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DIAGNOSTIC IMAGING OF
LAMENESS IN SMALL ANIMALS
James J. Hoskinson, DVM, and Russell L. Tucker, DVM

Diagnostic imaging is a fundamental part of the evaluation of the

lame small animal patient. Diagnostic imaging is not, however, intended
to serve as a shortcut to diagnosis or to take precedence over a thorough
physical examination. Imaging alone rarely provides a specific indication
of the cause of a particular disease, although it may provide the basis
for establishing potential diagnoses from which the final diagnosis can
be determined with discrimination. 35
The indications for diagnostic imaging include to confirm or refute a
clinically suspected lesion, to suggest or document the site of a suspected
lesion, to characterize the nature and extent of a known or suspected
lesion, to follow the progression of disease or healing, to aid in establish-
ing prognosis, to plan or evaluate surgical therapies, to suggest or guide
additional diagnostic procedures, and to screen for diseases with obscure
clinical signs. 35
The selection of the appropriate diagnostic imaging study is deter-
mined by the anatomic structure to be evaluated and the type of informa-
tion sought. With the advent of newer imaging modalities, anatomic
and functional information about the musculoskeletal system can be
determined with increasing diagnostic accuracy and anatomic resolution.
Survey and contrast radiography, although replaced in some areas
by newer imaging modalities, continue to be readily available, cost-
effective, and accurate tools in the evaluation of the lame patient. It is
recommended that survey radiographs precede any special imaging
studies.
The demand for advanced diagnostic imaging procedures such as

From the College of Veterinary Medicine, Kansas State University, Manhattan, Kansas
(JJH); and the College of Veterinary Medicine, Washington State University, Pullman,
Washington

VETERINARY CLINICS OF NORTH AMERICA: SMALL ANIMAL PRACTICE

VOLUME 31 • NUMBER 1 • JANUARY 2001 165

166 HOSKINSON & TUCKER

nuclear scintigraphy, ultrasonography, computed tomography (CT), and

magnetic resonance (MR) imaging has increased dramatically over the
last 10 years. Veterinarians seeking to improve their diagnostic capabili-
ties and clients willing to pursue "best medicine" have driven this
demand, resulting in the installation of advanced imaging facilities at
most academic and private referral practices. Knowledge of the potential
benefits of various imaging modalities allows veterinarians to optimize
their use of diagnostic imaging in their own practice or in a referral
practice.

SURVEY RADIOGRAPHY

Survey radiography remains the primary diagnostic imaging tech-

nique for evaluation of the lame patient. After localization of the lame-
ness by means of a physical examination, survey radiographs can
quickly and accurately provide morphologic information about the area.
This morphologic characterization of bone and soft tissue abnormalities
can lead to formation of a definitive or differential diagnosis. It can also
delineate the nature and extent of involvement and characterize the
aggressiveness of the lesion. These factors guide further diagnostic tests,
therapeutic plans, and prognoses for the patient. By combining serial
radiographic studies of an area, physiologic information can be inferred
(i.e., fracture healing). The survey radiographic findings in orthopedic
disease are well described in various textbooks. 23,36

FLUOROSCOPY

Fluoroscopy involves the use of a continuous beam of x-rays passed

through the patient and directed toward an image-intensifying system
or digital image-recording system. These systems are linked to a video
monitor, allowing real-time evaluation of the patient.
Heat buildup limits the x-ray tube current (and the number of x-rays
that can be produced) during an exposure. Because of the continuous
x-ray production during the fluoroscopic study, the x-ray tube current
(and the number of x-rays produced per unit of time) is much lower
than that used for standard radiographic exposures. Fluoroscopy results
in a much smaller number of x-rays being used to create a single
image (and thus less detail). Fluoroscopy, however, has the advantage
of allowing evaluation during motion or movement of the patient.
Fluoroscopy can be combined with spot filming to take advantage
of motion and detail. Spot filming involves the temporary increase in the
fluoroscopic x-ray tube current for the production of a higher resolution
radiographic image during fluoroscopy. These spot films may be stored
in a digital format or on radiographic film.
Fluoroscopy may be of value in the evaluation of a number of
musculoskeletal abnormalities. 3D By manipulation of a limb under the
 DIAGNOSTIC IMAGING OF LAMENESS 167

