2019 WINTER MEETING

2019

WINTER MEETING

Sunday, February 10, 2019 Burlington Hilton Hotel

Kurt Selberg, MS, DVM, DACVR Assistant Professor of Veterinary Diagnostic Imaging

Colorado State University [email protected]

SEEING CLEARLY: MUSCULOSKELETAL IMAGING

FOR THE EQUINE PRACTITIONER

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Friday, June 21, 2019

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Charley Abernathy – BEVS Kathryn Miller – West River Valley Vet. Services

Ashley Ackert – Green Mountain Vet. Hospital Nicole Poppenger – Animal Hospital of Hinesburg Dana Ames – West Mountain Animal Hospital Matthew Reimert – East Haven Veterinary Service *Lauren Blume – Peak Veterinary Referral Ctr. *Michael Romp – Vermont Air National Guard Shannon Bradley – Essex Veterinary Center Nicholas Sherman – Essex Veterinary Center Earl Brady – Cold Hollow Veterinary Services Allaire Smith-Miller Adrian Flanders – Fitzgerald Animal Hospital Lainie Springer – BEVS

*Miranda Fritz – Mountain View Animal Hospital Mallory Sullivan – BEVS *Jeanne Harding Kathereen Tamburello – Newport Vet. Hospital Brian Hurley – Gardner Animal Care Center Jaclyn Torzewski – VT-NH Veterinary Clinic Krista Jones Elisabeth Zenger – BEVS Andrew Koenitzer – Ark Veterinary Hospital Courtney Zwahlen – Peak Veterinary Referral Ctr. Kayla Miner – Affectionately Cats

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Life members are veterinarians who have been state VMA-dues paying members for thirty-five (twenty of

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Thank you to the following members who reached Life Member status this year. We appreciate your long-

time commitment to the VVMA!

Steven Carey – Retired *Chris Mangini – Retired

*David Lamb – Vermont Equine Medical Steve Wadsworth – Northwest Veterinary Associates

Barbara LeClair – Riverbend Veterinary Clinic

* Attending this 2019 Winter Meeting!

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2019 Winter Meeting Exhibitors Thank you for your support of our Meeting!

Boehringer-Ingleheim Kara Kirchherr [email protected] Sponsor of Dr. Kurt Selberg Paige Willson [email protected] Burlington Emergency Whitney Durivage [email protected] & Vet. Specialists Brenna Mousaw [email protected]

Christian Veterinary Mission Dr. Amy St. Denis [email protected] Dechra Lauren Baker [email protected] Sponsor of Dr. Patty Lathan Scott Rowe [email protected] Eastern States Compounding Pharmacy Kim Johnson [email protected] Elanco Animal Health Elizabeth Hall [email protected] Sponsor of VVMA Reception Ethos – Peak Veterinary Referral Ctr. Linda Story [email protected] Haun Specialty Gases Jamie Badger [email protected] Erik Eliason [email protected] Henry Schein Animal Health Martha Rose [email protected] Jazz Heath [email protected] Hill’s Pet Nutrition Dr. Andrew Hagner [email protected] Idexx Colin Dudnake [email protected] Sponsor of Dr. Armell De Laforcade Bob Lynch [email protected] Carmelita Castlellon [email protected] K-Laser Barry Levine [email protected] Merry Xray Jon Nealy [email protected] Chuck Gilroy [email protected] MWI Veterinary Supply Danielle Preece [email protected] Nestle Purina PetCare Company Lauren Koron [email protected] Patterson Veterinary Supply George White [email protected] Art Yanke [email protected]

























Phibro Animal Health Seth Johnson [email protected] Sponsor of Dr. Mike Hutjens Purina Animal Nutrition Kelsey Bornt [email protected] Rusty Suher [email protected] Universal Imaging Michael McElhinney [email protected] VetCor Bryan Brackett [email protected] VetriScience Laboratories Kelley Lucarell [email protected] Patti Rosenberg [email protected]

Thank you also to

• CareCredit for sponsoring Wendy Myers’ presentation

• Zoetis for sponsoring Sunday morning’s break








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Review: A Field Guide to Better Radiographs

Kurt Selberg MS, DVM, MS Dipl ACVR

Colorado State University

Portions of this abstract reprinted with permission from Selberg K. Review: A field Guide to

Improving Radiographs: Proceedings of the Am Assoc Equine Pract 2017.

Introduction

Lameness is a frequent medical problem in horses. Aside from localizing techniques such as

palpation and subsequent diagnostic blocking, radiographic investigation of the limbs, neck and

back is often the first choice in diagnostic testing. Digital radiography is widespread and

arguably considered the standard of practice. The advantages of digital systems include the

ability to manipulate images, apply post processing, centrally store and quickly obtain and

review images immediately after acquisition. Despite these advances in technology, the basics of

radiographic exposure and patient positioning haven’t changed. When producing radiographic

images using digital technologies, the veterinarian or technician must still correctly position and

choose a technique appropriate for the body part being imaged. Faulty imaging due to poor

positioning or inappropriate exposure can lead to under or over diagnosis of pathologic changes.

The goal of diagnostic imaging is to reach an accurate diagnosis to target treatment specifically.

Well positioned radiographic images acquired with the appropriate technique are a key

component to reaching the correct diagnosis.

Principles of X-rays

When a radiographic image is obtained, about 90% of the x-ray photons are absorbed by the

tissue and 10% of the photons pass through the patient and reach the detector. Many of the

absorbed photons generate scattered radiation (Compton scatter). These scattered photons travel

in all directions creating noise and degrading image quality. The effect of scattered radiation can

be minimized by collimating the x-ray beam to reduce the number scattered photons (Figure 1).

The Inverse Square Law states that 'the intensity or quantity of photons reaching the xray

detector is inversely proportional to the square of the distance from the source'. In other words,

the farther away you are from the patient the less intense the photons are that strike plate. This is

especially important for obtaining radiographic images in large body parts with portable

generators. The typical film focal distance (distance from the plate to the generator) is 60 cm.

When imaging larger body parts such as the caudocranial stifle, neck or back it is important to

maintain this distance. We can also use the Inverse Square Law to our advantage and stand

closer to the image detector and patient to improve image quality when imaging larger body

parts. By standing closer when obtaining radiographs of larger body parts, the increased quantity

and intensity of photons reaching the plate will help to reduce the commonly obtained gray,

grainy images (also known as quantum mottle) (figure 2).

Despite the ability to use electronic markers, the lead marker is still the gold standard in

displaying laterality. The positioning of the plate can vary the placement of the electronic

marker, making it unreliable for denoting laterality. While a proper physical label (displaying

limb and projection) is ideal, even a penny or paperclip taped to the plate to denote lateral is

better than no marker at all.

A large amount of patient data can be displayed on the digital image. While it is essential to

include patient information in the radiographic study, the amount of text burned onto the subject

matter of the image should be minimized. The overlaying patient demographics, if burned into

the image, can superimpose on the included anatomy and mask pathologic change; this is

especially true when collimating as the resultant image is small in relation to the text size. Thus,

take care not to compromise the value of the radiograph by poor positioning of study labelling ,

particularly as this information is readily available in all DICOM viewers and is not necessary to

include on the images.

Patient and x-ray positioning

The ideal conditions for obtaining most radiographs of equine joints is with the horse standing

square; except for non-weight bearing views. Unfortunately, not all of our equine patients are

willing to stand square. As such, the equine practitioner must accommodate the patient to make

quality radiographs. Radiographic examination of the stifle, especially the caudocranial image is

a good example of this principle. For example, the optimal angle for the caudocranial image is 10

degrees from caudal proximal to cranial distal 1 with the horse standing square (the tuber

calcaneus is in line with the tuber ischii); However, if the limb is slightly behind the vertical

(camped out), or under the horse (camped under), the angle must be adjusted to accommodate

the stance of the horse. If the horse is standing with the limb behind it, the angle (caudoproximal

to craniodistal) will increase (be steeper) and vice versa for the horse that is stood under itself

(Figure 3). When evaluating the caudocranial stifle image for adequate positioning, the tibial

plateau should superimpose itself from cranial to caudal and the tibial tuberosity should be distal

(10 to 15 mm) to the tibial plateau (Figure 4). If the tibial tuberosity is proximal to the tibial

plateau, the angle is typically too steep. The x-ray generator should be centered about 8- 10 cm

proximal to the indentation created by the distal aspect of the thigh musculature as it transitions

to the proximal crus area. Joint narrowing in the stifle may be masked or falsely created by

inadequate positioning. The most common areas of pathologic change in the stifle are

associated with the medial femoral condyle and the lateral trochlear ridge2,3, the caudo45 lateral

– craniomedial oblique highlights these areas well. A well-positioned Cd45L-CrM oblique

should project the medial femoral condyle caudal to the tibial eminence and show the joint

clearly (Figure 5). The superimposition of the medial femoral condyle with the tibial eminence

can mask subtle concave defects. Just as with the caudocranial projection of the stifle, the angle

of the x-ray generator should be 5-10 degrees proximal to distal in a square standing horse. The

most common mistakes are to is be at too steep of an angle or being too lateral. The Cd60L-CrM

oblique seemingly highlights the lateral trochlear ridge. However, a well-positioned lateral

projection has a similar sensitivity to the Cd60L-CrM oblique projection 77 vs 84 % respectively

4. Limb positioning also affects acquisition of the lateral radiographic projection. If the horse is

standing base wide the x-ray generator will have to be angled distally; if base narrow, the

generator angle will be slightly proximal. Judging placement of the x-ray generator in a cranial

to caudal fashion is best done by lining up with the heel bulbs and tarsus. The most common

mistake is being too far cranial.

