Computed Tomography and ComputedTomography Arthrography of the Equine Stifle:Technique and Preliminary Results in 16 ClinicalCases

Erik H. J. Bergman, DVM, Diplomate ECAR;Sarah M. Puchalski, DVM, Diplomate ACVR; Henk van der Veen, DVM; andPeter Wiemer, DVM, Diplomate RNVA

Stifle lameness remains a diagnostic challenge. Computed tomography (CT) and CT arthrography areusable techniques in the horse, and they were useful for the evaluation of osseous and soft tissuestructures in 16 clinical cases. This technique provided more complete diagnostic information, whichallowed for directed therapeutic plans and more accurate prognoses. Authors’ addresses: LingehoeveDiergeneeskunde - VetCT, Veldstraat 3a, 4033 AK Lienden, The Netherlands (Bergman, van der Veen,Weimer). Department of Surgical and Radiological Sciences, School of Veterinary Medicine, University ofCalifornia, Davis, CA 95616 (Puchalski); e-mail: e.bergman@delingehoeve.nl. © 2007 AAEP.

1. Introduction

The stifle is a large and complex joint that is fre-quently implicated in equine lameness.1–3 Al-though its anatomy has been described in detail, thedefinitive diagnosis of stifle injuries, particularly in-tracapsular soft tissue injuries, remains elusive.3–6

Radiography, nuclear scintigraphy, ultrasonogra-phy, and diagnostic arthroscopy have been describedfor diagnosing equine stifle injuries, but limitationsexist for each modality. Radiography and nuclearscintigraphy of the stifle are limited by the superim-position of the hindlimb musculature and the sheersize of the bones comprising the joint. These mo-dalities, although useful for osseous, enthuses, andperiarticular margin evaluation, are generally con-sidered to be less useful for the diagnosis of soft

tissue injuries. Currently, ultrasound is commonlyused to diagnose many soft tissue injuries of thestifle; however, some specific anatomic structurescannot be visualized or are extremely difficult toexamine consistently.4,5,7–9 Diagnostic arthros-copy is used in the evaluation of cartilage, portionsof the menisci, and associated ligaments, but certainregions of the femorotibial joints are very difficult orimpossible to visualize.10

In people, magnetic resonance imaging (MRI) isthe dominant imaging modality for evaluation ofknee injuries, and it has largely replaced most othermodalities.11 When MRI is unavailable, computed-tomography (CT) arthrography of the knee has beenused with very good accuracy to diagnose cruciateligament, cartilage, and meniscal injuries.12–20

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NOTES

The use of CT has been reported for the diagnosisof equine locomotor pathology, and some reportsvalue CT over MRI for the evaluation of osseouslesions.21–25 The addition of intravascular contrastmaterial has also been described as a useful tool forthe evaluation of tendon and ligament injury in theequine distal limb.26,27 One report describes theuse of CT for evaluation of the equine stifle andshows its utility in evaluating the caudal aspect ofthe joint.28 Stifle CT arthrography has been de-scribed in the dog but to our knowledge, not in thehorse.14 The purpose of this paper is to describe atechnique for CT arthrography in the equine stifleand report preliminary results from routine CT andCT arthrography in 16 cases.

2. Materials and Methods

Control Group

Two cadaver hindlimbs obtained from two horses,euthanized because of colic, with no history of hind-limb lameness were used to develop the CT arthrog-raphy technique. The limbs were disarticulated atthe coxofemoral joints and placed on the humantable of a four-slice CT scanner.a On each limb, onestudy consisting of four series was performed for thestifle. One study was performed without contrastmaterial. The three sequential series were ob-tained after injection of contrast into the medialfemorotibial joint (MFTJ) followed by the femoropa-tellar joint (FPJ) and the lateral femorotibial joint(LFTJ). For all imaging sequences, the tube outputparameters were 140 Kv and 266 mAs/slice. Thetilt of the gantry was zero, and the pitch was 0.625.The rotation time was 1.5 s, and overlapping 1.3-mmslices were made. The images were obtained fromproximal to distal and included 5 cm distal to thearticular margin of the tibia to just proximal to thetrochlear ridges of the femur. On these series, thefield of view (FOV) was 20 � 20 cm, and the pixelmatrix was 512 � 512. Each series took �90 s.

