week 3

Question 1

young modulus

Answer 1

relationship bw stress and strain
represents elasticity

Question 2

bone is strongest during

Answer 2

compression

Question 3

Tension

Answer 3

If sufficient in magnitude & duration, may cause tendinosis or
inflammation of bone-tendon attachment

Question 4

avulsion fracture’

Answer 4

• Portion of the bone torn away with ligament/tendon)

Question 5

Bending

Answer 5

Walking & running creates large
bending force on femoral neck
several times greater than body
weight!
Tensile force on superior aspect,
compressive force on inferior aspect
Contraction of muscles gluteus
medius alters the stress distribution

Question 6

Torsion

Answer 6

• Bone fails first in shear –
  initial crack parallel to neutral
  axis of bone
• Second crack forms along
  plane of maximal tensile
  stress

Question 7

Anisotrophy

Answer 7

describes tissues that respond differently depending on the direction of applied load.

Question 8

Viscoelasticity

Answer 8

describes tissues that respond differently depending on the rate and duration of loading.

Question 9

articular cartilage- 1. The superficial zone

Answer 9

the superficial zone is thin (10-20% volume) with the collagen fibres aligned parallel and close together on the surface. This zone is important for protecting the deeper layers and is responsible for resistance of tensile and shear loads.

Question 10

articular cartilage- 2. The middle zone

Answer 10

The middle zone (40-60% volume) contains less chondrocytes, more PGs and thicker collagen fibrils, organized tangentially to the surface. The middle zone is the first line of defense against compressive loads.

Question 11

articular cartilage- 3. The deep zone

Answer 11

The greatest resistance to compressive load is from the deep zone (30% volume) due to the arrangement of collagen fibrils perpendicular to the articular surface. The deep zone also has the largest diameter collagen, highest PG concentration and lowest water content.

Question 12

Articular cartilage has high or low ability to repair?

Answer 12

limited capacity for repair & regeneration

Question 13

Permeability

Answer 13

• Measure of the ease with which fluid can flow through a porous
  material
  Inversely proportional to the frictional drag exerted by fluid flowing
  through porous material
• Permeability low in articular cartilage
• Affected by magnitude of load

Question 14

Fluid film lubrication

Answer 14

utilises a thin, viscous fluid-film that provides separation of the joint surfaces under less severe conditions when loads are low, oscillatory, and when the contacting surfaces are moving quickly

Question 15

Boundary lubrication

Answer 15

utilises a specific glycoprotein, “lubricin” which forms a gel that prevents direct, surface-to-surface contact. Boundary lubrication is more important under severe loading conditions – high loads, long duration (and relatively low speeds)

Question 16

In the absence of lubrication

Answer 16

articular surfaces come into direct contact causing adhesions or abrasions.

Question 17

Foot angle

Answer 17

Degree of in-turning or out-turning of the foot

Question 18

Step width

Answer 18

he small distance between heels when barefoot (8-10 cm)

Question 19

Cadence

Answer 19

The number of steps (foot falls) per minute

Question 20

Gait kinetics

Answer 20

Kinetics describes the forces that cause joint and limb motion during gait

Question 21

INTERNAL FORCES during gait

Answer 21

Ligaments/Other soft tissue forces
Muscle forces

Question 22

EXTERNAL FORCES during gait

Answer 22

gravity
inertia
ground reaction force

Question 23

Inertia

Answer 23

Inertial forces due to acceleration of body segment

Question 24

ground retraction force

Answer 24

forces acting bw the foot and the ground

Question 25

woffs law

Answer 25

bone responds to demands placed on it