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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 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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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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  • Multifactorial ds process

  • Usually bilateral front

  • Must think about the future

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  • Lateral view

  • If acute, rads may be normal

  • Early changes

    • Dorsal hoof wall thickening

      • Normal ~18mm for Thoroughbreds/ QH

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  • 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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  • 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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  • Progressive changes

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

      • Laminar necrosis with rotation

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  • 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







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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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Mineralization of the Collateral Cartilages (Side bone)

  • Draft horses especially

  • Usually incidental

  • May have separate ossification center

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  • Mass in hoof wall causes pressure necrosis

    • Focal resorption (lysis) in P3

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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)

Lateral l.jpg

  • 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

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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)

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Navicular Degeneration/ Disease

  • Sclerosis/ decreased CM distinction

  • Flexor surface erosions

    • Flattening of sagittal ridge

    • Thinning of flexor surface

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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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Degenerative Joint Disease

  • Standard views

    • Lateral, DP, Obliques

  • Distal interphalangeal joint (coffin jt)

    • Low ringbone

  • Proximal interphalangeal joint (pastern jt)

    • High ringbone

Fractures l.jpg

  • P1 fxs more common

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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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DP (30 degree DP)

  • 30 degree downhill angle

  • Lateral sesamoid more pointed at apical margin


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  • DLPMO (dorsolateral palmaromedial oblique)


  • 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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  • 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

Osteochondrosis l.jpg

  • 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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  • 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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  • 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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  • 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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  • Non-infectious

  • Strain on suspensory branches and distal sesamoidean ligaments

    • Can US

  • Enlarged vascular channel in sesamoids

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  • Primarily ST disease

  • May indicate current or be d/t previous disease

  • Cyst formation

  • Pathologic fractures

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Metacarpus/ Metatarsus III (Cannon Bone)

  • Standard views

    • Lateral

    • DP

    • DLPMO

    • DMPLO

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  • “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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  • “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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  • 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

Osteomyelitis l.jpg

  • MC (MT) III very prone to sequestration

    • Esp. dorsal cortex with focal trauma

      • Minimal protection by soft tissue

      • Periosteal blood supply easily damaged