Iodinated contrast materialb was diluted 1:1 withnormal saline. All intra-articular injections wereguided using a 12- to 5-MHz blended linear-arrayultrasound transducer.c For the FPJ, 80 ml of di-luted contrast was applied. For the MFTJ andLFTJ, 60 ml of the same substance was used. Aftereach intra-articular injection of contrast material,the leg was extended and flexed several times todistribute the contrast throughout the entire syno-vial cavity.

After the CT and CT arthrogram, the stifle jointswere disarticulated and evaluated to confirm that nogross pathology was present involving the bone sur-faces, menisci, or ligaments. The images generatedfrom these limbs were used as controls for the clin-ical cases described.

Clinical Group

Sixteen horses (450–650 kg body weight [BW]) wereincluded in the clinical group. All horses were re-

ferred between October 2006 and March 2007 to theequine referral hospital (Lingehoeve Dier-geneeskunde, Lienden, The Netherlands) for evalu-ation of a moderate (2–4 of 5 on the AmericanAssociation of Equine Practitioners [AAEP] lame-ness grading scale) hindlimb lameness. The lame-ness was localized to the stifle joint by intra-articular diagnostic anesthesia and by static anddynamic lameness examinations. In each case, acomplete radiographic examination, including cau-docranial, lateromedial, and caudolateral to cranio-medial oblique projections, was performed. Anultrasound examination of the affected stifle wasperformed in all horses using the cranial, medial,lateral, and flexed cranial approach previouslydescribed.5

All of the horses in the study group had a CTcombined with a CT arthrography examination per-formed on at least one suspected compartment.

CT Technique

Each horse had an IV catheter placed in one jugularvein and was pre-medicated with detomidined (0.01–0.02 mg/kg, IV). They were induced with ketam-inee (1 mg/kg) and midazolamf (0.1–0.2 mg/kg, IV).An endotracheal tube was placed, and oxygen wasadministered while general anesthesia was main-tained using an infusion of 500 ml of 5% guaifen-esing with 1000 mg of ketamine and 10 mg ofdetomidine.

The horses were positioned in dorsal or dorsolat-eral recumbency on a custom-built CT tableh withthe lame leg down and positioned within the gantry(Fig. 1).

The lame limbs were positioned in full extensionso that the longitudinal axis of the limb was parallelto the table and perpendicular to the plane of the CTgantry (Fig. 2). The opposite hindlimbs were in fullflexion.

After the initial (pre-contrast) series was ob-tained, the suspected compartment of the abnormalstifle was clipped and aseptically prepared for ultra-sound-guided intra-articular contrast injection.For the FPJ, 80–100 ml of the diluted contrast-material mixture was injected. For the femo-rotibial joints (FTJ), 60 ml of the same substancewas used. After contrast administration, the legwas extended and flexed several times to allow thecontrast to distribute throughout the entire synovialcavity. After injection and flexion and extension ofthe limb, the stifle was repositioned within the CTgantry, and another series using the same imagingparameters was obtained.

CT-Scanning Protocol

Tube parameters and imaging techniques were aspreviously described for the cadaveric limbs with theexception of the FOV. The FOV was adjusted to amaximum of 50 � 50 cm when and if the stifle waseccentrically positioned within the gantry.

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Patient ManagementHorses recovered unassisted in a routine fashion.The horses were maintained under supervision inthe hospital for the two days after the procedure.They were observed for clinical signs related to com-plications of either the anesthesia and positioning orthe intra-articular contrast injection.

Image AnalysisThe images were evaluated using either eFILMWORKSTATION 2.0i or OsiriX 2.7j DICOM viewingsoftware. All images were reviewed by two of theauthors (HJB and SMP). Abnormalities were de-termined by consensus and by comparison to thecontrol-group images. Two horses were euthanizedon humane grounds and dissected for gross-pathol-ogy examination of the stifle joint.

