Joints of the Skeletal System

Joints are the junctions between the bones of the skeletal system. That is, a joint occurs wherever two or more bones come together. Most joints function in lever systems that make movements possible by bending or straightening. Others, however, are relatively rigid structures that help hold bones in place or enable bones to grow.

Wherever two or more bones meet, a joint is formed. Such joints, or articulations, represent the functional junctions between bones. They bind various parts of the skeletal system together, allow bone growth to occur, permit certain parts of the skeleton to change shape during childbirth, and enable body parts to move in response to skeletal muscle contractions.

Classification of Joints

Although joints vary considerably in structure and function, they can be classified according to the type of tissue that binds the bones together at eachjunction. On this basis, three general groups can be identified - fibrous joints, cartilaginous joints, and synovial joints.

Joints can also be grouped according to the amount of movement possible at the bony junctions. In this scheme, joints are classified as immovable (synarthrotic), slightly movable (amphiarthrotic), and freely movable (diarthrotic).

Types of Joint Movements

Movements at synovial joints are produced by actions of skeletal muscles. Typically, one end of a muscle is attached to a relatively immovable or fixed part on one side of a joint, and the other end of the muscle is fastened to a movable part on the other side. When the muscle contracts, its fibers pull its movable end (insertion) toward its fixed end (origin), and a movement occurs at the joint.

Post-text assignments

1 Give full answers to the following questions:

1 How would you explain to an athlete why damaged joint ligaments and cartilages are so slow to heal following an injury?

2 Compared to the shoulder and hip joints, in what way is the knee joint poorly protected, and thus especially vulnerable to injuries?

3 Based upon your knowledge of joint structures, which do you think could be most satisfactorily replaced by a prosthetic device, a hip joint or a knee joint? Why?

4 If a patient's lower arm and elbow were immobilized by a cast for sevcral weeks, what changes would you expect to occur in the bones of the arm?

5 Why is it important to encourage an inactive patient to keep all joints mobile, even if it is necessary to have another person or a device move the joints (passive movement)?

6 How would you explain to a person with a dislocated shoulder that the shoulder is likely to become dislocated more easily in the future?

2 Match the movements in column I with the descriptions in column II:

I II

1) rotation a) turning palm upward

2) supination b) decreasing angle belween parts

3) extension c) moving part forward

4) eversion d) moving part around an axis

5) protraction e) turning sole of foot outward

6) flexion f) increasing angle between parts

7) pronation g) lowering a part

8) abduction h) turning palm downward

9) depression i) moving part away from midline

3 Render the text Skeletal System: Bones and Joints.

Use some of the following expressions: