05: Forelimb 2

How do horses bear weight more efficiently

Replacing some muscle mass with connective tissue

Structure that allows horses to stand with low energy

Passive stay apparatus

When does the say apparatus engage

When the proximal serratus ventralis attachment is in line with the center of the hoof

Goal of the stay apparatus

• Limit flexion of the shoulder

• Maintain extension of the elbow and carpus

• Prevent hyperextension of the fetlock

Parts of the stay apparatus

1. Triceps

2. Dorsoscapular ligament

3. Lacertus fibrosus

4. Collateral ligaments

5. Palmar carpal ligament

6. SDF and DDF

7. Suspensory apparatus

Which part of the stay apparatus is the “essence of the stay apparatus”

Lacertus fibrosus

Which part of the stay apparatus is also present in cows

Suspensory apparatus

Which part of the stay apparatus functions while the horse is standing or in motion

Suspensory apparatus

Function of the triceps in the stay apparatus

Brings the horse from recumbency to standing/weight bearing

T/F: the triceps stays engaged while the say apparatus is engaged

False, that’s too much energy

Function of the dorsoscapular ligament in the stay apparatus

Stability and shock absorption, transferring the weight of the trunk to the limb, reinforces serratus ventralis attachment

Function of the lacertus fibrosus in the stay apparatus

Limits flexion of the shoulder, maintains extension of the elbow and carpus

Attachment of the lacertus fibrosus

Metacarpal tuberosity of the cannon bone

How does the biceps/lacertus fibrosus limit shoulder flexion

When the shoulder flexes, it pulls on the proximal biceps tendon, which then stops the scapula from flexing further

How does the biceps/lacertus fibrosus maintain extension of the elbow

Slight passive extension as it pulls on the cranial surface of the radius while under tension

How does the biceps/lacertus fibrosus maintain extension of the carpus

Pulls on the metacarpal tuberosity

Function of the collateral ligaments of the elbow in the stay apparatus

They lie caudal to the axis of joint rotation, pulling the elbow into extension

Function of the palmar carpal ligament in the stay apparatus

Binds the carpal bones together and limits carpal hyperextension

What provides the opposite force to the palmar carpal ligament

Lacertus fibrosus

Function of the digital flexors and check ligaments in the stay apparatus

Provides stability to the proximal and distal carpus, as well as limiting the hyperextension of the fetlock

Function of the suspensory apparatus in the stay apparatus

Limits fetlock hyperextension and stabilizes the interphalangeal joints

Parts of the suspensory apparatus

• Interosseous/suspensory ligament

• Proximal sesamoids

• Distal sesamoidean ligaments

Where does the suspensory ligament insert

• Bifurcates on palmar aspect to both proximal sesamoids

• Extensor branches insert on P1 dorsally

Extensor branches of the suspensory ligament join up with what muscle

Common digital extensor

Function of the extensor branch of the suspensory ligament in the stay apparatus

Prevents dorsal buckling of the digit

List the distal sesamoidean ligaments

• Straight/superficial sesamoidean ligament

• Oblique/middle sesamoidean ligament

• Cruciate/deep sesamoidean ligament

Attachments of the straight sesamoidean ligament

Proximal sesamoids → P1 and P2

Attachments of the oblique sesamoidean ligament

Proximal sesamoids → P1

Attachments of the cruciate sesamoidean ligament

Proximal sesamoids → P1

Extra sesamoidean ligament that is not technically part of the suspensory apparatus

Intersesamoidean ligament

Intersesamoidean ligament function

Provides a gliding surface for flexor tendons

What ligament encircles the proximal sesamoid bones

Palmar annular ligament

How do you locate lameness

Careful observation

How do you know which leg is fine and which is lame

“Down on sound”

Nerves from the brachial plexus that provide sensation to the carpus and distal limb

• Musculocutaneous

• Radial

• Ulnar

• Median

Musculocutaneous sensory function in antebrachium

Sensation to the metacarpal

Radial sensory function in antebrachium

Sensation to the carpus

Branches of the ulnar nerve that provide sensation to the antebrachium

• Dorsal branch of the ulnar nerve

• Palmar branch of the ulnar nerve

Branches of the median nerve that provide sensation to the antebrachium

• Lateral palmar

• Medial palmar

  • Communicating branch

• Lateral palmar metacarpal

• Medial palmar metacarpal

• Lateral digital palmar

• Dorsal branch of the lateral digital palmar

• Medial digital palmar

• Dorsal branch of the medial digital palmar

Which nerves are desensitized by a palmar digital nerve block

Palmar digital nerve

Palmar digital nerve block function

Desensitizes the caudal 2/3 of the foot

What structures desensitized by a palmar digital nerve block are a common source of lameness

Navicular bone and navicular bursa

Which nerves are desensitized by an abaxial sesamoidean nerve block

Palmar digital nerves and dorsal branches

Abaxial sesamoidean nerve block function

Desensitizes all of the foot and P2

Which nerves are desensitized by a low palmar/4-point nerve block

Lat/med palmar and lat/med palmar metacarpal

Low palmar/4-point nerve block function

Desensitizes from the fetlock down

Landmarks for the low palmar/4-point nerve block

Buttons of the splint bones

Which nerves are desensitized by a high palmar/4-point nerve block

The same 4: lat/med palmar, lat/med palmar metacarpal

High palmar/4-point nerve block function

Desensitize palmar structures of the metacarpus and below

Main branches of the median artery in the distal forelimb

• Median artery

• Medial palmar artery

• Lateral digital palmar artery

• Medial digital palmar artery

Vein in the bovine forelimb that drains and becomes the accessory cephalic vein

Dorsal common digital vein III

Local anesthetic block used in foot procedures in cows

Bier block

Bier block process

• Tourniquet

• Catheter and exsanguinate limb

• Inject anesthetic IV