Page 195 - Adams and Stashak's Lameness in Horses, 7th Edition

Examination for Lameness 161

VetBooks.ir (A)

(B)

c

Figure 2.151. Low palmar or 4‐point block. (A) Site for palmar
nerve block, but it is recommended to go 1 cm proximal to the distal b
end of the small metacarpal bones. (B) Site for palmar metacarpal
nerve block at the distal end of the splint bones.
a
48
distally. Anesthesia of the skin over the dorsal aspect of
the pastern and fetlock indicates that the block was suc­ Figure 2.152. High 4‐point block. (a and b) Needle positioned
cessful. Some skin sensation may be present over the lateral and medial to block the palmar nerves. (c) Needle positioning
dorsal surface of the fetlock joint as a result of the sen­ to perform the lateral approach to block the lateral palmar nerve.
sory supply from the medial cutaneous antebrachial Needle positioning to block the palmar metacarpal nerves is not
distribution. 56 shown but is located axial to the heads of the splint bones.

aspects of the deep digital flexor tendon (DDFT). A 5/8‐
High Palmar (High 4‐Point Block)
inch (1.5 cm), 25‐gauge needle is inserted through the
The high 4‐point or high palmar block is analogous heavy fascia, and 3–4 mL of anesthetic is deposited
48
to the low 4‐point block because the same four nerves (Figure 2.152a and b). Blocking just the palmar nerves
are anesthetized in the proximal aspect of the metacar­ will not completely desensitize the deep structures of the
75
pus just below the carpometacarpal joint. However, the metacarpus. The palmar metacarpal nerves run parallel
high palmar block is more difficult to perform because and axial to the second and fourth metacarpal bones, and
the soft tissue structures are more closely confined to the each can be desensitized by infiltration of 3–4 mL of local
metacarpus and the palmar metacarpal nerves are anesthetic along the axial surfaces of the metacarpal
located deeper within the axial borders of the second bones (Figure 2.153b and b ). A 20‐ to 22‐gauge, 1.5‐
2
1
and fourth metacarpal bones. In addition, the distal out­ inch needle is directed toward the palmar metacarpus
pouchings of the carpometacarpal joint extend approxi­ along the axial borders of the splint bones until bone is
mately 2.5 cm distal to the joint in close proximity to the contacted. The needle is withdrawn slightly and aspirated
nerves and can be entered when blocking the palmar to be certain that the needle is not within the carpometa­
metacarpal nerves. 23,34 Therefore, aseptic preparation of carpal joint before the anesthetic is deposited. Blocking
the injection sites is recommended when blocking the the palmar metacarpal nerves is usually performed with
palmar metacarpal nerves. the limb held, whereas anesthesia of the palmar nerves is
The proximal palmar nerves are anesthetized in the often easier with the limb weight‐bearing. 48
groove between the suspensory ligament and the DDFT. These four nerve blocks will effectively desensitize
The nerves lie under heavy fascia, palmar to the vein and the deep structures of the metacarpus with the exception
artery, and rest against the dorsal, lateral, and medial of the origin of the suspensory ligament. The medial
34