Joints

three cuneiform bones also make up this part of the hind and mid-foot. Figure 48 shows the

bones of the foot:

There are five metatarsal bones that connect to the more proximal bones of the foot. These

are labeled 1-5, starting with the great toe side. Both the head of the first and the head of the

fifth metatarsal can be felt on either side of the foot as prominences of the foot. There are 14

phalanges that are arranged similarly to the fingers. The toes are numbered like the

metatarsals with the hallux being known as the big or great toe. The hallux has two phalanges,

while the rest of the toes have the three phalanges.

JOINTS

A joint or articulation is the place where two bones or bone and cartilage come together to

make a connection. There are several types of joints, some of which are moveable and others

are immoveable. The immoveable joints serve mainly a protective function—to protect internal

structures and organs and to give the body some stability. Moveable joints allow for body

motion.

The structural classification of joints involves whether or not the joint is fibrous or contains

cartilage. There are three structural joint classifications: 1) a fibrous joint, where adjacent

bones are united by fibrous connective tissue; 2) a cartilaginous joint, where fibrocartilage or

hyaline cartilage connects the two bones; and 3) a synovial joint, where the two bones

articulate but do not directly connect. Instead, there is a synovial fluid space between the

articulating surfaces of the two bones.

There are many different types of joints according to the functional classification of joints.

These consist of these types of joints:

• Synarthrosis—this is a nearly immobile joint or an immobile joint that includes sutures

of the skull that protect the brain. The manubriosternal joint also acts as a synarthrosis.

• Amphiarthrosis—this is a limited-mobility joint that includes those joints that connect

adjacent vertebrae. The joint moves slightly but together the entire spine can move a

great deal. The pubic symphysis is an amphiarthrosis that is connected by fibrocartilage.

• Diarthrosis—this is a freely mobile joint that includes all the synovial joints of the body.

These are found in the appendicular skeleton and allow for a wide range of motion.

These joints can be uniaxial (move in one plane), biaxial (move in two planes), or

multiaxial (moves in all three planes).

Typical uniaxial joints include the elbow, which only bends or straightens in one plane. The

knuckle joint is a typical biaxial joint, in that it allows for bending at the knuckles and widening

of the fingers. A typical multiaxial (or triaxial) joint is the hip joint, which can move in all

directions.

• Suture—all the bones of the skull (besides the mandible) are joint by fibrous joints

called a suture. There is fibrous material that connects the two bones together. These

are considered synarthroses. Infants have more fibrous tissue and open areas between

the bones, called fontanelles; these close in the first few years after birth as the skull

bones get bigger. Some sutures will ossify ad become a synostosis, which means “joined

by bone.” This happens late in life so that the suture lines gradually disappear.

• Syndesmosis—a syndesmosis is a fibrous joint in which two parallel bones are connect

by connective tissue. An example of this is the interosseous membrane. This type of

fibrous connection is seen between the tibia and fibula, and the radius and ulna. The

purpose is to unite parallel bones so they don’t separate.