BACK TO BASICS: FOUNDATIONAL CLINICAL SKILLS FOR EQUINE PRACTICE
limbwhen the radiograph is taken. This ensures the ra- diographic reviewer knows which aspect of the limb is lateral vs medial and is especially beneficial on the oblique views. In the case of radiographic oblique views, themarker is placed on the lateral aspect of the limb.
2. Radiographic Positioning
Regarding proper radiographic positioning, first ensure the patient is standing square on a flat and level sur- face. This is especially important in evaluating feet for balance. When evaluating feet for balance, both feet should be on equal height blocks with the horse stand- ing and positioned squarely. The height of the blocks should be high enough that the center of the radio- graphic beam, where the laser pointer is centered, is at the solar margin of the third phalanx. For a dorsopal- mar viewof the foot, the radiographic plate is positioned parallel to the heel bulbs and perpendicular to the ground surface. For the lateral view, the heel bulbs can also serve as a guidewith the plate and generator being perpendicular to the heel bulbs. For the rest of the joints radiographed in the horse, the general concept is the ra- diographic plate is held and maintained perpendicular to the radiographic generator. The center of the radio- graphic beamis aimed directly at the center of the bone or joint of interest and at an angle where the radio- graphic beamis parallel to the joint surface. In general, a minimum of 2 radiographic views at right angles to each other (lateromedial and dorsopalmar/plantar views) may be taken for survey films in the distal limb of the horse. This is theminimal views needed to assess a 3-dimensional structure in a 2-dimensional image. However, in the lame horse, a complete radiographic study should be performed of the area of interest. In the lower limb, this includes the oblique views but could also entail special projections unique to that bone or joint involved.
3. Radiographic Views
Beyond the basics of patient positioning and projecting the radiographic beam, there are the specificviews and angles of radiographs for each area of interest. Several equine textbooks1,2 along with journal articles on spe- cific anatomical locations can serve as useful guides for consultation of radiographic positions. The common views taken for a radiographic study can vary by the breed, age, discipline of use, and preference of the veteri- nary practitioner. Common basic radiographic views of each anatomical area of the horse in relation to lame- ness localization and clinical scenarioswill be discussed.
Distal Phalanx/Navicular Bone Region
The most common area evaluated for lameness is the foot. Here are some scenarios and what radiographic views thatwould be warranted. Scenario 1: A horse is presented with a unilateral
non-weightbearing limb lameness, with heat at the coronary band, increased digital pulses, and is posi- tive to hoof testers across the toe. The most likely
212 2022 / Vol. 68 / AAEP PROCEEDINGS
diagnosis is a foot abscess, but no definitive tracts are seen. Rather than randomly paring on the foot for an abscess, radiographic evaluation would be warranted, especially to rule out a P3 fracture. The basic radio- graphic views for a foot/distal phalanx study in this scenario would include a lateromedial view, horizon- tal dorsopalmar view, and a 65-degree dorsoproximal- palmarodistal view of the solar margin. These views allow for evaluation of the foot for potential gas tracts seen with some abscesses, coffin bone fractures, kera- tomas, osteitis, as well as coffin joint osteoarthritis, subchondral bone cysts, and osteochondral fragments. Even when the cause of lameness is an obvious abscess, it is good practice to obtain these radiographic views to rule out other underlying causes for the abscess and to have a baseline set of radiographs if the problem pro- gresses. These 3 main basic views are also obtained in cases of laminitis. The lateral viewallows for evaluation of potential rotation, sinking, and dorsal laminar thick- ening. Some horses can sink medially as well, thus the reasoning for a dorsopalmar (DP) view. The so- lar margin view allows for evaluation of solar mar- gin fragmentation and osteitis of P3. Further radiographic evaluation in a laminitic case would include a venogram. Scenario 2: A horse is presented with a forelimb
lameness, negative to hoof testers and blocks out to a palmar digital nerve block. A palmar digital nerve (PDN) block is not specific to just blocking out the heels but regionalizes the lameness to the foot/pastern region. The lateromedial (LM) and DP views dis- cussed above along with radiographs of the navicular bone, including a collimated 60-degree dorsoproximal- palmarodistal oblique view and palmaroproximal-pal- marodistal oblique skyline view, would be the basic radiographs obtained in this case. Lateral and medial oblique views from a horizontal plane or from the 65- degree dorsoproximal-palmarodistal oblique view are taken to further examine areas of interest in the region of the phalanges, navicular bone, solarmargin, and wings of the third phalanx. When radiographs of the navicular bone are taken, it is imperative to ensure the foot/sulci of the frog are clean and any exfo- liating false sole or detached frog is pared away to avoid radiographic artifact. The addition of packing material to fill in the voids of the sulci of the frog decreases artifact, improves radiographic detail, and avoids inadvertently suspecting a frog/solar artifact as a fracture. The addition of navicular radiographs allows for evaluation of navicular cysts, flexor cortical lysis, loss of corticomedullary junction, distal mar- ginal fragmentation, enthesiophytes, and synovial invaginations. Other causes of lameness that can block out to the foot involve the soft tissues of the foot such as the deep digital flexor tendon, impar liga- ment, suspensory ligament of the navicular bone, and collateral ligaments. Also, bone bruising/bone edema and navicular bursitis can be causes of foot lameness. Further diagnostics such as ultrasound of the soft tissues that can be accessed can be performed, but complete evaluation is limited. Magnetic resonance imaging
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