The Biomechanics of Lameness

Question 0

What does stress take into account?

Answer 0

Force and cross-sectional area

Question 1

How is a safety factor calculated?

Answer 1

Maximum stress a structure withstands until breakage/stress most likely to undergo during life time

Question 2

What are the factors of failure?

Answer 2

Magnitude, frequency, speed of loading and duration of loading

Question 3

What are the influences on the factors of failure?

Answer 3

Body mass (higher body mass higher force)
Speed (higher force)
Gait (length of time leg is on the ground not the number of limbs)

Question 4

What forces do bones experience?

Answer 4

Tension, compression and bending

Question 5

What forces are tendons exposed to?

Answer 5

Tension

Question 6

What forces are joints exposed to?

Answer 6

Compression and shear forces

Question 7

Why is failure of a structure in a live animal more complex than a man made structure?

Answer 7

Due to internal repair mechanisms and compensatory mechanisms

Question 8

How has the horse adapted to be more efficient at locomotion?

Answer 8

Reduced muscle mass, reduces swing time, move at a greater speed with less force as foot spends more time in contact with ground
Leg is straight so decreased joint forces/moments

Question 9

What strains do the tendons in the horses leg experience?

Answer 9

SDFT and SL are both high strain tendons and experience a similar force but the SDFT experiences highest stress
DDFT and DAL are both low strain tendons

Question 10

What is strain?

Answer 10

% length change

Question 11

What are the characteristics of muscles involved with flexor tendons?

Answer 11

Highly pennate

Stretch about 1cm under pressure so have a limited capacity for length change

Question 12

How much energy is released as heat in tendons and what are the consequences of this?

Answer 12

7% of energy is released as heat
Results in temperatures of up to 45C at gallop with has been proved as non-lethal to tendon cells but could cause a predilection to core tendon injuries

Question 13

What bone characteristics make locomotion more efficient?

Answer 13

Reduced by fusion of the radius and ulna
Lengthening of the limb to reduce mass but maintain stride length
One large bone has higher bending strength

Question 14

What is the function of joints?

Answer 14

For movement and shock absorption

Question 15

How has the fact that a horses leg only moves in the sagittal plane helped with efficiency?

Answer 15

The interlocking configuration only requires collateral ligaments and no muscles decreasing weight and metabolic cost

Question 16

What are the functions of different parts of the hoof?

Answer 16

Horn capsule = protection (limits expansion)
Distal phalanx, frog and lamellae = shock absorption
Hoof wall and sole = grip and support

Question 17

What are the protective mechanisms of the hoof?

Answer 17

Shape of the solar surface allowing heel movement, suspension of the distal phalanx transfers forces to distal border of hoof wall, digital cushion provides shock absorption, hoof sliding reduces impact and ground reaction force, rotation and translation of DIP joint

Question 18

What are the different phases of locomotion?

Answer 18

Stance phase (impact, loading and propulsion)
Swing phase

Question 19

What is the duty factor?

Answer 19

Ratio of stance and stride time

Question 20

How does speed affect forces in the limb?

Answer 20

Speed decreases stance time so force is generated in less time increasing energetic cost and peak limb fore is also increased which in turn increases the risk of injury

Question 21

What occurs in first impact? What injuries are most likely during first impact?

Answer 21

Large accelerations and low forces so bruising to soft tissues and vibrations in bones

Question 22

What occurs in second impact?

Answer 22

Low accelerations and high forces which is important for natural breaking action

Question 23

What occurs in loading?

Answer 23

Large vertical force with excessive dorsiflexion of the fetlock causing tendon stress with force acting parallel to long bones with very tight safety margins

Question 24

What stress occurs in the propulsion phase?

Answer 24

Tensile stress

Question 25

How does high speed exercise influence strain?

Answer 25

Increases tendon strain but reduces fatigue life and is a potent stimulus for changes in structural properties

Question 26

What is the PZM?

Answer 26

Point of zero moment

Force point of the foot where it hits the ground and is in the middle of the foot

Question 27

What influences the PZM?

Answer 27

Toe length or foot angle

Question 28

What happens if the PZM is in the wrong place?

Answer 28

Uneven loading or loading of structures with a low safety factor increasing the chance of injury

Question 29

What do heel wedges do the PZM? What is the purpose of heel wedges? What are the disadvantages of heel wedges?

Answer 29

Move the PZM towards the heels unloading the DDFT and NB giving longer support through stance
Increases DIP joint pressure and shifts articular contact dorsally