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Equine Imaging


Equine Imaging. LeeAnn Pack DVM Diplomate ACVR. The “Usual” Exam. Routine views – four DP, lateromedial and two oblique views of the limbs below the radius and tibia Stifle joints are usually 3 views CdCr, lateromedial and caudolateral-to-craniomedial

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Equine Imaging

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Equine imaging l.jpg

Equine Imaging

LeeAnn Pack DVM

Diplomate ACVR


The usual exam l.jpg

The “Usual” Exam

  • Routine views – four

    • DP, lateromedial and two oblique views of the limbs below the radius and tibia

    • Stifle joints are usually 3 views

      • CdCr, lateromedial and caudolateral-to-craniomedial

    • Proximal aspects of limbs often a single view

    • Additional views as needed to project tangentially areas prone to specific lesions

  • Patient preparation

    • Clean, dry hair coat, for foot rads remove shoes and pack sulci with Play-Doh


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Equine Rads and Safety

  • Exposure must be adequate to see bone detail, but still preserve visibility of adjacent soft tissues (at least with a hotlight)

    • Make sure portable X-ray tube is at proper distance from cassette

  • Follow strict radiation safety practices

    • Always wear lead gloves/ apron

    • Collimate

    • Cassette holders (inverse square law)


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The Radiographic Examination

  • Labeling

    • R or L markers are ALWAYS placed laterally, or in the case of the lateral view, dorsally

  • Horses usually standing (weight bearing) for radiographs

    • Allows accurate assessment of joint space/ cartilage loss

  • Be aware of slang terms/ abbreviations for views or anatomy


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Ambulatory Equine Medicine

  • Commonly radiographed areas

    • Limited by the power of the X-ray tube and film-screen combo

    • Feet

    • Fetlocks (metacarpo(tarso)phalangeal joints)

    • Carpi

    • Tarsi

    • Stifles

  • Less common

    • Cervical spine, Skull (including teeth), Shoulder, Elbow, Neonatal Thorax/ Abdomen

  • Adult horse thoracic, abdominal, spinal, shoulder, and skull exams are best done with a high mA in-house machine, specially designed for horses

    • Extremely high dose rates for staff unless strict radiation safety measures taken


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Equine Musculoskeletal Diseases

  • The anatomy, views, and learning common locations of lesions is the tough part!!!

  • Although the etiology of various bone disease in horse is slightly different, the appearance of the actual lesion is very similar

    • Fractures, fragments, osteophytes, sclerosis, lysis…


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Equine Musculoskeletal Diseases

  • Horses don’t really get that many musculoskeletal diseases

    • Fractures (chip, slab, stress, regular types)

    • Infection (abscess, osteomyelitis, septic arthritis)

    • Degenerative Joint Disease (osteophytes, entheseophytes)

    • Osteochondrosis (joint mice, cyst-like lucencies)

    • Laminitis

    • Navicular disease

    • Angular limb deformities


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Radiographic Evaluation

  • Always hang films “head to the left”

  • Soft tissues (use hotlight)

  • Bone alignment

  • Bone cortex, medulla, periosteum

  • Joint spaces and articular margins

  • ***Rads may be normal in a lame horse

  • Abnormal radiographic findings may not necessarily be the cause of lameness


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The Distal Phalanx


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Distal Phalanx (Pedal or Coffin Bone, P3)

  • Standard views

    • Lateral

    • 45 degree DP

  • Optional

    • 45 degree lateral and medial obliques (off 45 degree DP view)

    • Horizontal DP


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Lateral (Lateromedial) View

  • P3 should be parallel to hoof wall

    • Metal object on hoof wall

  • Horse standing on block

  • Center on coronary band

  • Cassette on medial side as close as possible

    • Minimize magnification


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45 Degree DP (Dorsal 45 degree proximal-palmaro distal)

  • Cassette in tunnel

  • Center on coronary band


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Lateral and Medial Obliques

  • Dorsal 45 degree proximal 45 degree lateral-palmaro distomedial oblique

  • Dorsal 45 degree proximal 45 degree medial-palmaro distolateral oblique

  • Basically a 45 degree DP shot at the lateral or medial side of the foot


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Horizontal DP

  • Cassette vertical

  • Beam horizontal (flat)


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Pedal Osteitis

  • Non infectious, uncertain etiology

  • Inflammation of P3

  • 45 degree DP view

    • Irregular solar margin of P3 due to resorption

    • Enlarged vascular channels


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Infectious or Septic Osteitis

