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ImagIng EssEnTIals
Peer reviewed
Small Animal
radiography
Stifle Joint
and CruS
Danielle Mauragis, CVT, and
Clifford R. Berry, DVM, Diplomate ACVR
This is the fourth article in our Imaging Essentials series,
which is focused on providing comprehensive information on
radiography of specific areas of dogs and/or cats. The first 3
articles are available at todaysveterinarypractice.com:
•Small Animal Thoracic Radiography (Sep/Oct 2011)
•Small Animal Abdominal Radiography (Nov/Dec 2011)
•Small Animal Pelvic Radiography (Jan/Feb 2012).
Stifle RAdiogRAphy oveRview
stifle radiographs are routinely needed in
cases of trauma and lameness associated with
common stifle joint abnormalities including:
• Medialandlateralluxatingpatella
• Ligamentousinstabilitysecondarytocranial cruciate injury.
High-quality, correctly positioned radiographs are required in order to provide
accurate assessment of the osseous and
soft tissue structures of the stifle joint. This
becomes even more critical when corrective
osteotomies that alter joint alignment (tibial
plateau leveling osteotomy or tibial tuberosity
advancement) are performed.
The standard of care in small animal veterinary medicine for stifle radiographic series
should include straight mediolateral and
caudocranial views. Following a consistent,
repeatable technique for obtaining stifle
radiographs helps optimize the quality of the
images.
T
he stifle joint is one of the most common orthopedic
radiographic studies. In addition to discussing new
radiographic techniques for evaluation of dogs with
stifle disease, this article also covers stifle anatomy, radiographic positioning, image formation, and quality control.
RAdiogRAphic Stifle AnAtoMy
The components of the stifle joint (Figure 1, page 54) include
the:
•Distalfemur
•Proximaltibia
•Foursesamoidbones,includingthepatella,fabellaeofthe
origin of the lateral and medial gastrocnemius muscles,
andfabellaoftheinsertionofthepopliteusmuscle.
The patella normally articulates with the trochlear groove of
the cranial distal surface of the femur. There are two femoral
condyles (medial and lateral) that articulate with the medial
andlateralmenisci,twoc-shapedfibrocartilagestructuresthat
coverthetibialcondyleandalleviatetheincongruitybetween
thetwosurfaces.Thefemoralandtibialcondylesbarelydirectly
articulateinthenormalstiflebecauseofthemenisci.
The fibular head forms a fibrous connective tissue joint
with the proximal aspect of the lateral proximal tibia. The
fibulaisalateralanatomicstructureandthetibiaislocated
in a medial anatomic position.
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| small anImal PElVIc RadIogRaPHy
A
B
Figure 1. Mediolateral (A) and
caudocranial (B) radiographic
images of the stifle joint of a mature dog: (A) femur; (B)
tibia; (C) fibula; (D) patella; (E) fabellae of the gastrocnemius muscles; (F) fabella of the popliteus muscle
withthesidetoberadiographedclosesttothetableand
marked with a lead marker in the collimated area as right
(R) or left (L). This radiopaque marker is placed along
thecranialaspectofthelimbandshouldnotbesuperimposed over any anatomic structure (Figure 2).
•The thoracic limbs should be taped together and
pulled cranially to assist with restraint and ensure lateralpositionofthebody.
•Placeasmallspongeunderthedorsalaspectofthepelvis to help the femoral condyles remain superimposed
overeachotherintheproximaltodistaldirection.
•Thepelviclimbnotbeingradiographedistapedsoitis
abductedawayfromthestiflebeingradiographed.This
isaccomplishedbytapingaroundthestifleandtarsus
andsecuringthetapetothetable.Ifseveredegenerative joint disease of the coxofemoral joints is present,
thelegmaybepulledforwardandtapedtothetable.
•Asmallspongemayneedtobeplacedundertheplantar surface of the tarsus to rotate the stifle; this will
assist in aligning the femoral condyles in the cranial to
caudal direction.
Thelateralfabella(sesamoid)oftheoriginofthehead
ofthegastrocnemiusmuscleiselongatedinaproximalto
distaldirectioncomparedwiththemedialfabella.Both
fabellae are located at the proximal, caudal margin of
the femoral condyles. The popliteal sesamoid is located
along the medial Collimation
aspect of the caudal •Palpate the epicondyles of the femur and place the
center of the collimator light at this point.
proximalmarginof
•Collimatesothefieldofview(FOV)includesthedistal
thetibialcondyle.
thirdofthefemurandtheproximalthirdofthetibia.
