40 • Equine Health Update •

Indications• Investigation of pain causing lameness localised to the fetlock region by clinical signs and/or diagnostic analgesia.• Investigation of traumatic/penetrating wounds to the fetlock region.• May be requested as part of a pre-purchase examination.• Assessment of angular limb deformities.• Monitoring and re-evaluation of pathology.

Patient preparation• Ensure the hair coat is clean as debris will appear radiopaque on radiographs and may mimic or mask

abnormalities.• Radiography of this region is usually well-tolerated. However, sedation will usually aid the acquisition of well

positioned and good quality radiographs and reduce procedure time, number of repeated acquisitions and risk to personnel and equipment.

• The horse should be weight-bearing evenly on the forelimbs with the metacarpus of the limb to be radiographed as vertical as possible in both planes (i.e. when viewed from both the front and the side). The same principles of positioning apply when radiographing the hindlimb fetlock.

Radiographic views• There are four standard views of the fetlock joint:

- Lateromedial - Dorsopalmar(/plantar) - Dorsolateral-palmaro(/plantaro)medial oblique - Dorsomedial-palmaro(/plantaro)lateral oblique

• There are various other additional views for identifying specific lesions or visualising specific areas.• The technique for radiography of metacarpophalangeal joint (forelimb) is described below, however the same

principles apply for radiography of the metatarsophalangeal joint (hindlimb).

Radiography of the Equine Fetlock Joint

IMVi Clinical teamLaura Quiney BVSc MRCVS

Holly Johnson BVSc Cert AVP MRCVS

41• Volume 21 Issue 2 | May 2019 •

Lateromedial (LM)• The X-ray beam should be horizontal.• For a true lateromedial the beam must be perpendicular to the

dorsopalmar axis of the leg at the level of the fetlock joint. Palpating the medial and lateral epicondyles of the third metacarpal bones may aid determination of the correct angle.

• Centre at the level of the distal condyles of the third metacarpal bone.• Collimate to include the distal one third of the metacarpus and at least the

proximal one half of the proximal phalanx in the image.

For a true lateromedial radiograph (left image), the sagittal ridge of the third metacarpal bone (arrow) should be visible and the condyles should be superimposed (arrowhead), allowing clear visualisation of the joint space. If the radiograph is oblique (right image) then sagittal ridge cannot be evaluated and realignment of the beam relative to the fetlock is necessary to achieve adequate diagnostic quality.

42 • Equine Health Update •

Flexed lateromedial• Compared with the weight-bearing lateromedial, the flexed

lateromedial view offers better visualisation of the sagittal ridge (arrow) of the third metacarpal bone and the dorsal surfaces of the proximal sesamoid bones (arrowheads).

• To flex the fetlock, either rest the foot on a raised wooden block or hold the toe with a lead gloved hand.

• To acquire a true lateromedial first ensure that the limb is vertical and not rotated by viewing the position of the limb from the front. The X-ray beam should be perpendicular to the dorsopalmar direction of the fetlock.

• Acquire the radiograph by centering and collimating as for the weight-bearing view (above).

For a flexed lateromedial radiograph to be of good diagnostic quality the limb must first be assessed from the front to ensure that the limb is both vertical and not rotated (left image).

A good quality flexed lateromedial radiograpgh allows the distal aspect of the sagittal ridge (arrowhead) to be visualised.

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Dorsopalmar (DP) • Angle the X-ray beam 10° distally i.e. dorso10°proximal-palmarodistal oblique.• Ensure the beam is parallel to the dorsopalmar direction of the limb.• Centre at the level of the condyles of the third metacarpal bone and collimate.

N.B. A steeper distal angle of at least 15° is usually required for the metatarsophalangeal joint (hindlimbs), i.e. dorso 15°proximal-plantarodistal oblique.

A horizontal X-ray beam will lead to superimposition of the proximal sesamoid bones over the metacarpophalangeal joint which will hinder evaluation (left image).

By angling 10° distally, the proximal sesamoid bones will be superimposed proximal to the joint space, allowing improved evaluation of the joint margins (right image).

44 • Equine Health Update •

Dorsolateral-palmaromedial oblique (DLPMO)• Skylines the dorsomedial and palmarolateral aspects of the fetlock joint, and the

lateral proximal sesamoid bone.• The X-ray beam should be horizontal, and at a 45° angle to the dorsopalmar axis

of the leg, aiming from a dorsolateral position towards a palmaromedial position.• Centre at the level of the condyles of the third metacarpal bone and collimate.

A marker to identify the limb being images should be placed, by convention, to either the dorsal or lateral aspect of the limb. This is essential not only to help identify which limb has been imaged, but also to identify which are the medial and lateral aspects of the limb and therefore which view has been acquired. In this DLPMO image, the L marker is on the plantarolateral side of the fetlock.

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Dorsomedial-palmarolateral oblique (DMPLO)• Skylines the dorsolateral and palmaromedial aspects of the fetlock

joint, and the medial proximal sesamoid bone.• Acquire as for the DLPMO image, but from a dorsomedial position

aiming towards a palmarolateral position. Alternatively, to avoid crossing the horse aiming from the palmarolateral position towards a dorsomedial position will produce the same image.

In this DMPLO image, the L marker is on the dorsolateral side of the fetlock. If this image was not labelled as a DMPLO view, it could be easily identified as such because of the location of the marker.

46 • Equine Health Update •

Additional radiographic views

Angled-down obliques (DPrM-PaDiLO and DPrL-PaDiMO)

• Useful for assessment of the palmar aspects of the medial or lateral condyles of the third metacarpal bone because the proximal sesamoid bones will be superimposed proximally to them (arrow).

