Nerve blocks Flashcards
What nerve block is this?
Palmar digital nerve block (palmar digital nerves)
This is the most distal nerve block – performed in the palmar/plantar region of the pastern.
Where is it?
Palpate the lateral and medial borders of the Deep Digital Flexor Tendon (DDFT) in the pastern. The neurovascular bundles lie in a groove, just dorsal to this tendon and can be felt ‘rolling’ underneath your fingers. The Vein, Artery and Nerve are always positioned so that the Vein lies dorsal, Artery in the middle and Nerve palmar. This means you need to inject towards the palmar aspect of the bundle to avoid entering the blood vessels. Remember, the nerves are present on both the medial and lateral aspect of the leg, and both must be injected.
How to inject it?
Insert in the needle under the skin, aiming the needle down the leg (point directed towards the foot), and parallel to the tendons. The needle needs to be just underneath the skin, so angle it so that it does not go too deep, but is inserted far enough to make it stable in case the horse moves. Hold the needle and syringe firmly together, and gently inject a maximum of 0.5ml. If you get resistance, reposition the needle. It will be very difficult to inject if it is still in the skin (reposition deeper) or in the tendon (reposition more dorsally). Repeat on the opposite side of the limb
What effect does it have?
This block desensitises the caudal 1/3 rd of the foot and sole, including the navicular structures, heel bulbs etc. Skin sensation is lost on the heel bulbs, and this site is used to test whether the block has worked – remember to test both sides (medial and lateral) to make sure both have worked. Sometimes this blocks out the dorsal aspect of the foot (depending on nerve branches and how high you placed the block), so check whether this sensation is still present or not. This will tell you whether you have anaesthetised the whole foot or just the palmar aspect.
What nerve block is this?
Abaxial sesamoid nerve block (palmar digital nerves)
This block desensitises the caudal aspect of the fetlock joint, and all the structures of the pastern and foot.
Do medial and lateral sides.
This block is performed on the palmar / plantar aspect of the fetlock joint.
Where is it?
The neurovascular bundles lie on the abaxial surface of the medial and lateral proximal sesamoid bones (abaxial means away from the axial or midline). The Vein, Artery and Nerve are positioned as for the palmar digital nerves, with the nerve most palmar. Again you must inject the nerves on both the medial and lateral aspects of the limb.
How to inject it?
The technique is similar to that used for the palmar digital nerve block. Inject the medial nerve first. Insert the needle under the skin in a proximal to distal direction, aiming to deposit the local anaesthetic at the base of the proximal sesamoid bones. Again ensure you hold the needle and syringe together and do not spray dye around. Again, if you cannot inject easily, reposition the needle. Repeat on the lateral aspect of the limb.
What effect does it have?
This block desensitises the caudal aspect of the fetlock joint, and all the structures of the pastern and foot. Skin sensation is lost on the dorsal pastern and dorsal coronary band, as well as on the heel bulbs.
What nerve block is this?
Low 4 point nerve block (palmar nerves and palmar metacarpal nerves)
One needle distal to the button of the splint bone . Other needle between the DDFT and suspensory ligament.
Do medial and lateral sides.
This block is performed in the distal third of the metacarpal bone.
Where is it?
The palmar metacarpal nerves emerge from underneath the distal part of the splint bones. Palpate and identify the suspensory ligament and DDFT - the palmar nerves lie in the groove between these structures The neurovascular bundles themselves are not palpable at either site.
How to inject it?
Palpate the button of the splint bone (swelling at distal end) and inject directly beneath it (palmar metacarpal nerves). Inject the palmar nerves between the suspensory ligament and DDFT approximately 2-3cm proximal to the button of the splint bones. This block is also performed on both the medial and lateral aspects of the limb, and again it is easiest to start with the medial nerves.
What effect does it have?
This block desensitises all structures distal to the block. Skin sensation is lost on the dorsal pastern and fetlock.
What nerve block is this?
High 4 point nerve block (high palmar nerves and palmar metacarpal nerves)
This block is performed in the proximal third of the metacarpal bone.
Where is it?
The palmar metacarpal nerves lie between the suspensory ligament and metacarpal bones. The palmar nerves lie in the groove between the suspensory ligament and DDFT. Palpate and identify these landmarks. The neurovascular bundles themselves are not palpable.
How to inject it?
Injections are made 2-3cm distal to the carpometacarpal joint. Palmar metacarpal nerves (between the suspensory ligament and metacarpal bones) - angle the needle towards the cannon bone and insert it axial (inside) the splint bones until it hits bone to reach the nerves. Do not remove the needle from the leg, but re-direct it between the suspensory ligament and DDFT to inject the palmar nerves.
Again block both the medial and lateral nerves, and it is easiest to start with the medial ones.
What effect does it have?
This block desensitises all structures distal to the block. It is tested by squeezing the suspensory ligament.
What are the injection sites for joint blocks?
Synovial blocks:
- Coffin joint (distal interphalangeal joint)
- Pastern joint (proximal interphalangeal joint)
- Fetlock joint (metacarphophalangeal joint)
- Hock joint (tarsocrural and tarsometatarsal joints)
- Digital flexor tendon sheath
What are injection sites for nerve blocks?
Nerve blocks:
- Palmar digital
- Abaxial sesamoid
- Low four point
- High four point
How is the distal interphalangeal joint (coffin joint) injected?
Distal interphalangeal joint
This joint is approached from the dorsal aspect in the midline.
Insert the needle 1cm proximal to the coronary band, angled from proximal to distal at 45 degrees to the horizontal.
What are the 4 main synovial joints of the hock?
- Tarsocrural (tibiotarsal)
- Proximal intertarsal
- Distal intertarsal
- Tarsometatarsal
Of these, you are most likely to need to inject the tarsocrural and tarsometatarsal joints.
How is the proximal interphalangeal joint (coffin joint) injected?
Proximal interphalangeal joint
This joint can be difficult to find, as the joint space is very narrow.
Palpate the proximal tubercles of the second phalanx. The joint space is palpable as a small indentation on firm palpation, 1-2cm proximal to this.
How is the fetlock (metacarpophalangeal joint) injected?
The fetlock joint can be approached from the dorsal, lateral or palmar aspect
From the dorsal aspect, palpate the proximal tubercles of the first phalanx. The joint space is palpable, 1-2cm proximal to this. If in any doubt, flex the joint to identify the space.
What are the five sites for injecting the digital flexor tendon sheath?
- Lateral and medial proximal pouches
- Lateral and medial pouches below the annular ligament
- Distal pouch (midline of pastern)