Just as with the stifle, the x-ray generator angle on dorsoplantar radiographic projection of the

tarsus must change depending on conformation and stance. A horse with a normal angle to the

tarsus, standing square, will require a 5-10 degree proximal to distal angle, centered on the

central tarsal bone to see the distal joints. If instead the horse has a post-legged conformation the

x-ray generator angle should be relatively parallel with the ground. Similarly, if the limb is held

behind the vertical, and has a normal tarsus angle, the x-ray generator will be parallel with the

ground. It is also important to note that on the true DP image the calcaneus can superimpose over

the distal tibia and talus, masking lesions found there (Figure 6). In most circumstances shifting

the x-ray beam slightly laterally (Dorso 10°lateral -plantaromedial oblique) will eliminate

calcaneal superimposition from the majority of the tibiotarsal joint and highlight the medial

malleolus to evaluate for osteochondral disease. Medial malleolus articular lesions may also be

masked on conventional DP images by summation of the malleolus with the talus. The

lateromedial projection should have the trochlea of the talus superimposed and the distal joints

well visualized. This is performed by centering the x-ray beam at the level of the central tarsal

bone. The dorsal-plantar positioning can be judged by palpating the trochlea of the talus. Laying

a finger across the trochlea will give you a guide for the position of the x-ray generator.

Additionally, using the heel bulbs to line up will also help to direct positioning of the x-ray

generator in a cranial to caudal fashion. The most common error in positioning is obtaining the

radiography too far dorsal. This will project to the medial trochlear ridge dorsal to the lateral

trochlear ridge (Figure 7). Failing to be tangential to the distal joints is typically a result of beam

angle. More often than not the beam is angled slightly proximal, or up the leg. This is typically

secondary to horse stance (wide base). Correction can be achieved by angling slightly distal, or

by repositioning the leg. The image highlighting the dorsolateral and plantaromedial surfaces of

the tarsus is generally referred to as the DMPLO, suggesting that the image is obtained with the

beam on the dorsomedial aspect of the joint. However, it is typically easier and faster to

transition from lateral positioning to PLDMO positioning, by staying on the same side of the

horse rather than adjusting to shoot from underneath the horse with a DMPLO projection. Ideal

positioning of the PLDMO should partially superimpose the medial trochlear ridge with the

lateral trochlea-- “split the nose” so to speak (Figure 7). Often a slight (5 degree) plantarolateral

distal to dorsomedial proximal angle is needed to be tangential to the distal tarsal joints.

Radiographic examination of the neck has seen a dramatic increase in frequency in recent years.

Unlike the distal extremities, the radiographer cannot see the x-ray detector on the opposite side

of the neck. This creates positioning problems and often results in images with one vertebral

body or facet joint that is not centered on the x-ray detector. Furthermore, the articular facets on

the lateral radiographs may not be perfectly superimposed, which can lead to interpretation

errors. However, if a moment is taken to palpate the transverse processes and apply white tape

to these sites, this can serve as a guide to detector placement and x-ray generator focus (Figure

8). Centering just proximal to the transverse process will render well positioned radiographs,

when the horse’s poll is in line with the withers. Articular facets at the cranial and caudal aspect

of the plate may not be superimposed however, due to beam divergence or parallax. This issue is

typically exacerbated with the short film focal distance used with portable x-ray generators.

Symmetrical anatomy of the neck can make lesions difficult to lateralize. Oblique radiographs

obtained in a left/right 45-55 degree ventral to right/left dorsal fashion can help localize lesions5

(Figure 9). The xray generator is typically centered at the jugular furrow and the x-ray detector

is placed with the transverse process centered at the bottom 1/3 of the x-ray detector.

Radiographic images are named from where the x-generator is located and subsequently where

the x-rays enter to where the x-rays exit the neck, and where the x-ray detector is located. In the

example of a L55V-RD oblique the left articular facets will be projected dorsally and the right

transverse processes will be projected ventrally. Properly labeled, opposite oblique radiographs

should be obtained to accurately localize the lesion. Well positioned oblique radiographs should

project one side of the articular facets dorsal and show the intervertebral foramen well. The

other articular facet joint will be superimposed over the vertebral body highlighting the joint

width. Oblique radiographs obtained with portable units centered at the articular facets at C6-7

are challenging due the shoulder superimposition. This may be overcome by offsetting the

forelimbs, with the leg near the x-ray generator pulled caudally.

Radiographic projections are used to highlight specific areas and document pathologic change.

The fetlock is an area with a multitude of pathologic change in which appropriately positioned

radiographs make the pathologic change easy to identify. For example, palmar/plantar process

osteochondral fragmentation is a common abnormality in the fetlock and depending on the

location may be a source of lameness. The oblique views (dorso 20 proximo 45 lateral-

palmaromedial oblique and dorso 20 proximo 45 medial –palmarolateral oblique) should show

these lesions best. However, if the proximal sesamoid bones superimpose this area, the

fragmentation could be easily missed. Ideal oblique and DP radiographs of the fetlock project the

proximal sesamoid bones proximal to the joint margin (Figure 10). The flexed lateral of the

fetlock highlights the sagittal ridge to document subchondral bone defects and fragments.

Lesions in this area are a documented source of lameness 6, and can be difficult to fully evaluate

on a lateral and DP radiographic projection due to summation with the proximal phalanx. The

ideal flexed lateral radiograph should have the medial and lateral aspects of the condyles

superimposed. This will allow visualization of the mid to dorsal aspect of the sagittal groove

without superimposition. Obliquity is the most common challenge with this projection and can

superimpose lesions in the sagittal ridge, masking their appearance. More often the obliquity in

the flexed lateral image arises from the x-ray generator angled in a dorsomedial to palmarolateral

fashion. This may be due to limb positioning or angle of the x-ray generator. While in the flexed

position, the medial and lateral aspects the condyle are typically more conspicuous and are

easier to palpate to help guide the angle at which the x-ray generator should be to acquire a well-

positioned radiograph. (Figure 11 ).

The typical digital radiographic protocol for the foot is 4 views (LM, DP, palmaroproximal-

palmarodistal oblique/skyline, dorso60 proximal – palmardistal oblique). The skyline projection

can be one of the more difficult views to obtain, and is often the go to projection for assessing

pathologic change. The lateral projection can aid in obtaining well positioned skyline

radiographs. The angle of the bony column and navicular bone flexor surface can be judged on

the lateral images to guide the angle of the skyline. Typically, the angle is 55 degrees. However,

in the upright or low heel conformed foot it is necessary to change the angle of the x-ray

generator to get a well-positioned radiograph. When evaluating for radiographic positioning,

you should see the joint space between the middle phalanx and the navicular bone well, and mild

summation with the distal phalanx centrally and at the level of the palmar processes. Pseudo

sclerosis of the trabecular bone of the navicular bone caused by summation of the flexor cortex

can lead to misinterpretation (Figure 12). Thus, proper positioning is paramount for judging

corticotrabecular bone definition. The addition of oblique images (Dorso 60 proximal 45-55

lateral/medial- palmarodistal oblique) may help to highlight the fossa of the collateral ligament

and potentially any occult fractures on the D60P images 7,8 Acute fracture may only be seen on

D60P 50L- P oblique images and should be considered in all lame horses localizing to the foot.

Conclusions:

Patient preparation and positioning, adequate technique and knowing how to correct

malpositioned radiographs are skills in achieving diagnostic radiographic images. Taking a

moment to assess unintentional obliquity, patient conformation and stance can reduce retakes

and reduce radiation exposure.

Disclosures:

The authors have no financial conflicts of interest. When applicable the author adhered to the

Principles of Veterinary Medical Ethics of the AVMA.

1. Trencart P, Alexander K, De Lasalle J, Laverty S. Radiographic evaluation of the width of

the femorotibial joint space in horses. Am J Vet Res. 2016;77(2):127-136.

doi:10.2460/ajvr.77.2.127.

2. Clarke KL, Reardon R, Russell T. Treatment of Osteochondrosis Dissecans in the Stifle and

Tarsus of Juvenile Thoroughbred Horses. Vet Surgery. 2014;44(3):297-303.

doi:10.1111/j.1532-950X.2014.12277.x.

3. Grevenhof EM, Ducro BJ, WEEREN PR, Tartwijk JMFM, Belt AJ, Bijma P. Prevalence of

various radiographic manifestations of osteochondrosis and their correlations between and

within joints in Dutch Warmblood horses. equine vet j. 2009;41(1):11-16.

doi:10.2746/042516408X334794.

4. Beccati F, Chalmers HJ, Dante S, Lotto E, Pepe M. Diagnostic sensitivity and interobserver

agreement of radiography and ultrasonography for detecting trochlear ridge osteochondrosis

lesions in the equine stifle. Vet Radiol Ultrasoun. 2013;54(2):176-184.

doi:10.1111/vru.12004.

5. Dimock A, Puchalski S. Cervical radiology. Equine Veterinary Education. 2010;22(2):83-

87.

