Lecture 8 -- Equine Forelimb Anatomy Flashcards

What type of gait does the equine forelimb exhibit?

Unguligrade

To which group of animals with odd toes does the equine belong?

Perissodactyla

On what part of bone does the equine weight bear?

Distal phalanx of 3rd digits

What does chestnut refer to in horses?

1st vestigial metacarpal bone

Where is the ergot located on the equine forelimb? What is that?

Palmar aspect of the MCP joint

→ Remnant of metacarpal pad

→ Hidden by hair/ feathers

What is the difference between horses and small animals in terms of the tendon of origin of the biceps brachii?

In horses, there are two tendon of origin for biceps brachii → They have two inter-tubercular grooves

Where does the biceps brachii insert in horses?

Only proximal radius

What is the fibrous extension of the biceps, which involves in part of the stay apparatus?

Lacerates fibrosis

• Fibrous extension of the biceps brachii that connects to the extensor carpi radialis → Insert proximal metacarpal 3

What structure does the lacertus fibrosis join?

Extensor carpi radialis

What is the function of laceratus fibrosis?

Maaintain shoulder and carpus in extension

Part of the stay apparatus

Where does the lacerates fibrosis insert to?

Proximal MP3

Do horses have annular ligament between radius and ulna?

No

• Because the radius and ulna are fused

• BUT they do have collateral ligament

What movement is not possible in the elbow joint of the forelimb?

Rotation

How many heads does the deltoid muscle have in the equine forelimb?

One

• Absence of acromion

• Deltoid only originates from the spine of scapula

How many heads does the triceps muscle have in the equine forelimb?

Three (Accessory head of triceps, which located right under the lateral head of triceps, is absent)

Apart from bicitpial bursa, what are the other bursas in horses?

Tricpital bursa - Between tendon and olecranon

Subcutaneous bursa - Between skin and tendon of insertion of triceps

Which carpal bone is vestigial or absent in horses?

• 1st carpal bone

• Radial and intermediate does not fuse

Which carpal bone is the largest in horses?

3rd carpal bone

Why antebrachio-carpal joint can be also named as radoiocarpal joint?

The ulnar does not extend right up to the distal end of carpus → Only radius is present and articulates with the carpal bones = Radiocarpal joint

What is the difference between the carpus joint in dogs and horses?

Dogs: Carpal bone are pack tightly together with little synovial fluid between them

Horses: Separate compartments between bones

What tendons pass through the carpal canal in the horse?

DDFT & SDFT

What is the clinical name for fluid accumulation in the tendon sheath?

Thoroughpin

What is the common name for the 3rd metacarpal bone?

Cannon bone

What is the function of metacarpal 3 of horses?

Weight bearing

Are the 2nd and 4th metacarpal bones weight bearing? What are the other name for these two bones?

No

• 2nd and 4th metacarpal bones are vestigial - They are non-weight bearing

• Splint bone

What type of joint between metacarpals?

Fibrous joints

• Limited movement

• Mineralise as age

What is another name for the proximal phalanx (P1)?

Long pastern bone

What is the characteristic of horses’ proximal phalanx? What is its function?

Raised “V” on palmar surface

Function: Attachment oblique distal sesamoidean ligament

What is another name for the middle phalanx (P2)?

Short pastern bone

What is the key structure of the proximal phalanx and middle phalanx on the lateral and medial aspect? What is its function?

Bony contours, named “ringbone” are noted

Function: Attachment collateral ligaments

What is another name for the distal phalanx (P3)?

Pedal/coffin bone

To what does the extensor process of P3 attach?

Common digital extensor tendon

Where does the deep digital flexor tendon attach to?

Solar/ palmar aspect of the distal phalanx

Different from dogs, where does the lateral digital extensor of horses insert to?

Proximal phalanx (P1)

What are the specific feature in the dorsal surface of distal phalanx?

1. Striations - Hoof attachment

2. Nutrient foramen (Extensive holes on the dorsal aspect of P3)

   • Since P3 is responsible for the weight bearing → Need extensive blood circulation

What type of sesamoids bone is absent in horses, but present in dogs?

Dorsal sesamoid bone

Where does the proximal sesamoid bones sit on to?

Sagittal ridge

Where are the proximal sesamoid bones embedded in?

Embedded in the suspensory ligament

What is the function of proximal sesamoid?

Protect SDFT and DDFT

Unlike ruminants, which have two distal sesamoid bones, what structure does the horse have instead?

Navicular bone

What articulates with the navicular bone on the dorsal surface and palmar surface?

2 flat articular surface

• Dorsal surface: Articulates with p2 + p3

• Palmar surface: Articulates with the DDFT

Is navicular bone vascular or avascular

Vascular

What type of cartilage covers the navicular bone?

Hyaline cartilage

What joint is known as the Metacarpo-phalangeal (MCP) joint?

Fetlock

What are the special features of metacarpi-phalageal joint in horses?

Extensive joint capsule

• Large dorsal pouch

  • Protects extensor tendons

• Large palmar pouch

  • Incorporates with proximal sesamoid bone

What ligament functions to prevent hypertension of MCP joint?

Suspensory ligament + Sesamoidean ligaments

Instead of interosseous muscle in dogs, what does horse have instead? Where does it originate and insert to?

Suspensory ligament
Originate from proximal metacarpal 3 → Divide into axial + abaxial at the bottom of splint bone → Fuses with common digital extensor tendon

What are the functions of suspensory ligament?

1. Prevent collapse of MCP joint during weight bearing

2. Return MCP from hyperextension to normal extended position

3. Relies on stability of proximal sesamoid bones

What is the sesamoid ligament shown in the picture?

Inter-sesamoidan ligament

• Located between two proximal sesamoidian ligament

• Sits underneath the scutum

What are the names of the ligaments that connect the proximal sesamoid bones to the metacarpus and proximal phalanx?

Collateral sesamoidean ligaments

List out all the distal sesamoidean ligament

1. Cruciate DSL

2. Short DSL

3. Oblique DSL (V-shaped trough on PP)

4. Straight DSL (Insert with SDFT)