Diagnostic analgesia Flashcards
Why is diagnostic analgesia important in equine veterinary?
Integral part of the lameness examination
What do you need to be able to perform diagnostic analgesia?
- Lame horse: not always obvious!
- Good handler: safety!
- Good technique: precision/accuracy!
- Logical step-wise approach
- Ability to recognise improvement: try and avoid bias!
- Understand structures desensitised
- Plenty of time: not always available in busy equine practice!
How do local anaesthetics work?
Act by blocking sodium channels and preventing depolarisation
Which local anaesthetics are most commonly used in equine practice?
Mepivicaine
Bupivivcaine
Compare the onset time and duration of mepivicaine and bupivicaine
Mepivicaine: 1-2min onset/45-60min duration
Bupivicaine: 4-5 min onset/1-2hr duration
List the 3 contraindications for using diagnostic analgesia
- Suspect fracture - Don’t find out the hard way!
- Cellulitis
- Uncooperative horse
Why is diagnostic analgesia not indicated in cellulitis cases?
Risk of iatrogenic sepsis
Local anaesthetics don’t work well in acidic conditions
What complications can occur when using diagnostic analgesia
- Broken needles: small needles, bent needles, horse moves suddenly
- Severe lameness after block
What are the possible reasons for severe lameness following a nerve block?
“Flare” - Usually occurs soon after block (e.g. 30-60 mins)
Synovial sepsis - Usually occurs 12-24hrs after block
List the possible reasons for a poor response to local anaesthesia
- Severe pain e.g. P3 fractures and subsolar abscessation
- Poor technique/inadequate volume
- Subchondral bone pain
- Pain originating more proximal e.g. neck pain
- Neurological/ mechanical
List the options for forelimb nerve blocks
Perineural:
- Palmar digital nerve block
- Abaxial sesamoid nerve block
- Low 4-point nerve block
- High 4-point; subcarpal; lateral palmar nerve block
- Median/ulnar
Synovial:
- DIPJ; NB; PIPJ; DFTS; MCPJ; carpal joints; carpal sheath; elbow; shoulder; bicipital bursa
List the options for hindlimb nerve blocks
Perineural:
- (Plantar digital nerve block)
- Abaxial sesamoid nerve block
- Low 6-point nerve block
- High 6-point; subtarsal; deep branch lateral plantar nerve block
- Tibial/peroneal
Synovial:
- DIPJ; NB; PIPJ; DFTS; MTPJ; tarsal joints; calcaneal bursa; tarsal sheath; stifle; hip;
What is the injection site for a palmar digital nerve block?
Just proximal to collateral cartilage, abaxial to edge of DDFT
Describe the technique used for the palmar digital nerve block
- Limb non‐weightbearing
- Palpate neurovascular bundle with thumb
- Place needle angled distal and over bundle
- Needle: 23/25G 5/8”
- Volume: 1.5‐2ml
- Wait 5-10 mins then test by checking skin sensation to the heel bulbs
Which structures are desensitised by the palmar digital nerve block?
Localises lameness to palmar aspect (navicular bone) of the foot
In reality:
- Navicular bone, navicular bursa, collateral sensory ligaments, distal sesamoidean impar ligament
- DDFT, insertion of SDFT
- Digital cushion
- Palmar processes of the pedal bone; collateral cartilages; +/- collateral ligaments of DIP joint
Where is the site of injection for the abaxial sesamoid nerve block?
Immediately palmar to neurovascular bundle at the abaxial surface of the base of the proximal sesamoid bone
Describe the technique to perform the abaxial sesamoid nerve block
- Limb non-weightbearing
- Palpate neurovascular bundle with thumb
- Needle inserted distal and parallel to bundle
- Needle: 23/25G 5/8”
- Volume: 2ml
- Wait 5-10 mins then test by checking skin sensation to the dorsal coronary band
List the structures desensitised by the abaxial sesamoid nerve block
The same structures as the palmar digital nerve block plus:
- Rest of P3/P2 and palmar P1
- Collateral ligaments of the DIP and PIP joints; DIP and PIP joints
- Distal sesamoidean ligaments
- Lamellar corium and coronary band
- Distal digital extensor tendons
- Dorsal extension branch of the suspensory ligament).
Where is the injection site to block the distal interphalangeal joint?
Dorsal approach
Describe the technique to block the distal interphalangeal joint
- Weight‐bearing; midline
- Palpate depression just proximal to coronary band (1‐2cm) on dorsal aspect of pastern
- Insert needle vertically through skin and extensor tendon
- Can also be done via dorsolateral or dorsal inclined approach
- Needle: 20G 1.5” (smaller needle)
- Volume: ~6ml (larger volume)
Which structures are desensitised in the distal interphalangeal block?
- DIP joint
- +/– Collateral ligaments of DIP joint
- Navicular bone/bursa
- Toe region of sole (not heel)
Where is the injection site to block the navicular bursa?
Palmar approach between bulb of heels
Describe the technique to block the navicular bursa
- Weight‐bearing (horizontal midline) or flexed, both approaches through DDFT
- Skin bleb bulb of heels
- Use radiographic control (+ contrast) – difficult!
- Needle: 18G spinal
- Volume: 2‐4ml
- Desensitises navicular region and toe only
List the structures desensitised by the navicular bursa block
Desensitises navicular region and toe only