6. Yovich JV, McIlwraith CW, Stashak TS. Osteochondritis dissecans of the sagittal ridge of

the third metacarpal and metatarsal bones in horses. Javma-J Am Vet Med A.

1985;186(11):1186-1191.

7. Selberg K, Werpy N. Fractures of the distal phalanx and associated soft tissue and osseous

abnormalities in 22 horses with ossified sclerotic ungual cartilages diagnosed with magnetic

resonance imaging. Vet Radiol Ultrasoun. May 2011. doi:10.1111/j.1740-

8261.2011.01813.x.

8. Martens P, Ihler CF, Rennesund J. Detection of a Radiographically Occult Fracture of the

Lateral Palmar Process of the Distal Phalanx in a Horse Using Computed Tomography.

Vol 40. 1999:346-349.

Table 1: Radiology positioning checklist

Positioning checklist

Tarsus

-DP -Calcaneus should be projected over the lateral cortex of the

tibia.

-Distal joints should be lucent and equal width

-LM -Trochlea should be superimposed

- Distal joints should be lucent and equal width

-PLDM-0 -The medial trochlear ridge should split the lateral trochlear

ridge.

Stifle

-CdCr -Tibial plateau should superimpose.

-Tibial tuberosity should be 10-15 mm distal to tibial condyle.

-Cd45L-CrM-O -Medial femoral condyle should be separated from tibial

eminence.

-Medial femorotibial Joint should be clearly visible.

Foot:

-Skyline -Joint between middle phalanx and navicular bone should be

well seen

-D60P -Distal aspect of navicular bone should be projected proximal

to distal interphalangeal joint.

-Distal border should be well delineated

Fetlock:

DP -Proximal sesamoid bone should be projected 10 -15 mm

proximal to fetlock joint

DLPM-O/DMPL-O -Proximal sesamoid bones should be projected 5 mm proximal

to the palmar/plantar tuberosity

-The abaxial surface of the sesamoid should superimpose with

the metacarpus should superimpose the palmar/plantar margin

of the sagittal ridge

Figure 1. DP tarsus images. The image on the left is obtained with the collimator left open. The

image on the right is obtained with the collimator narrowed to the boundaries of the tarsus.

There is moderate improvement of contrast and fine detail in the image obtained with the

narrowed collimator. This the bottom images represent the corresponding images magnified to

better illustrate the improved detail and contrast due to the reduction in scatter. This is best seen

in the medial malleolus and medial aspect of the talus (arrows).

Figure 2. Radiographic image of the cranial thoracic spinous processes. The structures in the

lower right portion of the images is highlighting quantum mottle/under exposure which is

characterized by a grainy appearance. Compared the dorsal aspect of the spinous processes,

there is good anatomic definition and contrast.

Figure 3: The left image illustrates a horse that is standing camped under. The red arrow

illustrates the flat angle and proper center for the x-ray generator. The right image illustrates a

horse that is slightly camped out. The yellow arrow illustrates a steeper angle (approximately 15

degree) of the x-ray generator.

Figure 4. Caudocranial images of the stifle. The left image is well positioned with 10 degrees

angle. The curved red line is highlighting the tibial tuberosity. The tibial tuberosity is projected

distal (10-15 mm) to the lateral tibial condyle. The cranial and caudal aspects of the medial tibial

condyle superimpose. A comparison image (right image) of a caudocranial image that is

obtained at too steep of an angle. Note that the tibial tuberosity (yellow line) is projected at the

level of the lateral tibial condyle and the caudal (yellow arrow) and cranial (red arrow) aspects of

the medial tibial condyle are separated.

Figure 5. Caudo45Lateral-craniomedial oblique images. The left images is a well positioned

Cd45L-CrM obique image. The cranial aspect (site of most medial femoral condylar pathologic

change) of the medial femoral condyle is separated from the tibial eminences. The medial and

lateral aspects of the medial tibial condyle are superimposed. The right image is obtained too

lateral and at too steep of an angle. The medial femoral condyle is superimposed with the

eminences of the tibia.

Figure 6. Dorsoplantar images of the tarsus. The left image is a D10L-P oblique image. Note

the calcaneus is superimposed over the lateral cortex of the tibia, the medial maleous is

highlighted and the distal tarsal joints are well seen. The middle and right images show smooth

fragmentation along the medial aspect of the tibiotarsal joint. However, the D10L-P image (right

image) highlight the fragmentation along the medial malleolus. There is also an indistinct area

of lucency (red arrow) in the proximal talus in the intertrochlear groove seen in the right image,

not visualized in the middle image.

Figure 7. Images of the tarsus. The lateral image (top left) is well positioned. The trochlear are

superimposed and the joints are well seen. This is image was obtained centering just proximal to

the head of the 4th metatarsal bone and being tangential to the heel bulbs. The right image is an

example of a mildly obliqued lateral image. The x-ray generator is positioned too far cranial.

The bottom left image is a well position PLDM-O of the tarsus. The lateral trochlear ridge is

partially summating with the medial trochlear ridge. The distal tarsal joints are well seen. This

oblique is obtained with a slight proximal angle (5 degrees) in a square standing horse. The

image was obtained centering the x-ray beam just proximal to the 4th metatarsal bone and

moving plantar approximately 30 degrees.

Figure 8: The skin has tape applied to at the level of the transverse processes (top image). The

transverse processes typically the first transverse process easily palpated. This 3rd cervical

transverse is ventral to the C3-4 articular facet. Moving caudal the transverse processes are

centered on the vertebral body. Centering the x-ray been just dorsal to the transverse process

should center the vertebral body and allow for well positioned radiographs.

Figure 9. A left 55 ventral-right dorsal oblique (LVRD) radiographs of the caudal cervical spine.

This highlights the left dorsal and right ventral aspects of the cervical spine. The blue arrow is

showing the left articular facet joint and periarticular margins. The yellow arrows highlight the

right articular facet joint and joint space. The red arrows are highlighting the shoulder

musculature which summates with the C6-7 articular facets joints.

Figure 10: A well positioned DP (Dorsal 15-20 proximal-palmar oblique; top right) and oblique

(Dorso 45 Lateral/medial 15-20 proximal –palmar medial/lateral –oblique; top left) radiograph of

the fetlock. Note that in both images the sesamoid bones are projected proximal to the joint

margin and margins of the proximal phalanx. The bottom images are of the same horse

illustrating how the sesamoid bones when superimposed with the palmar process can mask

lesions ( Yellow arrow).

LD

RV

Figure 11: A well positioned flexed lateral (top) highlight the mid to dorsal aspect of the sagittal

ridge. The medial and lateral aspects of the condyles should be superimposed. The bottom left

images is oblique in dorsal to palmar fashion. The distal aspect of the condyles are at the same

level, however the dorsal and palmar aspects are offset. Note that when the limb is flexed

(horizontal to the ground) the x-ray generator angle is oblique (down or up) in relation to the

horizontal plane not the dorsal to palmar. The bottom right image is oblique in a proximal to

distal fashion. The dorsal aspect of the condyles superimpose, however the distal aspect of the

condyles are offset.

Figure 12: A well positioned skyline image of the navicular bone (left image). The joint

between the navicular bone and middle phalanx is well seen. There is good corticotrabecular

bone definition. The image on the right is the navicular bone of the same limb that is

inadequately positioned. The joint between the middle phalanx and navicular bone is

artifactually narrow and the corticotrabecular bone is obscured due to summation of the cortex

and trabecular bone. The bottom lateral images of the foot. The left image has a foot that has a

slightly broken back hoof-pastern conformation. The right image has a foot that has an upright

conformation. The yellow line in the left shows a slight less angle needed to be tangential to the

navicular cortex, while the upright conformation requires a steeper angle (red line).

Where to Image after Blocking Kurt Selberg MS DVM MS Dipl ACVR Colorado State University Lameness in the horse is diagnostic challenge. In addition to physical exam, diagnostic anesthesia is often used to localize lameness in the horse. The nerve to supply to the extremities has a repeatable anatomy among horses with little variation. This similar neural anatomy is useful to use diagnostic anesthesia and desensitize regions. Regional diagnostic anesthesia starts from the distal aspect, meaning proximal. Typically proper digital nerves are first to be desensitized. Originally, it was thought that this nerve block will desensitize palmar two thirds of the foot (heel region). In recent years, literature shows that there are a wide variety diffusion characteristics of positive contrast around the neurovasculuar bundle that make the exact region less reliable 1,2Error! Bookmark not defined.. Similar information has been relayed about regional diagnostic anesthesia in metacarpus and metatarsus. Studies show more widespread proximal and distal diffusion and synovial administration associated with positive contrast around the neurovascular bundles than previously thought 3-5. Intrasynovial diagnostic anesthesia has similar cross-reactivity in digits, digital sheath and tarsus. Adjacent synovial structures and regional nerves may be desensitized due to diffusion of the diagnostic anesthesia6-8. Additionally, this diffusion typically increases with time. More recently accuracy of needle placement has been called into question especially in the tarsus region, with less 50% achieving intrasynovial injection 9. Given the recent purview of diagnostic anesthesia cross reactivity, known diffusion and increased diffusion over time rethinking where to image is prudent. Using a regional approach of imaging such as including fetlock views and ultrasound in horses that improve to distal proper digital nerve (PDN) and resolve with regional anesthetic at the base of the sesamoid. In the authors practice, fetlock lesion that are the primary source of lameness block to a distal digital nerve block. Albeit, these are often seen in advanced imaging as subchondral bone injury in the proximal phalanx. There are number instances that improvement is seen in the in the proximal aspect of the sesamoidean ligaments and intersesamoidean ligament. In many cases there are several injuries in a region that can be contributory to the lameness. Literature in the tarsus suggests that greater than 40% of the most severe injury from horses blocking to the deep branch of the lateral plantar nerve are originating in the tarsus 10. In conclusion, if physical exam findings and imaging findings are not coinciding with blocking patterns, open the scope of where to image should be considered (Table 1).