  • No medullary cavity therefore osteitis NOT osteomyelitis

  • Solar abscess, penetrating wound

  • Lucent defect due to lysis

    • Usually no periosteal reaction


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Pedal Osteitis


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Laminitis

  • Multifactorial ds process

  • Usually bilateral front

  • Must think about the future


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Saw Horse Stance


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Laminitis

  • Lateral view

  • If acute, rads may be normal

  • Early changes

    • Dorsal hoof wall thickening

      • Normal ~18mm for Thoroughbreds/ QH


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Laminitis

  • Progressive changes

    • Sinking of P3 relative to hoof

      • May appear as dorsal hoof wall thickening

      • Alignment of P3 unchanged

      • Thin sole

      • Soft tissue bulge at coronary band


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Laminitis

  • Progressive changes

    • Rotation of P3

      • Separation from hoof wall

      • Palmar (plantar) rotation with loss of parallel alignment

      • P3 may penetrate sole


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Laminitis

  • Progressive changes

    • Gas between sensitive (dermal) and insensitive (epidermal) laminae

      • Laminar necrosis with rotation


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Laminitis

  • Chronic changes

    • Any of previously described features

    • “Ski-tipped” remodeling to dorsodistal P3

    • Pedal osteitis changes


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Objective Evaluation for Laminitis

  • Measure dorsoproximal and dorsodistal hoof thickness

    • Is the hoof too thick?

      • You only know this if the breed has established normals

        • Magnification or obliquity will severely skew this measurement

        • a and c should be less than 18 mm for THB, QH

    • You can use an alternative method to correct for magnification (hoof wall to pedal ratio)

      • Measure dorsoproximal hoof wall (a)

      • Measure mid P3 length (b)

      • Divide a/b

      • a/b ratio should be < 0.27

16.5

a

65.5

16.5

c

b


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Objective Evaluation for Laminitis

  • Determine if rotation is present

    • Is the distal hoof wall measurement greater? If so, what is the rotation angle?

      • Method 1

        • Line on dorsal hoof wall

        • Line on dorsal P3

        • Measure angle of intersection

          • May extend off the radiograph


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Objective Evaluation for Laminitis

  • Method 2

    • Measure dorsal hoof angle relative to horizontal surface of wooden block

    • Measure dorsal P3 angle relative to block

    • Subtract angles


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Objective Evaluation for Laminitis

  • Don’t get too caught up with exact angles of rotation because we are just not that precise!!!

    • The angles are estimations

    • You will have 1-2 degrees of variation each time you measure

    • Is the rotation mild, moderate, or severe?


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Fractures of P3

  • Make sure “fractures” are not packing artifacts

    • 45 degree DP and obliques if needed

  • Fibrous healing occurs

  • Classification system

    • Type I- Non-articular of Palmar process

    • Type II- Articular fxs from DIJ to solar margin

    • Type III- Articular midsagittal fx

    • Type IV- Extensor process fx

    • Type V- Comminuted fx

    • Type VI- Solar margin only


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Fractures of P3

  • Linear radiolucent defect in P3

  • Often need multiple rads inc obliques

  • Rads repeated in 7-10 days

  • May need nuclear scintigraphy

  • Healing difficult to asses – may see fx line for years


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Type I P3 Fracture


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Type II P3 Fracture


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Type III P3 Fracture


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Type VI Fracture


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Seen on Oblique Rad


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Mineralization of the Collateral Cartilages (Side bone)

  • Draft horses especially

  • Usually incidental

  • May have separate ossification center


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Keratoma

  • Mass in hoof wall causes pressure necrosis

    • Focal resorption (lysis) in P3


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Navicular Bone


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Navicular Bone

  • Standard views

    • Lateral and 45 degree DP (same as for P3)

    • Horizontal DP (same as for P3)

    • 65 degree DP Cone-down

    • Skyline (palmaroproximal palmarodistal oblique)


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Lateral

  • Flexor surface

  • Articular surface

  • Proximal border

  • Distal border


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Horizontal DP

  • Evaluation of proximal navicular border


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65 degree Cone-down

  • 2 methods (use grid with both)

    • Center on coronary band

      • Upright pedal

        • Cassette vertical

      • High coronary

        • Horse stands on cassette tunnel flat on ground

        • Easier but more distortion

  • Tightly collimated to reduce scatter and film fog

  • Navicular bone is superimposed on P2

    • Must not be superimposed on DIJ

  • Best view for evaluation of distal navicular border


Normal navicular bone l.jpg

Normal Navicular Bone


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Skyline (Palmaroproximal palmarodistal oblique)

  • Cassette in tunnel

  • X-ray beam angled along back of distal pastern

  • Flexor surface

  • Corticomedullary distinction


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Navicular Degeneration/ Disease

  • Changes may be present in sound horses

  • Distal border

    • Increased size and number of synovial invaginations

  • Cyst like lucencies

  • Entheseophytes

    • Collateral ligaments (proximal border)

    • Impar ligament (distal border)


Navicular degeneration disease47 l.jpg

Navicular Degeneration/ Disease

  • Sclerosis/ decreased CM distinction

  • Flexor surface erosions

    • Flattening of sagittal ridge

    • Thinning of flexor surface


Navicular degeneration disease48 l.jpg

Navicular Degeneration/ Disease


Navicular change l.jpg

Navicular Change


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Navicular Bone

  • Fractures

    • Esp. lateral and medial borders

  • Osteomyelitis

    • Penetrating wound to navicular bursa

    • Lysis/ flexor surface erosions


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Coffin and Pastern Joints


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Degenerative Joint Disease

  • Standard views

    • Lateral, DP, Obliques

  • Distal interphalangeal joint (coffin jt)

