How to Perform a Standardized Ultrasonographic Examination of the Equine Stifle

HOW-TO SESSION
How to Perform a Standardized Ultrasonographic
Examination of the Equine Stifle
Michel Hoegaerts, DVM; and
Jimmy H. Saunders, DVM, PhD, CertVR, DipECVDI
Authors’ address: Department of Medical Imaging, Faculty of Veterinary Medicine, Ghent University, Salisburylaan 133, 9820 Merelbeke, Belgium. © 2004 AAEP.
1.
Introduction
Injuries of the equine stifle are frequent causes of
hind limb lameness.1–9 Diagnostic intra-articular
anesthesia and scintigraphy can be used to localize
the lameness, but these techniques do not give a
definitive diagnosis. Radiography may provide a
definitive diagnosis, but it offers little information
on soft tissue structures. Ultrasonography (US)
has a high resolution for the evaluation of soft-tissue
structures. It has been proven to be useful for the
diagnosis of stifle injuries.10 –18 However, performing a US examination of the equine stifle requires a
systematic approach and an adequate knowledge of
the cross-sectional anatomy of this joint.
The aim of this study was to establish a protocol
for the standardized and systematic US examination of the equine stifle and to evaluate its usefulness in horses suspected of stifle joint disease.
2.
Materials and Methods
Nine hind limbs of horses euthanized for gastrointestinal disease were used. The animals had no
history of orthopedic problems. Body weight
ranged from 350 to 400 kg. The limbs were properly prepared by clipping the hair, washing the skin
with hot water, and applying acoustic gel. The ex-
NOTES
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aminations were performed with a linear 6- to
9-MHz transducer, a convex 4- to 6-Mhz transducer,a and a linear 7- to 12-MHz matrix transducer.b A protocol was established in five steps (a
“five-step-tour”) for a complete standardized US examination of the equine stifle based on a systematic
approach.
First, the medial femorotibial joint (MFT; step I),
the femoropatellar joint (FP; step II), and the lateral
femorotibial joint (LFT; step III) were evaluated
while the leg was bearing weight. Second, the joint
was flexed 90° for the evaluation of the femoral
condyles, the cranial meniscotibial ligaments
(MTL), the tibial attachment of the cranial cruciate
ligament (CrXL), and the femoral attachment of the
caudal cruciate ligament (CdXL; step IV). Third,
the evaluation of the caudal parts of the MFT, LFT,
and the tibial attachment of the CdXL (step V) was
done while the leg was bearing weight.
Through every step, the movement of the transducer is described using anatomical landmarks.
●
1.
Step I: MFT while the leg was bearing weight
(Fig. 1)
Palpate the medial collateral ligament (MCL),
HOW-TO SESSION
Fig. 3. Reference US picture of the MFT, craniomedial approach. Left, proximal; right, distal; 1, MFC; 2, medial tibial
condyle; 3, fat; MFT REC, medial recess of the MFT.
Fig. 1. Step I: US examination of the MFT. 1, 2, and 3: evaluation of the intermediate, craniomedial, and caudomedial part of
the MM, respectively.
Fig. 2. Reference US picture of the MFT, medial approach. Left, proximal; right, distal; 1, MFC; 2, medial tibial
condyle; 3, medial collateral ligament.
place the transducer on the ligament in a
vertical plane, and scan the MCL and the
medial meniscus (MM) with the US beam
perpendicular to the fibers. Move proximally and distally to scan the femoral and
tibial attachments of the MCL and its connection to the MM. Evaluate the articular
margins of the femoral condyle and the tibial
plateau (Fig. 2).
2. Move cranially to visualize the craniomedial
part of the MM and tilt the transducer in a
craniomedial-caudolateral direction to have
the US beam perpendicular to the fibers of
Fig. 4. Step II: US examination of the FP. 1, evaluation of
lateral (LR) and medial trochlear ridge (MR) of the femur; 2a, 2b,
and 2c, evaluation of the middle, lateral, and medial patellar
ligament, respectively.
the MM. The medial recess of the MFT is
proximal to the MM between the MCL and
the medial patellar ligament (MPL). This
recess contains fluid in clinically normal
horses (Fig. 3).
3. Scan again the craniomedial part of the MM,
pass the MCL, and scan the caudomedial of
the MM. Tilt the transducer in a caudomedial-craniolateral direction to have the US
beam perpendicular to the fibers of the MM.
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HOW-TO SESSION
Fig. 5. Reference US picture of the FP, cranial approach. Left, lateral; right, medial; lr, lateral trochlear ridge; mr, medial trochlear
ridge; s, sulcus; midpl, middle patellar ligament; cart, cartilage of the lr.