3. Results

Images from the control group were easily obtainedusing the technique described above. The initial

series and each sequential series with intra-articu-lar contrast material provided quality diagnostic im-ages. Beam-hardening artifact was observed onseveral images in all series obtained at the level ofthe distal femur and patella.

The horses in the clinical group had a mean age of10.3 yr (range � 3–18 yr). Twelve Dutch Warm-bloods, two German Warmbloods, one Appaloosa,and one American Paint Horse were included in thestudy group. Intra-articular anesthesia of theMFTJ was positive in nine horses; four horses re-quired anesthesia of all compartments of the stifle,and one horse improved after anesthesia of theLFTJ only. Ten horses had negative radiographs.Five horses had bone remodeling—three at the in-sertion of the cranial-medial meniscotibial ligament(CrMMTL), and two at the insertion of the caudal-cruciate ligament. One horse had an avulsion atthe insertion of the caudal-cruciate ligament. Ul-trasound examination revealed abnormalities ineight horses. The abnormalities included joint ef-fusion in four horses and either medial meniscus(MM) or CrMMTL lesions in four horses. In two ofthe latter cases, the ultrasound findings were con-sidered equivocal. The remaining eight horses didnot have any abnormalities identified on a completeultrasound examination. Three cases with no ul-trasound abnormalities had abnormalities of thecruciate ligaments and/or entheses identified on CT.

Diagnostic CT and CT arthrography images wereobtained for all horses in the clinical group. Insome cases, size of the patient caused difficulty inpositioning so that several attempts to position thestifle centrally in the gantry were made. In allcases, the proximal portions of the FPJ and entirepatellae were not included in the examination be-cause of the physical constraints of the gantry andthe size of the horse. In all cases, the FTJs werecompletely imaged. Beam-hardening artifact waspresent in the images of the proximal aspects of the

Fig. 1. (A) CT gantry with custom table. (B) Horse positioned in dorsal to dorsolateral recumbency with the right hindlimb withinthe CT gantry for evaluation.

Fig. 2. The left hindlimb is positioned in full extension in the CTgantry.

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regional anatomy and in images where the con-tralateral tarsus was within the gantry duringscanning.

Ultrasound-guided intra-articular contrast ad-ministration was successful in all cases. In threecases, contrast material was observed outside of theMFTJ in the periarticular tissues. Flexion and ex-tension of the joint resulted in adequate distributionof contrast medium throughout the joint. For twodays after administration, no clinical signs of reac-tion to the intra-articular contrast injection wereobserved.

The anesthetic time was �45 min in all cases.None of the clinical cases had complications relatedto the anesthesia. Four horses appeared stiff theday after the CT examination. The stiffness wasinterpreted as a result of positioning on the CTtable. These clinical signs abated with conserva-tive management: handwalking and using non-steroidal anti-inflammatory drugs. At dischargefrom the hospital, these horses had returned to theirbaseline lameness.

In all studies, software tools were used to increasethe ability to identify and characterize the bone andsoft tissue structures. Tools that were used in ev-ery case included window and level tools, and themultiplanar reformat (MPR) tool in both DICOMviewers were used in this study. The MPR tool wasconsidered particularly important for evaluation ofthe cruciate ligaments and the menisci.

In the cadaver series obtained before contrast ad-ministration, the following soft tissue structureswere consistently identified: the collateral liga-ments (CL), MM and lateral meniscus (LM), cranial-cruciate ligament (CrCL) and caudal-cruciateligament (CaCL), and three patellar ligaments (PL).After CT arthrography, the aforementioned struc-tures were consistently identified along with severalmore structures: CrMMTL and lateral cranial me-niscotibial ligament (CrLMTL), medial-caudal me-niscotibial ligament (CaMMTL) and lateral-caudalmeniscotibial ligament (CaLMTL), and menis-cofemoral ligament (MFL). Multiplanar recon-structions (MPR) enabled further and betterevaluation of the CrCL, CaCL, MM, and LM afterCT and CT arthrography.

In the cadaver studies, the bony structures com-prising the stifle joint were consistently well visual-ized. Attachment sites of the above-listedligaments were consistently visible. The contrastmaterial in the CT arthrograms allowed for indirectevaluation of articular cartilage as a thin hypo-at-tenuating interface between the subchondral boneand the contrast material within the synovial fluid,but complete evaluation was inconsistent.