fluoroscope, normal and abnormal joint motion can be assessed under a

range of movements and angles. Fractures may be identified in patients
with inconclusive radiographic findings by manipulation of the limb to
cause the fracture to be seen in tangent to the beam or by removing
overlying osseous and soft tissue structures. This same principle can be
applied to identification of small cartilage lesions of osteochondrosis or
localizing osteochondral bodies in or around joints.
Fluoroscopy can also be used in combination with contrast proce-
dures for the evaluation of a lame patient. Contrast arthrography is
often guided by fluoroscopy. Evaluation of the contrast arthrogram can
be done in real time and during a range of patient motion so as to
more accurately identify small cartilage defects and characterize lesions.
Fluoroscopic guidance can also be of value in guiding biopsy of sus-
pected lesions. In the management of lame animals, fluoroscopy can
guide reduction of osseous structures and placement of orthopedic appli-
ances.

ULTRASONOGRAPHY

Ultrasonography offers a real-time noninvasive method for evalua-

tion of muscular and tendinous structures. Although its role in small
animal musculoskeletal imaging continues to evolve, its use has become
well established in the assessment of equine lameness. 12 Recent improve-
ments in image quality and resolution have resulted in expanded appli-
cation of this technique.
Sound of a specific frequency is directed into a region of the body
by an ultrasound transducer. The interaction of propagated sound waves
with tissue interfaces (differing acoustic impedances) in the body results
in reflection of some of the sound. The transducer detects these reflected
sound waves and converts them into an electric signal that is then
displayed as an ultrasound image.
This imaging modality is particularly well suited to evaluation of
soft tissue structures. Ultrasound travels well through soft tissues and
fluids, and the magnitude of signal is dependent on the number and
orientation of reflectors within the tissue. Because normal tendons and
ligaments consist of many closely aligned parallel fibers, abnormalities
are easily recognized as either high- or low-signal areas in an otherwise
uniform structure. The echogenicity of the lesion also suggests the type
of tissue involved in the lesion (i.e., hypoechogenicity within a tendon
suggests acute hemorrhage or edema and hyperechogenicity suggests
fibrous tissue) (Fig. 1).
In additional to evaluation of tendons and ligaments, ultrasonogra-
phy has a number of other clinical indications in the lame animal.
Ultrasonography can be useful in evaluating the amount and nature of
joint fluid as well as the thickness of the synovium and articular cartilage
and in localizing periarticular mineralization. Although unable to visual-
ize structures beyond the surface of bone, ultrasonography can provide
168 HOSKINSON & TUCKER

Figure 1. Longitudinal ultrasound image of the calcanean tendon of a 5-year-old Viszla

with a history of chronic intermittent lameness. Proximal is to the left, and distal to the right
of the image. There is normal fiber alignment and echogenicity proximally (arrowheads).
Distally there is decreased echogenicity and loss of normal fiber pattern (arrows) . A focal
area of mineralization associated with previous injury is noted resulting in hyperechogenicity
with acoustic shadowing.

accurate evaluation of the periosteum, soft tissue tumors invading bone,

and, in some instances, fractures and sequestration. Abscesses, seromas,
hematomas, and other fluid or cystic masses within soft tissues are
easily visualized and can be aspirated with ultrasound guidance for
therapeutic or diagnostic purposes. Diffuse soft tissue changes such
as cellulitis, edema, or hemorrhage can be identified, localized, and
characterized using ultrasonography. Foreign bodies of the soft tissues
of the musculoskeletal system are easily identified (Fig. 2). Using ultra-
sound imaging and Doppler ultrasound, the integrity of the blood sup-
ply to a region can be assessed.

NUCLEAR MEDICINE

Skeletal scintigraphy is one of the most commonly performed veteri-

nary nuclear medicine procedures. l l Skeletal scintigraphy (or bone scan-
ning) offers high sensitivity for detecting early disease, and the ease of
evaluation of the entire skeleton (or a region) makes it an ideal tool for
screening cases of obscure or occult lameness. Scintigraphy also offers
an easily quantified method for determining the activity of a bone lesion,
allowing assessment of the significance of radiographically identified
lesions of questionable activity and monitoring of lesions in response
to therapy.
 DIAGNOSTIC IMAGING OF LAMENESS 169

Figure 2. A transverse image from the plantar surface of the metatarus of a dog with a
chronic swelling of the distal real limb. The plantar aspects of the metatarsal bones (MT2
and MT3) are identified as curved hyperechoic lines. There is increased thickness to the
soft tissues with a distinct curved hyperechoic structure corresponding to a wooden foreign
body (FB) located plantar (above) the metatarsal bones.