Block Region to image

PD Foot to fetlock

Abaxial Foot to fetlock/distal meta

4/6-Point Fetlock/tendon sheath and Proximal metacarpus/tarsus

PSL Carpus/Tarsus and proximal metacarpus/tarsus

1. Schumacher J, Schramme MC, DeGraves FJ. Diagnostic analgesia of the equine digit.

Equine Veterinary Education. 2013;25(8):408-421. doi:10.1111/eve.12001.

2. Livesey L, GRAVES FJ, Schumacher J, et al. Effect of anaesthesia of the palmar digital nerves on proximal interphalangeal joint pain in the horse. equine vet j. 2004;36(5):409-414. doi:10.2746/0425164044868404.

3. Seabaugh KA, Selberg KT, Valdés-Martínez A, Rao S, Baxter GM. Assessment of the tissue diffusion of anesthetic agent following administration of a low palmar nerve block in horses. Journal of the American Veterinary Medical Association. 2011;239(10):1334-1340. doi:10.2460/javma.239.10.1334.

4. Claunch KM, Eggleston RB, Baxter GM. Effects of approach and injection volume on diffusion of mepivacaine hydrochloride during local analgesia of the deep branch of the lateral plantar nerve in horses. Journal of the American Veterinary Medical Association. 2014;245(10):1153-1159. doi:10.2460/javma.245.10.1153.

5. Nagy A, Bodò G, Dyson SJ. Diffusion of contrast medium after four different techniques for analgesia of the proximal metacarpal region: an in vivoand in vitrostudy. equine vet j. 2012;44(6):668-673. doi:10.1111/j.2042-3306.2012.00564.x.

6. Schumacher J, Schumacher J, GRAVES F de, et al. A comparison of the effects of local analgesic solution in the navicular bursa of horses with lameness caused by solar toe or solar heel pain. equine vet j. 2001;33(4):386-389. doi:10.2746/042516401776249543.

7. Schumacher J, Steiger R, Schumacher J, et al. Effects of Analgesia of the Distal Interphalangeal Joint or Palmar Digital Nerves on Lameness Caused by Solar Pain in Horses. Vet Surgery. 2000;29(1):54-58. doi:10.1111/j.1532-950X.2000.00054.x.

8. Harper J, Schumacher J, DeGraves F. Effects of analgesia of the digital flexor tendon sheath on pain originating in the sole, distal interphalangeal joint or navicular bursa of horses - Harper - 2010 - Equine Veterinary Journal - Wiley Online Library. Equine Veterinary …. 2007. doi:10.2746/042516407X216336/pdf.

9. Seabaugh KA, Selberg KT, Mueller POE, et al. Clinical study evaluating the accuracy of injecting the distal tarsal joints in the horse. equine vet j. 2017;49(5):668-672. doi:10.1111/evj.12667.

10. Barrett MF, Selberg KT, Johnson SA, Hersman J, Frisbie DD. High field magnetic resonance imaging contributes to diagnosis of equine distal tarsus and proximal metatarsus lesions: 103 horses. Vet Radiol Ultrasoun. 2018;25(Suppl A):30–10. doi:10.1111/vru.12659.

How I Ultrasound the Equine Stifle

Kurt Selberg MS DVM MS Diplomate of the American College of Veterinary Radiology

Equine Radiology Colorado State University

The equine stifle is a complex joint made of articulation of the femur, tibia and patella. The articulation creating three joint spaces: the medial femorotibial joint, the lateral femorotibial joint and the femoropetellar joint. Congruency in the femorotibial joint is created by the meniscus. The joint is stabilized by the collateral ligaments, and multiple extensor and flexor muscles and their attachments. It is important to have a robust understanding of this anatomy to accurately diagnose problems associated with the stifle1,2. Many of the injuries or lesions in the stifle occur in the medial femorotibial joint; the lateral femorotibial joint is affected less frequently1,3. The lesions of the equine stifle, such as osteochondrosis, subchondral cyst like lesions, osteoarthrosis, fractures, synovial membrane changes/synovial effusion, meniscal injury, meniscotibial ligament injury, cartilage damage and collateral and patellar, desmopathies may be a cause of hind limb lameness 4-7. Ultrasound is often employed to diagnose both soft tissue and osseous injuries of the stifle in horses that respond to intra-articular anesthesia. 5,8,9. A systematic approach to ultrasonographic examination facilitates visualization of common sites of the pathologic change. It is important to evaluate and document the key structures in the equine stifle that may become injured (Table 1).

Table 1. Checklist of key structures to evaluate in the equine stifle

Medial femorotibial joint recess Femoral trochlea/intertrochlear groove

Medial meniscus (weight bearing and non-weight bearing, cranial insertion)

Extensor fossa (origin of fibularis tertius, long digital extensor tendon)

Periarticular margins Lateral meniscus

Collateral ligaments Lateral femoral tibial joint recess (subjacent to fibularis tertius)

Patella/Patellar ligaments (medial, intermediate, lateral)

Medial and lateral femoral condyles

A linear ultrasound probe with a variable megahertz (8-13) is used for the majority of the imaging. The caudal aspect of the stifle requires a convex probe with a variable megahertz of 4-8 depending on the size of the horse. The ultrasound frequency should be set to the highest megahertz available and still be able to visualize the intended structure in its entirety. An appropriate scanning depth should be used. This is often 3-6 cm in depth for the medial, cranial and lateral and 6-8 caudally. The intended anatomic structure should fill the screen and the focal zones be set at the depth of the intended piece of anatomy. The stifle region should be properly prepared by clipping the hair, washing the skin with a mild detergent and water, and applying acoustic gel.

A starting point at the medial aspect of the joint, moving cranial and then lateral is often employed10. This is followed by evaluation in a flexed position to visualize the cranial attachments of the menisci and femoral condyles. Finally the caudally aspect of the joint is evaluated. Each structure should be imaged in cross section and longitudinally. A five point tour has been established for a complete evaluation of the stifle 10.

Step 1. Place the traducer in a longitudinal plane over the medial tibia condyle and image the medial meniscus with the ultrasound perpendicular the plane of the meniscus (point: the meniscus is C-shaped) (Figure 1 and 2). Evaluate the peri-articular margins of the femur and tibia. Evaluate the medial collateral ligaments in longitudinal at its origin and insertion. From the medial meniscus move cranial to the collateral ligament and slightly proximal to visualize the medial femorotibial joint recess. Moving cranially the medial patellar ligament will be encountered. This ligament is located cranial to the medial femoral trochlea

Step 2. With the ultrasound probe placed in the transverse plane, the medial and lateral trochlear ridges of the femur are evaluated (articular cartilage, bone margin, and synovium). The intermediate patellar ligament is located between the trochlea. The lateral patellar ligament is located cranial the lateral femoral trochlea. Scan each ligament proximal to distal in bone scan planes to evaluate the fiber pattern. The femoropatellar joint recess is present caudolateral to the lateral trochlear ridge at its mid aspect.

Step 3. Place the probe in longitudinal at the distal aspect of the lateral trochlear ridge. This is where the extensor fossa is located. Rotate the ultrasound transducer and follow the tendons of the long digital extensor and fibularis tertius. The small joint recess of the lateral femorotibial joint is seen subjacent to the fibularis tertius. Moving proximal to the extensor fossa in longitudinal, angle the transducer slightly caudally to visualize the lateral meniscus. Moving caudally, the lateral collateral ligament is seen. Placing the ultrasound transducer in the transverse plane over the collateral ligament at the level of the femoral epicondyle will facilitate visualization of the popliteal tendon.

Step 4. With the leg in flexion, palpate the “V” created by the medial and intermediate patellar ligaments and place the transducer in the transverse plane to evaluate the cranial tibial meniscal ligament (figure 3). The cranial meniscal tibial ligament has normal striations. Tears are typically ovoid in configuration. The bone margin should be smooth (Figure 4). Rotating the transducer in the longitudinal plane and moving slightly proximal and medial to facilitate visualization of the medial femoral condyle. The subcondral bone should be smooth and the overlying cartilage hypoechoic. The lateral femoral condyle is visualize by placing the transducer in longitudinal lateral the intermediate patellar ligament, over the tendon of the long digital extensor muscle.

Step 5. Using a macro convex probe the caudal aspect of the joint is best seen on the longitudinal plane. The ultrasound transducer is placed medial the proximal aspect of the calcaneal tendon to visualize the medial femoral condyle. The lateral aspect of the stifle joint is best seen by placing the ultrasound probe in the groove created by the biceps femoris caudally.

