Page 617 - Adams and Stashak's Lameness in Horses, 7th Edition

Lameness of the Distal Limb 583

local anesthesia; therefore, the risk of diffusion is less- poor definition of margins, central or peripheral areas of
ened, and interference with subsequent ultrasonography hypoechogenicity, diffuse reduction in echogenicity,
VetBooks.ir gin of the SL or a high four‐point block with anesthesia tex of the third metatarsal bone (enthesophyte forma-
hyperechogenic foci, and irregularity of the plantar cor-
is decreased. Alternatively, direct infiltration of the ori-
Normally, the SL is the
tion or avulsion fracture).
of the palmar/plantar nerves and palmar/plantar meta-
36,37
carpal/metatarsal nerves can be performed. most echodense structure in the palmar or plantar MC/
In the forelimb, perineural anesthesia of the lateral MT. 37,143 Comparison to the contralateral limb should
palmar nerve usually improves forelimb lameness and be performed, but the disease condition can be bilateral
can be performed just below the accessory carpal bone in 18% of horses, so standardized normal compari-
37
from the palmar or lateral aspect of the limb or on the sons should also be used. Repeat ultrasonographic
medial aspect of the accessory carpal bone. In a minority exams can be performed every 60 days to evaluate
of horses, the ulnar nerve needs to be blocked to com- response to treatment. Although ultrasonography is the
pletely abolish the lameness. Diffusion of local anesthe- most commonly used diagnostic tool, lack of ultrasono-
sia into the middle carpal joint following anesthesia of graphic abnormalities in the proximal SL does not nec-
the proximal suspensory region has been reported. essarily rule out a problem. MRI of horses should be
89
Diffusion occurs most commonly with anesthesia of the considered in horses with lameness localized to the
medial and lateral palmar nerves with needle insertion proximal SL with diagnostic analgesia but without
just axial to the splint bones and can be minimized by ultrasonographic abnormalities. Increased signal inten-
anesthesia of the lateral palmar nerve performed just sity and enlargement or alteration in shape of the origin
below the accessory carpal bone. Additionally, anesthe- have been seen on MRI in horses with PSD, despite nor-
sia of the lateral palmar nerve can lead to penetration of mal ultrasonographic exams. 22,38
the carpal sheath. Inadvertent anesthesia of the middle Radiographic examination may be negative for acute
46
carpal joint and carpal sheath needs to be considered high SL desmitis and tearing of Sharpey fibers. However,
during the diagnostic process of a horse with suspected bone sclerosis of the proximal plantar metatarsal bone,
PSD. It should also be noted that low four‐point block alteration of the plantar subcortical trabecular pattern,
may cause partial improvement in lameness associated and enthesophyte formation were noted in 23 of 47
with PSD due to proximal diffusion of local anesthesia. 88 horses diagnosed with hindlimb PSD (Figure 4.162).
39
In the hindlimb, the desensitization of the deep Additionally, radiography can be used to rule out causes
branch of the lateral plantar nerve is the preferred nerve of lameness attributable to the carpal or tarsal joints. CT
72
block. This block can be performed just distal to the can be used to better define this proliferation. Early
head of the lateral splint bone with the needle directed bone resorption can occur at the origin of the heads of
axial to the splint (Figures 2.156 and 2.157). As in the the SL. Avulsion fracture associated with the origin of the
forelimb, diffusion of local anesthesia or direct penetra- SL can also be observed on radiographic examination.
tion into the tarsometatarsal joint or tarsal sheath can Nuclear scintigraphy can diagnose cases with bone
occur, especially when the direct infiltration of the origin involvement or remodeling, but in horses with con-
of the SL or both the medial and lateral plantar nerves is firmed origin of suspensory lesions has been shown to
blocked. It is often worthwhile to perform intra‐articu- be less sensitive than expected and cannot reliably diag-
lar anesthesia of the tarsometatarsal joint on a separate nose the condition. CT can identify enthesophytes that
41
occasion to confirm diagnosis of PSD. surround the ligament that are not well delineated on
In the forelimbs, desmitis of the distal accessory liga- radiographs.
ment of the deep digital flexor tendon (ALDDFT) must Desmitis of the body and branches of the suspensory
22
also be considered. In one study, lameness due to can be diagnosed with a combination of ultrasonogra-
lesions created in the flexor tendons or proximal SL phy and radiography. Radiographs should be included
with collagenase injection was not reliably abolished to identify the concomitant bone abnormalities such as
until the ulnar block was added. Similar results were distal splint bone fractures and proximal sesamoid bone
69
obtained with hindlimb blocks. 61,70 fractures. Ultrasonography commonly identifies enlarge-
ment and hypoechoic areas within the body or branches
Diagnostic Imaging of the ligament.
Ultrasonographic examination, radiographic exami-
nation, nuclear scintigraphy, MRI, and to some degree, Treatment
CT, particularly contrast CT, are the current methods Treatment for horses with a structural abnormality
for determining the damage within the origin of the on ultrasound and/or radiography consists of a conva-
SL. 22,36,43,72,143,148 Ultrasonography is by far the most lescence program of confinement and slow return to
commonly used modality as it is accessible and relatively exercise. Immediate medical management, including
simple to perform. That being said, lesions in the proxi- anti‐inflammatories, hydrotherapy, and bandaging, is
mal SL are often subtle and difficult to detect, especially recommended to reduce any swelling that may occur
considering interference by both splint bones (particu- and to support the fetlock. If a lesion is present on ultra-
larly in the hindlimb) and the variability in hypercho- sound, initially, stall rest for 2 months followed by
genicity due to differences in the amount of muscle repeat ultrasound is recommended. Hand walking for
present. The entire SL should be imaged in transverse 15 minutes twice daily for the first 4 weeks and for 20
and longitudinal planes. Ultrasonographic abnormali- minutes twice daily for the last 4 weeks can be per-
ties of the SL that are often identified include enlarge- formed if the horse is sound at the walk, the origin lesion
ment of the ligament (linear width and circumference), is not greater than 50% of the cross‐sectional area