Science & Technology in Action

6th Edition

Replacing Damaged Joints


This lesson describes the joint types in the human skeleton. It looks at the functioning of two major synovial joints - the hip and the knee. The modern technology that allows the components of these joints to be replaced with artificial prosthetic implants is discussed.
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Lesson excerpt

The Wonderful Mechanics of the Human Body
The internal components of the human body are contained in a framework of some 206 bones called the skeleton. The skeletonis flexible, with joints that allow us to move. There are many different types of joints including:

  • hinge joints such as the elbow, knee, and ankle. Hinge joints allow the body parts to bend and straighten
  • Gliding joints that allow two flat bones to slide over each other. There are gliding joints in the foot and wrist.
  • Ball and socket joints allow twisting and turning movements. In a ball and socket joint, one of the bones has a rounded head which is the ball. The other bone has a cup-like area that is known as the socket. The shoulder and the hip are in this category.

Joints in which bones come into contact with each other must be lubricated in order to reduce the friction between the moving parts. The body produces its own lubricant, which is a jelly-like substance called synovial fluid. Of course, other physical components are involved in movement of the joints. These are ligaments, cartilage, tendons and muscles. Whileligaments normally connect one bone to another, tendons connect bones to muscles. Tendons are sometimes called sinews. For example, your fingers are moved by muscles. However these muscles are not in your hand; they are in your lower arm. There are separate muscles for each finger and when they contract they pull tendons that are connected to the bones in your fingers. If you open and close your fingers you can easily see thesetendons at work in your wrist, especially if your arm is pointing towards the light. Muscles can pull but they cannot push and so they usually occur in antagonistic pairs.

True or False?

  1. Synovial fluid is the transparent liquid in the eye. false
  2. The main bones in the lower arm are the tibia and the fibula. false
  3. Ceramic coatings are commonly used in replacement ball-and-socket joints. true
  4. Osteoporosis is a weakening of bone due to loss of calcium. true
  5. Arthritis is inflammation of a joint. true
  6. Arthritis can be cured by medication. false
  7. Tendons connect bones together. false
  8. A layer of cartilage on the inside of a hip joint prevents friction between the bones. true
  9. The synovial fluid which reduces the friction between the ball and the socket is produced by the membrane that covers the joint. true
  10. Muscles can push or pull. false