This systematic approach is used in every horse examined ultrasonographically by the author. This stepwise manner allows for appropriate visualization of areas where pathologic change commonly occurs and may be seen with ultrasound.

Figure 1. Medial femorotibial joint ultrasound images with the transducer in long axis. The ultrasound trasducer is place at the periarticular margins of the medial tibial condyle and medial femoral condyle.

Figure 2: Anatomic specimen with the femur removed. Medial is to the left. Ultrasound transducer placement for the medial meniscus at cranial, mid and caudal aspects. Note that for the meniscus to be echogenic, the transducer must be perpendicular to the meniscus.

Figure 3: Patient positioning and ultrasound transducer placement for imaging the cranial meniscal tibial ligament.

Figure 5: Images of the cranial mensicotibial ligament; lateral and proximal are to the left. The left images long axis (top left) and transverse images (bottom left) are normal. The yellow arrow is showing normal striation in the ligament. The right image has a focal ovoid hypoechoic area of fiber disruption (white arrow) and fluid distal to the ligament. 1. Hoegaerts M, Nicaise M, Van Bree H, SAUNDERS JH. Cross-sectional anatomy and

comparative ultrasonography of the equine medial femorotibial joint and its related structures. January 2006:1-10.

2. Maulet B, Mayhew I, Jones E, Booth T. Radiographic anatomy of the soft tissue attachments of the equine stifle. equine vet j. 2005;37(6):530.

3. Nelson BB, Kawcak CE, Goodrich LR, WERPY NM, Valdés-Martínez A, McIlwraith CW. COMPARISON BETWEEN COMPUTED TOMOGRAPHIC ARTHROGRAPHY, RADIOGRAPHY, ULTRASONOGRAPHY, AND ARTHROSCOPY FOR THE DIAGNOSIS OF FEMOROTIBIAL JOINT DISEASE IN WESTERN PERFORMANCE HORSES. Vet Radiol Ultrasoun. 2016;57(4):387-402. doi:10.1111/vru.12366.

4. COHEN JM, RICHARDSON DW, McKNIGHT AL, ROSS MW, BOSTON RC. Long-Term Outcome in 44 Horses with Stifle Lameness After Arthroscopic Exploration and Debridement. Vet Surgery. 2009;38(4):543-551. doi:10.1111/j.1532-950X.2009.00524.x.

5. Walmsley JP. Diagnosis and treatment of ligamentous and meniscal injuries in the equine stifle. Vet Clin North Am Equine Pract. 2005;21(3):651–72–vii. doi:10.1016/j.cveq.2005.08.003.

6. Textor J, Nixon A, Lumsden J, Ducharme N. Subchondral cystic lesions of the proximal extremity of the tibia in horses: 12 cases (1983-2000). Journal of the American Veterinary Medical Association. 2001;218(3):408-413.

7. Carolyn E Arnold TPSDKBBBM. Conservative Management of Tibial Tuberosity Fractures in 15 Horses. October 2001:1-2.

8. De Busscher V, Verwilghen D, BOLEN G, Serteyn D, Busoni V. Meniscal damage diagnosed by ultrasonography in horses: A retrospective study of 74 femorotibial joint ultrasonographic examinations (2000–2005). J Equine Vet Sci. 2006;26(10):453-461. doi:10.1016/j.jevs.2006.08.003.

9. BOURZAC C, ALEXANDER K, ROSSIER Y, LAVERTY S. Comparison of radiography and ultrasonography for the diagnosis of osteochondritis dissecans in the equine femoropatellar joint. equine vet j. 2010;41(7):686-692. doi:10.2746/042516409X452134.

10. Hoegaerts M, Saunders JH. How to perform a standardized ultrasonographic examination of the equine stifle. Proc AAEP. 2004.

Diagnosing Lameness in the Tarsus and Proximal Suspensory metatarsal region Kurt Selberg MS DVM MS Dipl. ACVR Colorado State University Hind limb lameness due to pathologic changes in the distal tarsus and proximal metatarsus is common and affects many breeds and disciplines. The complexity of diagnosis of distal tarsal pain and proximal metatarsal pain lies in the in reliability in localization of lameness via local and intra-articular analgesia in this region1,2. Additional challenges are met imaging the complex region of the tarsus and proximal metatarsus. Osteoarthrosis, is the one most common cause of lameness associated with the tarsus in horses. It has been linked with repeated trauma to the bones and ligaments that comprise the distal aspect of the tarsus, most commonly the structures of the distal intertarsal and tarsometatarsal joints. Radiography is typically the first diagnostic imaging modality used for screen joint disease, including the tarsus. Radiographic findings consistent with osteoarthrosis include periarticular osteophyte production, periarticular and subchondral lysis, narrowing of the affected joints, and development of enthesophytes at the attachment of the ligaments surrounding the tarsometatarsal and distal intertarsal joints. The most common areas to identify these changes are the dorsal, dorsomedial and dorsolateral aspects of the distal intertarsal and tarsometatarsal joints. A full radiographic series is typically indicated inlcuding dorsoplantar, lateromedial, dorsolateral – plantaromedial oblique and dorsomedial – plantarolateral oblique images to fully evaluate the tarsus3-5. However, some lesions of the distal tarsus may be undetected or be underestimated by radiographic evaluation alone. There tends to be poor correlation of the degree of lameness and alteration in performance with radiographic changes of the tarsus and metatarsus6. It is likely that this poor correlation stems in part from the under-diagnosis of pathologic changes. There is evidence to suggest that location of the pathologic change may have some bearing on clinical significance. Those horses with osteoarthritis along the medial aspect of the tarsometatarsal joint tended to lame in that limb. Talocalcaneal joint osteoarthrosis typically lame because of the disease process7. Nuclear medicine may help diagnose radiographically occult lesions. The use of MR and correlation back with nuclear medicine has helped the understanding of disease process and location8. Additionally locations thought to be uncommonly affect by osteoarthritis, such as the plantar aspect of the distal tarsal joints may be overlooked on radiographs alone (figure 1). Bone contusions or better called bone marrow lesions are typically occult radiographically and may present with normal radiographs despite having a consistent moderate to severe lameness Advanced imaging progresses this knowledge and helps target treatment. Fractures involving the distal tarsus are not common. However, when horses present with an acute lameness suspicious of a fracture; diagnosis may be a challenge as the fractures may be radiographically occult with conventional views. The central tarsal bone tends to be more affected. Often the fracture configuration is biarticular extending in a dorsomedial to plantarolateral fashion. These may be most apparent on a Dorso 15-25 lateral-plantar lateral oblique image (figure 2). Fragmentation is may be seen with traumatic injury collateral

ligament injuries or be benign. Fragmentation in the proximal tubercle of the talus are typically benign9, but may be met with uncertainty due to the low frequency encountered. It is important in cases of fragmentation to have an comprehensive understanding of anatomy what soft tissue may be affected or causing the fragmentation to discern potentially significant from insignificant. The muscle interosseous medius also known as the suspensory ligament due to its transformation to mainly fibrous tissue is a well documented source of hind limb lameness in the horse10-12. The bulk of the suspensory ligament originates on the plantaroproximal aspect of the 3rd metatarsal bone. At is proximal extent, the origin is bilobed and trapezoid in shape. A small bundle of fibers continues proximally to the fourth tarsal bone and plantar aspect calcaneus12. Hindlimb suspensory ligament injury is a common problem in the sport horse. Despite the frequency of this injury, diagnosis can be challenging as horses can vary in their presenting signs and the often bilateral nature of the disease confounds the diagnosis. Palpation of the proximal suspensory ligament, despite moderate injury may have minimal response during the physical exam. Response to hind limb flexion is generally moderate to marked, which may overlap with clinical signs associated with lameness originating primarily from the tarsus. Techniques to image the proximal metatarsus vary from plantar, plantaromedial in weight bearing and non-weight bearing. The non-weight bearing approach in the author’s opinon is a more sensitive imaging approach for evaluation of the suspensory ligament at its origin. Imaging/pathologic findings associated with the hind suspensory ligament vary. Pathologic changes may include one or more of finding including diffuse enlargement, dorsal or plantar margin tearing, diffuse fiber damage, fibrosis/scarring and osseous changes. Persistent hypoechoic areas regardless the angle of beam incidence are typically indicative of areas of fiber damage. Variations of anatomy do occur are important to realize. For example, there is a hypoechoic region on both on and off angle approximately just distal to the origin of the suspensory ligament. This site may be confused for a core lesion, which are less common in the hind suspensory ligament. Focal or diffuse areas of increased echogenicity independent of angle of incidence are consistent with fibrosis/scar tissue (figure3). Dystrophic mineralization can also occur and if subtle can be difficult to distinguish from scarring. Measuring the cross sectional area (CSA) can be helpful for comparing the size to the opposite limb. Assessing mild enlargement can be difficult, particularly as there is no guarantee that the contralateral limb is normal. Measurements on cross sectional area of the hind suspensory ligament are not standardized for each bread. Normal CSA for a Warmblood may not be the same as a reining Quarter Horse. For the warmblood this may be up to 2 cm2 and for the quarter horse it may be 1.8 It is helpful to get a sense of normal variations in measurements in non-lame horses that are similar in size, breed and discipline. It is more helpful to use imaging characteristics to assess size and margin. These include loss of the normal space between the dorsal margin of the suspensory ligament and plantar bone margin, displacement of the medial plantar vessels, and extension of the

