Diagnostic analgesia

Question 1

What is the onset of action + duration of different local anaesthetics?

Answer 1

• Mepivicaine = 1-2min onset + 45-60min duration
• Bupivicaine = 4-5min onset + 1-2hr duration

Question 2

What are contraindications for using diagnostic anaesthesia?

Answer 2

• Suspect fracture
• Cellulitis - risk of iatrogenic sepsis
• Uncooperative horse

Question 3

What are complications of diagnostic anaesthesia?

Answer 3

• Broken needles - small / bent needles, horse moving suddenly
• Severe lameness after block =
  -Flare (30-60mins)
  -Synovial sepsis (12-24hrs)
  -Fracture

Question 4

What are reasons for poor response to local anaesthesia?

Answer 4

• Severe pain - e.g. P3 fractures + subsolar abscessation
• Poor technique / inadequate volume = re-block
• Sub-chondral bone pain - bone pain modelling not desensitised by intra-articular anaesthesia
• Pain originating more proximal = neck pain
• Neurological / mechanical = lameness/gait abnormality may not improve = perform neuro exam

Question 5

What are diagnostic analgesia options for the forelimb?

Answer 5

Perineural =
* Palmar digital nerve block
* Abaxial sesamoid nerve block
* Low 4-point nerve block
Synovial =
* Distal interphalangeal joint
* Navicular bursa

Question 6

What are diagnostic analgesia options for the hindlimb?

Answer 6

• Perineural
  -Abaxial sesamoid nerve block
  -Low 6-point nerve block

Question 7

How is Palmar digital analgesia carried out?

Answer 7

• Proximal to collateral cartilage, abaxial to edge of DDFT
• Technique = limb non-weightbearing, palpate neurovascular bundle w thumb, place needle angled distal + over bundle
• wait 5-10mins the test be checking skin sensation to heel bulbs
• 25G needle

Question 8

What structures are desensitised by PDNB?

Answer 8

• Navicular bone + bursa, collateral suspensory ligaments, distal sesamoidean impar ligament
• Distal DDFT + tendon sheath, insertion of SDFT
• Digital cushion, palmar third of lamellar corium + corium sole
• Palmar process of pedal bone, collateral cartilages, palmar aspect of DIP

Question 9

How is abaxial sesamoid nerve block carried out?

Answer 9

• Immediately palmar to neurovascular bundle at the abaxial surface of the base of the PSB
• 25G needle

Question 10

What structures are desensitised by ASNB?

Answer 10

• Same as PDNB + rest of digit
• Rest of P3 + P2
• Distal seasmoidean ligaments
• Corium + coronary band
• Dorsal branch of suspensory ligaments

Question 11

Where do you go with DIP block

Answer 11

• Dorsal approach - palpate depression proximal of coronary + insert needle vertically through skin + extensor tendon
• Weight bearing
• Needle = 20G + 1.5”

Question 12

What does the DIPJ block desensitise?

Answer 12

• DIP joint
• Navicular bone + bursa
• Toe region of sole - not heel

Question 13

How is navicular bursa block carried out?

Answer 13

• WEight bearing or flexed
• Through DDFT, May need radiograph control
• 18G spinal needle

Question 14

How is the low 4 block carried out?

Answer 14

• Forelimb, 2-3ml per site 23G needle
  -Lateral + medial palmar metacarpal nerves (just below buttons of splints)
  -Lateral + medial palmar nerves (dorsal to DDFT laterally + between DDFT + SDT medially)

Question 15

How is the low 6 point block carried out?

Answer 15

• Hindlimb - 2-3ml per site 23G needle
  -Lateral + medial plantar nerves
  -Lateral + medial plantar metatarsal nerves
  -Lateral + medial dorsal metatarsal nerves - fan dorsally