Lecture 9 -- Equine Forelimb Anatomy

What is another name for proximal interphalangeal joint?

Pastern joint

Where do the collateral ligaments of the Proximal Interphalangeal Joint run?

Collateral ligament x2 pairs
1. Runs from the Proximal Phalanx (P1) to the Middle Phalanx (P2)
2. Proximal Phalanx (P1) to navicular bone extension running to the navicular bone

What structures make up the Distal Interphalangeal Joint (DIP)?

Middle Phalanx (MP), Distal Phalanx (DP) and navicular bone

In the distal interphalangeal joint, there is an extensive joint capsule. What is the name of this joint capsule? What is its function?

Navicular bursa (Extensive joint capsule forms bursa)

Function: Protects extensor tendon + deep digital flexor tendon

Where is the Navicular / podotrochlear bursa located?

Between the sesamoid and Deep Digital Flexor Tendon (DDFT)

Different from dogs and cats, what ligament is absent in horses in their distal interphalangeal joint?

Dorsal elastic ligament

What are the collateral ligaments attached between the P3 and navicular bone?

Impar ligament

Where are the ungual cartilages located? What are the function of ungual cartilages?

Located at the lateral + medial aspect of the palmar processes of distal phalanx

Function: Shock absorption

Are ungual cartilages able to be visualise in radiograph?

Normally not → Cartilage not visible (Slightly darker than bone) → BUT Mineralise as age (Able to identify in radiograph) = Sidebone

Where does the Common digital extensor (CDE) insert?

Crosses the dorsal aspect of the carpus and inserts on PP, MP & DP

Where does the Lateral digital extensor (LDE) insert?

Inserts on the Proximal Phalanx (PP)

How do the deep digital flexor tendon and the superficial digital flexor tendon interact?

SDFT + DDFT pass through carpal tunnel → SDFT splits to allow the DDFT at metacarpal phalangeal joint → DDFT runs over the navicular bursa → Insert DP (while SDFT inserts into MP)

What are the accessory check ligaments?

Superior check ligament - Originates proximal to carpal canal and inserts on the SDFT

Inferior check ligament - Originates from fibrocartilage plate on palmar aspect of carpus and inserts on the DDFT.

What structure holds the Deep Digital Flexor Tendon (DDFT) and Superficial Digital Flexor Tendon (SDFT) against the bones in the digital region?

Annular ligaments

List out all the annular ligaments in digital region

1. Proximal annular ligament - Attach around the metacarpo-phalangeal joint

2. Proximal phalanx annular ligament - Attach at the proximal phalanx

3. Distal annular ligament - Attach around the distal interphalangeal joint

What covers the SDFT and DDFT?

Connective tissue tendon sheath

What is the stay apparatus?

Mechanism for passive weight bearing → Horses can stand for extended period of time without using energy

Which structure cooperates in maintaining extension and preventing flexion in the stay apparatus?

1. Biceps brachii tendon

2. Lacertus fibrosus → Connect the biceps to the extensor carpi radialis → If one joint is extended, the other joint atomically become extended e.g. shoulder joint is extended, it pulls the carpal joint to be extended

3. Collateral ligament (between humerus and radius and ulna) → Support the attachment of radius and humerus

4. Serratus ventralis → Suspends weight of body between forelimbs

Which structure works to prevent hyperextension of the forelimbs in the stay apparatus?

1. Carpus by SDFT, check ligament, palmar fibrocartilage joint reinforcement and retinaculum

2. MCP joint by suspensory ligament, proximal sesamoids, distal sesamoidean ligament, common digital extensor

3. MCP, PIP and DIP joint by DDFT, SDFT, check ligament and annular ligaments

Describe the arterial supply in horses.

Similar to dog

Subclavian artery → Axillary → Brachial artery → Median artery

The brachial plexus in horses has the same motor functions but supplies different sensory areas. Describe which regions are innervated by which nerves.

Musculocutaneous nerve: Medial aspect of antebrachium

Axillary nerve: Cranial aspect of the shoulder region and lateral aspect of elbow joint

Medial and ulnar nerve: Palmar aspect of carpus, metacarpus and digits

Radial: Lateral aspect of elbow joint + a bit of antebrachial joint

Median and ulnar nerves combine with musculocutaneous nerve → Supply the pastern and foot + medial aspect of metacarpal

Which nerves combine distal to the carpus?

Median & ulnar nerves

Which two major branches that the median and ulnar nerves that branches off?

1. Palmar metacarpal nerve

   → Runs between MC3 and splint bones (MC2 + MC4) → Supply the dorsal aspect of digit

2. Palmar nerves → Runs between suspensory ligament and SDFT → Cross abaxial aspect proximal sesamoids → Become palmar digital nerves → Divides into dorsal and palmar branches → Supplies hoof components

Nerve blocks