ligament beyond the plantar confines of the splint bone. Pathologic changes in the suspensory ligament often do no result is marked enlargement, but focal marginal change (dorsal most frequent). As a consequence using CSA only, may result in underdiagnoses or potentially over diagnosis. Pitfalls exist as in all interpretation. It is important to realize the suspensory ligament is comprised of multiple tissue types and has different echogenicity as it is image with ultrasound (Figure 4) Pathologic changes to the bone can occur in additional to ligamentous pathologic change or can be the primary abnormality. Both long axis and transverse imaging are important for evaluating the plantar cortex of MT3. Abnormalities can include bone proliferation, resorption and avulsion fragmentation. MR imaging is very good for assessing changes to surface, cortical and medullary portions, ultrasound can actually be superior for identifying small avulsions and enthesopathies. This is part due to acoustic shadowing from fragmentation, good contrast between bone and ligament structures and thin tissue sampling. The axial margins of MT2 and MT4 should also be evaluated for proliferative changes that could impinge on the suspensory ligament. In conclusion, a combination of history, lameness evaluation, response to diagnostic analgesia and multiple imaging modalities is needed to make a diagnosis. Imaging modalities should be viewed complementary modalities and be used as such. To get the most out of imaging findings, it is important to take into consideration clinical history, physical and moving examinations and diagnostic anesthesia findings. 1. Claunch KM, Eggleston RB, Baxter GM. Effects of approach and injection volume on

diffusion of mepivacaine hydrochloride during local analgesia of the deep branch of the lateral plantar nerve in horses. http://dxdoiorgproxy-remotegalibugaedu/102460/javma245101153. October 2014. doi:10.2460/javma.245.10.1153.

2. Dyson SJ, ROMERO JM. An Investigation of Injection Techniques for Local Analgesia of the Equine Distal Tarsus and Proximal Metatarsus. equine vet j. 1993;25(1):30-35.

3. Eksell P, Uhlhorn H, Carlsten J. Evaluation of different projections for radiographic detection of tarsal degenerative joint disease in Icelandic horses. Vet Radiol Ultrasoun. 1999;40(3):228-232.

4. ttir SBORO, Ekman S, Eksell P, Lord P. High detail radiography and histology of the centrodistal tarsal joint of Icelandic horses age 6 months to 6 years. August 2005:1-7.

5. ttir SBORO, Axelsson M, Eksell P, Sigurdsson H, Carlsten J. Radiographic and clinical survey of degenerative joint disease in the distal tarsal joints in Icelandic horses. April 2006:1-5.

6. Fairburn A, Dyson S, Murray R. Clinical significance of osseous spurs on the dorsoproximal aspect of the third metatarsal bone. equine vet j.

7. Shelley J, Dyson S. Interpreting radiographs 5: Radiology of the equine hock. equine vet j. 1984.

8. Daniel AJ, Judy CE, Rick MC, Saveraid TC, Herthel DJ. Comparison of radiography, nuclear scintigraphy, and magnetic resonance imaging for detection of specific conditions of the distal tarsal bones of horses: 20 cases (2006-2010). Journal of the American Veterinary Medical Association. 2012;240(9):1109-1114. doi:10.2460/javma.240.9.1109.

9. Espinosa P, Lacourt M, Alexander K, David F, Laverty S. Fragmentation of the proximal tubercle of the talus in horses: 9 cases (2004-2010). Journal of the American Veterinary Medical Association. 2013;242(7):984-991. doi:10.2460/javma.242.7.984.

10. Tóth F, Schumacher J, Schramme M, Kelly G. Proximal suspensory desmitis of the hindlimbs. Compendium Equine. 2009.

11. Dyson SJ, Weekes JS, Murray RC. Scintigraphic Evaluation of the Proximal Metacarpal and Metatarsal Regions of Horses with Proximal Suspensory Desmitis. Vet Radiol Ultrasoun. 2007;48(1):78-85. doi:10.1111/j.1740-8261.2007.00208.x.

12. Dyson S. Hindlimb lameness associated with proximal suspensory desmopathy and injury of the accessory ligament of the suspensory ligament in five horses. Equine Veterinary Education. 2014;26(10):538-542. doi:10.1111/eve.12217.

Figure 1. The left image is the left tarsus, the middle image is the right tarsus and the right image is a fused radiograph and nuclear scintigraphy. The blue arrow is highlighting mild linear abnormal radiotracer at the distal extent of the talocalcaneal joint. This corresponds to focal areas articular lysis bordered by sclerosis on the lateral radiograph (yellow arrow). The left talocalcaneal joint is normal.

Figure 2. Dorso 25 medial - plantarolateral oblique of a western performance horse with an acute lameness localizing the tarsus. The arrows highlight a biarticular fracture of the central tarsal bone.

Figure 3 : Lateral is to the left. Non-weight bearing images perpendicular (left) and off angle (right) to the fiber of the suspensory ligament. There is a focal area of hyperechogenicity along the dorsolateral aspect of the suspensory ligament (red arrow), consistent with (chronic) focal fiber disruption/desmopathy. The proximomedial bone margin is mildly irregular in the right image (yellow arrow). Note that the ultrasound transducer is placed plantar to slightly medial to make the bone margin parallel with the bottom of the ultrasound screen. This increase conspicuity of the bone and ultimately lesions.

Figure 4:Lateral is the left. This is a medial approach to ultrasound examination of the suspensory ligament. The image is at the level of the body of the suspensory ligament. There is a central hypoechogenic area (yellow arrow) in the suspensory ligament and the periphery is hyperechogenic. In this case, the hypoechogenic areas is off angle imaging of the fiber and the hyperechogenic periphery is the fat/muscle, which is not angle dependent. This a normal suspensory ligament and is showing a pit fall in examination and interpretation.

Ultrasonographic and radiographic exam of the head and neck Kurt Selberg MS DVM MS DACVR Colorado State University Fort Collins, CO 80523 Portions of this abstract reprinted with permission from Selberg K. Imaging of A Pain in the Neck: Imaging the Equine Neck, in 360° Proceedings. Am Assoc Equine Pract 2017. Additional acknowledgments to Dr. Myra Barrett for some portions of the text. INTRODUCTION The equine cervical spine is receiving increased attention as a source of dysfunction in the equine patient. This includes neurologic abnormalities, pain and stiffness, decreased performance and forelimb lameness. In most practice circumstances, imaging of the equine neck is confined to radiography and ultrasound.

The cervical spine is a complex region of anatomy. Accurate acquisition and interpretation of cervical imaging studies requires understanding the complexity of the anatomy and identifying normal variants and incidental findings. RADIOGRAPHY OF THE CERVICAL SPINE

Cervical vertebrae are wider and longer compared to other vertebrae and have large articular and transverse processes1. The articular processes are oval in outline with large articular surfaces. The cranial processes are directed dorsomedially, while the caudal processes are directed ventrolaterally.1 The sixth cervical vertebrae generally have shorter, thicker caudal articular processes that are situated farther apart. Correspondingly, the cranial articular facets of the seventh cervical vertebrae are wider and longer.1 As the equine ages, the articular facet joints may normally increase in size with little clinical significance.2

A complete study of the cervical spine should include the caudal skull through the first thoracic vertebra. Lateral radiographs are often obtained in the field with a portable x-ray generator and detector. Coordinating both x-ray generator and x-ray detector can be challenging as direct visualization from the x-ray generator is not typically possible. This may be easily overcome by palpating the transverse processes of the cervical vertebral and marking them with tape. The first transverse process palpated is typically associated with the third cervical vertebra. This is ventral to the C3-4 articulation. Centering the x-ray generator light and x-ray detector at the transverse process/tape will typically allow for adequately positioned radiographs (figure 1a). The addition of lead markers in the jugular furrow with overlapping x-ray images will also allow for easy identification of location on the cervical vertebral column. The resultant images should have the articular processes superimposed centrally (figure 1b). Towards the periphery of the x-ray image the articular facets may be slightly oblique/off set in a craniocaudal fashion due to x-ray beam divergence (figure 2). A common artifact in obtaining cervical vertebral column radiographs is underexposure, which results in a grainy appearance of

the digital radiographs. This may be overcome in the field by using a shorter distance to the x-ray plate. The film focal distance should be approximately 60 cm for a normal mobile x-ray set up . This can be slightly reduced if the horse is large in stature to obtain quality radiographs to 40 cm. However, the shorter film focal distance may make it more difficult to superimpose both dorsal articulations.

The symmetrical anatomy causes superimposition of osseous structures and has the potential to obscure osseous lesions on radiographs. In a small study, there was no significant association with radiographic scores of osteoarthritis and gross pathologic scoring.3 This highlights the limitations of standard lateral images. Oblique radiographic projections that better visualize the facet joints individually have been described4,5 and can be utilized to more completely assess the pathologic changes within the cervical spine.

