A30 - Statics of the forelimbs in horses, the phases of the step on the distal end of the forelimb

Question 1

Statics of the forelimb

General

Answer 1

• Major role: support the weight of the body
  
  • Reduction in the skeletal structure of the shoulder girdle, where only the scapula, and in some species a much reduced clavicle
  • Eq: Carry 55% of the body weight
• FL has less musculature than HL
• Elastic, springlike apparatus
  
  • Scapula is attached to the trunk at the cranial end of the bow and string construction
• Restricted movement in large animals due to:
  
  • Fascia
  • Ligaments
• Shock-absorber system
  
  • Proximal:
    
    • Buffer the power from the weight → ground
    • M. biceps brachii: tendon of origin, tendon of insertion
    • M. triceps brachii, caput longum
    • Lecertus fibrousus
    • M. extensor carpi radialis
    • M. flexor carpi ulnaris
  • Distal:
    
    • Elastic support
    • Sesamoid ligaments
    • Deep flexor tendon
    • Superficial flexor tendon
    • Tractus appositus (goes to cranial), holds against collaps
• Three jointed column
• In normal position the point of impact of load on the scapula lies at the middle of the insertion area of the m. serratus ventralis
• The bearing area of the foot (paw, hoof) lies vertically below this impact point

Question 2

Statics of the forelimb

Stay apparatus

Answer 2

• ​Horse
• FL and HL
• Tendinous-ligamentous support mechanism
• Allows the body to carry its body weight with a minimum of muscular effort and reduces muscular fatigue
• Tendon of m. biceps brachii of lacertus fibrosus prevents the shoulder joint from locking
  
  • Weight of body = flexion of shoulder
    
    • Isometric contraction starts to increase to prevent flexing of sholuder in:
      
      • M. supraspinatus
      • M. biceps brachii
    • SDF and DDF:
      
      • ​Tensed by dorsoflexion of fetlock joint
      • ​Passive tension will maintain the elbow extension through caput humeri
    • Isometric contraction of m. triceps brachii
• Vertical line between radius and cannon bone leads to less effort for carpus
• 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
• Lacertus fibrosus:
  
  • ​Keeps the carpus from collapsing forward​
  • Arises from m. biceps brachii
  • Inserts on cannon bone
• The carpal joint protected against overextension by:
  
  • Ligaments of the caudal aspect of the carpus
  • Ligaments of the accessory bone
  • Check ligament of:
    
    • M. flexor digitorum superficialis
    • M. flexor digitorum profundus
• Suspensory ligaments of the palmar and plantar aspect of the metacarpus/tarsus:
  
  • ​Main support of the fetlock
  • Prevents overextension​​
• SDF and DDF:
  
  • ​Suplements the suspensory ligament
  • Accessory ligament: distal end of radius → SDF tendon (proximal check ligament)
  • Accessory ligament: carpus → DDF tendon (distal check ligament)

Question 3

Statics of the forelimb

Statics

Answer 3

1. Shoulder girdle muscles lifts the limb of the groud
2. Flexion of all joints
3. M. brachiocepalicus draws the flexed limb cranially
   
   • The action is complemented by:
     
     • M. omotransversarius
     • M. trapezius
   • They rotate the distal end of scapula craniodorsally, and the caudal angle caudovenrrally → swing phase of locomotion
4. All jounts gets extended, through the action of:
   
   • M. triceps brachii
   • Radial extensor muscles of the carpus
   • Digital extensor muscles
5. Limb hits the ground in front, weight is transformed
6. Draws scapula in opposite direction by:
   
   • M. rhomboideus
   • M. pectoralis profundus
7. Limb gets ready to be lifted again
   
   • SDF tendon & suspensory ligament: relaxed
   • Coffin joint: extended maximally
   • DDF tendon & check ligament: tensed
8. Phalangeal joints flex immediatly when the foot is lifted off the ground

Question 4

Statics of the hindlimb

General

Answer 4

• Bear less bodyweigth and are more angled than FL
• Fixation of the other joints of the HL is mainly done without any muscular effort – almost exclusively by tendons and ligaments
• Proximal HL: thight suspension between sacrum and inner surface of ala iliaca (sacroiliac joint)
  
