A13 - The art. metacarpophalangea and the suspensory apparatus of the horse

Question 1

What is another name for the art. metacarpophalangea?

Answer 1

Fetlock joint

Question 2

Classification of the fetlock joint

Answer 2

• Diarthrosis
• Hinge joint (monoaxial)
  
  • ​Movement: flexion - extension (and minimal side movement)

Question 3

Between where does the fetlock joint articulate?

Answer 3

• Joints between metacarpal bones → proximal phalanges and proximal sesamoid bones

Question 4

1. Give the structures of the fetlock joint in the horse
2. Draw the fetlock joint in the horse

Answer 4

• Capsula articulares
  
  • Recessus dorsalis
  • Recessus palmaris
• Lig. collaterale mediale
• Lig. collaterale laterale
• Proximal sesamoid ligaments
  
  • M. interosseus medius
    
    • Metacarpal bones, basis → proximal sesamoid bones
    • Givingtractus appositus toward m. extensor digitorum communis (part of the passive stay apparatus)
  • Ligg. metacarpointersesamoideum
    
    • ​Lig. palmare → MCIII
• Middle sesamoid ligaments
  
  • Ligg. palmaria
    
    • ​Unites with the two sesamoid bones
    • Forms the scutum proximale
  • Ligg. sesamoidea collateralia
    
    • ​Proximal sesamoid bones → metacarpus, and Ph1
• ​Distal sesamoid ligaments
  
  • M. interosseus
  • Lig. sesamoideum rectum (eq)
    
    • ​Proximal sesamoid bones → Ph1 and Ph2
    • Also called Y-ligament
  • Ligg. sesamoidea obliqua (eq)
    
    • ​Proximal sesamoid bones → Ph1
    • Also called V-ligament
  • Ligg. sesamoidea cruciata
    
    • ​Crossing fibers from the distal border of sesamoid bone → Ph1
    • Also called X-ligament
  • Ligg. sesamoidea brevis (Un, ø ca)
    
    • ​Distal border of sesamoid bone → Ph1
• Arrangement of the sesamoid ligaments function as a suspensory or stay apparatus for the fetlock joint

Question 5

List the structures in the fetlock joint

Answer 5

• Capsulae articulares
  
  • Recessus dorsales
  • Recessus palmares
• Ligg. collateralia (mediale/laterale)
• Ligg. palmaria (Tissue containing transverse fibers attached to the sesamoid bones, but extending beyond them in un, especially proximally, serving as bearing surface for the flexor tendons)
  
  • Scutum proximale
• Ligg. sesamoidea collateralia (sesamoid bone → Mc & Ph1)
• Lig. metacarpointersesamoideum (eq)
• Lig. intersesamoideum interdigitale (bo)
• Lig. sesamoideum rectum (eq)
• Ligg. sesamoidea obliqua (eq)
• Ligg. sesamoidea brevia (Un, ø ca) (sesamoid bone → Ph1)
• Ligg. sesamoidea cruciata (Crossing from sesamoid bone → Ph1)
• Lig. phalangosesamoideum interdigitale (bo)
• Lig. metacarpeum transversum profundum (ca, su) (Connects lig. annulare of the flexor tendons of adjacent digits)
• Lig. interdigitale proximale (bo, su)

Se definisjoner i egene notater

Question 6

Manica flexoria

Answer 6

Proximal to the fetlock joint, the superficial flexor tendon forms within the synovial sheath a ring-like sleeve around the deep flexor tendon

Question 7

Suspensory apparatus of the horse

Forelimb

Answer 7

Passive stay apparatus:

• The passive stay apparatus is a group of ligaments, tendons and muscles which “lock” major joints in the limbs of the horse. It is best known as the mechanism by which horses can enter a light sleep while still standing up
• Components:
  
  • Lacertus fibrosus
  • M. interosseous medius + tractus appositus
  • M. flexor digitorum superficialis et profundus with lig. accessorium (proximal, distal check ligaments)
  • Suspensory apparatus (fetlock)
• Shoulder/elbow:
  