Oblique radiographs help project the dorsolateral and ventrolateral aspects of the cervical vertebra. This aids in the separation of symmetrical anatomy and allows for lateralization of bone pathologic change. To accurately evaluate both sides, orthogonal oblique images must be obtained. Oblique radiographs are typically obtained from a right/left dorsolateral to left/right ventrolateral fashion at approximately 45 to 55°. These are often more easily obtained while the neck is in a neutral position. The x-ray generator light is approximately 6 to 8 cm dorsal to the tape, while the x-ray detector is placed slightly ventral to the neck to accommodate the angle of the x-ray beam (figure 3). Obtaining a right dorsal to left ventral oblique will highlight the left articular facets dorsally, and the right transverse process ventrally (figure 4). This allows for more complete evaluation of the pathologic changes and lesion localization (figure 5). The C6-C7 articular facet is rounder, larger and more prominent that the cranial and mid-cervical articular facets. This should not be confused with a pathologic process. The C7 vertebra has a variably sized spinous process. In some horses it is barely visible, while in others it can be quite prominent. The spinous process is found just caudal to the articular facet and can be misinterpreted as an osteophyte or remodeling. There are numerous physes within the vertebral bodies in young horses that should be recognized as normal and can persist until approximately five years of age. A separate center of ossification is present in the C6 transverse process that be easily mistaken for a fragment (figure 6). The caudal occiput has a somewhat variable shape at the level of the attachment of the nuchal ligament and the appearance will also vary depending on obliquity. The occipital crest can be rounded or have a square contour, and a prominent protuberance that maintains smooth margins should not be interpreted as nuchal ligament enthesopathy.

The most common indications for acquisition of cervical radiographs are neurologic disorders, neck pain, stiffness, poor performance and occasionally forelimb lameness and trauma.6-8 Diseases of the equine cervical articular processes such as osteoarthritis and osteochondrosis may lead to decrease performance and morbidity such as stiffness, reluctance to flex the neck and forelimb lameness.8,9

Well-positioned lateral images are imperative in order to accurately assess articular facet changes and look for any evidence of cervical vertebral malformation and stenosis. Small changes in obliquity can easily create the appearance of facet enlargement and alter the appearance of the cervical canal. Cervical vertebral malformation (wobblers) is a common differential for horses with a neurologic condition. Radiographs can be helpful for screening, and can often accurately diagnose cervical vertebral malformation but cannot definitively allow for diagnosis of spinal cord compression. There are several reported methods for measuring inter and intra-vertebral ratios for evaluation of evidence of cervical stenosis and malformation. Of these methods, the intervertebral measurement may provide stronger evidence of compression.10 However, myelography is needed to further evaluate the sites of suspicion for evidence of spinal cord compression. Even myelography has limitations to rule lesions in or out;11 however, due to the limited availability of advanced imaging of the equine cervical spine, it is currently the best option in most cases. Enlargement or malformation of the cervical facet joints can result in multiple clinical signs, including neck pain, poor performance, neurologic deficits and forelimb lameness. Enlargement can occur secondary to multiple pathologic processes, including osteochondrosis (figure 7), osteoarthritis and previous trauma. Radiographically it is difficult to distinguish osseous fragmentation due to osteochondrosis versus chronic traumatic fragmentation and the clinical signs and history must be taken into account. Interestingly, there can be patients with marked radiographic abnormalities of the cervical facets secondary to osteochondrosis who exhibit few or no clinical deficits. Including oblique images is very helpful for identification and laterality localization of fragments. Common signs of degenerative change include enlargement, periarticular bone production and joint capsule enthesopathy. Periarticular osteophytes are manifested as thin sclerotic line best seen when the affected facet is projected dorsally on the oblique images. Subchondral cystic lesions or erosions are not common but are more likely noted on the oblique images. With facet enlargement, the intervertebral foramen becomes narrower and less distinct; this is a useful radiographic gauge to help assess the severity of the enlargement. The radiographic changes must be interpreted in conjunction with clinical signs as there is often poor correlation between radiographic changes and clinical signs in the cervical spine, and radiographic abnormalities may be incidental.2 In horses that have a history of resisting flexion or working in collection, throwing their heads or are sensitive to poll pressure, nuchal ligament enthesopathy is a potential contribution. Lateral radiographs of the occipital region may demonstrate irregular spicules of new bone in more active cases and undulating osseous proliferation in chronic cases. Dystrophic mineralization may be seen within the nuchal ligament. Complementing radiographic findings with ultrasound examination is useful for assessment of the integrity of the nuchal ligament. Additionally, correlation with clinical signs is essential, as bone proliferation of the caudal occiput can be found incidentally.

ULTRASONOGRAPHY OF THE CERVICAL SPINE The ultrasound exam should be performed from the caudal occiput to the most caudally visible articular facet, which is usually C7-T1. In horses with a short haircut, the neck only needs to be wetted with warm water; in horses with longer hair coats or thicker skin, clipping may be necessary. A linear transducer should be utilized for as much of the scan as possible in order to obtain images with the best resolution. A macroconvex probe can be used in conjunction to image deeper structures and provide a broad overview of the structures. (figure 9) The depth should be set so that the facet is centered in the image, and the gain and frequency should be at a level that maximizes image quality. The occiput should be examined on either side of the mane to image the entire area of insertion of the attachment of the longus capitis tendon and nuchal ligament. There can be varying prominence of the nuchal crest, as mentioned above, which should not be confused for enthesopathy. Generally, unless there is concern regarding the integrity of the nuchal ligament, the standard examination is confined to the origin. Palpation of the transverse processes of C1 provides a helpful anatomic reference point. From there, the facet joints can be imaged from cranial to caudal. It is helpful to count backward during a dynamic scan while simultaneously marking the sites of the facets with white tape or white correction fluid (Wite-Out®). The caudal limit of the exam is the slope of the shoulder. Ultrasonographically, C6-C7 is usually located just cranial to the slope of the shoulder. The ability to visualize C7-T1 varies, and in horses with longer, thinner necks, it may be readily visualized; whereas in horses with shorter necks, C7-T1 may not be visible beyond the shoulder. The initial examination is made in the transverse with the probe oriented perpendicular to the facet joint, and the probe marker oriented at approximately 11-12o’clock, depending on the horse’s head position (figure 10). This positioning places dorsal to the left of the ultrasound image. The authors prefer to do a screening scan of the length of the cervical spine, localizing the joints and getting an overview of any abnormalities. Following this, each facet joint is examined in detail in the transverse and long axis planes (figure 11). The rest of the visible portion of the vertebral body, including transverse process and region of the intervertebral foramen are evaluated for any osseous abnormalities. In our experience, ultrasound evaluation of muscle abnormalities is generally unrewarding, except in more severe cases that result in gross structural change such as mineralization or diffuse fibrosis or muscle damage secondary to trauma. Normal findings: The articular facet vary somewhat in shape from cranial to caudal. The joint capsule attachment site is more prominent at the cranial articular facets, giving the facets a more angled appearance. The C5-C6 and C6-C7 articular facets have a rounded contour and the C6-C7 is larger than the other articular facets. (figure 12). The joint capsule enthesis has smooth bone, even if there is a more prominent angle. The periarticular margins are smooth and create an

even contour across the joint space. The joint capsule is a thin, well-defined hyperechogenic structure overlying the articular facet, separated from the bone margin by a thin rim of anechoic joint fluid. The attachment of the nuchal ligament and semispinalis capitis should be smooth and well defined. Linear, echogenic fibers characterize the normal tendinous and ligamentous structures. Normally the nuchal bursa is not visualized. The cervical musculature should be symmetric from side to side and is normally of mixed, but well defined, echogenicity. The musculature and large ligaments are rarely injured; but import to examine in a full exam of the neck. Abnormalities of the muscles may be enlargement or atrophy with changes in the echogenicity. Acute muscle strain may present at hypoechogenic areas, while areas of fibrosis are hyperechogenic compared to normal muscle. The base of the skull is an origin for the semispinalis capitis and nuchal ligament. At the interface, there may be bone proliferation, consistent with enthesophyte formation. Bone proliferation at the nuchal ligament is a frequent finding in horses performing dressage and may not manifest clinically. The bursa of the nuchal ligament can become inflamed and infected. This may manifest as effusion and/or mineralization. The bones and synovial structures of the neck are the most common focus of ultrasound examinations. Techniques for ultrasonographic examination of the cervical facet joints have published,1,2 showing good correlation with gross pathology. As discussed elsewhere in these proceedings, diseases affecting the articular facets can include osteoarthrosis, osteochondral fragmentation, and fractures. (figure 13) The margins of the articular facets may become sharp with varying degrees of osteophyte formation. At the insertion of the joint capsule, there may be enthesophyte formation in cases of chronic capsulitis and osteoarthritis. Articular facet effusion is seen as expansion of the joint capsule away from the bone margin, with increased anechoic fluid between the bones and the joint capsule. (figure 7) Assessment of the degree of effusion can be difficult, as there is a fair amount of the joint recess not visible via ultrasound. In cases of severe degeneration or osteochondral fragmentation, hyperechogenic speckling with the joint may occur. This may be cartilaginous and or fibrinous debris. Fractures of the facet joints are rare events. Ultrasound findings may include regional hematoma, severe effusion of the joint and defects within the echogenic bone margin. The atlanto-occipital joint is made up of a large synovial space. In juvenile animal may become infected. This results in synovial thickening, effusion and possibly bone erosions and irregularity. The intervertebral discs are not well visualized because of the anatomic relationship of the cervical endplates. However, in cases of spondylosis, intervertebral disc disease, bone proliferation may be evident ventrally.

