Biological Materials

Question 1

What three things do bones contain?

Answer 1

1. Water (25-30%)
2. Collagen (30% of dry weight)
3. Minerals (70% of dry weight)

Question 2

Bone is capable of withstanding what?

Answer 2

Loads six times those experienced in normal life

Question 3

A specialised form of connective tissue, bone consists of many cells (osteocytes), which have what three properties?

Answer 3

Light

In a collagen matrix

Packed with minerals

Question 4

Biomechanically what are the two types of bones?

Answer 4

Cortical
(Thick layer outside the bone)

Trabecular
(Layered maze like mass within the bone)

Question 5

The two main forms of bone damage comes in what forms?

Answer 5

1. Fractures, which can be either traumatic (usually a one-off impact)
2. Fatigue-induced (these are often called stress fractures although this term is slightly misleading).

Question 6

A diaphyseal impaction fracture is caused by what load?

Answer 6

Axial compression

Question 7

A transverse fracture is caused by what load?

Answer 7

Bending

Cortical bone weaker in tension than compression, so bone under tension fails first.

Failure mechanism is break propagation perpendicular to bone’s long axis, from surface layer inwards

Question 8

A spiral fracture is caused by what load?

Answer 8

Torsion

Question 9

A oblique transverse is caused by what load?

Answer 9

Axial compression

Bending

Torsion

Question 10

Cells are widely separated within a fibrous, organic matrix which may:

Answer 10

Appear (but isn’t) structureless as in rigid hyaline cartilage, Contain more connective tissue fibres in the matrix (e.g. fibrocartilage)

Question 11

Cells (chondrocytes) account for less than what percentage of the tissue volume?

Answer 11

10%

Question 12

The organic matrix of cartilage consists of what?

Answer 12

Collagen fibrils within a proteoglycans solution

Question 13

What is a tissue made up of?

Answer 13

60-87% is made up of

Water
Inorganic salts
Small quantities of matrix proteins / glycoproteins / lipids

Question 14

What does a cartilage mechanical properties depend on?

Answer 14

The direction of loading (anisotropic)

Question 15

Cartilage shows what three typical viscoelastic behaviours?

Answer 15

1. Initial deformation followed by more gradual increase
2. Returns to initial shape on load removal (hysteresis)
3. Prolonged standing causes creep of intervertebral discs (hence shortening of the body’s overall height)

Question 16

Articular cartilage (Fact Card)

Answer 16

Capable of deformation; decreases stress on joints by increasing load-bearing area.

Avascular with few nerve endings, injured cartilage shows little external symptoms and repairs poorly.

Overuse injuries cause cartilage to wear away, leading to osteoarthritis.

High impact loads lead to swelling; if severe enough may fracture.

Question 17

What are Aponeuroses tendons?

Answer 17

Sheet-like tendons that attach muscles to bones and transmit tensile loads so that movement can occur.

Question 18

What are tendons?

Answer 18

Tough cords of closely packed collagen fibres that attach muscles to bones

Question 19

What are ligaments?

Answer 19

Like tendons but contain some elastic fibre (elastin).

Ligamentous joint capsules connect bone to bone, guide joint motion, enhance mechanical stability and prevent excessive motion

Question 20

What is Intermuscular septa?

Answer 20

Separates muscle groups passing from the deep fascia to the bone.

Question 21

What is the ultimate failure train of tendons? (%)

Answer 21

8-10%

Question 22

What hysteresis % do tendons have?

Answer 22

Limited viscoelastic behaviour with only 2.5% to 20%

Question 23

What is considered the main site for high energy return during elastic recoil in the muscle-tendon unit?

Answer 23

Tendons due to there Limited viscoelastic behaviour (For example the achilles tendon for jumping athletes)

Question 24

Ligaments (Fact Card)

Answer 24

Ligaments are designed to cope best with tensile forces.

Ligaments have mechanoreceptors which may initiate tension in nearby muscles in order to assist in maintaining joint stability. This can be important, for example, during rapid knee extension

Question 25

Ligament injuries (Fact Card)

Answer 25

Sprains caused by excessive joint motion, most not severe.

Direct blows can cause stretching and permanent deformation.

Failure often due to bending and torsional loads applied to distal limb, as in a tackle, and depends on load rate

Question 26

What are the four effects of a ligament tear?

Answer 26

1. Loss of stability
2. Joint misalignment
3. Abnormal contact
   pressure
4. Loss of proprioception

Question 27

Muscles (Fact Card)

Answer 27

Most commonly injured form of connective tissue because of its low stiffness.

However, the quickest to recover because of its large blood supply.

Muscle stiffness is related to the force produced in relation to its length.

Maximal stiffness is encountered during eccentric contraction, up to 200 times that in concentric and is probably under reflex control.

Question 28

How far can muscles stretch of resting length before rupture?

Answer 28

160%