Page 192 - Adams and Stashak's Lameness in Horses, 7th Edition

158 Chapter 2

the nerve, the more specific or smaller the region is that to the point of injection. This can be performed with a
is anesthetized. In most cases perineural anesthesia is blunt object such as a pen, hemostat, or needle cap.
VetBooks.ir distal to the site of injection. However, aberrant nerves applied gently at first with a gradual increase in pres­
These objects should not be jabbed into the skin, but
thought to desensitize the skin and all deep structures
sure. Most horses are receptive to this technique and
exist and should be remembered when interpreting the
response to a block. Some feel that ring blocks are more will quietly respond if the nerves are not totally desensi­
reliable to completely desensitize the skin than local tized. However, some horses are difficult to read, and
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perineural blocks. However, ring blocks are not com­ skin sensation may persist even with an effective block.
monly performed when attempting to accurately locate In contrast, one recent study indicated that lidocaine
the site of lameness. Guidelines for performing perineu­ blocked skin sensation without resolving an experimen­
ral anesthesia are given in Table 2.5. tally induced lameness in 3/8 horses. This difficulty of
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A thorough knowledge of the neuroanatomy of the using skin sensation to indicate the success of a block is
involved region and a good understanding of the limita­ especially amplified for those performed more proxi­
tions of perineural anesthesia are necessary to properly mally in the limb (above the fetlock). Other manipula­
apply and interpret perineural anesthesia. Accurately tive tests that previously caused pain (such as hoof tester
determining whether the nerve has been completely examination, deep palpation, and flexion) may need to
desensitized by the block is often the first step in inter­ be repeated to accurately determine if the block worked.
preting the result. Complete desensitization of the nerve The ultimate test is whether lameness is no longer
is often evaluated by checking the skin sensation distal present, but for those horses that have not improved,

Table 2.5. Guidelines for perineural local anesthesia.

Volume of Sterile skin prep
Specific block Needle size anesthetic recommended (Yes or No) Location
Palmar/plantar digital (PD) 25 g, 5/8″ 1–1.5 mL No Just above collateral cartilages

Basisesamoid (high PD) 25 g, 5/8″ 1.5–2 mL No At the base of the proximal
sesamoid bone
Pastern ring block 22 g, 1–1.5″ 2–3 mL No Above collateral cartilages and
directed dorsally
Abaxial sesamoid 25 g, 5/8″ 1.5–2 mL No Abaxial surface of proximal
sesamoid bone
Low palmar or 4‐point 22–25 g, 5/8–1″ 2–3 mL/site Yes Distal metacarpus (above buttons
of splint bones)

High palmar or 4‐point 25 g 5/8″ and 20–22 g 1.5″ 3–4 mL/site Yes Proximal metacarpus
Lateral palmar (lateral 20–22 g 1″ 4–6 mL Yes Distal to accessory carpal bone
approach)
Lateral palmar (medial 25 g, 5/8″ or 22 g 1″ 3–4 mL No Medial aspect of accessory carpal
approach) bone

Ulnar 20 g 1.5″ 10 mL No 4″ above accessory carpal bone
Median 20–22 g 1.5–2.5″ 10 mL No Caudal to radius below pectoralis
muscle
Medial cutaneous 22–25 g 1–1.5″ 5–10 mL No Mid‐radius near cephalic and
antebrachial accessory cephalic veins
Low plantar or 6‐point 25 g, 5/8″ or 22 g 1″ 2–3 mL/site Yes Distal metatarsus and each side of
long digital extensor tendon

High plantar, high 4‐point 25 g 5/8″ and 20–22 g 1.0″ 3–4 mL/site Yes Proximal metatarsus
or subtarsal
Deep branch of lateral 20–22 g 1.0″ 3–5 mL Yes Lateral aspect of proximal
plantar metatarsus
Tibial/peroneal 20–22 g 1.5″ 10–20 mL/site No 4″ above point of hock on lateral
and medial aspects of limb