Page 198 - Adams and Stashak's Lameness in Horses, 7th Edition

164 Chapter 2

inches (2.5–5 cm). The needle should be kept as close to structures. In addition, a low PD block is difficult to per­
the radius as possible to avoid the median artery and form in the hindfeet because the fetlock flexes when the
VetBooks.ir 10 mL of anesthetic is usually injected. Blocking this formed with the limb extended behind the horse in a
limb is picked up.
vein which lie caudal to the nerve, and approximately
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The PD and abaxial sesamoid blocks are best per­
nerve alone accomplishes little more than a medial and
lateral palmar nerve block. However, blocking the position similar to that when performing a fetlock flex­
median nerve in conjunction with the ulnar nerve effec­ ion test or applying a horseshoe. The point of the hock
tively anesthetizes most of the important areas of lame­ is held fast by cradling it with the inside of the arm and
ness distal to the blocks. axilla. This position reduces the ability of the horse to
The two branches of the medial cutaneous antebra­ withdraw the limb to kick. Perineural blocks performed
chial nerve are blocked on the medial aspect of the fore­ proximal to the abaxial sesamoid block are usually per­
arm halfway between the elbow and the carpus, just formed while standing close to the horse and with the
cranial to the cephalic vein and just cranial to the acces­ limb on the ground. If the horse is prone to kicking, the
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sory cephalic vein (Figure 2.155b and b ). The nerve is limb can be held fast by grasping the foot, after which
2
1
usually just below the skin; however, its location can the limb is brought forward (similar to that done with a
vary. It is best to block the subcutaneous tissues both cra­ spavin test) to perform the block. 9
nial and caudal to the cephalic vein. A 22‐gauge, 1‐inch
(2.5‐cm) needle is used to deposit 5 mL of anesthetic High Plantar Block
solution. Alternatively, the medial cutaneous antebra­
chial nerve may be blocked as it crosses the lacertus The high plantar block anesthetizes the medial and
fibrosus before it branches (Figure 2.155b). 48,75 lateral plantar and plantar metatarsal nerves just below
the tarsus analogous to the high palmar block of the
forelimb. Anesthesia of the dorsal metatarsal nerves just
The Hindlimb
below the TMT joint may be included in this block to
The neuroanatomy of the distal hindlimb below the provide complete analgesia to structures in the metatar­
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tarsus is somewhat similar to that of the forelimb below sal region and below. The plantar metatarsal nerves
the carpus. The majority of perineural techniques described can be blocked using a 1.5‐inch (3.8‐cm), 20‐gauge nee­
previously for the forelimb are similar in the hindlimb. dle inserted axial to the second and fourth metatarsal
However, limb positioning, restraint, and the technique bones and directed dorsally toward the plantar aspect of
may vary slightly. One difference in the neuroanatomy is the metatarsus. Three to four mL of local anesthetic is
that lateral and medial dorsal metatarsal nerves from the injected into the region of the origin of the suspensory
deep peroneal (fibular) nerve course over the dorsolateral ligament. Inadvertent administration of anesthetic into
and dorsomedial surfaces of the third metatarsal bone and the tarsal sheath or the TMT joint can occur when per­
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digits. Therefore, it is recommended to anesthetize the forming anesthesia of the plantar metatarsal nerve. 20,34,48
dorsal metatarsal nerves dorsally when performing plantar Because of the potential for intrasynovial injection, care­
digital nerve blocks at the pastern and proximal (abaxial) ful skin preparation prior to performing this block is
sesamoid bones and low and high 4‐point plantar nerve recommended. 20,34
blocks. This is accomplished by injecting 2–3 mL of The medial and lateral plantar nerves can be anesthe­
anesthetic subcutaneously, lateral and medial to the tized by placing 3–4 mL of anesthetic through the heavy
long digital extensor tendon using a 5/8‐inch (1.5‐cm), fascia adjacent to the dorsal surface of the DDFT in the
25‐gauge needle. proximal metatarsal region using a 25‐gauge, 5/8‐inch
Intrasynovial anesthesia is performed most frequently needle. If a large volume of anesthetic is used at the site
proximal to (above) the metatarsus in the hindlimb. of the lateral plantar nerve block, the deep branch of the
However, perineural anesthesia of the tibial and pero­ lateral plantar nerve (DBLPN) can also be anesthe­
neal nerves can be used to desensitize the tarsal region. tized. This will block both the medial and lateral plan­
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The tibial and peroneal nerve blocks can also be used to tar metatarsal nerves, negating the need to block these
determine whether the pain from a severe lameness nerves individually. The high plantar block effectively
without clinical findings is located proximal or distal to desensitizes the second and fourth metatarsal bones, the
the hock region. Horses exhibiting subtle lameness are suspensory ligament and its origin, and the flexor ten­
generally not good candidates for tibial and peroneal dons in the metatarsal region. One study concluded that
anesthesia because blocking the peroneal nerve may the high plantar nerve block cannot be used to differen­
affect the horse’s ability to extend the digit, thus making tiate between flexor tendon and suspensory ligament
interpretation of the results difficult. 9 lesions because horses with both conditions improved
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When dealing with the hindlimb, proper restraint and after the block. Because the high plantar block is dif­
body positioning are important to prevent bodily harm. ficult to perform and interpret and can inadvertently
In most cases a twitch is applied, and the handler should block the tarsal sheath or TMT joint, it is not commonly
stand on the same side as the veterinarian. All blocks performed. Most clinicians will perform the DBLPN
should be performed with the veterinarian facing toward block instead.
the back of the horse. The authors routinely begin diag­
nostic nerve blocks at the level of the proximal sesamoid Deep Branch of the Lateral Plantar Nerve (DBLPN) Block
bones unless there is uncertainty regarding foot involve­
ment. If the foot is suspected, a high PD nerve block The DBLPN innervates the proximal suspensory in
in the pastern is usually performed because often there the hindlimb and is removed to treat some horses with
is less concern about anesthetizing more proximal hindlimb proximal suspensory desmitis. This nerve can