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9.3 Medical technology - Bionics 3. The skeletal system
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 
at Enchanted Learning.com
identify the role of the skeletal system particularly in relation to maintaining an upright stance and protecting vital organs
- The axial skeleton is made up of the skull, backbone and rib cage. It has
two main functions:
- to support the main body axis (achieved by the spinal column), and
- to provide protection for vital organs such as the brain (protected
by the skull), the heart and lungs (protected by the rib cage) and the
spinal cord (protected by the spinal column).
- The appendicular skeleton is made up of the pelvic girdle, shoulders, arms
and legs. The main function of the appendicular skeleton is to support the
arms and legs (the appendices).
- Apart from support and protection, the skeleton also serves to:
- store mineral salts, such as calcium and phosphorus
- produce blood cells in the marrow.
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.
- Perform each first-hand investigation by selecting the appropriate procedure and carrying it out, recognising where and when modifications are needed, and analysing the effect of any adjustments that you make. The three procedures have been sequenced to minimise wastage.
Procedure for examining the joints of a chicken
- 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? - 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? - 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? - 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.
- 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
- 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.
- 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.
- 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.
- 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
- 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.
- Leave it overnight and observe what effect the acid has on the calcium carbonate. (It should break it down.)
- 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.
- 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.
- Describe how it has changed. If there has been no change, put it back in fresh acid for another 24 hours.
- Find out by research or discussion what is left in the bone when the calcium carbonate is removed.
describe the different types of synovial joints as
- ball and socket
- hinge
- double hinge
- sliding
- pivot
- and identify their location
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:
- Ball and socket joints, which occur where a rounded head (ball)
fits into a cup-shaped socket on another bone. These allow side-to-side,
back-and-forth and rotational movements. Examples include the hip and
shoulder joints.
- Hinge joints, which occur where a bone with a concave shape meets
a bone with a convex shape, permitting only back and forth movement, such
as bending and straightening. Examples include the knee, knuckle and elbow
joints.
- Double hingejoints, which are found where two saddle-shaped
surfaces join at right angles to each other. The joint allows side-to-side
and back-and-forth movement, but no rotation. An example is the double
hinge joint between the carpal and metacarpal bones of the thumb, which
allows the thumb to be placed across the palm of the hand. A double hinge
joint is also known as a saddle joint.
- Sliding joints, which occur where two bones with flat surfaces
slide on each other. Their movement is restricted by a number of ligaments.
Sliding joints permit side-to-side and back-and-forth movement. Examples
include those between the ribs and thoracic vertebrate, between the carpels
and between the tarsals.
- Pivot joints, which occur where a cylindrical bony point rotates within a ring composed of bone and ligament. Rotational movement is the main movement allowed. An example is the radioulnar joint just below the elbow, which allows us to rotate our forearm inwards and outwards.
describe the role of cartilage and synovial fluid in the operation of joints
- Cartilage is a tough and fibrous substance that is between bone ends
in some joints. The cartilage allows the bones to move freely over each other,
reducing friction and protecting the bone ends. Cartilage is thicker in the
leg joints where the load is greater.
- Synovial fluid keeps the joints well oiled and acts like a cushion, keeping the bones apart. It is secreted by the synovial membrane, the amount being dependent on the level of activity of the joint.
process secondary information to compare the shock absorbing abilities of different parts of bones
- Process information from secondary sources to compare the shock-absorbing abilities of different parts of bones. You may need to read the following notes to identify the issues that will need to be examined. When you have identified a source of information, evaluate its validity by checking the reputation of the source and by looking to see how the information compares to information from other sources.
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.
Bone Tissue
Faculty of Medicine Technion, Israel Institute of Technology, Israel
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
- Plan the activity by considering how you will test silicone. The
easiest way to obtain some may be to buy a tube of silicone sealant from a
hardware store. You will need to squeeze out a line of it, let it dry and
then cut sections for your experimentation. You could trial one strip in water
and another in acid. You could also try different concentrations of acid.
You will need to decide how much silicone you will need for each part of the
investigation. Will you use a control? For testing imperviousness to water,
you could coat some material, such as a sugar cube, in silicone, allow it
to dry and leave it immersed in water. Coat the material with the silicone
and then leave time for it to set before you put it in water. You could then
cut through it and see if there is any moisture soaked into the material.
Will you leave them for an hour or over night?
- Choose what equipment you will need and check that it is available.
You may need some cleaning material for cleaning up any excess silicone that
may have spilled. Read packaging labels to determine recommended procedures
for safety, cleaning and disposal.
- Perform the investigation for whatever criteria you decided to test. You may need to make modifications to your planned procedures as you go.
identify the properties of silicone that make it suitable for use in bionics
- Silicone possesses many characteristics that allow it to be used in bionics:
- It may be combined with silica (a filler) to improve its mechanical properties. This allows the silicone to be manufactured to the mechanical strength required for most applications.