Fig. 7. Reference US picture of the LFT, lateral approach. Left, proximal; right, distal; 1, lateral femoral condyle;
2, lateral tibial condyle; LCL, lateral collateral ligament; LM,
lateral meniscus; POP, popliteal tendon.
lear groove (Fig. 5). The lateral patellar
ligament (LPL) is cranial to the lateral trochlear ridge, and the MPL is medial to the
medial trochlear ridge. Scan each ligament
from proximal to distal. Evaluate its fiber
structure and its patellar and tibial attachments. The patellar attachment of the MPL
bends 90° and attaches to the medial parapatellar fibrocartilage. Close to the distal part
of the MIDPL, the cranial recess of the LFT
can be visualized if distension of the joint is
present.
Fig. 6. Step III: US examination of the LFT. LM, lateral meniscus; 1, 2, and 3, evaluation of the intermediate, craniolateral,
and caudolateral part of the LM, respectively.
●
Step II: FP with the leg bearing weight (Fig. 4)
1.
With a horizontal approach, locate the medial and lateral ridges of the femoral trochlea. Scan each ridge from proximal to
distal. Evaluate the subchondral bone, the
articular cartilage, and the synovial membrane. The lateral and medial recesses of
the FP are lateral and medial to the lateral
and medial trochlear ridge, respectively.
2. With a horizontal approach, locate the middle patellar ligament (MIDPL) in the troch214
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● Step III: LFT with the leg bearing weight
(Fig. 6)
1.
Palpate the lateral collateral ligament
(LCL), place the transducer on this ligament
in a vertical plane, and scan the LCL and the
HOW-TO SESSION
Fig. 8. Reference US picture of the LFT, craniolateral approach. Left, proximal; right, distal; fossa ext, extensor fossa of the femur;
sulcus ext, extensor sulcus of the tibia; js, joint space; m. ext long, extensor digitorum longus muscle; per tert, peroneus tertius muscle.
lateral meniscus (LM) with the US beam perpendicular to the fibers. Move proximally
and distally and scan the femoral and fibular
attachment of the LCL. The popliteal tendon is between the LM and LCL (Fig.
7). Evaluate the articular margins of the
femoral condyle and the tibial plateau.
2. Move cranially to visualize the craniolateral
of the LM and tilt the transducer in a craniolateral-caudomedial direction to have the US
beam perpendicular to the fibers of the
LM. Evaluate the tendon of the peroneus
tertius and extensor digitorum longus muscle and the subextensor recess of the LFT
between the LCL and LPL at the level of the
sulcus extensoris of the tibia (Fig. 8). This
recess does not contain fluid in clinically normal horses.
3. Scan again the craniolateral part of the LM,
pass the LCL, and scan the caudolateral of
the LM. Tilt the transducer in a caudolateral-craniomedial direction to have the US
beam perpendicular to the fibers of the meniscus.
●
1.
Step IV: cranial approach with the flexed leg
(90°) (Fig. 9)
Palpate the medial femoral condyle (MFC)
between the MPL and MIDPL and place the
transducer on the condyle in a vertical plane.
Examine the cartilage and subchondral bone
of the MFC (Fig. 10). Go distally and visualize the cranial part of the MM (Fig.
11). Move laterally, turn the transducer 70°
counterclockwise (left limb), and visualize
the MTL and its tibial attachment (Fig.
12). With the convex transducer in a verti-
Fig. 9. Step IV: US examination of the cranial part of the
medial (MM) and lateral meniscus (LM) and its related structures with the leg in flexion. 1 and 2, the cranial meniscotibial
ligaments are visualized by sliding the transducer axially.
cal plane at the level of the MIDPL, visualize
the tibial attachment of the CrXL, tuning the
transducer 20° clockwise (left limb), lateral
to the MTL and the medial intercondylar
eminence of the tibia. With the transducer
in the same position, visualize the femoral
attachment of the CdXL in the intercondylar
fossa of the femur (Fig. 13).
2. With the convex transducer in a vertical
plane and lateral to the LPL, examine the
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Fig. 10. Reference US picture of the MFC with the leg in flexion,
cranial approach. Left, proximal; right, distal; 1, subchondral
bone of the MFC; 2, cartilage of the MFC.
Fig. 12. Reference US picture of the cranial MTL of the medial
meniscus (MM) with the leg in flexion, cranial approach. Left,
lateral; right, medial; 1, MTL of the MM; 2, tibia; 3, medial
patellar ligament.
Fig. 11. Reference US picture of the cranial part of the medial
meniscus (MM) with the leg in flexion, cranial approach. Left,
proximal; right, distal; 1, MFC; 2, medial tibial condyle; 3, cranial
part of the MM.
cartilage and subchondral bone of the lateral
femoral condyle (LFC) through the tendon of
the extensor digitorum longus muscle. Go
distally and visualize the cranial part of the
LM. Move the transducer medially and
turn it 70° clockwise to visualize the MTL of
the LM and its tibial attachment.
