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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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LeeAnn Pack DVM
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 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 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 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 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 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 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) Standard views Optional 45 degree lateral and medial obliques (off 45 degree DP view) Horizontal DP 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 45 Degree DP (Dorsal 45 degree proximal-palmaro distal) Cassette in tunnel Center on coronary band 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 Cassette vertical Beam horizontal (flat) 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 No medullary cavity therefore osteitis NOT osteomyelitis Solar abscess, penetrating wound Lucent defect due to lysis Usually no periosteal reaction Laminitis Multifactorial ds process Usually bilateral front Must think about the future Laminitis Lateral view If acute, rads may be normal Early changes Dorsal hoof wall thickening Normal ~18mm for Thoroughbreds/ QH 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 Laminitis Progressive changes Rotation of P3 Separation from hoof wall Palmar (plantar) rotation with loss of parallel alignment P3 may penetrate sole Laminitis Progressive changes Gas between sensitive (dermal) and insensitive (epidermal) laminae Laminar necrosis with rotation Laminitis Chronic changes Any of previously described features “Ski-tipped” remodeling to dorsodistal P3 Pedal osteitis changes 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 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 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 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 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 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) Draft horses especially Usually incidental May have separate ossification center Keratoma Mass in hoof wall causes pressure necrosis Focal resorption (lysis) in P3 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 Flexor surface Articular surface Proximal border Distal border Horizontal DP Evaluation of proximal navicular border 65 degree Cone-down 2 methods (use grid with both) Center on coronary band Upright pedal 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) Cassette in tunnel X-ray beam angled along back of distal pastern Flexor surface Corticomedullary distinction 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/ Disease Sclerosis/ decreased CM distinction Flexor surface erosions Flattening of sagittal ridge Thinning of flexor surface Navicular Degeneration/ Disease Navicular Bone Fractures Esp. lateral and medial borders Osteomyelitis Penetrating wound to navicular bursa Lysis/ flexor surface erosions
Coffin and Pastern Joints
Degenerative Joint Disease Standard views Distal interphalangeal joint (coffin jt) Proximal interphalangeal joint (pastern jt) 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) 30 degree downhill angle Lateral sesamoid more pointed at apical margin
Obliques DLPMO (dorsolateral palmaromedial oblique) DMPLO 30 degrees lateral or medial of dorsal Must get labeling correct!!! Flexed Lateral Non weight bearing Best for viewing sagittal ridge of MC (MT) III Articular surfaces of sesamoids 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 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 Disease Osteophytes Entheseophytes Subchondral sclerosis Joint space narrowing Soft tissue swelling 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 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 Fractures P1 osteochondral fragments Dorsoproximal esp. dorsomedially Palmar proximal Proximal sesamoids Apical, midbody, basilar, abaxial, sagittal Prognosis depends on soft tissues involved/ articular involvement Fractures Distal MC (MT) III condylar fx More commonly lateral to sagittal ridge Thoroughbreds, Standardbreds, QHs Multiple obliques may be necessary 125 degree DP Sesamoiditis Non-infectious Strain on suspensory branches and distal sesamoidean ligaments Enlarged vascular channel in sesamoids Sesamoiditis 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) 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 Bucked shins See in racing TB and QH Localized heat, pain, swelling Non adaptive stress response Nuclear scintigraphy may be needed to see 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 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 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.