In the 16 clinical cases, identification of the ana-tomic structures, both bone and soft tissues, wassimilar to the cadaver studies. In the majority ofcases (14 of 16), lesions were identified that corre-lated to the clinical examination. Most (12) of those14 cases had multiple abnormalities identified.

The distribution of lesions by anatomic location islisted in Table 1. In three cases, communicationbetween the MFT and the FPJ was documented.

In the clinical group, the most frequent lesioninvolved the CrMMTL and its insertion onto theproximal tibia (6 of 16 cases). Ultrasound and ra-diographs consistently underestimated the extent ofbone remodeling in these cases (Figs. 3 and 4).CrMMTL abnormalities were best identified on CTarthrography of the MFTJ and were characterizedas enlarged size, evidence of contrast materialwithin the ligament, and irregular margination ofthe ligament borders (Fig. 5). Bone remodelingwas commonly characterized by irregularly mar-gined osseous proliferation or resorption at the en-theses (Fig. 6).

The second most frequently observed abnormalitywas lesions of the MM (5 of 16 cases). These lesionswere also most identifiable on CT arthrography ofthe MFTJ. Lesions were characterized by abnor-mal medial margination of the meniscus (medialbulging) or contrast-material extension into the me-niscus from the joint space, which indicates a me-niscal tear that has communication with the joint(Fig. 7). In two cases, the CT findings were con-firmed with gross pathology (Fig. 8).

Evaluation of the entire cruciate ligament, eithercranial or caudal, was inconsistent. They were bestidentified in horses having CT arthrography of allcompartments of the stifle. Software tools werenecessary to identify these ligaments. Cruciate-lig-ament abnormalities were identified in 8 of 16horses. The CaCL (five of eight cases) was morefrequently abnormal than the CrCL (three of eightcases). Lesions were characterized as enlarging ormineralizing of the ligament, fragmenting at theorigin or insertion site, or bone remodeling througheither loss or production at the origin or insertionsite (Fig. 9).

Table 1. CT and CT Arthrography Findings in 16 Clinical Cases of StifleLameness

CT and CT Arthrography Findings n � 16

Meniscotibial ligament lesions/entheses 6Meniscofemoral ligament lesions/entheses 1Meniscal lesions 4

Medial 4Lateral 0

Cruciate ligament lesions/entheses 8Caudal CL 5Cranial CL 3

Others 8Cartilage lesions MFTJ 2Subchondral bone lesion MFTJ 2Patellar ligament lesions 2Entheses semitendinosis insertion/deep

digital flexor origin 2Negative (no clinical correlation with

findings) 2

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Other lesions involved cartilage, subchondralbone, patellar ligaments, and enthesopathies ofthe deep digital flexor muscle and the tibial por-tion of the semitendinosus tendon of insertion (8 of16 cases). Cartilage defects were identified byloss of the hypodense line between the subchon-dral bone shelf and the intra-articular contrastmaterial (Fig. 10). In two cases, subchondral os-seous cyst-like lesions with articular communica-tion were identified on CT that could not beconfirmed on radiographic examination. Therewere cases where the CT examination confirmedknown lesions of the patellar ligaments, colla-teral ligaments, and lateral trochlear ridge ofthe femur.

4. Discussion

This study describes a feasible technique for equinestifle CT and CT arthrography and shows its clinicalutility in 16 cases. Historically, CT has been infre-quently used to evaluate the anatomy of the upperlimbs for a variety of reasons, such as the physicalconstraints of the horse, gantry size, X-ray tube

output, and difficulties in linking a table strongenough to support a horse to the CT scanner. Ad-vances in all of these areas in addition to CT-scan-ner software and hardware improvements havemade the technique reported possible. Multislicehelical CT provides overlapping, cross-sectional im-ages with very thin slices, which improves the res-olution and the quality of images produced usingsoftware tools. Multiplanar reformatting, a soft-ware tool, is considered essential for complete eval-uation of the stifle.

