Local Anaesthesia Techniques

Question 1

Which muscles of the axial skeleton are easy to find?

Answer 1

An easy one to find is sternomandibularis, then brachiocephalicus. Within the axial system it is hard to find specific muscles, but try to find the fascial boundaries between the three lanes (transversospinalis, longissimus and iliocostalis) in the Th-L region.

Question 2

What is ventroflexion?

Answer 2

Pressure over the gluteal muscle mass lateral to the caudal vertebrae.

Question 3

What is dorsoflexion?

Answer 3

Pressure around L5/S1 area (cranial to the tuber sacrale).

Question 4

What is lateroflexion?

Answer 4

Opposed pressure between ipsilateral iliopsoas and contralateral tuber ischium.

Question 5

What flexion do normal horses have in the spine?

Answer 5

They should have an easy flexion over a few degrees

(the equine spine is a supporting structure, so is not as mobile as the carnivores’ spine).

Question 6

During flexion of the equine spine, what do we observe for?

Answer 6

• Pain reactions
• Resistane
• Muscle spasms

Question 7

How do we lameness exam for a horse at rest?

Answer 7

1. Evaluate conformation
2. Examine the musculoskeletal system (visual evaluation, palpation, manipulation)
   
   1. Distal limb (from hock/carpus), including foot

• A substantial proportion of lamenesses originate in the foot so this is an important part of your examination
  
  1. Shoes/shoeing
  2. Hoof testing
  3. Proximal limb
• In your evaluation of the musculoskeletal system you should:
  
  1. Look for asymmetry
  2. Once identified, examine both the sound and lame limbs
  3. Look particularly for evidence of pain, swelling, heat, etc. as indicators of inflammation/injury/trauma

Question 8

How do we do a horse lameness exam in motion (dynamic)?

Answer 8

1. Assess the gait in walk and trot in a straight line
2. Evaluate and grade any lameness (see below for more details)
   
   1. Is the animal lame?
   2. If so, which leg is it lame on?
   3. What grade (how severe) is the lameness?
3. Perform exacerbation tests (flexion tests, lunging)
   
   1. During each exacerbation test, evaluate the animal as above (i.e., is it lame, which leg, what grade?)

Question 9

How can conformation affect a horse’s risk of lameness?

Answer 9

Because abnormal weight distribution may overload specific parts of the musculoskeletal system, leading to pathology.

Question 10

How do we evaluate where the weight is distributed through each limb/joint?

Answer 10

o Viewed from in front/behind:

• Forelimb: Is the limb bisected by a vertical line dropped from the shoulder joint to the ground?
• Hindlimb: Is the limb bisected by a vertical line dropped from the region of the hip joint to the ground?
• Carpus, tarsus and metacarpophalangeal / metatarsophalangeal joints: Is there any medial or lateral deviation in the frontal plane?
• Forelimb and hindlimb: Do the horse’s toes point towards the front or is the horse ‘toed-in’ (internal rotation of distal extremity) or ‘toed out’ (outward rotation)?

o Viewed from the side:

• Forelimb: Does a vertical line intersect the elbow, carpal and metacarpophalangeal joints, or is the carpus positioned cranial or caudal to this line?
• Hindlimb: Does a vertical line dropped from the tuber ischium touch the point of the hock and the entire plantar aspect of the metatarsus?
• Tarsus: Is the joint overly flexed (‘sickle-hocked conformation’) or overly straight?
• Is the fetlock angle 125-135o (i.e., neither too upright nor ‘dropped’)?

Question 11

How do you assess the horse’s foot conformation?

Answer 11

o Viewed from the side (evaluation of dorsopalmar balance):

• A line that bisects the third metacarpal bone should intersect the ground at the most palmar point of the foot’s weight-bearing surface.
• The distal interphalangeal joint (the articulation over which the entire limb rotates) should be vertically above the mid-region of the solar surface of the foot.
• You can learn to estimate where the distal interphalangeal joint is by looking at radiographs.
• The pastern and dorsal hoof wall should be parallel to each other.
• The dorsal hoof wall and heel should be parallel to each other
• The ground:dorsal hoof wall angle is typically 45-50o in forelimbs and 50-55o in hind limbs.

o Viewed from in front/behind (evaluation of mediolateral balance):

• The coronary band and the weight-bearing surface of the foot should be parallel to the ground and perpendicular to a vertical line that bisects the third metacarpal bone.
• The medial and lateral heels should be the same height.

Question 12

What are the shapes of the ground surfaces of the feet?

Answer 12

The ground surfaces of the front feet are more circular than the hind feet. The hind feet are shaped more like a diamond with one end resected.

Question 13

What should the feet look like?

Answer 13

• The soles should be concave and the white line should be the same width all the way around the foot.
• The surface of the wall should be smooth and shiny.
• The frog should be located on the sagittal plane within the foot.
• The width of the ground surface should be approximately equal to the length and the maximum width should be halfway between the toe and the heels.
• The palmar aspect of the ground surface of the wall should be at the same level as the base of the frog

Question 14

How do we know if a horse is lame on the hindlimbs?

