Page 199 - Adams and Stashak's Lameness in Horses, 7th Edition

Examination for Lameness 165

be selectively desensitized to aid more accurate diagno­
sis of this condition (Figure 2.156). Two different tech­
VetBooks.ir approach, a 20–22‐gauge, 1‐inch (2.5‐cm) needle is
niques have been described (Figure 2.157). With the first
inserted 15 mm distal to the head of the fourth metatar­
sus and directed perpendicular to skin between the axial
border of the fourth metatarsus and the SDFT to a depth
of approximately 25 mm (Figure 2.156–2.158). 12,35 This
single‐injection technique was considered to be 95%
accurate to block the DBLPN in a cadaver and live horse
study. Alternatively, a 20–22‐gauge, 1.5‐inch (3.8‐cm)
needle can be inserted 20 mm distal and plantar to the
head of the fourth metatarsus and directed proximodor­
25
sally and axial to the bone (Figure 2.157). The needle Tarsometatarsal
is advanced to a depth of 1–2 cm and anesthetic is depos­ joint
25
ited. It is usually best to hold the limb to perform
either of these techniques, and it is the author’s opinion Head of 4th
that the perpendicular approach is easier to perform metatarsus
(Figures 2.156 and 2.157). The single‐injection tech­
nique for the DBLPN is thought to provide a reliable
method for perineural analgesia of the DBLPN for diag­ (A)
nosis of proximal suspensory desmitis of the pelvic limb
with a minimal risk of inadvertently desensitizing struc­
tures within the tarsal sheath and the TMT joint. 25,35
However, two different in vivo studies have shown that (B)

Figure 2.157. The deep branch of the lateral plantar nerve
Tibial n. (DBLPN) can be desensitized by inserting a needle 15 mm below
the head of the lateral splint bone directed perpendicular to the limb
(A) or 20 mm below the head of the lateral splint and directing the
needle proximodorsally and axial to the bone (B).

anesthetic can enter the TMT joint and the tarsal sheath
following this block regardless of the technique used. 12,13
Diffusion of anesthetic both proximally and distally in
the limb can also occur following injection, and the
Medial amount of diffusion is volume dependent. Therefore, a
plantar n. small volume of anesthetic (no more than 5 mL) is rec­
Lateral ommended when performing the DBLPN block to pre­
plantar n. vent inadvertent desensitization of other structures. 2,12

Tibial and Peroneal Block
Anesthetizing the tibial and deep and superficial per­
Head of 4th oneal nerves above the point of the hock desensitizes the
metatarsal entire distal limb. These blocks can be helpful to diag­
48
Deep branch
of lateral bone nose some horses with hock lameness, or they can be
used to rule out whether the pain causing the lameness
plantar n. Lateral is located within the hock or distal limb. However,
plantar blocking the peroneal nerve, particularly the common
metatarsal n. trunk, can affect the ability of the horse to extend the
limb and may cause dragging of the toe or knuckling of
the fetlock. 9,75 This may complicate the ability to assess
improvement in the lameness and injure the horse dur­
ing the lameness evaluation.
The site for injection of the tibial nerve is approxi­
mately 4 inches (10 cm) above the point of the hock on
Figure 2.156. Innervation of the proximal suspensory ligament the medial aspect of the limb between the Achilles ten­
in the hindlimb and the location and positioning of the needle don and the deep digital flexor muscle (Figure 2.159).
following the perpendicular approach to block the DBLPN just below When the horse is weight bearing, the nerve lies close
the tarsus. to the caudal edge of the deep digital flexor muscle.