- It has high elongation properties before the addition of a filler i.e. it can be stretched if required.
- The polymeric structure of silicone closely resembles the structure of natural polymer components, like collagen. This allows compatibility between living tissue and silicone.
- It has a similar density to natural tissue (0.99 to 1.5 g cm-1), which reduces problems during the lifetime of the implant.
- It has a high permeability to oxygen, which means minimal obstruction to the distribution of oxygen around the body.
explain why silicone joints would be suitable substitutes for small joints in the fingers and toes that bear little force
- Silicone joints would be suitable substitutes for small joints in the fingers
and toes because they can be made as strong and as flexible as natural joints.
They are biocompatible, as they allow the flow of oxygen and do not react
with living tissue. They would last a long time, as they do not dissolve in
Artificial Joint Replacement of the finger Orthogate, Internet Society of Orthopaedic Surgery and
Trauma, Canada
analyse secondary information to compare the strength of UHMWPE and “superalloy” metal
- Analyse suitable information, such as that referred to or provided
below. Make some generalisations from the data, then justify your generalisations
by providing explanations of your thinking.
Table: Comparison of the properties of UHMWPE and metal alloys
(Source: Biomaterials: An Introduction, by Parks & Lakes, 2nd edition)
| 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 Wikipedia
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
- biocompatibility with surrounding tissue
- low friction
- durability
- Ultra-high molecular weight polyethylene (UHMWPE) is biocompatible with
surrounding tissue. It possesses a similar density to living tissue, and therefore
tends not to cause problems in the body.
- UHMWPE has a low friction coefficient and this, along with other exhibited
characteristics, such as high hardness, high tensile strength, high elasticity,
add to its suitability of it for use in joints as artificial cartilage.
- UHMWPE is durable: it has no known effective solvent at mild temperatures. High temperatures and pressures must be used to manipulate the material and gain the desired product. UHMWPE also exhibits a very high creep resistance. Creep resistance is the tendency for polymers to deform when under constant stress.
explain why artificial joints have the articulating ends covered in polyethylene
- The articulating ends of a natural joint are covered by a cartilage which
cushions the bones in the joint and provides ease of movement when lubricated
with synovial fluid.
- When constructing artificial joints, it is important to replicate the natural
structure of the joint.
- Polyethylene is used to coat the articulating ends of artificial joints
because:
- it has a similar density to living tissue
- it is relatively elastic (especially high-density polyethylene)
- it has a low coefficient of friction
- it has low creep properties i.e. it will not deform under stress.
- Recently, ultra-high molecular weight polyethylene (UHMWPE) has been developed, which exhibits superior characteristics under stress.
describe the properties of the materials, including ‘superalloy’ that make a ball and stem for the bone components of a large joint including:
- high strength
- low weight
- good compatibility with body tissue
- inertness
- Many newly-developed alloys are designed to have the properties required for successful implantation. Some properties, with examples, are discussed below:
- Many alloys - especially metal alloys - are very strong. Co-Ni-Cr-Mo (cobalt-nickel-chromium-molybdenum) alloy is used for making stems of prostheses for heavily loaded joints like the knee.
- Large loads lead to high friction for Cobalt-Chromium (Co-Cr) alloys, so Co-Cr alloy-polyethylene and stainless steel-polyethylene alloys have been developed to reduce the friction in artificial joints bearing large loads.
- Many metals are not suitable for implantation because they are heavy, and may lead to damage of surrounding living tissue. Titanium-based alloys are very lightweight (lighter than stainless steel and Co-alloys), as are the polymer components of the artificial joint.
- Carbon-based alloys show a high level of biocompatibility. For this reason, carbon or carbon-based alloys are integrated into the development of new materials.
- Corrosion is a major concern, as it may lead to the breakage of load-bearing joints like the artificial hip joint. Metal alloys generally have much lower corrosion factors than stainless steel. Co-Cr alloys are inert in the body, remaining literally unchanged under physiological conditions. Ceramics also exhibit inertness under physiological conditions.
identify that artificial implants can be either cemented or uncemented into place
- There are two main ways to attach an artificial joint to the living tissue:
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.
describe the properties of the cement that is used in implants and discuss how an uncemented implant forms a bond with a bone
- The cement used in a cemented implant serves many purposes. These include
the following:
- It allows the initial fixation of the implant to the bone.
- It acts as a shock absorber for the joint, as it is a viscoelastic polymer.
- It helps to spread the load more evenly over a large area and reduces
the stress concentrated on the bone by the prosthesis.
- In contrast, a cement-free implant is coated with a porous layer, which comes into contact with the bone, placing less pressure on the bone (which sometimes leads to bone reabsorption and therefore loosening). The porous layer of cement-free implants allows the bone to grow into the implant, creating a dynamic interface of bone and implant.
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