It is also important to include all of the soft tissues
Stifle
cranialtocaudaltothepelviclimbatthelevelofthe
RAdiogRAphic
stifle joint.
expoSuRe
The technique used •Caudally,itisimperativetovisualizethefascialstripe
that normally runs in a proximal to distal direction
for an average
along the caudal aspect of the joint as well as the soft
weight, medium to
tissuemusculatureandpopliteallymphnode.Caudal
largedogis60kVP
displacementofthisfascialstripecanbeindicativeof
Figure 2. A patient positioned for
and 3 mAs for a lata mediolateral radiograph of the left
stifle joint effusion and/or capsular thickening.
eral projection and
stifle joint. Note the positioning of the
66 kVP and 3 mAs •Cranially,thecollimatedFOVshouldincludetheskin
sponges beneath the pelvis and the
margin and the patellar ligament along the inside of
for a caudal cranial
tarsus to allow correct positioning
theskinmargin(thinsofttissueligamentseenextendprojection, with
and alignment of the femoral coning from the distal margin of the patella to the cranial
the stifle placed
dyles. The collimated area includes
and proximal tibial tuberosity). When technique is
directly
on
the
casthe caudal and cranial skin margins
correct,theskinmarginandpatellarligamentwillbe
sette
or
detector
and the distal femoral diaphysis and
easily visualized along the cranial aspect of the stifle
(no grid used).
proximal tibial diaphysis. The limb
joint (Figure 1A).
not being radiographed is taped in
To
s et
t he
an abducted position.
technique for a
lateral projection, caudal to cranial or cranial to caudal images
measure the stifle at the level of the femoral condyles in Positioning
themedialtolateralplane.Forthecaudaltocranialstifle Fortheorthogonalview,thestifleshouldbeimagedina
projection, measure the level of the distal femur in the caudal to cranial or cranial to caudal direction. The caucaudal to cranial plane. The cranial caudal measurement dal to cranial projection will place the stifle joint nearest
will be larger than the medial lateral measurement for to the radiographic cassette or digital detector, reducing
image magnification and potential geometric distortion.
most dogs and cats.
Averticalorhorizontalbeamradiographcanbemade;
however,theabilitytotakehorizontalbeamimageswill
Routine viewS of the Stifle Joint
beconstrainedbythemachinebeingused.Inallcases,the
Mediolateral projection
radiopaqueIDmarker(RorL)shouldbeplacedalongthe
Positioning
Foramediolateralimageoftherightorleftstiflejoint,the lateral aspect of the stifle joint, avoiding superimposition
patient is positioned on the table in lateral recumbency overanystructuresbeingradiographed.
54
Today’s Veterinary Practice March/April 2012
A
B
Figure 3. (A) Patient positioned for a vertical beam
caudal to cranial radiograph of the left stifle joint; (B)
Photograph taken from the side showing the angle
of the x-ray tube head and position of the patient in
sternal recumbency for the caudal to cranial radiographic projection.
nial aspect of the limb and secured to allow the
radiographertoleaveduringexposure.
Collimation
For the ventrally recumbent patient (Figure 3), palpate the femoral epicondyles at the level of the stifle joint
and place the center (cross hairs) of the collimator light
at this point.
•CollimatesothattheFOVincludesthedistalthirdof
thefemurandtheproximalthirdofthetibia.
•Thex-raytubeheadshouldberotatedapproximately5
to 10 degrees caudally (angle light from caudal to cranial as seen from the dog) to prevent superimposition
ofthefemurandtibiaatthelevelofthestiflejoint.
•Thetubeangleisdependentonthemusclemassofthe
dogwhenthelimbisinanextendedposition.
For the laterally recumbent patient (Figure 4), the
x-raytubeheadisrotated90degrees,positioningitpar1. Vertical Beam Positioning: Caudal to Cranial Technique allel with the tabletop and perpendicular to the pelvic
•Thistechniqueworkswellforsmallerdogsandcats. limbbeingradiographed.
•Thepatientcanbeplacedinventral(sternal)recum- •The x-ray beam is centered on the femoral condyles,
bency with the pelvic limbs pulled caudally, placwith the horizontal line of the collimator light cross
ing the affected stifle in the center of the cassette/
hairpositionedmidlinewiththefemur/tibia.Collimate
detector (Figure 3A).Thepatientcanbeplacedina
toincludethedistalthirdofthefemurandtheproxiV-troughtohelpkeepthethoraxandpelvisstraight.
malthirdofthetibia.
