1. Diagnostic anaesthesia

Question 1

Why is diagnostic anaesthesia applied? What to consider?

Answer 1

• to localise lameness, establish source of pain

Know where to inject, where the local anaesthetic solution can diffuse, which regions can be desensitised

Question 2

Local anaesthetic solutions. Mechanism of action

Answer 2

Reversibly inhibit nerve transmission by blocking voltage-gated sodium channels in nerve plasma membrane —> suppress action potential in nociceptive fibers = block the transition of pain impulses

Question 3

Which local anaesthetic solution are used?

Answer 3

• MEPIVACAINE 2%
  Least tissue irritative. Onset in 5-10 min. Duration about 1,5-3h
• BUPIVACAINE
  Slower onset. Longer lasting
• LIDOCAINE 2%
  Similar in onset and duration to Mepivacaine but more irritative in synovial environment

Question 4

What needle sizes are used?

Answer 4

• Generally 24-25G, 13mm needle for perineural blocs in distal limb
• more proximal site, larger volume: 20-21G
• joints: 20G

Question 5

Do we usually start distally or proximal with diagnostic anaesthesia?

Answer 5

Start distally and progress proximally.
(Exceptions in special circumstances)

Question 6

Should horse stay still or walk after injection?

Answer 6

Usually it should stand still after nerve block and walk after intra-synovial injections

Question 7

Palmar/plantar digital nerve block

Answer 7

• just proximal to the cartilages of the foot
• 1,5 ml mepivacaine
• 24-25G 13mm needle pointing distally

Question 8

What origins of pain palmar/plantar digital nerve block can alleviate?

Answer 8

• sole
• distal interphalangeal joint - after 15 minutes
• proximal interphalangeal joint
• dorsal laminae
• pastern region
• Fetlock region

Question 9

Palmar/plantar (abaxial sesamoid) nerve blocks

Answer 9

• forelimb: flexed
• hindlimb: weight-bearing
• at the level of the base of the proximal sesamoid bones
• needle directed distally
• 2 mill mepivacaine
• 23-25G 13mm needle pointing distally

Question 10

Abaxial sesamoid nerve blocks can alleviate …

Answer 10

• Foot pain
• Pastern region pain
• Fetlock region pain – very common

Question 11

Low 4-point nerve block

Answer 11

• Weight-bearing (Easier to palpate the DFTS)
• Palmar / plantar nerves: Between SL & DDFT; Proximal to the DFTS
• Needle directed distally
• 2 ml mepivacaine at each site • 23-25G 13 mm needle

• Palmar metacarpal / plantar metatarsal nerves: Just distal to the head of McII/IV, MtII/IV
• Needle perpendicular to the skin
• 2 ml mepivacaine at each site
• 23-25G 13 mm needle

Question 12

Low 4-point nerve block can alleviate pain from …

Answer 12

Foot, pattern and fetlock region pain

Potential risk of penetration of the DFTS and fetlock joint

Question 13

Subcarpal block

Answer 13

• Several different techniques
• Preferred: lateral palmar nerve: Medial and lateral approach
• Palmar metacarpal nerve injections: risk of carpometacarpal joint penetration

Question 14

Subcarpal block: lateral approach

Answer 14

Lateral palmar nerve
• Standing or flexed
• Nerve within the accesoriocarpal ligament
• 23-25 G 13 mm needle, 3 ml mepivacaine
• Carpal sheath can be penetrated

Question 15

Subcarpal block: medial approach

Answer 15

• No risk of carpal sheath penetration
• Horse may strike out

Question 16

Median and ulnar nerve blocks

Answer 16

• Mostly done in referral hospitals
• Can desensitise the carpus and part of the
antebrachium
• Use skin bleb
• Reassess lameness in 15-20 minutes

Question 17

Subtarsal block

Answer 17

• Deep branch of the lateral plantar
nerve unless clinical indication
of flexor tendon lesion
• Not specific to
suspensory ligament
• Medial & lateral plantar nerves can be added
• Limb flexed, SDFT pushed medially
• 23G 1” needle 15 mm distal to head of MtIV
OR
• Weight-bearing or flexed (the horse is resting)
• 22 G 1.5” needle
• 3-4 ml mepivacaine
• Inserted just distal to the head of McIV
• Most effective in horses with proximal suspensory desmopathy

Question 18

Tibial nerve blocks

Answer 18

• 10 cm proximal to the tuber calcanei
• Cranial to the common calcaneal tendon
• Skin bleb
• 20 G 25 mm needle
• 10-15 mL mepivacaine

Question 19

Perineal nerve block

Answer 19

• Between long & lateral digital extensor tendons
• Superficial and deep branches
• 10 cm proximal to the tuber calcanei
• Skin bleb
• 19-20 G 1.5-2” needle directed medially & slightly caudally
• 20 mL mepivacaine
• 10 mL injected with needle to the hub • 10 mL as the needle is withdrawn

Question 20

Tibial & peroneal nerve blocks

Answer 20

• Re-assess in 20 minutes
• Negative response cannot be concluded until 1 hour
• Desensitises the entire hock region, distal crus and the
distal aspect of the limb
• Toe drag is reassuring that the block works

Question 21

RE-assessment

Answer 21

Has it worked?
• Distal limb – can check skin sensation
• Not always reliable
• Always assess the gait

• After most nerve blocks – wait for 10 minutes
• Proximal limb – at least 15-20 minutes

Question 22

Distal interphalangeal joint

Answer 22

• Not entirely specific
• Lameness should be assessed 5 min after the block • Horse should stand still

Can also alleviate
• Solar toe and heel pain
• Navicular region pain

Question 23

Navicular bursa

Answer 23

• 18G 9 cm spinal needle between heel bulbs
• Skin bleb
• Always with radiographic control!
• Reasonably specific if assessed in 5 minutes

Question 24

Proximal interphalangeal joint

Answer 24

Dorsolateral/dorsomedial approach
• At the level of or just distal to distal palmar process of PP & just lateral or medial to CDE
• Direct needle slightly distal & axial
• 20 G 25 mm needle
• 3-4 ml mepivacaine

Question 25

Metacarpophalangeal joint

Question 26

Why nerve blocks i should know? (How to perform and what they desensitise) (7 blocks)

Question 27

What aspects of lameness should I know?