●
Step V: caudal approach with the leg bearing
weight (Fig. 14).
With the US beam in a vertical plane and a
caudo-cranial direction, visualize the caudal
part of the MFC, the caudal part of the MM,
the synovial membrane, and the caudal recess of the MFT through the caudal muscles
of the stifle. Visualize the tibial attachment
of the CdXL lateral to the MFC.
2. With the US beam in a vertical plane and a
caudo-cranial direction, visualize the caudal
Fig. 13. Reference US picture of the cranial cruciate ligament
(CrXL) with the leg in flexion, cranial approach. Left, proximal;
right, distal; 1, intercondylar fossa of the femur; 2, tibia; 3, CrXL;
4, caudal cruciate ligament.
part of the LFC, the caudal part of the LM,
the synovial membrane, and the popliteal recess of the LFT through the caudal muscles
of the stifle. Visualize the meniscofemoral
ligament medially to the LFC in an oblique
plane (30° clockwise for the left leg).
1.
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2004 Ⲑ Vol. 50 Ⲑ AAEP PROCEEDINGS
This “five-step-tour” was applied to 20 horses suspected of stifle pathology. The limbs were properly
prepared by clipping the hair, washing the skin with
hot water, and applying acoustic gel. The examination was performed in all horses with a linear 6- to
9-MHz transducer and a convex 4- to 6-MHz transducer.a Five horses had a meniscal tear, collapse,
or mineralization of the MM; 1 horse had a caudal
HOW-TO SESSION
medial MTL, and the CdXL were visualized. The
visualization of the cranial part of the LM and the
lateral MTL were less obvious because these structures are covered by the tendon of the extensor digitorum longus muscle. The tibial attachment of the
CrXL was always anechoic because the fibers could
not be orientated perpendicular to the US beam
because of their oblique orientation.
On step V, the visualization of the femoral condyles and the caudal parts of both menisci depended
on the thickness of the thigh. Because of the complex topographical anatomic orientation, the tibial
attachment of the CdXL was difficult to visualize,
and the MFL was impossible to see.
4.
Fig. 14. Step V: 1 and 2, US examination of the caudal parts of
the medial (MM) and lateral meniscus (LM), respectively.
prolapse of the MM; 1 horse had an avulsion fracture of the tibial attachment of the CdXL; 4 horses
had a desmitis of the MCL or LCL; 5 horses had
osteochondrosis of the lateral and/or medial trochlear ridge; 13 horses had a synovitis of the MFT,
LFT, and/or FP; and 4 horses had patellar ligament
desmitis.
3.
Results
A protocol was established, allowing visualization of
the main soft tissue structures of the stifle joint.
The protocol divided the examination of the stifle in
five steps based on the anatomy of the stifle joint
(three compartments, large muscular mass caudally) and the position of the leg (weight-bearing or
flexed). The more consistent features were an easier and better visualization of the MM compared
with the LM and a lesser organized proximal attachment of the MCL compared with the proximal attachment of the LCL. The visualization of the LM
and the caudomedial part of the MM was consistently better with the convex transducer.
On the 20 living horses, steps I–III allowed an
appropriate visualization of all the anticipated
structures in all horses. The approach with the leg
in flexion (step IV) was difficult because the flexion
was only well tolerated for 3–5 min. Moreover, the
topographical anatomy is complicated. If the horse
permitted us to evaluate the stifle joint in flexion,
the femoral condyles, the cranial part of the MM, the
Discussion
Most US images of the equine stifle joint may be
obtained using a linear transducer with a frequency
ranging from 7 to 12 MHz, although for the deeper
structures, a 4- to 6-MHz convex transducer must be
used. Initially, the evaluation of all the structures
of the stifle joint may be overwhelming for a moderately trained practitioner. Initially, practitioners
may choose to perform routinely steps I (MFT), II
(FP), and III (LFT) of the protocol. When comfortable with these, steps IV and V of the protocol can be
added to the examination. However, even with appropriate training, some structures, such as the
CdXL, can not always be correctly visualized.
US of the equine stifle still represents a technical
challenge. However, with an appropriate knowledge of the cross-sectional anatomy, a standardized
protocol, and sufficient training, the practitioner
will be able to investigate the equine stifle US at an
appropriate level.
References and Footnotes
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a
Logiq 200 pro, General Electric Medical Systems, Milwaukee,
WI 53207.
b
Logiq 7, General Electric Medical Systems, Milwaukee, WI
53207.