CT provides high-quality diagnostic images that,with the addition of intra-articular iodinated con-trast material, enabled visualization and evaluationof the clinically important, currently problematicsoft tissues. The technique of arthrography wasrelatively simple using ultrasound guidance. Thediagnostic quality of images was improved by activemanipulation of the stifle after injection. CT wasvastly superior to radiography for evaluation of hardtissues including bone and dystrophic soft tissuemineralization. Mild radiographic abnormalitieswere generally markedly abnormal on CT images.

Fig. 3. (A) Caudocranial, (B) lateromedial, and (C) flexed lateromedial radiographic projections of the left stifle of a horse with clinicalsigns of MFTJ disease. Lateral and cranial views are to the left. There is irregularly margined lucency in A that is distal and medialto the intercondylar eminence of the tibia in the region of the insertion of the CrMMTL. There is periosteal proliferation on the medialaspect of the femoral epicondyle and periarticular margin of the medial aspect of the proximal tibia. On the lateromedial projectionsin B and C, irregular bone proliferation is present at the base of and cranial to the intercondylar eminence of the tibia.

Fig. 4. Ultrasound images from the horse shown in figure 3. (A) A reference image was obtained from the sound hindlimb. (B) Inthe affected limb, the CrMMTL is enlarged, heterogenous, and hypoechoic. The bone surface of the proximal tibia (T) is irregular.

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This improved visualization of bone remodeling iscaused by the elimination of superimposition of boneand surrounding structures.

In veterinary medicine, reports of CT for evalu-ation of the stifle are limited.14,28 One reportdescribes the use of CT for evaluation of the

Fig. 5. (A and B) Transverse CT MFT arthrogram and (C and D) CT images obtained at the level of the proximal tibia. Medial isleft, and cranial is at the top. Images on the left (A and C) were obtained from a control horse. Images on the right (B and D) wereobtained in the clinical case shown in figures 3 and 4. The arthrogram in B shows the irregular margin of the CrMMTL (arrowheads)and irregular bone loss with surrounding sclerosis at its insertion site in the clinical case (arrows).

Fig. 6. Transverse images through the subchondral bone of the proximal tibia in (A) a control horse and (B) the clinical case shownin figures 3–5. Medial is left, and cranial is at the top of the image. There is a region of sclerosis caudal, medial, and distal to theinsertion site of the CrMMTL (arrowhead). There is irregular bone loss associated with the CrMMTL enthesis that extends distallyinto the proximal tibia and away from the joint surface (arrow).

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equine stifle and similarly concludes that CT addsinformation to radiography regarding bone frag-mentation, bone remodeling, and evaluation of the

soft tissue structures of the caudal aspect of theFTJs.28 In this report, negative-contrast ar-thrography using carbon dioxide also helped to

Fig. 7. Sagittal plane images (A, C, and E) through the MFTJ of a control horse on the left and (B, D, and F) through the MFT of aclinical case on the right. Cranial is to the left. Images progress from abaxial (A and B) to axial (E and F) from top to bottom.In the control horse, contrast material distributes around the medial meniscus. The margins of the meniscus are clearly demarcatedand smoothly margined compared with the clinical case on the right (B, D, and F). Contrast material is present within the cranialhorn of the MM. The contrast material has an arborizing pattern axially and a more linear pattern abaxially that is consistent witha complex meniscal tear. There is increased synovial volume in the caudal aspect of the MFTJ of the clinical case.

Fig. 8. Gross pathology pictures obtained from the clinical case shown in figures 3–6. Medial is left, and cranial is at the top.(A) The proximal aspect of the tibia with the menisci in place are shown. The CrMMTL is abnormal (arrow), and a tear is identifiedwithin the axial margin of the meniscus (arrowhead). This meniscal tear was identified on the CT exam but not the ultrasoundexamination. (B) A close-up image of the CrMMTL (arrow) and meniscal tear (arrowhead) are shown.