•The x-ray tube head is then angled toward the pes
(pelviclimbdistalextremity)withthecenterofthe
x-raybeamatthelevelofthejunctionbetweenthe
A
thigh and crural musculature (Figure 3B).
•This positioning may not be possible in dogs with
severe hip dysplasia, trauma, or degenerative changesofthelumbarorlumbosacralspinewithoutheavy
sedation or general anesthesia.
2. Vertical Beam Positioning: Cranial to Caudal Technique
NOTE: This positioning results in the greatest degree of
magnification and geometric distortion due to the distance between the stifle joint and the cassette/detector.
•The patient is placed in dorsal recumbency as if
positioning for a pelvic ventrodorsal radiograph.
Thepelviclimbsareextendedtopositionthestifle
jointascloseaspossibletothetabletoporimaging
cassette/digital detector.
•Thex-raytubeheadisnotangled;instead,itispositioned perpendicular to the tabletop as routinely
usedforverticalbeamradiography.
3. Horizontal Beam Positioning: Caudal to Cranial
Technique (Figures 4A and 4B)
•This technique works well for medium- to largebreeddogs.
•Thepatientisplacedinlateralrecumbencywiththe
stiflejointtobeimagedinanondependentposition
away from the table. The affected limb is placed
on sponges and pulled distally so that the limb is
straight and parallel with the tabletop, being perpendicular to the pelvis.
•The cassette/detector is then placed along the cra-
B
Figure 4. (A) Patient in lateral recumbency for a
horizontal beam caudocranial radiograph of the stifle
joint. Note the sponges used to keep the leg aligned
with the dog’s pelvis so the stifle joint does not angle
toward the table. Also note the position of the x-ray
tube relative to the tabletop and the cassette. The
film focal distance is maintained at 40 inches; (B)
Photograph from the end of the table showing the
pelvic limb across the digital detector.
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small animal Radiography: The stifle Joint and crus
ImagIng EssEnTIals |
| small anImal PElVIc RadIogRaPHy
QuAlity contRol
•Distalthirdofthefemur
Forqualitycontrolofanydiagnosticimage,remember
•Proximalthirdofthetibia
the following 3-step approach:
•Patellaandothersesamoidbones
1. Is the technique appropriate?
•Softtissues,includingthemusculatureandpopli All bones should be sharply margined and clearly
teal lymph node along with the cranial and caudal
visualized. Enough x-ray penetration should be
skin margins.
present to clearly expose the normal cancellous 3. Is the positioning lateral and straight?
(intramedullary) bone pattern of the distal femur
•In a straight mediolateral image, the femoral
and proximal tibia. However, the exposure should
condyles should be superimposed over each
notbesogreatthatthesofttissuesareoverexposed
otherandthefibularheadshouldbeinacaudal
andnotvisualizedinthefinalimage.
positionalongtheproximalportionofthetibial
2. Is the appropriate anatomy present within the
condyle.
image?
•Onthecaudocranialimage,thepatellashouldbe
Giventhatthedesiredtechniquehasbeenattained,
inacentralposition,withnooverlapbetweenthe
make sure that the appropriate anatomy is included.
femoralcondylesandthetibialcondyle.
The lateral and caudal cranial projections should
•Thefemoralcondylesshouldbeequalinsizeand
include the:
shape.
RAdiogRAphic viewS foR Specific
oRthopedic SuRgicAl pRoceduReS:
preoperative, postoperative, & follow-up Studies
tibial plateau leveling osteotomy
Thetibialplateaulevelingosteotomy(TPLO)lateral
is a special projection. Its purpose is to position the
proximaltibiawheretheproximaltibialjointsurface
is highlighted. This allows the surgeon to consistently
and repeatedly determine joint orientation in order
toquantitatethetibialslope.Thisassessmentisthen
usedtoplantheosteotomythatwillbeperformed
during surgery (Figure 5).
Mediolateral Projection
• Themediolateral
projection includes
thecrus(tibiaand
fibula)fromthe
stifle joint (distal
femoral diaphysis)
distaltotheproximal metatarsus.
Boththestifle
and tarsal joints
areflexedata
90-degreeangle.
•Thecenterofthe
collimator light
shouldbeplaced
just distal to the
center of the stifle
joint(proximal
third). This will
allow medial and
lateraltibialcondyle margin imposition.
