Equine Imaging

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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
Equine Imaging

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Equine imaging l.jpgSlide 1

Equine Imaging

LeeAnn Pack DVM

Diplomate ACVR

The usual exam l.jpgSlide 2

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

Equine rads and safety l.jpgSlide 3

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)

The radiographic examination l.jpgSlide 4

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

Ambulatory equine medicine l.jpgSlide 5

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

Equine musculoskeletal diseases l.jpgSlide 6

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…

Equine musculoskeletal diseases7 l.jpgSlide 7

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

Radiographic evaluation l.jpgSlide 8

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

The distal phalanx l.jpgSlide 9

The Distal Phalanx

Distal phalanx pedal or coffin bone p3 l.jpgSlide 10

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

Lateral lateromedial view l.jpgSlide 11

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

45 degree dp dorsal 45 degree proximal palmaro distal l.jpgSlide 12

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

  • Cassette in tunnel

  • Center on coronary band

Lateral and medial obliques l.jpgSlide 13

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

Horizontal dp l.jpgSlide 14

Horizontal DP

  • Cassette vertical

  • Beam horizontal (flat)

Pedal osteitis l.jpgSlide 15

Pedal Osteitis

  • Non infectious, uncertain etiology

  • Inflammation of P3

  • 45 degree DP view

    • Irregular solar margin of P3 due to resorption

    • Enlarged vascular channels

Infectious or septic osteitis l.jpgSlide 16

Infectious or Septic Osteitis

  • No medullary cavity therefore osteitis NOT osteomyelitis

  • Solar abscess, penetrating wound

  • Lucent defect due to lysis

    • Usually no periosteal reaction

Pedal osteitis17 l.jpgSlide 17

Pedal Osteitis

Laminitis l.jpgSlide 18


  • Multifactorial ds process

  • Usually bilateral front

  • Must think about the future

Saw horse stance l.jpgSlide 19

Saw Horse Stance

Laminitis20 l.jpgSlide 20


  • Lateral view

  • If acute, rads may be normal

  • Early changes

    • Dorsal hoof wall thickening

      • Normal ~18mm for Thoroughbreds/ QH

Laminitis21 l.jpgSlide 21


  • 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

Laminitis22 l.jpgSlide 22


  • Progressive changes

    • Rotation of P3

      • Separation from hoof wall

      • Palmar (plantar) rotation with loss of parallel alignment

      • P3 may penetrate sole

Laminitis23 l.jpgSlide 23


  • Progressive changes

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

      • Laminar necrosis with rotation

Laminitis24 l.jpgSlide 24


  • Chronic changes

    • Any of previously described features

    • “Ski-tipped” remodeling to dorsodistal P3

    • Pedal osteitis changes

Objective evaluation for laminitis l.jpgSlide 25

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







Objective evaluation for laminitis26 l.jpgSlide 26

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

Objective evaluation for laminitis27 l.jpgSlide 27

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

Objective evaluation for laminitis28 l.jpgSlide 28

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?

Fractures of p3 l.jpgSlide 29

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

Fractures of p330 l.jpgSlide 30

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

Type i p3 fracture l.jpgSlide 31

Type I P3 Fracture

Type ii p3 fracture l.jpgSlide 32

Type II P3 Fracture

Type iii p3 fracture l.jpgSlide 33

Type III P3 Fracture

Type vi fracture l.jpgSlide 34

Type VI Fracture

Seen on oblique rad l.jpgSlide 35

Seen on Oblique Rad

Mineralization of the collateral cartilages side bone l.jpgSlide 36

Mineralization of the Collateral Cartilages (Side bone)

  • Draft horses especially

  • Usually incidental

  • May have separate ossification center

Keratoma l.jpgSlide 37


  • Mass in hoof wall causes pressure necrosis

    • Focal resorption (lysis) in P3

Navicular bone l.jpgSlide 38

Navicular Bone

Navicular bone39 l.jpgSlide 39

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.jpgSlide 40


  • Flexor surface

  • Articular surface

  • Proximal border

  • Distal border

Horizontal dp41 l.jpgSlide 41

Horizontal DP

  • Evaluation of proximal navicular border

65 degree cone down l.jpgSlide 42

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.jpgSlide 43

Normal Navicular Bone

Skyline palmaroproximal palmarodistal oblique l.jpgSlide 44

Skyline (Palmaroproximal palmarodistal oblique)