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identify meniscal lesions. In our study, CT wasuseful to evaluate the caudal and cranial aspectsof the joint, and intra-articular positive-contrast

arthrography aided in evaluation of not only themenisci but also their associated ligaments in ad-dition to the cruciate ligaments. This improve-

Fig. 9. (A) Caudocranial radiograph and (B and C) frontal-plane reformatted CT images from a horse with stifle lameness. On theradiograph in A, there is remodeling of the proximal aspect of the intercondylar eminence of the tibia and the margins of theintercondylar fossa. There is possibly a free osseous fragment superimposed over the intercondylar fossa. The radiograph alsoshows lucency in the region of the CrMMTL insertion. The CT images of the same region show all of those findings with more detailand show fragmentation or soft tissue mineralization in the CrCL and enthesophyte formation at its insertion.

Fig. 10. (A) Transverse CT image through the subchondral bone of the proximal tibia of a horse with CrMMTL injury and secondaryjoint disease. (B) The white line shows the plane from which the frontal plane reformatted CT image was obtained. (C) Thispathology specimen from the same patient shows the proximal tibia beneath the medial meniscus. Medial is left, and cranial is atthe top. The arrow in B shows that the thin, lucent line produced by the presence of cartilage between the contrast material and thesubchondral bone shelf has been lost. This cartilage lesion shown in C was associated with a focal subchondral lucency and markedsubchondral sclerosis that was not seen on the radiographs of the same horse shown in figure 3.

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ment over the previous report is in part caused bythe advances in CT-scanning hardware, wherecurrently, multi-slice CT can obtain overlapping,thin slices (�1.3 mm).

In human medicine, CT arthrography is proposedas an accurate alternative method to MRI for thediagnosis of cruciate ligament and meniscal inju-ries.16–20,29 In these studies, sub-millimeter over-lapping slices greatly increased the overallresolution of the images obtained. These studiesstate that the images developed through use of themultiplanar reformatting tool are greatly improvedwith overlapping thin slices and that with this tool,imaging planes similar to those acquired in MRI canbe evaluated. Likewise, we found that the MPRsoftware tools were invaluable for the identificationof soft tissue lesions, and we used it in all cases.In humans, the knee is not divided into separatecompartments, making contrast administration lesscomplicated than in the horse. To manage thisproblem, multiple compartments were injected inmost horses. It is interesting to note that commu-nication between the MFTJ and FPJ was docu-mented in only three clinical cases.

CT arthrography offers two distinct advantagesover radiography and ultrasound. The first advan-tage is identification of lesions not previously seenand additional concurrent lesions. The second ad-vantage is that CT arthrography enables a morecomplete evaluation of the extent of known or sus-pected lesions. In cases where the radiographic ex-amination was suspicious or positive for pathology,CT was consistently able to define the nature of theabnormality and the extent of the disease. Thiswas particularly true for the enthesis of the CrM-MTL, CrCL, and CaCL. In several cases, ultra-sound accurately identified the lesions (CrMMTLand MM), but the CT scan documented other lesionsor more extensive pathology than was suspected.In three cases, ultrasound examination did not findany abnormalities, and cruciate-ligament pathologywas identified on CT images. This is consistentwith the difficulty that is commonly encountered inobtaining diagnostic ultrasound images of thisstructure.4,5

Nuclear scintigraphy and arthroscopy are alsoused for the diagnosis of stifle pathology. Nuclearscintigraphy is a physiologic or functional test thatcan be used to identify sites of active bone remodel-ing and is useful for the identification of enthesopa-thies. CT is not a functional test, and activity orinactivity of bone lesions must be inferred using theimaging characteristics and clinical information.The depiction of the anatomy on CT images is supe-rior. Diagnostic arthroscopy is useful for direct vi-sualization of the cartilage and soft tissues in theregions of the joint that are accessible. In most ofthe clinical cases, the proximal portion of the FPJand PL were not included in the CT examinationbecause of the size or positioning of the patient.These regions of the joint are particularly amenable

to arthroscopic, ultrasonographic, and radiographicevaluation. Important regions of the FTJs are in-accessible to arthroscopic evaluation. Additionally,the extent of subchondral bone pathology can beunderestimated if the articular surface of the lesionis small.