56
A
•Theintercondylareminencesneedtobesuperimposedinproximaltodistalandcranialtocaudal
directions.
•However,duetotheanatomyofthefemurinsome
dogs,theintercondylareminencesmaybesuperimposedwhilethefemoralcondylesarenot.Forthe
purpose of surgical measurements, it is more important for this view to have the intercondylar eminences superimposed rather than the femoral condyles.
Caudocranial Projection
•Thecaudocranialprojectionshouldincludethe
distalfemur,entirestiflejoint,andcrusandextend
distaltotheleveloftheproximalmetatarsi.
B
c
d
Figure 5. (A) Lateral positioning of the patient for a TPLO lateral radiograph. In this image,
the dog has been placed in a similar position as seen in Figure 2A; however, the stifle and
tarsal joints are flexed at 90 degrees. (B) Pre-operative, postoperative, and (C) mediolateral
radiographs from a dog that has had a TPLO. The arrow in B points to the superimposed
intercondylar eminences. (D) Pre-operative caudocranial image of the stifle joint and crus.
In this dog there is central positioning of the patella (seen superimposed over the distal
femur) as well as central positioning of the medial cortex of the distal tibial intermediate
ridge or cochlea. The arrow points to the medial cortex of the calcaneous.
Today’s Veterinary Practice March/April 2012
A
and the stifle joint angle at a
135-degree angle.
B
Figure 6. (A) Lateral positioning of a
patient with external goniometer for a TTA
pre-operative radiograph; (B) mediolateral
radiographic image of a correctly positioned limb following a TTA procedure.
•Thefemoralcondylesshouldappearequalin
sizeontheimage.
•Thepatellashouldbesuperimposedcentrally
betweenthefemoralcondylesandatamid
position relative to the femoral condyles. This
maynotbethecaseifthedoghaspatellar
luxation(Figure 1).
tibial tuberosity Advancement
Thetibialtuberosityadvancement(TTA)procedure is also used for the surgical repair of cranial cruciate ligament rupture. The mediolateral
radiograph projection for the TTA differs from
theTPLOmediolateralprojectioninthatthe
femurandtibiaarenotflexedbutremainina
morenaturalextendedposition(Figure 6).
Positioning
•CorrectpositioningfortheTTAimagewillbe
determinedbystiflejointlateralityandangleof
thefemurandtibia.
•Thefemoralcondylesshouldbesuperimposed
as with a mediolateral stifle view.
•Usinganexternallyplacedgoniometer,the
stifle joint angle should measure 135 degrees
(Figure 6).
Specific Projections
•Thecaudocranial TTA projection should
includethedistalfemurthroughtheproximal
metatarsalbones.Thepatellashouldbesuperimposedcentrallybetweenthefemoralcondyles,whicharenormallyequalinsize.
•Forthelateral TTA projection, the center of
collimatorlightshouldbeatthecenterofthe
stiflejoint,withtheFOVopenedtoinclude
asmuchofthefemurandtibiaaspossible
Skyline of the patella
The skyline patella radiographicprojectionisusedtobetter
visualizethepatellaandtrochlear groove (Figure 7). This
view is typically used in cases
ofmedialorlateralluxating
patella. As with the caudocranial view of the stifle, there are
two approaches to positioning
basedonahorizontalorverticalpositionofthex-raytube.
Vertical Beam/X-Ray Tube
Radiograph
Positioning:
•Thepatientispositionedinventralrecumbency
withtheaffectedlimbflexedandpushedcranial and lateral.
•Thetibiaispositionedunderthefemurwith
the affected stifle centered in the middle of the
cassette/detector.
•Aspongeisplacedbetweenthebodywalland
femur to help push the stifle joint away from
thebody.
A
B
Figure 7. (A) Vertical positioning of a patient to image
the patella in a cranioproximal to craniodistal oblique
of the patella and trochlear groove of the distal femur;
(B) Correctly positioned skyline radiograph to evaluate
the patella and trochlear groove.
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small animal Radiography: The stifle Joint and crus
ImagIng EssEnTIals |
| small anImal PElVIc RadIogRaPHy
•Thepatientcanbeplacedinav-troughforstabilityandtohelpkeepthethoraxstraight.
Collimation:
•Withthepatientinventralrecumbencyandthe
stiflejointflexed,palpatethedistalfemurand
patella.
