stay apparatus

Question 1

stay apparatus is for

Answer 1

for standing for a long time while minimising fatigue, with minimal muscular activity

Question 2

Horse have 2 mechanisms to reduce fatigue & prolong
ability to monitor for danger (remain alert)

Answer 2

• Nuchal ligament: Enables head to be repeatedly raised without much muscular effort
• Stay apparatus (so-called passive stay apparatus): Permits standing for a long time while minimising
  fatigue, with minimal muscular activity: involves muscle, ligaments & tendons

Question 3

3 parts of the stay apparatus

Answer 3

• Stay apparatus of the forelimb (proximal to the carpus)
• Stay apparatus of hind limb (proximal to the tarsus)
• Suspensory apparatus (distal to the carpus/tarsus, identical fore & hind)

Question 4

basic principle of stay apparatus

Answer 4

Basic principle is that if the horse relaxes most of its muscles, the legs will remain in a standing position.

Question 5

sleep in horses; 2 types

Answer 5

slow wave sleep (SWS) &
paradoxical sleep (PS - includes REM sleep)

Question 6

describe muscle tone in slow wave sleep and paradoxical sleep

Answer 6

Some muscle tone in SWS but none in PS

Question 7

what position is horse in slow wave sleep

Answer 7

can stand, usually sternal recumbancy

Question 8

what position is horse in paradoxical sleep

Answer 8

lateral recumbency

Question 9

how long does paradoxical sleep last

Answer 9

only a few minutes at a time

Question 10

total daily sleep required

Answer 10

3 or 4hr but large individual variation

Question 11

the stay apparatus in part is a ____ support mechanism

Answer 11

fibrous support mechanism (FSM)

Question 12

describe the fibrous support mechainsm of the stay apparatus

Answer 12

The fibrous support mechanism includes those connective tissue structures found in the thoracic & pelvic limbs of the horse that mechanically FIX the respective joint of the limbs in order to support the weight of the animal in a relatively relaxed, standing position. The same structures are necessary for normal locomotor function.

Question 13

stay apparatus of forelimb

Answer 13

If the muscles of the forelimb relax,
ligaments & tendons should hold the leg
in normal resting position:
* Neutral shoulder & elbow
* Extended carpus
* Over-extended fetlock
* Extended pastern & coffin joints

Question 14

___% of BW is on thoracic limbs

Answer 14

60

Question 15

If left unsupported by opposing
ligaments & tendons, what
would happen to the jointed
bony column of the thoracic
limb?

Answer 15

• Flexion (elbow joint)
• marked flexion of shoulder joint
• Overextension (dorsiflexion) of
  the carpus
  -Marked overextension of the fetlock
• result; joints would collapse under weight of animal

Question 16

shoulder stability

Answer 16

• Weight of body tries to flex (collapse) the shoulder
• Prevented by internal (short) tendon of biceps whose RADIAL insertion effectively
  acts as a fixed point.
• ALSO via lacertus fibrosus (long tendon of biceps brachii) & the extensor carpi radialis

Question 17

Elbow stability

Answer 17

Body weight (& tension on biceps tendon) tries to flex elbow.
Flexion prevented by:
* Tension of triceps (medial head)
* Collateral ligaments
* Origins of digital flexor muscles (medial humerus)

Question 18

Carpus stability

Answer 18

• Body weight could either flex or hyperextend carpus
• Flexion prevented by tension on ECR from biceps tendon via lacertus fibrosus
• Overextension prevented by superior check lig. (Accessory lig. SDFT) (NOT IN HINDLIMBS)

Question 19

Fetlock, pastern, coffin joint
stability

Answer 19

• Suspensory Apparatus: Suspensory ligament, Proximal sesamoid bones (PSB), Ligament from PSB to cannon bone, and phalanxes
• Accessory ligament (check) DDFT
• Flexor tendons (DDFT, SDFT)

Question 20

Suspensory Apparatus:

Answer 20

• Suspensory ligament
• Proximal sesamoid bones (PSB)
• Ligament from PSB to cannon bone, and phalanxes

Question 21

Hindlimb passive stay apparatus Prevents leg from collapsing by preventing:

