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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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  1. Equine Imaging LeeAnn Pack DVM Diplomate ACVR

  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

  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)

  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

  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

  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…

  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

  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

  9. The Distal Phalanx

  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

  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

  12. 45 Degree DP (Dorsal 45 degree proximal-palmaro distal) • Cassette in tunnel • Center on coronary band

  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

  14. Horizontal DP • Cassette vertical • Beam horizontal (flat)

  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

  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

  17. Pedal Osteitis

  18. Laminitis • Multifactorial ds process • Usually bilateral front • Must think about the future

  19. Saw Horse Stance

  20. Laminitis • Lateral view • If acute, rads may be normal • Early changes • Dorsal hoof wall thickening • Normal ~18mm for Thoroughbreds/ QH

  21. 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

  22. Laminitis • Progressive changes • Rotation of P3 • Separation from hoof wall • Palmar (plantar) rotation with loss of parallel alignment • P3 may penetrate sole

  23. Laminitis • Progressive changes • Gas between sensitive (dermal) and insensitive (epidermal) laminae • Laminar necrosis with rotation

  24. Laminitis • Chronic changes • Any of previously described features • “Ski-tipped” remodeling to dorsodistal P3 • Pedal osteitis changes

  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 16.5 a 65.5 16.5 c b

  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

  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

  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?

  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

  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

  31. Type I P3 Fracture

  32. Type II P3 Fracture

  33. Type III P3 Fracture

  34. Type VI Fracture

  35. Seen on Oblique Rad

  36. Mineralization of the Collateral Cartilages (Side bone) • Draft horses especially • Usually incidental • May have separate ossification center

  37. Keratoma • Mass in hoof wall causes pressure necrosis • Focal resorption (lysis) in P3

  38. Navicular Bone

  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)

  40. Lateral • Flexor surface • Articular surface • Proximal border • Distal border

  41. Horizontal DP • Evaluation of proximal navicular border

  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

  43. Normal Navicular Bone

  44. Skyline (Palmaroproximal palmarodistal oblique) • Cassette in tunnel • X-ray beam angled along back of distal pastern • Flexor surface • Corticomedullary distinction

  45. 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)

  46. Navicular Degeneration/ Disease • Sclerosis/ decreased CM distinction • Flexor surface erosions • Flattening of sagittal ridge • Thinning of flexor surface

  47. Navicular Degeneration/ Disease

  48. Navicular Change

  49. Navicular Bone • Fractures • Esp. lateral and medial borders • Osteomyelitis • Penetrating wound to navicular bursa • Lysis/ flexor surface erosions

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