = “through ...