Answer 14

There is increased tuber coxae/pelvic movement (‘pelvic hike’) on the side of the lame limb (to reduce joint flexion/loading on the lame leg).

Question 15

How do you know if a horse is lame on the forelimb?

Answer 15

The head moves up as the lame limb contacts the ground (to reduce the weight taken by the lame limb), and moves down as the sound limb contacts the ground.

Question 16

What is the Standard 0-5 grading system for assessment of lameness in trot?

Answer 16

• 0 No lameness (sound)*
• 1 Mild or inconsistent lameness (subtle or inconsistent head nod/pelvic hike)*
• 2 Moderate, consistent lameness (consistent head nod/pelvic hike, with excursion of several centimetres)*
• 3 Obvious, marked lameness; head nod observed in association with unilateral hindlimb lameness (e.g. in grade* ³**3/5 LH lameness, the head moves down as the LH and RF contact the ground)
• 4 Severe lameness; extreme head nod/pelvic hike; horse is lame in walk but can be trotted*
• 5 Severe, non-weight bearing lameness; horse cannot and should not be trotted*

Question 17

What is lungeing and wy do we do it?

Answer 17

Moving in a circle often exacerbates a lameness. This is due to differences in limb movement and weight distribution between straight line movement and circling, and the introduction of bending/torsional forces that are less apparent when the horse moves in a straight line.

Question 18

What is the aim of flexion tests?

Answer 18

The aim of a flexion test is to assess the horse’s response to sustained, forced flexion of particular joints.

Question 19

What are the 4 main flexion tests?

Answer 19

o Distal forelimb (metacarpophalangeal joint and below)

o Proximal forelimb (carpus and above)

o Distal hindlimb (metatarsophalangeal joint and below)

o Proximal hindlimb (tarsus and above).

Question 20

How do you perform a flexion test?

Answer 20

• Flex the joints in question using moderate, even force for 45-60 seconds.
• While you are flexing the joints, assess whether joint flexion is restricted or resented.
• Trot the horse off as soon as you release the limb.
• Ignore the response in the first 2-3 strides (normal horses may show lameness for the first few strides).
• Determine which leg the horse is lame on in response to flexion, and grade the lameness.
• Compare the response to a flexion test with the response to flexion of the same joints in the contralateral limb.

Question 21

What three things do we consider when lungeing in a circle?

Answer 21

Differences between the outer and inner limbs in:

• Stride length
• Weight distribution
• Joint flexion

Question 22

What is the range of movement of the PIP joint?

Answer 22

Low motion joint so evaluation limited

Question 23

What is the range of movement of the MCP joint?

Answer 23

Bulbs of heel should almost touch ergot

Question 24

What is the range of movement of the carpus?

Answer 24

Large range of flexion movement – cannon almost parallel to radius

Question 25

What is the range of movement of the elbow and shoulder?

Answer 25

Difficult to flex separately – distal limb should be brought up and forward to evaluate any pain / limitations within these joints

Question 26

What is the range of movement of the tarsus and stifle?

Answer 26

Flexed together should be able to get cannon horizontal to ground

Question 27

What is the range of movement of the hip?

Answer 27

Some flexion will occur when flexing hock and stifle

Question 28

What are the 4 limb nerve blocks?

Answer 28

• Palmar digital
• Abaxial sesamoid
• Low four point
• High four point

Question 29

What are the 5 limb synovial blocks?

Answer 29

• Coffin joint
• Pastern joint
• Fetlock joint
• Hock joint (tarsocrural and tarsometatarsal joints)
• Digital flexor tendon sheath

Question 30

How do you go about a Palmar digital nerve block (palmar digital nerves)?

Answer 30

• This is the most distal nerve block. It is performed in the distal, palmar (plantar in hindlimb) region of the pastern.
• Palpate the Deep Digital Flexor Tendon (DDFT) in this region. The neurovascular bundles lie in the groove on the medial and lateral aspects of the leg, just dorsal to the DDFT. They are palpable as small bundles that roll under your fingers.

Question 31

What is de-sensitised by Palmar digital nerve block (palmar digital nerves)?

Answer 31

• A palmar digital nerve block desensitises the caudal 1/3^rd of the foot and sole, including navicular structures, heel bulbs etc.
• Skin sensation is lost on the heel bulbs.

Question 32

How do you go about an Abaxial sesamoid nerve block (palmar digital nerves)?

Answer 32

• This block is performed on the palmar/plantar aspect of the fetlock joint.
• Palpate the neurovascular bundles on the abaxial surface of the medial and lateral proximal sesamoid bones (abaxial means away from the axial or midline). There are both medial and lateral neurovascular bundles, and both must be injected. It is easiest to start with the medial nerves.