Answer 21

• flexion of stifle & hock
• overextension of fetlock & phalangeal joints

Question 22

important part of hindlimb passive stay apparatus is ____ mechanism

Answer 22

reciprocal: links stifle and hock

Question 23

hindlimb reciprocal mechanism links ____ and ____

Answer 23

stifle and hock

Question 24

locking of their patellas

Answer 24

(stabilising the limb with minimal muscular
effort). However, some muscular effort is needed, which is why horses tire
& alternate their resting hindlimbs

Question 25

check ligaments on hind limb

Answer 25

NO superior check ligament, SMALL inferior check ligament

Question 26

Normal locking of the patella; 3 steps

Answer 26

1) Stifle extended & patella lifted by quadriceps 2) Patella rotated medially approx 15 degrees by vastus medialis so parapatellar cartilage & medial patellar ligament sit over medial trochlear ridge 3) Quadriceps relax (?) to lower fibrocartilage onto medial trochlear ridge where it is hooked/locked in place

Question 27

3 steps of unlocking patella

Answer 27

1) Lift patella (extend stifle) 2) Rotate patella laterally with gluteofemoris & tensor fascia late 3) Relax quadriceps

Question 28

when unlocking patella; can get stuck, whats this called and why does it occur

Answer 28

“INTERMITTENT/PERMANENT UPPER FIXATION OF THE PATELLA”) - young horses/off work - poor conformation - neuromuscular problem?? ***Surgery (desmotomy-transection medial patellar lig.) only on severe permanent cases

Question 29

reciprocal apparatus comprised of 2 cords:

Answer 29

peroneus tertius & superficial digital flexor

Question 30

reciprocal apparatus flexes

Answer 30

stifle and hock together

Question 31

reciprocal apparatus is mostly

Answer 31

tendinous

Question 32

reciprocal apparatus

Answer 32

Aids in both (movement & stay apparatus) functions

Question 33

reciprocal apparatus when stifle is locked

Answer 33

When stifle is locked, the weight on the limb pressures the hock joint to flex. However, tension in the superficial digital flexor resists this pressure, and the hock does not flex

Question 34

Horse’s musculoskeletal system evolved to ____ metabolic cost of locomotion

Answer 34

reduce

Question 35

at high speed; increase stride length ____ energetic cost of limb protraction (bringing limb forward)

Answer 35

decreases

Question 36

how did horse evolve to reduce metabolic cost

Answer 36

* Bulk of muscles proximally in the limb, more distal aspect tendons provide energy for locomotion * Distal part limb elongated & number bones reduced to single digit * Cannon bone longer & lighter * Musculotendinous units in the forelimb: support body mass, generate forces used for propulsion, breaking & turning, stabilise joints during stance phase of the stride & flex joints during the swing phase

Question 37

For high speeds achieved at the gallop rapid protraction of the forelimbs is required, how is this achieved

Answer 37

special catapult action of biceps muscle

Question 38

describe catapult action in forelimb

Answer 38

* In horses, instead of hight output contraction of muscles, rapid protraction is achieved by the special catapult action of biceps muscle * In a catapult system energy is stored slowly with a large force & then released quickly to accelerate a small mass * During stance, the elastic biceps muscle is stretched, while carpus is locked in extension * Before limb lifts off, the carpus buckles forward, this releases the catapult, bringing the leg forward for the next stride * The power output of this catapult action of the biceps muscle is about 100 times its mass of a non-elastic muscle

Question 39

SDF and DDF have ____ muscle bellies and ___ tendons which is energy efficient

Answer 39

small long

Question 40

describe spring and coil mechanism of flecor tendonds

Answer 40

* During stance phase, flexor tendons are loaded under tension (this stress may be as high as twice of the bodyweight at the gallop) * During the first half of stance phase, flexor tendons store great amount of elastic energy, which is released in second half of stance phase --> propulsion * The muscles bellies of these tendons damp this spring-like action

Question 41

spring and coil mechanism: in thoroughbred horses the SDFT elongates by ___% its original length as response to sustained strength

Answer 41

12-16%