    • Low ringbone

  • Proximal interphalangeal joint (pastern jt)

    • High ringbone


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Fractures

  • P1 fxs more common


Fetlock joint l.jpg

Fetlock Joint


Fetlock joint metacarpo tarso phalangeal joint l.jpg

Fetlock Joint (Metacarpo(tarso) phalangeal Joint)

  • Standard views

    • Lateral

    • DP (30 degree DP)

    • DLPMO

    • DMPLO

  • Optional

    • Flexed lateral

    • 125 degree DP


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Lateral


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DP (30 degree DP)

  • 30 degree downhill angle

  • Lateral sesamoid more pointed at apical margin

Lat


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Obliques

  • DLPMO (dorsolateral palmaromedial oblique)

  • DMPLO

  • 30 degrees lateral or medial of dorsal

  • Must get labeling correct!!!


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Flexed Lateral

  • Non weight bearing

  • Best for viewing sagittal ridge of MC (MT) III

  • Articular surfaces of sesamoids


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125 degree DP

  • Misnomer (actually Dorsal 35 degree distal- palmaroproximal view)

    • Non weight bearing

    • Foot on elevated block= “bucket shot”

  • Sesamoids should be superimposed on fetlock jt

  • Assessment of palmar aspect of MC III condyle


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Synovitis

  • Soft tissue swelling

  • Villonodular synovitis

    • Resorption at dorsodistal MC (MT) III prox to condyles

  • Supracondylar lysis

    • Resorption at palmaro (plantaro) distal MC (MT) III prox to condyles


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Degenerative Joint Disease

  • Osteophytes

  • Entheseophytes

  • Subchondral sclerosis

  • Joint space narrowing

  • Soft tissue swelling


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Osteochondrosis

  • Sagittal ridge

    • Dorso proximal 1/3 of ridge

    • Flattening

    • +/- fragments

    • Best seen on flexed lateral view

  • Palmar/ plantar aspect of condyle

    • Flattening, sclerosis, +/- fragments

    • Traumatic induced in adults

    • 125 degree DP view may be necessary


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Physitis

  • Rapidly growing foals (non-infectious)

  • Distal MC (MT) III physis affected

    • Widened irregular physis

    • New bone at physeal margins

    • Angular limb deformities may result


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Physitis


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Fractures

  • P1 osteochondral fragments

    • Dorsoproximal esp. dorsomedially

    • Palmar proximal

  • Proximal sesamoids

    • Apical, midbody, basilar, abaxial, sagittal

    • Prognosis depends on soft tissues involved/ articular involvement


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Fractures

  • Distal MC (MT) III condylar fx

    • More commonly lateral to sagittal ridge

    • Thoroughbreds, Standardbreds, QHs

    • Multiple obliques may be necessary

    • 125 degree DP


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Sesamoiditis

  • Non-infectious

  • Strain on suspensory branches and distal sesamoidean ligaments

    • Can US

  • Enlarged vascular channel in sesamoids


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Sesamoiditis

  • Primarily ST disease

  • May indicate current or be d/t previous disease

  • Cyst formation

  • Pathologic fractures


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Sesamoiditis


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Metacarpus/ Metatarsus III (Cannon Bone)

  • Standard views

    • Lateral

    • DP

    • DLPMO

    • DMPLO


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Metacarpus/ Metatarsus III (Cannon Bone)


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Periostitis

  • “Bucked shins”

    • Cyclic loading of MC III

      • Microfractures of middle/ distal third dorsal MC III cortex

      • Microfractures not seen but secondary periosteal response is

      • Can lead to visible stress fractures


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Bucked shins

  • See in racing TB and QH

  • Localized heat, pain, swelling

  • Non adaptive stress response

  • Nuclear scintigraphy may be needed to see


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Periostitis

  • “Splints”

    • Damage to interosseous ligament

      • Between MC II and III in front

      • Between MC IV and III in rear

    • Proximal third of bones affected


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Fractures

  • Stress

    • Mid dorsal cortex of MC (MT) III

    • May not be visible initially

    • Lucent line eventually, often “saucer shaped”

    • Bone scintigraphy will diagnose sooner

  • Splints

    • External trauma

    • Often associated with suspensory desmitis


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Osteomyelitis

  • MC (MT) III very prone to sequestration

    • Esp. dorsal cortex with focal trauma

      • Minimal protection by soft tissue

      • Periosteal blood supply easily damaged


Thanks to dr paul rist for use of some of the slides in this equine lecture l.jpg

Thanks to Dr. Paul Rist for use of some of the slides in this Equine lecture.