• Acquisition is not as complex as it first seems- use the same principles as for the comparable oblique view, but rather than using a horizontal beam, angle down by 45°.

• The cassette should be positioned perpendicular to the direction of the X-ray beam to minimise distortion.

Flexed dorsopalmar

• Used to further assess different aspects of the sagittal ridge of the third metacarpal bone or the joint surface, for example if a fracture is suspected.

• Acquire several tangential dorsopalmar views using different proximal or distal angles to skyline different aspects of the joint surface. The cassette should be positioned perpendicular to the beam to minimise distortion.

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Flexing the limb by resting the toe on a block can aid acquisition of dorsodistal-palmaroproximal oblique views (example of one tangential view, left image). The metacarpus should be vertical. Flexed dorsopalmar radiographic image of a fetlock with a sagittal fracture of the proximal phalanx.

Skyline of the metacarpophalangeal joint

• Dorsoproximal- dorsodistal oblique image

• Skylines the distal articular surface (sagittal ridge and condyles) of the third metacarpal bone

• The limb should be flexed with the metacarpus vertical. Position the cassette horizontally and angle the beam distally by 40-70°, depending on which area of the dorsal joint surface is to be assessed.

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1. Which radiographic view is best for visualisation of the palmar aspect of the medial condyle of the third metacarpal bone?

a. DPrM-PaDiLOb. Lateromedialc. DM-PaLOd. Flexed lateromediale. DL-PaMO

2. Which of these statements regarding acquisition of a dorsoplantar radiograph is usually correct?

a. The x-ray beam should be horizontalb. The x-ray beam should be angled distally by 10°

(D10Pr-PlDiO)c. The x-ray beam should be angled proximally by 10°

(D10DiPlPrO)d. The x-ray beam should be angled distally by 15°

(D15Pr-PlDiO) e. The x-ray beam should be parallel with the surface

the horse is standing on

3. Which of these lateromedial radiographs (right) is of adequate diagnostic quality?

a. Image 01b. Image 02 c. Image 03 d. Image 04 e. Image 05

CPD QuestionsRadiography of the Equine Fetlock Joint

01 02 03

04 05

4. The marker (L) was placed to the lateral side of this left fetlock. Which view is this?

a. DL-PaMOb. DPrL-PaDiMOc. DM-PaLOd. DPrM-PaDiLOe. Lateromedial

AC/2119/19TO ANSWER: Download the Vet360 App or go tocpdsolutions co.za/?re=onlinevets

49• Volume 21 Issue 2 | May 2019 •

5. Which of these statements is correct?

a. Using sedation for radiography is virtually never required

b. Sedation will make fetlock radiography more difficult to perform

c. Sedation will often help with the acquisition of good quality radiographs in a shorter period of time

d. Sedation is likely to increase the number of repeated acquisitions required

e. Sedation never helps with acquisition of well positioned radiographs

6. Which of these radiographic views will offer the best visualisation of the dorsal surfaces of the proximal sesamoid bones?

a. DPb. Flexed DPc. LMd. Flexed LMe. DPrM-PaDiLO

7. In what instance would a flexed DP be particularly useful?

a. Further assessment of the proximal sesamoid bones

b. Further assessment of the dorsal aspect of the condyles of the third metacarpal bones

c. Further assessment of the sagittal ridge of the third metacarpal bone

d. All of the abovee. None of the above

8. Why is collimation important for all views?

a. To reduce scatter and optimise exposure factors to achieve optimum image quality

b. To prevent unwanted anatomy included in the radiographic image

c. To optimise radiation safety for personnel performing radiography

d. All of the above e. None of the above

9. When placing a marker in an image where does convention require the marker to be placed in relation to the anatomy being imaged?

a. Mediallyb. Distallyc. Proximally and medially d. Laterally e. Proximally

10. What is the most important reason for the horse to be stood standing squarely and weight bearing evenly through the limbs when performing fetlock radiography?

a. If the horse is sedated, it will always be unsteady and may fall over

b. Uneven weight bearing is likely to result in obliquity of the anatomy relative to x-ray beam in the radiograph resulting in a less diagnostic image

c. When the horse is not standing squarely it is difficult to get both limbs in the same radiograph

d. When the horse is standing unevenly it is difficult to take a full set of radiographs of the joint

e. Uneven weight bearing will always result in motion artefact in your radiograph

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Biography - Laura Quiney BVSc MRCVS

Laura qualified from the University of Bristol and subsequently completed an equine orthopaedic internship at the Animal Health Trust (AHT). Following a period working in ambulatory equine practice she returned to the AHT as a Junior Clinician, focussing on diagnostic imaging, lameness investigation and clinical research. She is currently a Clinical Manager at IMV Imaging where she develops educational content and provides CPD in diagnostic imaging to veterinary surgeons throughout the UK.

Biography – Holly Johnson BVSc Cert AVP MRCVS

Holly graduated from Liverpool Veterinary school, UK in 2007. She completed an equine internship at The Liphook Equine Hospital in Hampshire, UK, before moving to Australia to work as a primary stud vet in the Hunter Valley for Scone Equine Hospital. Her passion for internal medicine and diagnostic imaging, particularly ultrasound, led her to complete an RCVS Cert AVP when she returned to the UK. Holly currently works as one of the in house clinical team vets at IMV Imaging combining her love of ultrasound with teaching, delivering a wide variety of ultrasound training to veterinary clinicians in the UK and internationally.