Page 337 - Adams and Stashak's Lameness in Horses, 7th Edition

Diagnostic Imaging 303

evaluated with ultrasound. A working knowledge of the that may compromise image quality. When clipping and
normal anatomy is critical for accurate tendon and liga­ shaving is not possible, then the limb should be thor­
VetBooks.ir joints, sheaths, and bursae. 31,46,85,90,99 Ultrasonography is Application of alcohol to the hair coat may enhance the
oughly washed with warm water and detergent.
ment ultrasound examinations as well as those involving
sound transmission. To acquire the best image, a scan
routinely utilized for defining morphological change in
the superficial digital flexor tendon (SDFT) and deep head with a frequency of at least 7.5 MHz but frequen­
digital flexor tendon (DDFT), the suspensory ligament cies of 10–18 MHz is preferable. Low frame rates should
(SL), the accessory ligament of the DDF (ICL), and the be used to give higher‐line density and improved resolu­
distal sesamoidean ligaments (DSLs) of the pastern tion. Most superficial structures can be visualized at a
region. The subcutaneous tissue, paratendinous tissue, scan depth of 2–4 cm often with the use of a standoff
and vessels should be assessed as well. While the objective pad. The use of a standoff pad is helpful for the evalua­
is to evaluate the morphological characteristics of the soft tion of superficial structures, such as the palmar or plan­
tissues of the musculoskeletal system, the contour of the tar annular ligament and the SDFT in the pastern region.
cortical bone in this region should also be evaluated. A standoff pad is a gelatin‐based pad that is placed
Most importantly, diagnostic ultrasound is the most between the probe and the skin surface. By increasing
useful and practical tool to monitor the repair of these the distance between the probe and the skin surface, the
structures and guide the rehabilitation of tendinous and near‐field artifacts that are seen in the higher portion
ligamentous structures. Many other soft tissue structures (near field) of the image are now at the level of the
can also be evaluated including muscle, musculotendi­ standoff pad instead of being over the structure of inter­
nous junctions, tendon sheaths, and bursae associated est. In many cases, the footprint of the transducer is lim­
with the tendons and ligaments. Joint injury (which will ited and restricts the ability to examine the medial and
be discussed later in this section) is very effectively exam­ lateral margins of the tendons and ligaments. Utilizing a
ined with radiography and ultrasonography. These imag­ standoff may increase the footprint and improve the
ing tools are considered complementary and provide examination of the structures in the same field of view.
more information about a region/joint than either tool However, manipulation of the probe to a more abaxial
used alone. Joint examination should include evaluation position with the probe angled more medially and later­
of the periarticular structures such as the collateral liga­ ally may be required to evaluate the peripheral margin(s)
ments and extensor/flexor tendons, joint capsule, and of a structure.
joint fluid accumulations. Real‐time imaging capability The ultrasound examination should be performed in
of ultrasonography allows the use of interventional tech­ a systematic manner with each structure evaluated from
niques (like needle insertion for injection or aspiration/ proximal to distal to ensure a complete and thorough
biopsy), which can provide additional clinical infor­ tendon/ligament evaluation. The examiner should
mation. 10,16,60,93 Ultrasonography is also effective at eval­ develop a systematic approach to screening the limb
uating a variety of other musculoskeletal problems such such as the technique described by Genovese and
as fractures of long bones, osteitis/osteomyelitis, foreign Rantanen. 40,41,72–74 This approach provides a survey of
body penetration, and implant infection, as well as being all structures including veins, arteries, subcutaneous tis­
utilized intraoperatively to assist with some surgical sue, paratendinous tissue, and bone contour at specific
procedures. 11,81,104 levels in the metacarpus/metatarsus. A standardized
scanning protocol has numerous advantages, but most
importantly it provides a means for clinicians to effec­
tively screen the limb and as a tool to accurately com­
PATIENT PREPARATION AND SCAN PROTOCOL municate about their findings. This imaging protocol is
based on the metacarpus length being approximately
Confirmation that lameness is associated with a spe­ 24 cm in length or roughly three hand widths of a per­
cific structure or area is critical. Localization of lame­ son’s hand or 8‐cm/hand breadth. The metatarsus is
ness should include a clinical examination with detailed longer than the metacarpus and measures approximately
palpation of the limb with diagnostic nerve blocks per­ 32 cm or roughly four hand widths in length. These
formed when necessary. In most instances, injection of zones are numbered 1–3 in the front limb and 1–4 in the
diagnostic anesthesia into an area will not interfere with hindlimb. Each of these zones are further subdivided
the ultrasonographic examination. Occasionally gas into two equal zones named A and B (each being 4 cm)
bubbles in the injectate may inhibit sound transmission such that the front limb has zones 1A, 1B, 2A, 2B, 3A,
and necessitate performing the exam on a subsequent and 3B. The area associated with the proximal sesa­
day. Tranquilization may be necessary and can assist moid bones of the fetlock is considered zone 3C (or 4C
with uncooperative or anxious patients. Patient prepa­ in the hindlimb). Some authors utilize a simple numeri­
ration is very important, and both limbs should be cal scheme with the front limb having levels 1–7 and the
clipped and prepped as strain‐induced tendon and liga­ hindlimb having levels 1–9. These levels are the same
ment injury can occur bilaterally with one limb being zones mentioned above but without the letter designa­
more severely affected than the other. Shaving is fre­ tions (Figures 3.89–3.106).
quently required to give a higher‐resolution image. A To more completely assess the architecture of the SL
scrub with a detergent is generally necessary to remove branches, it is necessary to incline the transducer more
dirt and debris. Many clinicians do a 5‐minute sterile medial to lateral or lateral to medial as the examiner
prep with antiseptic solution/detergent followed by an progresses distally until they attach to the proximal
alcohol rinse. Liberal use of ultrasound gel is important aspect of their respective proximal sesamoid bone. The
although excessive gel can cause a lateral image artifact imaging protocol for the pastern is based on zones