Slightly Movable Joint

Definition

A slightly movable joint (amphiarthrosis) is an articulation between bones in which the motion is limited due to either fibrous tissue or cartilage.

Description

Joints are classified as either fibrous or cartilaginous. Only one type of fibrous joint is slightly movable. It is known as a syndesmosis. In a syndesmosis, bones are separated by a substantial space and united by fibrous connective tissue.

In another classification of joints, cartilaginous also has only one type that is considered slightly movable. It is known as a symphysis. In a symphysis, bony surfaces are united by fibrocartilage.

Function

The function of a syndesmosis and symphysis is to bind two bones together, thus holding portions of the skeletal system intact. Also, the limited motion available in either of these two types of joints allows certain movements to take place.

Role in human health

A syndesmosis connects two bones by connective tissue and is found throughout the human body. An example is the tibio-fibular syndesmosis, or the connective tissue that binds the distal ends of the fibula and tibia. A syndesmosis allows the fibula and tibia to work in unison as part of the lower leg. The limited motion available at this joint allows the tibia and fibula to move about each other yet still remain as a unit. This available movement is extremely important in the actions of the foot and ankle complex. This example describes how a syndesmosis provides stability as well as slight mobility.

A symphysis is a cartilaginous joint in which the uniting entity is fibrocartilage. Similar to the syndesmosis, the symphysis is stable but there is limited motion. In the syndesmosis, the bones are separated by a large space, unlike the symphysis, in which the articular surfaces are closer together. An example of a symphysis in the human body is the attachment of one vertebral body to another by way of an intervertebral disk. The intervertebral disk is a fibrocartilage ring that unites individual vertebral bodies. The sum attachment of many vertebrae gives rise to the vertebral column. The importance of this symphysis is that minimal motion occurs between vertebrae, thus maintaining stability. The combination of small movements between each successive vertebral attachment is what allows the vertebral column to move as a unit, that is, to flex and extend.

Common diseases and disorders

In the human body, a syndesmosis provides a stable environment between two bones and also allows for limited but important motion. In the example previously cited, the disorder that can affect a syndesmosis is primarily orthopedic. The tibio-fibular syndesmosis plays an integral role in stabilizing and allowing motion of the lower leg, foot, and ankle. Clearly, injury to this structure such as tearing would impair the stability and mobility of the lower leg, foot, and ankle. Thus, an injury to a syndesmosis described in this example could lead to impaired function such as walking.

A symphysis binds two bones by fibrocartilage. As cited previously, a good example of a symphysis in the human body is the attachment of one vertebra to another by a fibrocartilaginous disk. One of the most common and obvious disorders that can affect this joint is injury to the fibrocartilaginous disk. Injury to this fibrocartilage can be due to trauma, tumor, or osteoarthritis. Depending on which fibrocartilaginous disk is injured in the spine, associated problems could be pain, weakness, numbness, or tingling in the limbs, trunk, or both. Problems associated with an injured disk could affect overall human function and limit movement.

The syndesmosis and symphysis play important roles in human health. Moreover, injury to these joints could lead to reduced function and possible disability.

KEY TERMS

Connective tissue—Tissue that has pliable fibers, which provide strength to the tissue and thus support to the structures it attaches to.

Fibrocartilage—Connective tissue made up of collagen fibers that unites two bones together as a joint.

Fibula—The outer or lateral bone of the lower leg.

Intervertebral disk—A fibrocartilaginous structure that attaches one vertebra to another. An intervertebral disk provides force attenuation in the spine and aids in the overall movement of the spine.

Tibia—The larger weight-bearing bone of the lower leg.

BOOKS

Hall C.M., L.T. Brody. Therapeutic Exercise Moving Toward Function. Philadelphia: Lippincott, Williams & Wilkins, 1998.

Lehmkuhl L.D., L.K. Smith. Brunnstroms Clinical Kinesiology. Philadelphia: F.A. Davis Co., 1996.

Magee D. J. Orthopedic Physical Assessment. Philadelphia: W.B. Saunders Co., 1997.

Moore K.L., A.F. Dalley. Clinically Oriented Anatomy. Baltimore:Lippincott, Williams & Wilkins, 1999.

Rosse C., P. Gaddum-Rosse, W. Hollinshead. Hollinshead's Textbook of Anatomy. Baltimore: Lippincott, Williams & Wilkins, 1997.

Mark Damian Rossi, Ph.D., P.T.