Diagnostic anaesthesia for hindlimb lameness

Question 1

Kit list for perineurial anaesthesia

Answer 1

• mepivacaine hydrochloride (20mg/ml)
• hibi/skin cleaner
• sterile gloves
• sterile swabs
• needle
• syringe

Question 2

Why is restrain of the pt important?

Answer 2

Diagnostic anaesthesia on the hindlimb is one of the most dangerous procedures we undertake

Question 3

How to restrain the pt

Answer 3

• Capable handler
• Nose twitch?
• Chemical restraint
• Lift ipsilateral forelimb limb

Question 4

Where do nose twitches probably have a place?

Answer 4

• if we need to increase pt compliance in a very short time frame

Question 6

Should we clip for joint injections?

Answer 6

• Evidence would suggest that we should only clip if it makes palpation of landmarks easier
• Clipping unnecessarily may increase skin contamination

Question 7

Low 6-point block in the hindlimb use

Answer 7

• Textbooks may say that low 6 point is necessary, but evidence would suggest otherwise
  – study found that there was likely no benefit of medial and lateral dorsal metatarsal nerve anaesthesia when using regional anaesthesia to localise pain to the metatarsophalangeal joint during a lameness exam
• One exception though – the dorsal branches are important for skin sensitivity

Question 8

What are the most likely sites of hindlimb vs forelimb pain?

Answer 8

• Vast majority of forelimb lameness is localised to the distal limb
• Vast majority of hindlimb lameness is localised outside of the distal limb (fetlock region, tarsal region, stifle)

Question 9

Synovial vs perineurial blocks

Answer 9

Perineural blocks
* need to work sequentially from distal to proximal
* Each block adds additional areas of
desensitization to the previous one

Synovial blocks
* much more specific to the structure injected
* Can return to block more distal structures

Question 10

Where do you think is the most likely focus for an acute lameness, positive to proximal limb flexion
(unilateral), effusion of the medial femorotibial joint?

Answer 10

• the stifle

Question 11

Where do you think is the most likely focus for a chronic bilateral lameness in a sports horse, mild- moderate positive to proximal flexion?

Answer 11

• tarsal region
  – small tarsal joint or proximal suspensory ligaments

Question 12

Where do you think is the most likely focus for an acute unilateral lameness in a native pony with marked digital flexor tendon sheath effusion?

Answer 12

• DFTS

Question 13

Perineural options (proximal->distal)

Answer 13

• Tibial and peroneal nerve blocks
• Deep branch of the lateral plantar nerve block
• Low 4-point block
• Abaxial sesamoid nerve block
• Plantar digital nerve block

Question 14

The DBLPN nerve block: steps

Answer 14

1. Limb is held flexed and rested on the vets knee
2. The flexor tendons are pulled medially to open up injection site
3. Needle is advanced along the axial surface of the lateral splint bone
4. 3ml of LA is injected (resistance should be low)
5. The horse is re-examined after 10 minutes

Question 15

What is the DBLPN a good block for?

Answer 15

• the proximal suspensory ligament

Question 16

Where are ponies most prone to pathologies?

Answer 16

• within the tendon sheath

Question 17

Where do tibial and peroneal nerve blocks go in?

Answer 17

• at the level of the mid tibia

Question 18

What are tibial and peroneal nerve blocks useful for?

Answer 18

• to split the limb into 2 halves
• i.e. is the lameness coming from the tarsus or below OR from the stifle or above?

Question 19

Why is the DBLPN nerve block difficult to achieve in the standing limb

Answer 19

• the nerve is on the axial side, on the inside edge of the lateral splint (M4)

Question 20

Where are you aiming to inject LA for the DBLPN nerve block?

Answer 20

• about 2cm below the small tarsal joints and right around the axial surface of the lateral splint bone