What function does bone play in the human body? What are the different parts of a bone? What happens when a bone breaks? How does a splint protect a fracture? How does a cast aid in bone repair?

Broken Bones
What can cause a bone to break?
David gets wrapped up in a cast to learn about broken bones.
Segment length: 7:30


The human skeletal system is designed to support the human body, offer it protection, and provide a means of locomotion. Bone is the essential framework to which muscles are attached.

Bone is constructed in layers. The outside layer is known as the periosteum. This is where blood vessels and nerve cells are located. The next layer is the compact bone. This area has collagen and crystals of calcium and phosphorus. The next layer is of spongy bone, with shock-absorber qualities. Then the medullary cavity, filled with marrow, forms the inside of the bone. This layered-tube architecture allows the bone its compressional strength, while keeping it very light.

However, forces on bones are not always compressional. Lateral forces, twisting stresses, and powerful impacts may cause the bone to break, or fracture. There are two types of fractures: closed and open. A closed fracture occurs when the skin is not broken. An open fracture is when the skin has been broken and involves an open wound. This type of fracture is more serious because of the increased risk of infection and shock caused by blood loss and damaged tissue.

Keeping the broken body part stationary--immobilizing it--will stabilize the injured area and prevent the bones from shifting until further treatment is available. Splints are used to immobilize an area. They can be made from cardboard, newspapers, sticks, or any other rigid material.

When a cast is needed, the doctor first checks that the bones are in correct alignment to promote proper healing. A cast is then placed over the fractured area to immobilize it, allowing the bones to grow back and heal in the desired configuration.

Although fractures are an unfortunate occurrence, most of us can take precautions to avoid them. There are certain diseases, however, that make some people more susceptible to fractures. Diseases of the bone, including osteoporosis, rickets, and osteoarthritis can cause bone deterioration or fragility. This can increase the likelihood or severity of a bone fracture.


1. What are the effects of nutrition on bones?
2. Invite an orthopedic surgeon to your classroom to discuss some of these topics: high-technology materials used in joint replacements; the effects of aging on bones; and the healing process of bones.
3. Have you ever broken a bone? What did it feel like? What was it like to wear a cast?


cast a device used to immobilize an area or fracture for an extended period of time
collagen protein found in skin, tendons, bones and teeth
compressional strength describes the resistance of a material to compressive stress--a compressing or crushing force
marrow the soft tissue found inside bones
osteoarthritis a degenerative joint disease of unknown origin causing pain and decreased joint motion
osteoporosis a general progressive loss of bone tissue resulting in weak skeletal strength
rickets a childhood disease characterized by soft, deformed bones caused by a failure to absorb calcium due to inadequate vitamin D or sunlight


American Red Cross standard first aid workbook. (1988) Washington, DC: American Red Cross.

Gray, H. (1901, 1977) Gray's anatomy. New York: Bounty Books.

Kapit, W., and L. Elson. (1977) The anatomy coloring book. New York: Harper Collins.

Community resources:

American Red Cross chapter
School nurse
Emergency-response units
Hospitals or emergency-treatment centers

Main Activity

Take a Break!
Why is it important to immobilize a fractured bone?

Observe how to splint a fractured limb, and learn the importance of immobilization in the treatment of broken bones. You will also experience the sensation of limited movement created by a splint or a cast.


  1. Review the first-aid resources for information and diagrams on how to splint arms, legs, and fingers.
  2. Demonstrate the proper procedures for splinting an arm.
  3. Pair up and practice splinting each other. Try using different materials to splint the arm.
  4. When the arm splint is completed, repeat steps 2 and 3 for the leg splint and the finger splint.


1. List other types of materials that can be used for splinting.

2. Discuss possible ways people may break a bone.

3. Which is easier to splint, the arm or the leg?

Go to a butcher shop and ask for some bones with the joints attached. Use these as a visual aid to learn about the construction of the bone, joints, tendons, and ligaments. Draw pictures or write summaries about the structure of bones. (Bones can spoil, so make sure you refrigerate them!)

Obtain two different X-rays of a broken bone: one of the bone before the cast was applied and one of the healed bone. Study each X-ray. Is the break visible in the X-ray? Does the bone change in size or appearance after it has healed? (It may appear thicker in the area of the break.) Arrange for a trip to the X-ray department of an area hospital, or invite an orthopedic surgeon to visit your classroom to help in this study of X-rays.

Not all broken bones are treated in the same way. New medical techniques have improved the outcomes for those with broken bones, including better healing and increased mobility. Research the different methods for treating injured bones, such as the uses of different types of casts, the application of electronic equipment to relieve pain, or the use of artificial materials to create replacement bones and joints.

Have a chicken dinner and save the bones. Wash them and clean off any remaining meat. Let them dry thoroughly. Place half of the bones in a jar of vinegar and store the other half in a dry area until needed. The bones in vinegar should sit for three to four days. At the end of this time, drain the vinegar. The bones that were submerged in the vinegar should be flexible compared to the bones that have been left to dry. Compare the two different sets of bones, making sure you have an ample supply of each type. What is the difference between the two sets of bones? Find out what causes a bone to be hard. Why isn't one bone hard? What important mineral does the vinegar deplete? What other parts of your body are made of this type of material?

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