Skeletal scintigraphy involves the intravenous injection of a radio-

labeled phosphonate compound and subsequent imaging of the distribu-
tion of radioactivity within the patient. The most commonly used radio-
pharmaceutical is technetium-99m-labeled methylene diphosphonate
(99mTc-MDP). The distribution of 99mTc-MDP is dependent on delivery
(blood flow) and uptake (osteoblastic activity). Imaging at different times
after injection allows evaluation of different physiologic processes. The
initial vascular phase follows the course of the radiopharmaceutic
through vessels. After distribution in the blood pool, the 99mTc-MDP
rapidly distributes into the extracellular fluid (ECF) space, resulting in a
soft tissue phase. The 99mTc-MDP is taken up by metabolically active
bone over the next 20 minutes or so. The 99mTc-MDP that is not taken up
by the skeleton is renally cleared. Bone phase images are made 2 to 3
hours after injection to allow an optimal bone-to-soft tissue (target-to-
background) ratio.
Vascular phase images made immediately after injection are depen-
dent primarily on blood flow to a region. They are a sensitive method
of identifying hyperemia, ischemia, and abnormal patterns of flow. Un-
like other methods of evaluation of perfusion, the radionuclide readily
penetrates the (normal or abnormal) superficial soft tissues of the limb,
allowing evaluation of deep and superficial vascular supply. Decreased
flow may be seen after frostbite, degloving injuries, or wrapping of
170 HOSKINSON & TUCKER

objects around the limb. Increased vascular flow may be seen in acute
active lesions with hyperemia or neovascularization.
Soft tissue phase images made 2 to 10 minutes after injection repre-
sent the distribution in the ECF. ECF distribution is determined by
delivery to the region (blood flow), flux in and out of the local ECF
space, and the overall amount of ECF in a region. Decreased activity to
a region can occur with ischemia. 16 Increased activity is commonly seen
at sites of active inflammation as a result of increased blood flow and
capillary permeability. Although these changes are nonspecific, they can
be a sensitive indicator of the site of soft tissue injury such as synovitis,
tendinitis, cellulitis, or bicipital bursitis.
Bone phase images are dependent on blood flow, ECF distribution,
and bone metabolic activity. Although all normal bone is constantly
remodeling, areas of bone injury often demonstrate increased rates of
bone activity, which subsequently result in increased uptake of radio-
activity visible as "hot spots" on the scan. The degree of uptake of the
99mTc-MDP is determined by the activity at the lesion. Areas of mild
increased turnover occur with mild degenerative joint disease. More
intense uptake occurs at sites of high bone activity such as fractures,
tumors, or infection. Bone lesions typically exhibit increased activity
within 24 to 72 hours after injury, although radiographs may not demon-
strate lesions for up to 2 weeks.
Bone phase images are extremely sensitive and accurate in assessing
occult lameness caused by stress fractures or nonradiographically appar-
ent fractures. 26 Because bone phase imaging characterizes the metabolic
activity of bone, it can provide a more sensitive indicator of degenerative
joint disease versus radiographs, which are limited to demonstrating
anatomic changes. Scintigraphy may also identify sites of panosteitis or
bone metastasis before radiographic signs are evident,15
In addition to finding lesions that are not apparent, scintigraphy
can characterize the activity at known sites of disease or radiographic
abnormalities. Scintigraphy has been used to determine the level of
activity of degenerative changes at joints/5 confirm bone involvement
at sites of adjacent soft tissue infection, and monitor healing of bone
injuries. 42
Because scintigraphy involves the use of radioactive materials, cer-
tain restrictions to its use apply. Special training and licensing re-
quirements exist in most states for the use of radioactive materials.
Scintigraphy requires moderately expensive equipment ($30,000 and up).
Animals must be placed in radiation quarantine for some period,
usually 12 to 24 hours, during which time, there is a decrease in the
amount of radiation within the patient as a result of biologic and physi-
cal decay.
Scintigraphy is a sensitive but not specific method for assessing
bone lesions. Bone lesions are typically best seen when active. Lesions
may not be seen in animals that have been rested for an extended period
of time or in patients with mechanical causes for lameness.
 DIAGNOSTIC IMAGING OF LAMENESS 171