•Thecenterofthecollimatorlightispositioned
atthislevel(distalfemur).TheFOVshould
include the distal portion of the femur.
•Ifpossible,thex-raytubeshouldberotated
approximately5degreescranial(towardtheanimal’s head) to prevent superimposition of the
patella,femur,andtibia.Thisviewwouldthen
betermedacranioproximal to craniodistal
oblique projection of the patella or distal femur.
FoV = field of view; TPlo = tibial plateau leveling
osteotomy; TTa = tibial tuberosity advancement
Suggested Reading
Burk rl, feeney dA. Small Animal Radiology and Ultrasonography: A
Diagnostic Atlas and Text, 3rd ed. Philadelphia: Saunders elsevier,
2003.
dismukes di, tomlinson Jl, fox dB, et al. radiographic measurement of
canine tibial angles in the sagittal plane. Vet Surg 2008, 37: 300-305.
dismukes di, tomlinson Jl, fox dB, et al. radiographic measurement of
the proximal and distal mechanical joint angles in the canine tibia. Vet
Surg 2007; 36:699-704.
Keely JK, McAllister H, Graham JP. Diagnostic Radiology and
Ultrasonography of the Dog and Cat, 5th ed. Philadelphia: Saunders
elsevier, 2011.
lambert rJ, wendelburg Kl. determination of the mechanical medial
proximal tibial angle using a tangential radiographic technique. Vet
Surg 2010; 39:181-186.
Sirois M, Anthony e, Mauragis d. Handbook of Radiographic Positioning
for Veterinary Technicians. Clifton Park, nY: delmar Cengage
learning, 2010.
thrall de (ed). Textbook of Veterinary Radiology, 5th ed. Philadelphia:
Saunders elsevier, 2008.
thrall de, robertson id. Atlas of Normal Radiographic Anatomy and
Anatomic Variants in the Dog and Cat. Philadelphia: elsevier
Saunders, 2011.
SedAtion & AnAlgeSiA
although not required, sedation is recommended for
any orthopedic radiographic study as it allows the
patienttorelax,therebyallowingeasierpositioning
(particularlyextensionforcranialcaudalimages).In
addition, sedation also decreases the amount of time
required for repositioning due to lack of patient cooperation. For animals with painful joints, a neuroleptanalgesic protocol provides both sedation and pain control.
Horizontal Beam/X-Ray Tube Radiograph
Positioning:
•Thepatientispositionedindorsalrecumbency
usingaV-trough;thepelviclimbsareflexed.
•Thex-raytubeisrotated90degreesandplaced
inahorizontalposition,situatingthepatella
perpendiculartothecassetteandx-raytube
head.
•Asandbagisplacedoverthetarsusandpesfor
stabilization.
•Thecassette/detectoristhenplacedonthe
abdomenjustcranialtothestiflesandsecured
forexposure.
Collimation:
•Withthepatientindorsalrecumbency,thetube
headisrotated90degreestowardtheaffectedlimb.
•Thecenterofthebeamisfocusedatthepatellar level. The patella with a small portion of the
femurshouldbeincluded.
Duetovaryingthicknessofthelimb,keepthe
collimationoftheskylineFOVofthepatellatoas
smallanareaaspossible,whichreducessecondary radiation. ■
58
Today’s Veterinary Practice March/April 2012
Danielle Mauragis,
CVT, is a radiology
technician at University
of Florida College of
Veterinary Medicine.
She teaches veterinary
students all aspects of
the physics of diagnostic
imaging, quality control of
radiographs, positioning
of small and large animals, and radiation safety.
Ms. Mauragis coauthored the Handbook
of Radiographic Positioning for Veterinary
Technicians (2009) and was the recipient of
the Florida Veterinary Medical Association’s
2011 Certified Veterinary Technician of the Year
Award. This award recognizes an individual for
the many outstanding contributions that person
has made to the overall success of the veterinary
practice operated or staffed by an FVMA
member veterinarian.
Clifford R. Berry,
DVM, Diplomate ACVR, is
a professor in diagnostic
imaging at the University
of Florida College of
Veterinary Medicine. His
research interests include
cross-sectional imaging
of the thorax, nuclear
medicine applications in veterinary medicine, and
biomedical applications of imaging in human and
veterinary medicine. Dr. Berry has been a faculty
member at North Carolina State University and
University of Missouri. He received his DVM from
University of Florida and completed a radiology
residency at University of California–Davis.