Forelimb - nerve blocks

Question 1

What are the key principles of diagnostic anaesthesia?

Answer 1

• Use an aseptic technique – clean hands, new bottle of local, sterile needle and syringe, aseptic preparation of limb (only need clip if very hairy/dirty)
• Mepicaine mainly used as causes least tissue reaction. Bupivicaine can be used for longer action, but expensive
• Think about how you place needle and how horse will react (aim needle down leg)
• Place needle separately, attach syringe, draw back to check no blood, inject, remove everything together and dispose of appropriately
• Vein Artery Nerve – VAN – nerve is more palmar

Question 2

When should you not perform nerve blocks?

Answer 2

• Suspected fractures or severe soft tissue injuries (such as DDFT ruptures), as horse will weight bear once pain is removed and can have catastrophic consequences
• Risk of infection, e.g. existing skin disease, such as mud fever, or if the environment / leg cannot be cleaned adequately
• You cannot perform technique in a safe manner (consider risk to yourself, handler and horse)

Question 3

What order should you do nerve blocks in?

Answer 3

Start distally and work proximally
* Palmar digital nerve block
* Abaxial sesamoid nerve block
* Low four point (fetlock and below)
* High four point (metacarpal region and below)
* Lateral palmar nerve block (proximal suspensory ligament)
* Median and ulna nerve block (carpus and below)

Question 4

Which nerves are you aiming for?

Answer 4

**Radial nerve **
Extensors of elbow, carpus and digits
Skin sensation on craniolateral aspect of limb not dorsal digit. Stops at carpus

Median nerve
Flexors of carpus and digit
Skin sensation on palmar and dorsal digit

Ulna nerve
Flexors of carpus and digit
Caudal aspect of forearm, lateral and dorsal digit

Question 5

Where should you aim to block for palmar digital, abaxial sesamoid and low 4 nerve blocks? What nerves are affected in each?

Answer 5

1. Palmar digital nerves in pastern region (palmar digital nerve block) - Removes sensation to palmar foot
2. Palmar digital nerves on abaxial surface of proximal sesamoid bones (abaxial sesamoid nerve block) - Removes sensation to foot, pastern and palmar fetlock
3. Palmar metacarpal and palmar nerves in distal metacarpus (Low 4 point) - Removes sensation to fetlock and below

Question 6

Which local anaesthetic is normally used for nerve blocks in the horse?
A. Lignocaine
B. Procaine
C. Mepivicaine
D. Bupivicaine

Answer 6

Mepivicaine
(bupivicaine is longer acting)

Question 7

Which is the first nerve block you would start with on a horse which is forelimb lame with no localising signs?
A. High 4 point
B. Low 4 point
C. Abaxial sesamoid nerve block
D. Palmar digital nerve block
E. Median and ulnar nerve block

Answer 7

Palmar digital nerve block

Question 8

You have been asked to re-examine a horse which has previously had proximal interphalangeal (pastern) joint pain which resolved, and the horse has now gone lame again. What response to nerve blocks would you expect if the proximal interphalangeal joint was still painful?
A. The lameness would completely resolve with a palmar digital nerve block
B. The lameness would improve with a palmar digital nerve block and completely resolve with an abaxial sesamoid nerve block.
C. The lameness would improve with an abaxial sesamoid nerve block and completely resolve with a low 4 point nerve block.
D. The lameness would improve with a a low 4 point nerve block and completely resolve with a high 4 point nerve block.

Answer 8

The lameness would improve with a palmar digital nerve block and completely resolve with an abaxial sesamoid nerve block.