Figure 1a. Set up for a lateral radiograph of the cervical vertebral column with tape placed over the transverse processes.

Figure 1b. Metallic markers aid in localization of vertebra. This becomes particularly helpful with oblique images and/or when only a small plate is available for use.

Figure 2. An adequately positioned lateral radiograph of the cervical vertebral column. Note: there is a slight obliquity of the C4 – 5 dorsal articulation due to x-ray beam divergence (arrow). This should not be mistaken for an abnormality.

Figure 3. Plate placement and x-ray generator placement for obtaining oblique radiographs of the cervical vertebral column.

Figure 4. Right 550 dorsal-left ventral Oblique radiograph of the caudal cervical spine. The left dorsal aspect and periarticular margin of the articular facet is highlighted in this image (arrow). The right articular facet is superimposed over the vertebral body, highlighting the joint space (arrow heads). Note: the cranial aspect of the joint is widened while the neck is in a slightly extended position.

Figure 5: Comparison images of the caudal cervical vertebral column. A lateral radiograph (A) and comparison oblique radiograph (B) showing a crescent-shaped osseous fragment with smooth margins associated with the cranial articular process of C-5. The osseous fragment is visualized on the lateral images however laterality cannot be determined.

Figure 6: Normal separate center of ossification of the C6 transverse process.

Figure 7: Lateral and oblique radiographs of an ataxic 2 year old Quarter horse filly. The C5-C6 articular facet is markedly enlarged and irregularly marginated. The oblique image shows that the left C5-C6 is most affected facet. A transverse lucency, consistent with an osteochondrosis fragment, is best appreciated on the oblique view.

Figure 8: Transverse gross section of the articular facet of C4-C5. The caudal articular process of C4 is located dorsally and the cranial articular process of C5 is located ventrally. The yellow box represents the ultrasound beam.

Figure 9: Transverse ultrasound images of a cervical articular facet. Dorsal is to the left. The image resolution is superior using the linear ultrasound probe (A) when compared to the macroconvex ultrasound probe (B) at the same depth.

C4

C5

B A

Figure 10: Position of the ultrasound transducer to obtain transverse images of the articular facets.

Figure 11: A) Transverse ultrasound images of a cervical articular facet. Dorsal is to the left. The white arrow points to the joint space. B) Long axis image of a cervical articular facet. Cranial is to the left. The cranial aspect of the joint is wider, allowing beam penetration into the joint space (arrow).

Figure 12: Transverse ultrasound and corresponding gross images of the articular facets of C3 through C7. The facets vary in contour from cranial to caudal. The white arrow highlights the attachment site of the joint capsule.

A B

C5-6

C6-7

C4-5

C3-4

Figure 13: Transverse and long axis images of a C4-C5 articular facet with marked osseous remodeling, chronic osseous fragmentation and severe joint capsule thickening. These changes were secondary to a previous traumatic event.

Figure 14: Transverse ultrasound image of a C4-C5 articular facet with moderate joint effusion. The normally thin anechoic layer of fluid is thicker than normal and the joint capsule is expanded outward (red arrow). References 1. Getty R. Sisson and Grossman's: the Anatomy of the Domestic Animals, Vol. 1. Vol 5 ed.

W B Saunders Co; 1975.

2. Down S, Henson F. Radiographic retrospective study of the caudal cervical articular process joints in in the horse. Equine Veterinary Journal. 2009;41(6)518-524.

3. Unt V, Eliashar E, Piercy R. Examining the reliability of cervical vertebral radiography for assessment of equine cervical articular process joint arthritis. Veterinary Radiology & Utrasound. 2007;49(1):95.

4. Dimock A, Puchalski S. Cervical radiology. Equine Veterinary Education. 2010;22(2):83-87.

5. Withers J, Voute L, Hammond G, Lischer C. Radiographic anatomy of the articular process joints of the caudal cervical vertebrae in the horse on lateral and oblique projections. Equine Veterinary Journal. 2009;41(9):895-902.

6. Hudson N, Mayhew I. Radiographic and myelographic assessment of the equine cervical vertebral column and spinal cord. Equine Veterinary Education. 2005;17(1):34-38.

7. Birmingham S, Reed S, Mattoon J, Saville W. Qualitative assessment of corticosteroid

cervical articular facet injection in symptomatic horses. Equine Veterinary Education. 2010;22(2):77-82.

8. Ricardi G, Dyson SJ. Forelimb lameness associated with radiographic abnormalities of the cervical vertebrae. Equine Veterinary Journal. 1993;25(5):422-426.

9. Mattoon JS, Drost WT, Grguric MR, Auld DM, Reed SM. Technique for equine cervical articular process joint injection. Veterinary Radiology & Ultrasound. 2004;45(3):238-240.

10. Hahn CN, Handel I, Green SL, Bronsvoort MB, Mayhew IG. Assessment of the utility of using intra- and intervertebral minimum sagittal diameter ratios in the diagnosis of cervical vertebral malformations in horses. Veterinary Radiology & Ultrasound. 2008;49(1):1-6.

11. Van Biervliet J, Scrivani PV, Divers TJ, Erb HN, de Lahunta A, Nixon A. Evaluation of decision criteria for detection of spinal cord compression based on cervical myelography in horses: 38 cases (1981-2001). Equine Veterinary Journal. 2004;36(1):14-20.

Imaging Guided Treatment Kurt Selberg MS DVM MS Dipl ACVR Colorado State University Obtaining the correct diagnosis for the issue causing lameness or poor performance requires a good physical exam, moving exam and diagnostic anesthesia to localize the lesions. Once isolated to a specific area (s), then diagnostic imaging help visualize the area of pathologic change. The size shape, location margins and number of the areas of pathologic change can dictate what is the best treatment. Additionally, finding the best way to deliver the treatment to the area is of importance to get the perceived maximal effect. Image guided deposition can offer pin point control and delivery of a variety of treatment and diagnostic anesthesia options. Fluoroscopy, computed tomography, magnetic resonance imaging, radiography, and ultrasound tend to be the imaging modalities relied on most for targeted treatment; with the latter most commonly used in the hospital and field settings. Using a combination of imaging modalities is also help in areas that have a limit acoustic window. Imaging guided, especially ultrasound can reduce number of repositions, ultimately reducing regional tissue and ensure correct placement{Schneeweiss:2012ia}. The most common areas of imaging guided treatment in the authors practice are the proximal suspensory ligament, flexor tendons, sesamoidean ligaments, collateral ligaments of the distal interphalangeal joint, cervical facets joint, dorsal articulations of the back, sacroiliac region, hip, shoulder. Regardless of the anatomic area imaged, Initial preparation of the anatomic area and ultrasound is import to maintain sterile technique. The ultrasound machine is prepared by placing a sterile glove filled with coupling gel over the transducer, adjusting the ultrasound image to the appropriate depth and setting the frequency of ultrasound transducer to the region of anatomy (typically 7-10 mHz if a variable mHz probe is used). Proper transducer selection will facilitate the procedure. In small areas such at the heel, a microconvex is best to give room to manipulate the needle; tendons and ligaments of the pastern and meta(carpus)tarsus a linear transducer; and in thick areas such as the hip, a low frequency macroconvex. Patient preparation consists of a sterile surgical preparation of the anatomic region. Local anesthetic (sub-dermal injection at the injection site) is often used to desensitize the skin. Ideally the ultrasound machine is positioned where the ultrasound transducer is pointed toward the screen. In most instances using one imaging modality to guide needle or instrument placement will suffice. In the case of ultrasound, judging the initial needle from the ultrasound image can help reduce redirection. The initial angle of the needle can be judged by imaging the lesion and drawing a vertical line on the image. A second line is drawn form the edge of the image (typically where the probe indicator is) on the ultrasound screen to intersect the vertical line at the level of the joint. The vertical line acts as the transducer handle and angled line the needle (figure 1). Redirection of the needle is easily performed in the plane of the ultrasound beam

by pulling the hub of the needle toward the transducer to direct deeper or pushing the hub towards the skin to direct the tip of the needle more superficially. The needle should be visualized in the lesion or targeted tissue in a successful injection. A small test injection is often helpful in cases where needle placement is questioned. In the synovial structures distention of the capsule is seen in successful attempts. In soft tissues, hyperechoic material often fills the lesions, especially when imaged off angle. Using radiography require orthogonal images to triangulate and be sure the needle or instrument is in the correct location. Radiographic guidance is most often used for known lesions of the foot or injection of the tarsus (figure 2). Using radiographic guidance has proven useful, especially in the distal intertarsal joint where low percentages of intra-articular injection have been recorded {Seabaugh:2017jg} In conclusion using imaging guided techniques for a variety anatomy is recommended to ensure correct placement of the needle in to the synovial cavity, tendon/ligament lesion or perineural anesthetic for accurate drug or treatment delivery.

Figure 1. Parasagittal ultrasound image of the shoulder; proximal is to the left. Showing the proposed angle the needle (white line ) needs to be in relation to the ultrasound tranducer (yellow line) to have a successful arthrocentesis of the shoulder.

Figure 2. D60P45L-P oblique and DP of the left front foot; highlighting orthogonal images for needle placement. A 3.5 inch spinal needle has been placed in the lateral collateral ligament fossa. The fossa has focal moderate bone resorption and is irregular.

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