Forelimb nerve blocks

Question 1

What are nerve blocks used for?

Answer 1

• to identify site of lameness, either if no localising signs, or if need to confirm primary site of lameness

Question 2

Aseptic technique

Answer 2

• clean hands
• new bottle of local
• sterile needle and syringe
• aseptic preparation of limb
• chlorhexidine or another skin cleaner to be on the safe side
• (only need clip if very hairy/dirty)

Question 3

Why direct the needle down the leg?

Answer 3

• if the horse moves its leg away it will move onto the needle rather than away from it

Question 4

Why use an aseptic technique?

Answer 4

• it won’t matter if you accidentally go into the synovial structures
• just redirect the needle and try again
• won’t/shouldn’t cause synovial sepsis

Question 5

Which LA is used most commonly and why? (& what other one can you use?)

Answer 5

• mepivacaine
  – it causes the least tissue reaction
• can use bupivicaine
  – longer action
  – expensive

Question 6

Is the vein, artery or nerve more palmar in the neurovascular bundle?

Answer 6

• the nerve

Question 7

General technique

Answer 7

• Place needle separately
• attach syringe
• draw back to check no blood
• inject
• remove everything together
• dispose of appropriately

Question 8

Do not perform nerve blocks if any of the following are present

Answer 8

▪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 9

Do you start nerve blocks distally or proximally?

Answer 9

• distalyl and work proximally

Question 10

Radial nerve

Answer 10

▪ Innervates the extensors of elbow, carpus and digits
▪ Skin sensation on craniolateral aspect of limb not dorsal digit. Stops at carpus

Question 11

Median nerve

Answer 11

▪ Innervates the flexors of carpus and digit
▪ Skin sensation on palmar and dorsal digit

Question 12

Ulna nerve

Answer 12

▪ Innervates the flexors of carpus and digit
▪ Caudal aspect of forearm, lateral and dorsal digit

Question 13

The 6 forelimb nerve blocks

Answer 13

▪ 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 14

What does the palmar digital nerve block desensitise?

Answer 14

▪ Removes sensation to palmar foot

Question 15

What does the abaxial sesamoid nerve block desensitise?

Answer 15

▪ Removes sensation to foot, pastern and palmar fetlock
▪ i.e. takes out everything below the fetlock joint

Question 16

What does the Low 4 nerve block desensitise?

Answer 16

• removes sensation to fetlock and below
• the palmar metacarpal and palmar nerves in the distal metacarpus

Question 17

How to check the palmar digital nerve block worked

Answer 17

• tap the heel bulbs with a pen
• to check the dorsal aspect works tap a pen just above the hoof on the dorsal aspect of the leg/hoof