COMPUTED TOMOGRAPHY

CT has become a well-established diagnostic imaging modality for

small animal musculoskeletal diseases. 8, 10, 13, 14, 20, 28, 29, 31 In CT, multiple
radiographic projections of a particular slice of tissue are made, and
information from all projections is combined to create a single tomo-
graphic (slice) image, Typical orthopedic CT studies include acquisition
of several thin (1-10 mm) slices through the specific region of interest.
The images can be displayed one at a time or reformatted to create
two- or three-dimensional reconstruction images. Similar to conventional
radiography, the diagnostic information from CT is represented as a
gray-scale image based on the differential x-ray attenuation of tissues.
Unlike radiography, CT information is captured by several radiation
sensors, converted into a digital file, and finally viewed as a tomographic
slice on a computer screen. Whereas conventional radiographs have five
radiographic opacities (metal, bone, soft tissues, fat, and air), CT systems
can record thousands of separate opacities ranging from air to high-
density metal. Each of the possible densities (Hounsfield units) repre-
sents the differential linear coefficients of the x-ray absorption as it
passes through the specific section of tissue. In the development of CT,
water was designated to have a Hounsfield unit value equal to 0, air
was designated to be equal to -1000 Hounsfield units, and dense
cortical bone was designated to be equal to + 3000 Hounsfield units.
The fundamental concepts of CT and MR imaging have been reviewed
recently in the veterinary literature?,37
There are several advantages of CT in veterinary orthopedics. High
contrast and resolution of osseous tissues are the hallmarks of CT im-
aging. CT allows better visualization of osseous structures than conven-
tional radiography by eliminating opacities caused by superimposed
tissues13; thus, a more accurate view of articular surfaces and bone
contours is obtained with CT imaging. Additionally, tomographic dis-
play of CT slices imparts a perception of depth, a third dimension
lacking in conventional radiography.28 Furthermore, the ability to manip-
ulate the digital information can be helpful in orthopedic diseases. Once
the CT scan has been completed, clinicians can review the images in a
variety of display formats to enhance soft tissue or osseous structures
individually. This is accomplished by viewing the CT images under
display parameters selected to concentrate on certain attenuation ranges
(window and level). The "window" width selects the overall range of
Hounsfield units to be displayed. The "level" sets the center of the range
of Hounsfield units to be displayed. Orthopedic images are commonly
reviewed in a "soft tissue window" (e.g., window width = 400 Houns-
field units, window level = 40 Hounsfield units) and a "bone window"
(e.g., window width = 2000 Hounsfield units, window level = 400
Hounsfield units) (Fig. 3).
Another useful feature of CT is the ability to create reconstruction
images from the original acquisition data. 28 During CT acquisition, the
tissue slices must be oriented perpendicular to the body part as it is
172 HOSKINSON & TUCKER

Figure 3. Identical transverse CT slices of the elbow joint of a dog displaced in soft tissue
(A) and bone (B) windows.

moved through the imaging gantry. The x-ray attenuation information

from these slices is stored as a three-dimensional numeric matrix in the
computer's memory. It is later possible to create "reconstruction" slices
(i.e., images in a plane other than that in which the information was
obtained) along any desired image axis within the numeric matrix.
This may be helpful when alternate imaging planes provide additional
diagnostic information or determine treatment options. 28 Surface con-
tours of bones and joints can also be created by reconstructing original
slice data into three-dimensional surface views (Fig. 4).
Conventional radiographic arthrography techniques with negative
or positive (radiopaque) contrast agents can be used in combination

