Page 197 - Adams and Stashak's Lameness in Horses, 7th Edition

Examination for Lameness 163

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A

a
b 2
b 1
B

C

Figure 2.154. The medial approach to desensitize the lateral
palmar nerve is located on the axial border of the accessory
carpal bone.

Figure 2.155. Forelimb blocks. (A) Site for median nerve block.
of the high 4‐point block). When performed, all deep and (B) Site for medial cutaneous antebrachial nerve block. (C) Site for
superficial structures on the palmar aspect of the metacar­ ulnar nerve block. Inset: (a) Site for median nerve block. (b) Site for
pus distal to the block will be desensitized. This includes medial cutaneous antebrachial nerve block as nerve crosses the
the proximal aspects of the second and fourth metacarpal lacertus fibrosus, which blocks both the cranial (b1) and the caudal
bones and the origin of the suspensory ligament. (b2) branches.
This block can be used instead of the high 4‐point
and is easier to perform with less risk of complications.
However, some clinicians have found it unnecessary to carpi ulnaris and ulnaris lateralis muscles. A 20‐gauge,
block the medial palmar nerve in conjunction with 1.5‐inch (3.8‐cm) needle is inserted through the skin and
blocking the lateral palmar nerve. 75 fascia perpendicular to the limb. Although the depth of
this nerve varies, it is usually about 0.25–0.5 inches
Ulnar, Median, and Medial Cutaneous Antebrachial Blocks (1–1.5 cm) below the skin surface. The local anesthetic
(10 mL) is infused both superficially and deeply in this
Perineural anesthesia is used most frequently up to region. Because the palmar branch of the ulnar nerve
the level of the carpus because the nerves lie superficial gives rise to the lateral palmar and palmar metacarpal
and the injection techniques are relatively easy to per­ nerves, anesthesia desensitizes the lateral skin of the
form. Above this region intrasynovial anesthesia is often forelimb distal to the injection site down to the fetlock.
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used to identify the site of lameness. However, the car­ Also, the accessory carpal bone and surrounding struc­
pus and distal aspect of the limb can be desensitized by tures, palmar carpal region, carpal canal, proximal met­
blocking the ulnar, median, and medial cutaneous ante­ acarpus, SDFT, and suspensory ligament are partially
brachial nerves. The medial cutaneous antebrachial blocked by this technique. Lame horses with lesions in
nerve innervates only the skin, so it is primarily used to the very proximal aspect of the SDFT may only improve
anesthetize the limb for a surgical procedure. The after an ulnar block. 11
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median and ulnar nerve blocks may be used to locate a The median nerve is anesthetized on the caudomedial
painful condition in the distal limb during a lameness aspect of the radius, cranial to the origin of the flexor
examination. For instance, this procedure could be used carpi radialis muscle (Figure 2.155A). The injection site
to rule out lameness of the distal limb if lameness in the is located just below the elbow joint where the ventral
proximal forelimb was suspected. edge of the posterior superficial pectoral muscle inserts
The ulnar nerve is anesthetized approximately 4 in the radius. At this point the nerve is superficial and
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inches (10 cm) proximal to the accessory carpal bone on lies directly on the caudal surface of the radius. A 2‐ to
the caudal aspect of the forearm (Figure 2.155C). 2.5‐inch (5‐ to 6.2‐cm), 20‐gauge needle is inserted
Careful palpation reveals a groove between the flexor obliquely through the skin and fascia to a depth of 1–2