Page 358 - Adams and Stashak's Lameness in Horses, 7th Edition

324 Chapter 3

predominant range of motion. This necessitates a joint to some regions of the limb where diagnostic radiographs
have a redundant joint capsule at the dorsal and palmar/ can be difficult to obtain (such as the pelvis and cox­
VetBooks.ir pass over joints with a wide range of motion typically ful to assess both the soft tissues and bony contours of
ofemoral joint). Ultrasonography has proven very help­
plantar surfaces. In addition, tendon and ligaments that
this joint.
have sheaths or bursae to allow these structures to effec­
tively glide across the joint surface throughout their full The diagnostic workup of a joint may utilize ultra­
range of motion. In addition, many tendons that cross a sound to guide interventional procedures to improve
joint have retinacular bands and/or annular ligaments to the clinical information in the workup of a joint.
maintain the position of these structures through the range Visualization of needle placement into the joint can
of motion of that joint. Development of fluid or effusion document the placement of local anesthetic or medica­
within the joint in any of these structures needs to be tion into the appropriate structure (joints, sheaths, or
accurately defined to effectively manage the cause of the bursae) particularly in areas where it can be difficult to
effusion. ensure accurate needle placement (navicular bursa,
articular facets of the cervical spine, shoulder joint, bicip­
ital bursa, coxofemoral joint, etc.). 10,16,56,60,93 Documenting
needle placement and seeing that the injection is within
INDICATIONS FOR ULTRASONOGRAPHY the synovial space (of joints, sheaths or bursae) are
OF JOINTS important to reduce false‐positive and false‐negative
results. Collection of fluid samples can be directed by
The use of diagnostic ultrasound is an excellent ultrasonography improving the recovery rate in situations
adjunct to the radiographic examination of a joint. like septic arthritis. Ultrasound of a joint may guide the
While the soft tissue structures associated with the joint surgical approach to and/or the intraoperative retrieval
can be carefully evaluated, ultrasound examination can of bony fragments (i.e. lateral malleolar fractures of the
prove superior at detecting bony changes such as distal tibia).
the early periarticular changes (osteophyte) manifested Lacerations and puncture wounds to the distal limb
in osteoarthritis than radiographic examination. can traumatize tissue and introduce contaminates such as
Ultrasonography can be utilized in the examinations of hair or debris into a synovial structure. Such foreign
a joint to assess the cartilage, subchondral bone surface, material can act as a nidus for infection and inflammation
and some of the intra‐articular soft tissues of the joint. inducing immediate and delayed immune responses.
A complete ultrasonographic examination of joints Wounds or punctures that are close to a joint should be
requires examination of the joint in a weight‐bearing carefully evaluated for communication with and possible
position as well as imaging the joint in flexion (or contamination of the joint. The ultrasonographic appear­
through a range of motion). In joints that commonly ance of hair shafts within synovial structures has recently
manifest articular cartilage damage such as the fetlocks been reported in horses. Ultrasonographic evidence of
and carpi, the major weight­bearing regions of the joint intrasynovial contamination should direct the clinician to
that are not accessible with ultrasound when the limb is be more aggressive at removing the offending material.
weighted should be examined during joint flexion.
Hyperextension injuries that impact the dorsal articular
surfaces of the joint (such as the medial and lateral EQUIPMENT AND TECHNIQUE
proximodorsal proximal phalanx in the fetlock) can
also be more easily identified with the joint flexed. The same equipment utilized for tendon and liga­
Joints with radiographically obvious lesions should ment examinations is ideal for joint evaluations. The
not be excluded from an ultrasound examination joint should be prepared as for a tendon or ligament
because coexisting soft tissue‐type problems may alter the examination with the joint being clipped (and possibly
prognosis. Some bony abnormalities evident on radiographic shaved, depending on the operator’s preference);
exam are related to soft tissue attachment sites and cleansed to remove dirt, hair, and other surface debris;
require an ultrasound examination to more carefully and liberally coated with a conducting gel. Most joint
assess the extent of soft tissue injury (i.e. apical sesa­ examinations will require clipping and prepping the
moid fracture should be assessed for the degree of SL entirety of the joint surface. The majority of the struc­
involvement to provide a more accurate prognosis). tures evaluated during joint ultrasonography are super­
Some intra‐articular fragments may occur due to avul­ ficial in location well within the focal zones of most
sion of soft tissue attachments (i.e. lateral or medial high‐frequency transducer. Flat‐face linear transducers
malleolar fragments with collateral ligament attach­ of 10–18 MHz are often used because of superior near‐
ments), and ultrasound can help determine the full field resolution and broad field of view. It is helpful in
extent of injury to these structures. Ultrasound can also evaluating most of the structures of the joint at a scan
assist with the surgical approach to the fragment by depth of 2–4 cm. Standoff pads move the superficial
documenting the position as intra‐ or extra‐articular structures out of the near‐field artifact and into the near
and fixed or mobile. Ultrasonography of a joint injury is focal zone of the probe. Standoff pads also improve the
definitely indicated when the radiographic study is footprint by conforming to the skin surface. Lower‐
inconclusive especially when there is synovial effusion, frequency transducers (5 or 7.5 MHz) may be necessary
joint capsule thickening, or focal swelling of any of the to image deeper aspects of the joint such as the caudal
soft tissue structures associated with the joint (osteo­ aspect of the stifle. In the proximal limb the joints are
chondrosis, intra‐articular ligament pathology, periar­ farther from the skin due to muscle coverage. The over­
ticular tendon or ligaments, etc.). In addition, there are lying muscle mass provides a good window for the