Figure 4. Surface reconstruction CT images of the ventral (A) and dorsal (B) aspects of a
dog pelvis. The original data was acquired in axial slices, and reformated for three-
dimensional display.
 DIAGNOSTIC IMAGING OF LAMENESS 173

with CT scanning. 32 High-resolution thin-slice arthrogram images pro-

duced by CT scanning may demonstrate lesions undetected on standard
contrast radiography. Myelography and epidurography can also be per-
formed with CT, yielding superior visualization of the contrast columns
within the spinal canal.
Skeletal CT may be helpful in clinical cases in which standard
radiography is negative or inconclusive and there is a high suspicion of
osseous pa tho logy. 19, 28 CT allows detection of density differences as low
as 0.5% versus approximately 30% with conventional radiography. As
a result, CT reveals osteolysis and osteogenesis before conventional
radiography can detect such changes.
The ability to view images in several image planes may help to
better delineate fracture orientation or bone fragmentation. The use of
CT in complex fractures can aid in planning the repair process or may
reveal articular involvement unrecognized with standard radiographic
projections (Fig. 5). CT has also been helpful in the diagnosis of osteo-
chondral defects and other bone growth disorders. 19,28 The sensitivity of
CT to detect fragmented medial coronoid disease in young dogs has
been reported to be 88% compared with 50% sensitivity using conven-
tional radiography alone.lO CT has also been used to diagnose ununited
anconeal processes and incomplete ossification of humeral condyles. 2o,31
In addition to diagnostic imaging, CT has applications in orthopedic
research. For example, CT offers the ability to noninvasively quantitate
the volume and density of the osseous reaction to various implants,
compounds, or treatment protocolsY, 21 Mineral content of bone can be

Figure 5. Sagittal CT image of a fracture of the lateral trochlear ridge (arrow) that was not
visible on survey radiography.
174 HOSKINSON & TUCKER

approximated within user-defined regions of interest. Cross-sectional

area of long bones and volumetric analysis of bone sections can be
accurately calculated with CT.
There are certain limitations and artifacts that must be considered
with the use of CT in orthopedic diseases. Inherently, the diagnostic
strength of CT is its superior evaluation of bone; although better than
with conventional radiography, distinct contrast between different soft
tissues remains poor with CT. Metal devices create expansive CT artifacts
because of the sum effect of the high attenuation metal, which is of
particular concern to orthopedic imaging. Even small orthopedic im-
plants cast beam-hardening artifacts that partially obscure visualization
of the tissues surrounding them. Whenever the x-ray beam travels
through substantial volumes of dense bone and metal, lower energy
x-rays are absorbed by the dense material, and the mean energy of the
x-ray beam becomes increased. The tissues on the far side of the dense
object seem more radiolucent than expected because of the higher energy
beam overpenetrating the distal tissues. Such artifacts should be antici-
pated in specific anatomic regions, along certain anatomic planes, or if
metal implants or external devices are present.
Another misleading CT artifact is the "slice thickness" or "volume
averaging" artifact. The attenuation information of each tomographic
slice actually displays the average attenuation within each small volume
(voxel) of the tissue. At certain tissue interfaces, the margins or borders
are indistinct or fuzzy. These artifacts can lead to a false impression of
bony proliferation or periosteal reactions.
Several generations of CT 'scanners have been developed since its
original introduction in 1970. Each new generation improves the spatial
resolution and decreases the time required to perform examinations.
Modern helical CT systems are now available with spatial resolution of
less than 1 mm and require scan times of less than 1 minute for an entire
scan. A comprehensive CT examination can often be performed in less
time than that required for the multiple survey radiographic views
necessary to yield similar information. Despite the rapid scan times,
anesthesia or profound sedation is required to eliminate patient motion,
which results in image degradation.
With CT scanners becoming more common in veterinary medicine,
orthopedic applications should continue to expand. The excellent osse-
ous detail obtained with CT is unsurpassed with other imaging techno-
logies, and the ability to reconstruct images in any image plane can be
helpful in evaluating complex fractures and articular trauma.

MAGNETIC RESONANCE IMAGING

MR imaging characterizes the magnetic properties of tissues and

does not rely on the x-ray attenuation used in radiographic and CT
studies. MR imaging yields excellent tissue contrast based on emphasiz-
ing the differences in magnetic properties of each tissue. With increasing
 DIAGNOSTIC IMAGING OF LAMENESS 175

