Biomedical Engineering Reference
In-Depth Information
back-and-forth or side-to-side movement, and include the intercarpal articulations in the
wrist. Hinge joints, such as the elbow, permit bending in only one plane and are the most
common type of synovial joint. The atlas and axis provide an example of a pivot joint that
permits rotation. In condyloid articulations, an oval, convex surface of one bone fits into
a concave depression on another bone. Condyloid joints, which include the metacarpopha-
langeal joints (knuckles) of the fingers, permit flexion-extension and rotation and are
considered to be biaxial because rotation is limited to two axes of movement. The saddle
joint, represented by the joint at the base of the thumb, is a modified condyloid joint that
permits movement in several directions (multiaxial). Ball-and-socket joints allow motion in
many directions around a fixed center. In these joints, the ball-shaped head of one bone fits
into a cuplike concavity of another bone. This multiaxial joint is the most freely movable of
all and includes the shoulder and hip joints. Biomedical engineers have helped develop arti-
ficial joints that are routinely used as replacements in diseased or injured hips, shoulders, and
knees (Figure 3.34).
3.4.5 Muscular System
The muscular system (Figure 3.35) is composed of 600-700 skeletal muscles, depending
on whether certain muscles are counted as separate or as pairs, and makes up 40 percent
of the body's mass. The axial musculature makes up about 60 percent of the skeletal
muscles in the body and arises from the axial skeleton (see Figure 3.31). It positions the
head and spinal column and moves the rib cage during breathing. The appendicular
musculature moves or stabilizes components of the appendicular skeleton.
The skeletal muscles in the muscular system maintain posture, generate heat to maintain
the body's temperature, and provide the driving force that is used to move the bones and
joints of the body and the skin of the face. Muscles that play a major role in accomplishing
a movement are called prime movers, or agonists. Muscles that act in opposition to a prime
(a) (b)
FIGURE 3.34
Diseased or damaged hip (a) and knee (b) joints that are nonfunctional or extremely painful can
be replaced by prostheses. Artificial joints can be held in place by a special cement (polymethylmethacrylate
[PMMA]) and by bone ingrowth. Special problems occur at the interfaces due to the different elastic moduli of
the materials (110 GPa for titanium, 2.2 GPa for PMMA, and 20 GPa for bone).
