Page 372 - Adams and Stashak's Lameness in Horses, 7th Edition

338 Chapter 3

evaluated with elastography. These injuries showed a nutrients. Blood flow begins to increase in the early
progressive increase in stiffness of acute lesions over inflammatory stage, peaks in the fibroblastic phase, and
VetBooks.ir (SLBs) nearest to the insertion on the proximal sesamoid and ligaments receive blood supply from three potential
gradually subsides during the remodeling phase. Tendons
time. Most lesions of the suspensory ligament branches
sources. The primary supply is intratendinous coming
bone were detectable with elastography in longitudinal
orientation with the limb weight‐bearing. Lesions of the predominantly from the musculotendinous junction and
SLBs nearest to the insertion were only reliably detecta­ from its osseous insertion. Within a sheath, tendons
ble in transverse orientation when the limb was off‐ have blood vessels entering the tendon via mesotenon­
weighted. It should be noted that lesions of the PSL, ous attachments. Outside of the sheath blood vessels can
which caused detectable changes with elastography, enter the tendon from the paratenon. The relative con­
were moderate in size and severity, while small lesions of tribution of the blood supply from these different
the PSL near the origin were not detectable using elas­ sources depends on the specific structure and the loca­
tography or with grayscale ultrasound. tion within that structure. Some areas within tendinous
The main limitations of elastography are related to structures are thought to be at risk of injury due to a
the operator‐dependent elastographic images that are reduction in blood flow in specific areas of the tendon
obtained. Manual compression and tissue displacement (i.e. SDFT in mid‐metacarpus DDFT in the fetlock
are difficult to standardize. This study found elastogra­ region). For the metacarpal region of the SDFT, the
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phy to be a valuable and complementary imaging modal­ intratendinous supply is considered the most important
ity for soft tissue lesions of the equine distal limb. These source of blood supply as necrosis was only achieved by
findings would suggest that incorporating elastography ligation of the blood vessels within the tendon whereas
into routine US examinations may be of benefit for stripping the paratenon had no effect. The blood
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characterizing the age of the injury or the stage of heal­ flow in the SDFT has been recorded between 1 and
ing. Elastography may also prove to be valuable for 2 mL/min/100 g, which is similar to the blood flow of
guiding rehabilitation by monitoring the stiffness of resting skeletal muscle and has been shown to increase
lesions over time. two­fold with exercise. 94,105 Injury to the SDF tendon
was associated with an even greater increase in blood
Color Doppler Ultrasound to Evaluate Tendon flow (>300%). A recent study described the microvascular
and Ligament Injury anatomy of the SL of the equine forelimb and found
an abundant intraligamentous microvascular supply
Currently, grayscale ultrasonography is the most pop­ throughout its entire length. The absence of an obvious
ular means of diagnosing equine tendon/ligament inju­ hypovascular area suggests that regional variations in
ries and is the most practical soft tissue imaging tool healing rates of the SL are probably not associated with
available to the equine practitioner. Acute tendon injury the microvasculature anatomy. Alterations in vascula­
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53
manifests ultrasonographically as enlargement often ture are emerging as important diagnostic and prognos­
with hypoechogenicity of the tendon/ligament architec­ tic findings in tendon injuries in both equine and humans
ture on cross section and the appearance of a striated or (Figure 3.125). Neovascularization plays an important
fibrillar pattern in the longitudinal images. These changes role in tendon healing with proper blood supply required
are due to disruption of tendon matrix, with intratendi­ for adequate healing and the quality of repair related to
nous hemorrhage and edema. In more severe injuries the amount of neovascularization as seen in Achilles ten­
there may be changes in the overall shape, distortion of dons in humans. 63
the margins/outline of the structure, and a change in the In humans color Doppler (CD) is widely used in car­
normal anatomical position in relation to other struc­ diovascular examinations to evaluate changes in blood
tures in that area. Typical for any wound, a tendon or flow. It is utilized to visualize both the velocity and the
ligament injury precipitates an increase in blood flow direction of the blood flow that has been proven to be
during the acute inflammatory phase. Depending on the quite helpful in the diagnosis of venous thrombosis, ath­
severity of the injury, the inflammatory phase is usually erosclerotic changes in the carotids, and arterial aneu­
short lived and blends into the subacute fibroblastic rysms. High‐definition CD can allow the examination of
phase of tendon healing. Within a few days of injury, very small vessels in the near field, making it possible to
there is a pronounced angiogenic response with an visualize vessels with CD that are not visible with gray­
increase in the synthesis of collagen during the fibropro­ scale US. One equine study utilized CD to assess vascu­
liferative tissue. The fibroblastic phase of tendon healing lar flow after surgically created SDF tendinitis were
merges with the remodeling phase with a gradual trans­ treated with PRP and found increased blood flow out to
formation of collagen type III to type I as the scar tissue 23 weeks in the treated limbs. The use of CD in the
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matures. This corresponds to a gradual reduction in evaluation of horses with tendon/ligament injury can
blood flow. 33,43,91 Currently serial grayscale ultrasound prove to be problematic due to the creation of artifacts
imaging is the tool of choice at providing important that occur due to probe position. In addition, blood flow
morphologic information especially during this remode­ in the tendon/ligaments of horses can be different in
ling phase and has been found to be quite useful to assess weight‐bearing and non‐weight‐bearing positions.
and monitor healing of soft tissue injuries. However, few Consistent use of CD in equine injuries can hopefully
studies have evaluated blood flow in equine tendon and provide information to help stage an injury (acute,
ligament injury. 48,49,59,94,105 chronic, and acute on chronic) and to assess quality of
Soft tissue injuries such as acute tendon and ligament repair.
lesions rely on vascularization for cell recruitment and Power Doppler (PD) is an even more sensitive
to provide humoral mediators, growth factors, and Doppler method to study the flow of red blood cells