accessibility and decreasing costs, MR imaging has become a valuable

imaging modality for lameness evaluations in some small animal pa-
tients.
MR imaging is typically performed in several different MR imaging
acquisition sequences that emphasize different magnetic properties of
tissues. Tl-weighted, T2-weighted, and proton density (PD) properties
are commonly imaged. The time between the radiofrequency pulses and
the time from the radiofrequency pulse to the emitted signal are chosen
to emphasize one or more of these magnetic properties and determine
the specific contrast and appearance of tissues. The timing of acquisition
sequences can be selected to highlight tissue characteristics within articu-
lar cartilage, synovial fluid,30 or cortical and subchondral bone. A con-
ventional MR imaging examination called a spin-echo sequence includes
Tl-weighted, PD, and T2-weighted images. Simplified, Tl-weighted im-
ages emphasize the anatomic characteristics of tissue, PD images display
tissue contrast based on the relative free proton concentrations of each
tissue, and T2-weighted images emphasize the fluid characteristics of
tissue and are sensitive to certain types of pathologic changes. Special-
ized imaging sequences such as gradient echoes or fat-suppression tech-
niques can be used to eliminate or enhance specific tissues and are
helpful when evaluating orthopedic disease. 3o In addition to the type of
sequence, the MR operator selects several imaging parameters, including
slice orientation, the thickness and spacing between the slices, and the
use of contrast agents.
Paramagnetic contrast agents such as gadolinium can be combined
with MR imaging to characterize changes in vascularity and vascular
integrity within tissues, which can occur with neoplastic and inflamma-
tory diseases. Before contrast administration, images are obtained
through the area of interest. Immediately after administration of the
gadolinium, repeat Tl-weighted images are acquired through the same
region. Increased permeability and disruption of vascular integrity cause
leakage of the contrast agent into tissues, resulting in increased Tl-
weighted signal.
Magnetic field strength is measured in tesla (T). Currently, MR
imaging systems used in clinical veterinary medicine range from low-
field magnets (~0.064 T) to high-field magnets (2::1.0 T). The higher field
strength magnets are capable of faster scanning times and have better
signal-to-noise image quality. Unfortunately, high-field strength systems
are expensive to purchase and maintain, limiting them to referral centers
and veterinary colleges. Low-field permanent magnets are less expensive
to purchase and maintain but result in longer scan times and poorer
quality images. Because motion degrades the image quality, long scan
times are a problem for veterinary patients.
Because MR imaging requires the patient to lie motionless for sev-
eral minutes, general anesthesia is usually required for veterinary pa-
tients. In addition, the strong magnetic field prohibits ferromagnetic
metals from being situated close to the magnet system. Nonferrous
magnetic devices (most surgical implants) can be safely introduced into
176 HOSKINSON & TUCKER

the magnetic field, but even small nonferrous metallic implants may
create large imaging artifacts that interfere with visualization of adja-
cent tissue. 5
MR imaging has several advantages for imaging of orthopedic dis-
eases. One of the primary advantages of MR imaging is the ability to
acquire images in any desired anatomic plane. This ability to select the
slice orientation relative to specific structures improves the diagnostic
capabilities of this modality. Second, the high-resolution MR images
demonstrate remarkable tissue contrast in osseous and soft tissue struc-
tures.
Veterinary orthopedic applications of MR imaging have been re-
ported for evaluation of tendons, ligaments, and synovial linings such
as in examinations for bicipital tenosynovitis. 3, 13, 37 MR imaging has been
reported as an excellent method of imaging cruciate ligament (Fig. 6)
and meniscal injuries 4 (Fig. 7) and facilitates the early detection of articu-
lar cartilage destruction. 9 ,41 Other proven applications include the detec-
tion of osteochondrosis, subchondral bone necrosis, osteomyelitis, or
invasive neoplasia of osseous structures 19 (Fig. 8). MR imaging may also
be helpful in the diagnosis of elbow dysplasia. 2s, 33, 34 The potential to
detect early cartilage and subchondral changes is an obvious advantage
of MR imaging over other imaging modalities in orthopedic diseases. 38
The optimal imaging sequences for articular cartilage evaluation, how-
ever, are still under investigation. 30, 41 Development of quantitative MR
assessment techniques, including measurement of magnetic transfer,

Figure 6. Sagittal T1-weighted MR image positioned to visualize the normal cranial cruciate
ligament (arrow). Ligaments and cortical bone structures appear dark due to relatively low
content of unbound hydrogen atoms (fat and water).
 DIAGNOSTIC IMAGING OF LAMENESS 177

Figure 7. Sagittal T2-weighted image of a dog with a tear in the caudal meniscus (arrow).
The area of the meniscal tear appears white (high signal) from hemorrhage and edema at
this site.