  • M. serratus ventralis must be prevented from flexing the shoulder, and m. biceps brachii has to be prevented from flexing the elbow joint, this is achieved by:
    
    • SDF and DDF are tensed by dorsoflexion of the fetlock joint in normal standing position
    • Results in increased passive tension in their elastic components, which maintains elbow tension
  • Contraction of m. triceps brachii is the second mechanism
• Carpus:
  
  • ​Lactersu fibrosus:
    
    • ​Prevents the carpus from buckling forwards
    • Arising from tendon of m. biceps brachii → cannon bone
  • Tension in m. biceps brachii is transmitted and assists the fixed extension of the carpus
  • Overextension of carpus is prevented by:
    
    • Ligaments on palmar aspect of the carpus
    • Ligaments of the accessory bone
    • Check ligaments (accessory ligaments of SDF and DDF)
• Fetlock:
  
  • ​Suspensory ligament on the palmar aspect of Mc3 is the main support for the fetlock joint, preventing excessive overextension
• Pastern and coffin joints:
  
  • ​Branches of suspensory ligament:
    
    • ​Extend distally on the medial and lateral side of the digits → inserts on processus extensorius of Ph3
    • Prevents the pastern and coffin joints from buckling forward
  • SDF and DDF provides extra support
• Tendon of m. biceps brachii of lacertus fibrosus prevents the shoulder joint from locking
• To pervent the sholuder joint from collapsing they are supported by strong collateral ligaments:​
  
  • M. infraspinatus
  • M. supraspinatus
• The elbow joint will remain in equilibrium ad long as the vertical line of impact and the foot maintain its position
• The elbow joint must be prevented from building foreward, which is provided by:
  
  • M. trceps brachii (by isometric contraction)
  • M. flexor digitorum longus

Question 8

Suspensory apparatus of the horse

Hindlimb

Answer 8

Passive stay apparatus:

• The passive stay apparatus is a group of ligaments, tendons and muscles which “lock” major joints in the limbs of the horse. It is best known as the mechanism by which horses can enter a light sleep while still standing up
• Elements:
  
  • Patellar loop
  • Lig. accessorium toward the m. flexor digitorum profundus
  • Galea calcanea (formed by the tendon of m. flexor digitorum superficialis)
  • M. peroneus tertius
  • Interosseus medius + tractus appositus
  • Suspensory apparatus (fetlock joint)

Patellar lock:

• Allows the horse to immobilize the stifle joint
• The horse can rest the weight from the caudal part of the body on the immobilized limb
• During normal locomotion, the patella moves in the trochlear groove
• There are 3 patellar ligaments, and a medial patellar cartilage

1. The medial patellar ligaments attaches to the cartilage
2. To lock the stifle, the joint extends past a certain point, and then twist medially to hook the parapatellar cartilage over the trochlea tubercle
3. The medial and middle patellar ligaments are stabilized over the medial ridge
   
   1. 1. M. vastus medialis actively keeps the medial loop formed by the middle and medial patellar ligament, and the patellar and parapatellar cartilage in position
4. This locks the patella in place, preventing flexion of the stifle without any muscular effort (the patella is locked in a extended position)
5. To release the stifle and allow movement, the horse shifts its weight to the other leg, then contracts m. quadriceps femoris to move the patella proximally, allowing it to then move laterally, and then proximally to move it back into the trochlear groove

Reciprocal mechanism:

• Ensures that when the stifle is extended, the hock is also in extension, due to the muscle attachment
• When femur moves caudally, the distal limb moves caudally, and vice versa
• Composed of:
  
  • M. peroneus tertius (cranially and caudally)
  • SDF-tendon
  • M. gastrocnemius
• This adaptation also ensures that when the patella is locked, the hock is also immobilized
• These functions occurs without additional muscular effort or fatigue