Question 33

What is de-sensitised by an Abaxial sesamoid nerve block (palmar digital nerves)?

Answer 33

• An abaxial sesamoid nerve 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.

Question 34

How do you go about a Low 4 point nerve block (palmar nerves and palmar metacarpal nerves)?

Answer 34

• This block is performed in the distal third of the metacarpus.
• The palmar metacarpal nerve emerges below the distal limit or button of the splint bone.
• Palpate the button of the splint bone and inject directly beneath it.
• The palmar nerves lie in the groove between the suspensory ligament and DDFT. Palpate and identify both these soft tissue structures. This nerve should be injected 2-3cm proximal to the button of the splint bone, to avoid the tendon sheath of the DDFT.
• The neurovascular bundles themselves are not palpable.
• This block must be performed on both the medial and lateral aspects of the limb, and again it is easiest to start with the medial nerves.

Question 35

What areas are de-sensitised by Low 4 point nerve block (palmar nerves and palmar metacarpal nerves)?

Answer 35

• This block desensitises all structures distal to the block.
• Skin sensation is lost on the dorsal pastern and fetlock.

Question 36

How do you go about a High 4 point nerve block (high palmar nerves and palmar metacarpal nerves)?

Answer 36

• This block is performed in the proximal third of the metacarpus.
• The palmar metacarpal nerves lie between the suspensory ligament and metacarpal bones. Palpate these structures 2-3cm distal to the carpometacarpal joint. The neurovascular bundles themselves are not palpable. You need to angle the needle from palmar to dorsal and insert it axial to the splint bones to reach the palmar metacarpal nerves.
• The palmar nerves lie in the groove between the suspensory ligament and DDFT. Palpate and identify both these soft tissue structures.
• Note - There is a thick retinaculum in this region, and the injection must be made deep to this to be effective. The skin should not bulge, as the injection lies within the retinaculum.
• Again this block must be performed on both the medial and lateral aspects of the limb, and again it is easiest to start with the medial nerves.

Question 37

What areas are de-sensitised by a High 4 point nerve block (high palmar nerves and palmar metacarpal nerves)?

Answer 37

• This block desensitises all structures distal to the block.
• It is tested by squeezing the suspensory ligament.

Question 38

How do you go about a distal interpharyngeal ynovial joint block?

Answer 38

• 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^o to the horizontal.

Question 39

How do you go about a proximal interpharyngeal synovial joint block?

Answer 39

• 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

Question 40

How do you go about a fetlock (metacarpophalangeal) synovial joint block?

Answer 40

• 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.

Question 41

What are the four mai synovial joints of the hock?

Answer 41

• Tarsocrural (tibiotarsal)
• Proximal intertarsal
• Distal intertarsal
• Tarsometatarsal

Question 42

How do you inject the Tarsocrural joint?

Answer 42

• This is a large and easy joint to inject
• There are four access sites:dorsolateral, dorsomedial, plantarolateral and plantaromedial
• Palpate the large dorsal pouch over the trochlea of the talus. The medial aspect is usually used but avoid the saphenous vein!
• Plantar pouches are only used when there are wounds over the dorsal aspect. These are in the space between the calcaneus and the plantar aspect of the tibia.

Question 43

How do you inject the Tarsometatarsal joint?

Answer 43

• This is a narrow joint, best accessed from the lateral aspect.
• Palpate the proximal aspect of the fourth metatarsal bone, and use firm palpation to identify the groove between it and the fourth tarsal bone.
• Introduce the needle approx 1cm above the fourth metatarsal bone angled craniomedially and at a downwards angle of 45^o

Question 44

What are the 5 sites for approaching the digitial flexor tendon sheath?

Answer 44

• Lateral and medial proximal pouches
• Lateral and medial pouches below the annular ligament
• Distal pouch (midline of pastern)

Question 45

Where is the proximal pouch of the digtal flexor tendon sheath and how is it accessible?

Answer 45

• This lies in the palmar region of the distal cannon, proximal to the proximal sesamoid bones
• The tendon sheath is accessible between the DDFT and suspensory ligament (site of windgalls) from either the medial or lateral aspect

Question 46

How is the fetlock region of the digtal flexor tendon sheath accessible?

Answer 46

• This is accessed just below the proximal sesamoid bones on the lateral or medial palmar aspect of the fetlock
• There is a triangular space between the proximal annular ligament, the base of the sesamoid bones, the flexor tendons and the palmar aspect of the first phalanx

Question 47

How is the distal pouch of the digtal flexor tendon sheath accessible?

Answer 47

• This is accessed in the distal palmar pastern at the site where the Superficial Digital Flexor Tendon (SDFT) bifurcates and the DDFT becomes more superficial
• Palpate the bifurcation of the SDFT, introduce the needle from distal to proximal, beneath the skin and SDFT bifurcation, but superficial to the DDFT