MRI is commonly used for soft tissue injury of thehuman knee.11 It is a non-invasive technique thatdoes not use ionizing radiation to generate images.Furthermore, contrast resolution is generally con-sidered to be superior to CT for soft tissues. CTarthrography has sensitivities and specificities sim-ilar to MRI for the evaluation of menisci and cruci-ate ligaments.13,17,19,30 A comparison of the twotechniques for equine stifle pathology is not possibleat this time, because no reports of stifle MRI arefound in the literature. There are two comparisonreports of CT and MRI for locomotor pathology infoot lameness in the horse; they both conclude thatMRI was better for evaluation of the soft tissues, butCT was superior for evaluation of bone patholo-gy.24,25 CT has two major advantages over MRI.First, CT of the equine stifle is possible in clinicalcases, and second, image-acquisition time is consid-erably less, which reduces anesthetic time and riskfor the patient.

A thorough clinical examination is imperative be-fore recommending any advanced imaging tech-nique. Localization of the origin of lameness inaddition to some of the more readily available diag-nostic imaging techniques should be performed be-fore considering CT or CT arthrography. There areadvantages to this approach: major abnormalitiesmay be identified on less expensive tests, and inter-pretation of the clinical significance of abnormalitiesis facilitated. The results from this study suggestthat CT arthrography may be more sensitive andspecific; however, this has not been validatedagainst a gold-standard test. CT does offer a morecomplete evaluation of the stifle. In the authors’opinion, correlative or combination imaging or pa-thology will improve one’s ability to interpret moreroutine imaging studies.

CT arthrography has some limitations. Themost obvious limitation is not specific to this tech-nique and is that the horse must undergo generalanesthesia. In the current climate of equine prac-tice, it is acceptable to undergo general anesthesiafor diagnostic purposes either for imaging or arthro-scopy. Although the risks of anesthesia must bediscussed with the owner, this limitation is becom-ing less of a barrier. Another limitation that mustbe addressed is our ability to interpret novel imag-ing techniques. Until the body of knowledge in-creases about this and other advanced imagingtechniques, great care should be taken in imageinterpretation.

In conclusion, the techniques of equine stifle CTand CT arthrography are feasible and clinically use-ful. CT should be considered complementary to acomplete clinical examination and other diagnostic

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imaging modalities. In this group of clinical cases,CT was useful to define the extent of suspected orpreviously diagnosed injuries and to identify inju-ries that were elusive. This information allows cli-nicians to develop more directed therapeutic plansor provide a more accurate prognosis. Future useof the described technique will increase our knowl-edge of equine stifle disease.

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3. Sullins KE. The stifle. In: Stashak TE, ed. Adam’s lame-ness in horses. Baltimore, MD: Lippincott, Williams, &Wilkins, 2002;999–1027.

4. Hoegaerts M, Nicaise M, Van Bree H, et al. Cross-sectionalanatomy and comparative ultrasonography of the equine me-dial femorotibial joint and its related structures. Equine VetJ 2005;37:520–529.

5. Hoegaerts M, Saunders JH. How to perform a standardizedultrasonographic examination of the equine stifle, in Proceed-ings. Am Assoc Equine Pract 2004;50:212–218.

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12. Hadj-Salah M, Hadj-Salah M, Mourali S, Abdelali MA, et al.Spiral computed tomographic (CT) arthrography versus ar-throscopy in internal derangements of the knee. Tunis Med2006;84:734–737.

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aMX 8000, Philips, 5656 AE Eindhoven, The Netherlands.bOptiray 300, 30 mg iodine/ml, Mallinckrodt, 1755 ZG Petten,

The Netherlands.cATL HDI 3000, Philips, 5656 AE Eindhoven, The Netherlands.dDormosedan, Pfizer Animal Health, NL-2900 AA Capelle a/d

Ijssel, The Netherlands.eKetamine, AST Pharma, NL-3420 DC Oudewater, The Neth-

erlands.fDormicum, Roche Nederland, NL-3440 AA Woerden, The

Netherlands.gEurovet, 5531 AE Bladel, The Netherlands.hPhilips, 5656 AE Eindhoven, The Netherlands.ieFILM, Merge Healthcare North America, Milwaukee, WI

53214.jOsiriX, Open Source, www.osirix-viewer.com.

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