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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

Equine Imaging

LeeAnn Pack DVM

Diplomate ACVR

the usual exam
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
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
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
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
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
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
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
distal phalanx pedal or coffin bone p3
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
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
45 Degree DP (Dorsal 45 degree proximal-palmaro distal)
  • Cassette in tunnel
  • Center on coronary band
lateral and medial obliques
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
Horizontal DP
  • Cassette vertical
  • Beam horizontal (flat)
pedal osteitis
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
Infectious or Septic Osteitis
  • No medullary cavity therefore osteitis NOT osteomyelitis
  • Solar abscess, penetrating wound
  • Lucent defect due to lysis
    • Usually no periosteal reaction
  • Multifactorial ds process
  • Usually bilateral front
  • Must think about the future
  • Lateral view
  • If acute, rads may be normal
  • Early changes
    • Dorsal hoof wall thickening
      • Normal ~18mm for Thoroughbreds/ QH
  • 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
  • Progressive changes
    • Rotation of P3
      • Separation from hoof wall
      • Palmar (plantar) rotation with loss of parallel alignment
      • P3 may penetrate sole
  • Progressive changes
    • Gas between sensitive (dermal) and insensitive (epidermal) laminae
      • Laminar necrosis with rotation
  • Chronic changes
    • Any of previously described features
    • “Ski-tipped” remodeling to dorsodistal P3
    • Pedal osteitis changes
objective evaluation for laminitis
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
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
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
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
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
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
mineralization of the collateral cartilages side bone
Mineralization of the Collateral Cartilages (Side bone)
  • Draft horses especially
  • Usually incidental
  • May have separate ossification center
  • Mass in hoof wall causes pressure necrosis
    • Focal resorption (lysis) in P3
navicular bone39
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)
  • Flexor surface
  • Articular surface
  • Proximal border
  • Distal border
horizontal dp41
Horizontal DP
  • Evaluation of proximal navicular border
65 degree cone down
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
skyline palmaroproximal palmarodistal oblique
Skyline (Palmaroproximal palmarodistal oblique)
  • Cassette in tunnel
  • X-ray beam angled along back of distal pastern
  • Flexor surface
  • Corticomedullary distinction
navicular degeneration disease
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
Navicular Degeneration/ Disease
  • Sclerosis/ decreased CM distinction
  • Flexor surface erosions
    • Flattening of sagittal ridge
    • Thinning of flexor surface
navicular bone50
Navicular Bone
  • Fractures
    • Esp. lateral and medial borders
  • Osteomyelitis
    • Penetrating wound to navicular bursa
    • Lysis/ flexor surface erosions
degenerative joint disease
Degenerative Joint Disease
  • Standard views
    • Lateral, DP, Obliques
  • Distal interphalangeal joint (coffin jt)
    • Low ringbone
  • Proximal interphalangeal joint (pastern jt)
    • High ringbone
  • P1 fxs more common
fetlock joint metacarpo tarso phalangeal joint
Fetlock Joint (Metacarpo(tarso) phalangeal Joint)
  • Standard views
    • Lateral
    • DP (30 degree DP)
    • DLPMO
    • DMPLO
  • Optional
    • Flexed lateral
    • 125 degree DP
dp 30 degree dp
DP (30 degree DP)
  • 30 degree downhill angle
  • Lateral sesamoid more pointed at apical margin


  • DLPMO (dorsolateral palmaromedial oblique)
  • 30 degrees lateral or medial of dorsal
  • Must get labeling correct!!!
flexed lateral
Flexed Lateral
  • Non weight bearing
  • Best for viewing sagittal ridge of MC (MT) III
  • Articular surfaces of sesamoids
125 degree dp
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
  • 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
Degenerative Joint Disease
  • Osteophytes
  • Entheseophytes
  • Subchondral sclerosis
  • Joint space narrowing
  • Soft tissue swelling
  • 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
  • Rapidly growing foals (non-infectious)
  • Distal MC (MT) III physis affected
    • Widened irregular physis
    • New bone at physeal margins
    • Angular limb deformities may result
  • P1 osteochondral fragments
    • Dorsoproximal esp. dorsomedially
    • Palmar proximal
  • Proximal sesamoids
    • Apical, midbody, basilar, abaxial, sagittal
    • Prognosis depends on soft tissues involved/ articular involvement
  • Distal MC (MT) III condylar fx
    • More commonly lateral to sagittal ridge
    • Thoroughbreds, Standardbreds, QHs
    • Multiple obliques may be necessary
    • 125 degree DP
  • Non-infectious
  • Strain on suspensory branches and distal sesamoidean ligaments
    • Can US
  • Enlarged vascular channel in sesamoids
  • Primarily ST disease
  • May indicate current or be d/t previous disease
  • Cyst formation
  • Pathologic fractures
metacarpus metatarsus iii cannon bone
Metacarpus/ Metatarsus III (Cannon Bone)
  • Standard views
    • Lateral
    • DP
    • DLPMO
    • DMPLO
  • “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
Bucked shins
  • See in racing TB and QH
  • Localized heat, pain, swelling
  • Non adaptive stress response
  • Nuclear scintigraphy may be needed to see
  • “Splints”
    • Damage to interosseous ligament
      • Between MC II and III in front
      • Between MC IV and III in rear
    • Proximal third of bones affected
  • 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
  • MC (MT) III very prone to sequestration
    • Esp. dorsal cortex with focal trauma
      • Minimal protection by soft tissue
      • Periosteal blood supply easily damaged