Figure 8. Axial T2-weighted image of a dog with a fragmented medial coronoid process
(FMCP). A low signal (black) line separates the coronoid fragment from the remainder of
the ulna (U). While cortical bone appears dark, the fat in the marrow of the ulna has a high
signal (white area).
178 HOSKINSON & TUCKER

changes in signal intensity, and physical diffusion parameters, may offer

the best methods to detect early stages of cartilage abnormalities. 6 ,18
Gadolinium contrast agents can also be used for MR arthrography,
although the benefits are unproved in veterinary medicine. 5,38 Use of a
SOO-IIM solution of gadolinium-DTPA was found to be unrewarding in
delineation of normal articular cartilage and cartilage lesions in dogs
with scapulohumeral osteochondrosis. 39 It has been suggested that the
appearance of articular cartilage seen with contrast administration in
cadaver joint studies differs from that of articular cartilage in live ani-
mals. The use of specific imaging sequences to emphasize the appearance
of joint fluid (strong T2 effect) may yield a sufficient "arthrogram-like"
effect to eliminate the need for contrast. Future modifications of contrast
may include incorporating gadolinium into encapsulated liposomes to
reduce contrast agent diffusion into articular cartilage for better demar-
cation between the joint space and hyaline cartilage,22
The advantages of MR imaging for the diagnosis of spinal and
intervertebral disk disease have been well established in human beings.
In dogs, MR imaging has proven particularly valuable in evaluation of
the lumbosacral region, where conventional radiography, myelography,
and epidurography are often inconclusive. 1 MR imaging has also proven
helpful for the diagnosis of perispinal and nerve sheath tumors.
Several important limitations to MR imaging must be recognized.
The requirement of general anesthesia and the time required for scan-
ning must be considered. The costs of the purchase and maintenance of
the equipment limit availability to referral centers or to teaching institu-
tions. Some veterinarians have developed agreements with human facili-
ties to use their MR imaging systems on a fee basis. MR scanning is a
technical, involved, and interactive process; thus, skilled technical sup-
port is essential. In addition, interpretation of the images requires a
precise knowledge of anatomy and normal tissue patterns. MR imaging
examinations can include several images and multiple sequences, which
must be carefully reviewed and compared. Optimal imaging sequences
and parameters still need to be determined for most veterinary orthope-
dic applications. With continued clinical and research experience, this
modality should become an important orthopedic tool in veterinary
medicine.

CONCLUSIONS

The demand for advanced diagnostic imaging procedures such as

nuclear scintigraphy, ultrasonography, CT, and MR imaging has in-
creased dramatically over the last 10 years. Veterinarians seeking to
improve their diagnostic capabilities and clients willing to pursue "best
medicine" have driven this demand, resulting in installation of advanced
imaging facilities at most academic and private referral practices. Knowl-
edge of the potential benefits of various imaging modalities allows
 DIAGNOSTIC IMAGING OF LAMENESS 179

veterinarians to optimize the use of diagnostic imaging in their own

practice or in a referral practice.

References

1. Adams WH, Daniel GB, Pardo AD, et al: Magnetic resonance imaging of the caudal
lumbar and lumbosacral spine in 13 dogs (1990-1993). Vet Radiol Ultrasound 36:3-13,
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2. Baird DK, Kincaid SA, Hathcock JT, et al: Effect of hydration on signal intensity on
gelatin phantoms using low-field magnetic resonance imaging: Possible application in
osteoarthritis. Vet Radiol Ultrasound 40:27-35, 1999
3. Baird DK, Hathcock JT, Kincaid SA, et al: Low-field magnetic resonance imaging of
early subchondral cyst-like lesions in induced cranial cruciate ligament deficient dogs.
Vet Radiol Ultrasound 39:167-173, 1998
4. Baird DK, Hathcock JT, Rumph PF, et al: Low-field magnetic resonance imaging of the
canine stifle joint: Normal anatomy. Vet Radiol Ultrasound 39:87-97, 1998
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Address reprint requests to

James J. Hoskinson, DVM
College of Veterinary Medicine
Kansas State University
Manhattan, KS 66506