  • Cassette in tunnel

  • X-ray beam angled along back of distal pastern

  • Flexor surface

  • Corticomedullary distinction

Navicular degeneration disease l.jpgSlide 46

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.jpgSlide 47

Navicular Degeneration/ Disease

  • Sclerosis/ decreased CM distinction

  • Flexor surface erosions

    • Flattening of sagittal ridge

    • Thinning of flexor surface

Navicular degeneration disease48 l.jpgSlide 48

Navicular Degeneration/ Disease

Navicular change l.jpgSlide 49

Navicular Change

Navicular bone50 l.jpgSlide 50

Navicular Bone

  • Fractures

    • Esp. lateral and medial borders

  • Osteomyelitis

    • Penetrating wound to navicular bursa

    • Lysis/ flexor surface erosions

Coffin and pastern joints l.jpgSlide 51

Coffin and Pastern Joints

Degenerative joint disease l.jpgSlide 52

Degenerative Joint Disease

  • Standard views

    • Lateral, DP, Obliques

  • Distal interphalangeal joint (coffin jt)

    • Low ringbone

  • Proximal interphalangeal joint (pastern jt)

    • High ringbone

Fractures l.jpgSlide 53


  • P1 fxs more common

Fetlock joint l.jpgSlide 54

Fetlock Joint

Fetlock joint metacarpo tarso phalangeal joint l.jpgSlide 55

Fetlock Joint (Metacarpo(tarso) phalangeal Joint)

  • Standard views

    • Lateral

    • DP (30 degree DP)

    • DLPMO

    • DMPLO

  • Optional

    • Flexed lateral

    • 125 degree DP

Lateral56 l.jpgSlide 56


Dp 30 degree dp l.jpgSlide 57

DP (30 degree DP)

  • 30 degree downhill angle

  • Lateral sesamoid more pointed at apical margin


Obliques l.jpgSlide 58


  • DLPMO (dorsolateral palmaromedial oblique)


  • 30 degrees lateral or medial of dorsal

  • Must get labeling correct!!!

Flexed lateral l.jpgSlide 59

Flexed Lateral

  • Non weight bearing

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

  • Articular surfaces of sesamoids

125 degree dp l.jpgSlide 60

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

Synovitis l.jpgSlide 61


  • 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

Degenerative joint disease62 l.jpgSlide 62

Degenerative Joint Disease

  • Osteophytes

  • Entheseophytes

  • Subchondral sclerosis

  • Joint space narrowing

  • Soft tissue swelling

Osteochondrosis l.jpgSlide 63


  • 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

Physitis l.jpgSlide 64


  • Rapidly growing foals (non-infectious)

  • Distal MC (MT) III physis affected

    • Widened irregular physis

    • New bone at physeal margins

    • Angular limb deformities may result

Physitis65 l.jpgSlide 65


Fractures66 l.jpgSlide 66


  • P1 osteochondral fragments

    • Dorsoproximal esp. dorsomedially

    • Palmar proximal

  • Proximal sesamoids

    • Apical, midbody, basilar, abaxial, sagittal

    • Prognosis depends on soft tissues involved/ articular involvement

Fractures67 l.jpgSlide 67


  • Distal MC (MT) III condylar fx

    • More commonly lateral to sagittal ridge

    • Thoroughbreds, Standardbreds, QHs

    • Multiple obliques may be necessary

    • 125 degree DP

Sesamoiditis l.jpgSlide 68


  • Non-infectious

  • Strain on suspensory branches and distal sesamoidean ligaments

    • Can US

  • Enlarged vascular channel in sesamoids

Sesamoiditis69 l.jpgSlide 69


  • Primarily ST disease

  • May indicate current or be d/t previous disease

  • Cyst formation

  • Pathologic fractures

Sesamoiditis70 l.jpgSlide 70


Metacarpus metatarsus iii cannon bone l.jpgSlide 71

Metacarpus/ Metatarsus III (Cannon Bone)

  • Standard views

    • Lateral

    • DP

    • DLPMO

    • DMPLO

Metacarpus metatarsus iii cannon bone72 l.jpgSlide 72

Metacarpus/ Metatarsus III (Cannon Bone)

Periostitis l.jpgSlide 73


  • “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

Bucked shins l.jpgSlide 74

Bucked shins

  • See in racing TB and QH

  • Localized heat, pain, swelling

  • Non adaptive stress response

  • Nuclear scintigraphy may be needed to see

Periostitis75 l.jpgSlide 75


  • “Splints”

    • Damage to interosseous ligament

      • Between MC II and III in front

      • Between MC IV and III in rear

    • Proximal third of bones affected

Fractures76 l.jpgSlide 76


  • 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.jpgSlide 77


  • 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.jpgSlide 78

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

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