  • ​Ensures an effective transmission of the thrust of the HL onto the trunk
• Better developed musculature in the HL

Question 5

Statics of the hindlimb

Patellar lock

Answer 5

• Locking of patella → mobilization of stifle → mobilization of hock
• In normal flexion and extension of the stifle joint, the patella glides in the trochlear groove
  
  • ​Extension beyond the proximal extremity of the groove, together with a medial twist of the patella → medial ridge of the femur protruding between the medial and middle patellar ligament
  • The parapatellar cartilage becomes hooked over the tubercle of the trochlea → locking the stifle in an extended position
• M. vastus medialis actively keeps the medial loop formed by the middle and medial patellar ligament, and the patellar and parapatellar cartilage in position
• Release: the weight is shiflte to the other limb and the m. quadriceps femoris draws the patella proximally
• By a lateral twist, the patella returns to the trochlear groove

Question 6

Statics of the hindlimb

Reciprocal apparatus

Answer 6

• Stifle and hock is linked
• M. peroneus tertius: cranially
• M. gastrocnemius: caudally
• SDF: caudally
• Flexion of stifle = flexion of hock
• Extension of stifle = extension of hock

Question 7

Statics of the hindlimb

Statics

Answer 7

1. Joints are flexed
2. Limb moves forward as the following muscles contracts:
   
   • Tensor muscles of the fascia lata
   • M. gluteus superficialis
   • M. sartorius
   • M. iliopsoas
3. The abductionary effect of m. iliopsoas is counteracted by the following muscles (situated on the medial side of the tight):
   
   • M sartorius
   • M. pectineus
   • M. gracilis
4. At the end of the swing phase, joints are extended again
   
   • M. quadriceps stabilises the stifle
5. During the stance phase, the body is propelled foreward through the contraction of the extensors of the:
   
   1. Hip (m. gluteus medius)
   2. Stifle (m. quadriceps femoris)
   3. Hock (m. gastrocnemius)
   • ​Assisted by the hamstring muscles, which hold the stifle caudally relative to the forward moving body

Question 8

Gait, walk, stride

Name the different gaits

Answer 8

• Movement without change in location:
  
  • Sitting
  • Lying down
• Movement with change in location:
  
  • Walk
  • Trot
  • Gallop
  • Canter (collected gallop)
  • Backwards
  • Pass

Question 9

Gait, walk, stride

Walk

Answer 9

• 1 supporting and 1 swinging limb = 2 feets always in contact with the ground, there is no suspension period
• 4 beat gait
• RH - LF → LH - LF
• Head and neck are lowered at each swing phase of the FL and lifted during each support pahse
• Types of walk:
  
  • Quick walk
  • Normal walk
  • Shortened walk

Question 10

Gait, walk, stride

Trot

Answer 10

• Diagonal
• 2 beat
• Opposite FL and HL hits the ground together
• RH + LH / RF + LH / RH + LF
• Types of trot:
  
  • Slow/short trot
  • Brisk/medium trot
  • Quick/running trot

Question 11

Gait, walk, stride

Galoop

Answer 11

• 4 beat
• LF or RF leading
• Steps:
  
  1. RF (suspension)
  2. LH
  3. RH
  4. LF
• The vertebral column is held ridgid, the trunk is less actively involved
• Paried coordination between the HL and FL
• The direction of movement is determined by the diagonal from the driving HL to the FL along which the trunk is being propelled:
  
  • Left gallop
  • Right gallop (RF leads)

Question 12

Gait, walk, stride

Canter

Answer 12

• 3 beat
• 2 paired
• Collected gallop
• Non leading diagonal limbs land together
• Steps:
  
  • RF (suspension)
  • LH
  • RF + LF

Question 13

Gait, walk, stride

Backwards

Answer 13

• 2 beat
• RF move more together, as do RH + LH

Question 14

Gait, walk, stride

Pass

Answer 14

• RH + RF / LH + LF