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9.3 Medical technology - Bionics 3. The skeletal system

Syllabus reference (October 2002 version)
3. The wide range of movements, continual absorption of shocks and diseases make the skeletal system vulnerable to damage but new technologies are allowing the replacement of some damaged structures Students learn to: Students:

Extract from Senior Science Stage 6 Syllabus (Amended October 2002). © Board of Studies, NSW.

[Edit: 10 Sep08]

Prior learning:
Preliminary modules 8.4 (subsection 6)

Science Stages 4-5 syllabus: outcomes 4.8 (content 4.8.1 a, b, c, d; 4.8.4 b, c, d and 4.8.5 a, b), outcome 5.8 (content 5.8.1a), outcome 5.12 (content 5.12 d, f, g)

Background: The human body relies on the skeletal system for support and as a protective barrier between vital organs and the outside world. With age, the skeletal system becomes more vulnerable to disease and deterioration. However, the development of new materials and techniques has made possible the replacement of damaged bones and joints.

The skeleton (external website) at Enchanted Learning.com

identify the role of the skeletal system particularly in relation to maintaining an upright stance and protecting vital organs

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perform an investigation to demonstrate the different types of joints and the range of movements they allow

perform an investigation to examine the relationship between cartilage, muscle, tendon and bone in an animal limb

perform a first hand investigation to remove calcium compounds from chicken bones to examine the flexible nature of bones

The above three syllabus-required investigations can be conveniently conducted together, using a whole uncooked chicken. These are readily available from butchers or supermarkets. A number of suitable procedures for the investigations are provided below.

Procedure for examining the joints of a chicken

  1. Remove the skin and fat from the shoulder joint. Hold the body of the chicken and with the other hand take the upper arm and try moving it in different directions.
    Note in which directions it can move and the extent of the movement. Why is this joint called a “ball and socket” joint?
  2. Now do the same thing with the knee joint.
    What kind of movement does this joint allow, and what is the extent of the movement? What kind of joint is this?
  3. Observe the movement around the vertebral column.
    There is a lot less movement than in the previous two joints. This joint is called a “sliding joint”. Why is this name given to it?
  4. If the neck bones are included in your chicken look at the bones at the top. One sits over the other and allows greater movement than the rest of the vertebrae.
  5. If you have a model of a human skeleton you may be able to see the neck bones there better and the type of movement they allow.
    This joint is called a “pivot joint”.

Procedure to examine the parts of a chicken limb

  1. Remove the skin and any excess fat from a wing or a leg. Note the meat on the upper part of the limb. This is the muscle.
  2. Follow the muscle down to where it attaches to the bone.Note that there is a thin sinew-type part just before it joins the bone. This is a tendon.
  3. Look at the joint, where the upper and lower bones meet. Can you see tough white material that surrounds the joint? This is a ligament. If it is not obvious, it may help to look at a diagram of a joint in a text book. The ligament holds the joint in place.
  4. Can you see softer material at the end of the bones? This is called cartilage. The cartilage protects the bone from damage at the joint. (Hold the soft part of your nose. This is also cartilage.)

Procedure for removing calcium compounds from chicken bones

  1. Obtain some calcium carbonate from your teacher. You could use some chalk, as this is calcium carbonate. Put a small amount of the calcium carbonate in some dilute acid, such as dilute hydrochloric acid or even vinegar.
  2. Leave it overnight and observe what effect the acid has on the calcium carbonate. (It should break it down.)
  3. Examine and make observations of a long bone, such as a chicken’s leg bone. Note particularly how rigid the bone is. Place the bone in the same type of acid you used above, leaving the top of the bone out of the acid for a control and leave it overnight.
  4. Take the bone out of the acid and wash any remaining acid off the bone. Try bending the bone that was immersed in the acid and compare it with the bone that was out of the acid.
  5. Describe how it has changed. If there has been no change, put it back in fresh acid for another 24 hours.
  6. Find out by research or discussion what is left in the bone when the calcium carbonate is removed.
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describe the different types of synovial joints as

Background

A synovial joint is a freely moving joint because there is a space between the bones forming the joint. A synovial membrane surrounds the joint, secreting synovial fluid into the space to provide lubrication and allow easy movement.

There are five types of synovial joints:

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describe the role of cartilage and synovial fluid in the operation of joints

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process secondary information to compare the shock absorbing abilities of different parts of bones

Notes about the structure and function of parts of bone

A bone is generally made up of two types of tissue: spongy bone and compact bone. Compact bone provides protection and support, and forms a hard, thin layer over the inner spongy bone. It therefore has little role in shock absorption. Spongy bone is very porous and contains the bone marrow. Compact bone is much denser, with a porosity ranging between 5% and 10%. Spongy bone is soft and spongy and therefore more open to shock absorption. It distributes and dissipates the energy transferred to it by compact bone.

 

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plan, choose equipment or resources for and perform a first hand investigation to demonstrate properties of silicone such as acid resistance, flexibility and imperviousness to water that make it suitable for bionics

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identify the properties of silicone that make it suitable for use in bionics

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explain why silicone joints would be suitable substitutes for small joints in the fingers and toes that bear little force

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analyse secondary information to compare the strength of UHMWPE and “superalloy” metal

Biomaterial Tensile strength (MPa) Elongation (%)
Titanium alloy 860 10
Co-based alloy
(cast Co-Cr-Mo alloy)
655 8
UHMWPE 27 minimum 250-350

Ultra high molecular weight polyethylene (external website) Wikipedia

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describe the properties that make ultra-high molecular weight polyethylene (UHMWPE) a suitable alternative to cartilage surrounding a ball and socket joint in terms of its

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explain why artificial joints have the articulating ends covered in polyethylene

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describe the properties of the materials, including ‘superalloy’ that make a ball and stem for the bone components of a large joint including:

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identify that artificial implants can be either cemented or uncemented into place

Cemented implants

Background

Dr J. Charnley introduced bone cement for the fixation of artificial hip joints in the 1950s. Once the diseased femoral head of the bone is cut off, the medullary canal is filled with a doughy bone cement, and the implant is inserted. Alignment of the implant with the other components of the joint is verified before the bone cement sets.

Cement-free implants

Background

The artificial joint is designed to wrap around the remaining bone, once the diseased bone is removed. Cement-free implants possess a porous surface, which permits bone tissue to grow in and create an interface between bone and implant. Cement-free implants are more vulnerable to loosening than cemented implants, and it is expected that the time required before the patient can walk will be longer than for cemented implants.

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describe the properties of the cement that is used in implants and discuss how an uncemented implant forms a bond with a bone

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