VANA 102: STAY APPARATUS

• present in both feet that enables the horse to stand on its feet for long periods with minimum muscular effort. Older ones doze off while standing due to this

  passive stay apparatus
• principal defense of horses (a rather nervous and excitable animal) appears to be in perpetual readiness to run away from danger.

  flight
• preventing it from flexing

  joints stabilization
• reduces the effort of the intrinsic muscle. Stabilizes the joints in a position suitable for the support of the body

  non-tiring tendons and ligaments of stay apparatus
•  fleshy attachment (SYNSARCOSIS) of the forelimb to trunk is not part of the stay-apparatus
• serves as the principal weight-bearing connection and is heavily interlaced with non-tiring tendinous tissue

  serratus ventralis
• The movements of the shoulder joint are restrictedly FLEXION AND EXTENSION in sagittal plane by the SUBSCAPULARIS (medially) and INFRASPINATUS & SUPRASPINATUS (laterally)
• principal stabilizer of the shoulder joint in horses. Pressing against the cranial surface of the joint

  biceps tendon
• The way the tendon caps the intermediate tubercle of the intertubercular groove suggests PARTIAL LOCKING OF THE JOINT.
• prevents further collapsing/flexing of the shoulder joint, which anchors the muscle to the most proximal part of the radius and via the LACERTUS FIBROSUS and EXTENSOR CARPI RADIALIS.

  internal tendon of biceps
• principally stabilizes the elbow joint, that arises on medial and lateral epidondyles of humerus

  Tension from GROUP OF CARPAL AND DIGITAL FLEXORS
• inhibit flexion to a lesser degree in elbow joint

  eccentrically placed collateral ligament
• pulls on the flexor surface of the carpal joint to stabilize it

  FLEXOR CARPI RADIALIS and ULNARIS LATERALIS
• tend to supply the weight of the animal but in opposite direction distally.

  ACCESSORY LIGAMENTS of the SUPF. & DIGITAL FLEXORS
• 3 elements need for the fetlock joint not to overextend:

  • Suspensory apparatus ass. With interosseus
  • Superficial flexor tendon
  • Deep flexor tendo
• suspensory apparatus of the fetlock joint:

  1. interosseous
  2. proximal sesamoid bones
  3. sesamoidean ligaments (SOCS)
• arises from carpus and proximal end of large metacarpal bone and ends on the 2 sesamoid bones. (Before doing so it sends extensor branches around the proximal phalanx to common extensor tendon)

  interosseous
• articulate with distal end large metacarpal bone to reduce friction bwn suspensory apparatus and palmar surface of the fetlock join

  proximal sesamoid bones
• tie sesamoid bones to the canon bone and proximal phalanx

  collateral ligaments
• unites the sesamoid bone and forms a smooth bearing surface for digital flexor tendons

  palmar ligament
• continue the tension in the interosseous of which 3 ends on the proximal and last on middle phalanx

  sesamoidean ligaments
• assists the suspensory apparatus by providing a tendinous support

  SDF Tendon
• provide added and similar support. The accessory ligament, which arises with the interosseous from the caudal aspect of carpus, ends on distal phalanx

  DT Tendon and its accessory ligament
• carries complementary fibrocartilage into which SFT and ligaments reach the bone from above insert

  proximal border of middle phalanx
• flexes when fetlock sinks underweight and can be disregarded in the consideration of the stay apparatus

  coffin joint
• on the palmar surface of the coffin joint that is suspended by proximal and distal ligaments. Provides 3rd bearing surface for DFT which is protected from wear by navicular bursa

  distal (navicular) sesamoid bone
• prevents flexion in stifle and hock joints and overextension in fetlock and phalangeal joints

  passive stay apparatus in hindlimb
• an important part of PSA that links the actions of stifle and hock joints. Accomplished by the TENDINOUS PERONEUS TERTIUS MUSCLE and NEARLY TENDINOUS SDF muscle, both crossing the joint spaces of the two joints

  reciprocal mechanism
• arises from lateral condyle of femur and passing cranial to tibia ends by complex attachments on certain tarsal bones and proximal end of the large matetarsal bone

  peroneus tertius
• lies caudal to tibia and connects the caudal surface of the femur with the calcanean tuber.

  SDF
• arises proximal to fetlock, attaches on proximal sesamoid bones, and is functionally continued by distal sesamoidean ligaments that attach on plantar surface of the proximal two phalanges

  tendinous interosseous
• attach proximal and distl to fetlock and lend further support

  SDFT and DDFT
• is much thinner and may be absent

  accessory ligament of deep flexor
• has no accessory ligament, but this is compensated for in the hindlimb by its firm attachment on calcanean tuber

  SDFT
• horse converts the jointed column of its hindlimb into a weight-bearing pillar.

  patellar locking mechanism
• larger than the lateral and is prolonged proximally to form a rounded tubercle

  medial ridge of trochlea
• attaches directly on patellar apex

  intermediate patellar ligament
• connects to medial border of the patella via the patellar fibrocartilage


  medial patellar ligament