This week at KCC we had some excellent equine cases that generated plenty of discussion.
Case 1
8 year old warmblood that became lame in the right hind leg at a show. On radiographs of the fetlock, there was an ill-defined lucency of the border of the medial metatarsal condyle seen best on an oblique projection. Additional views were requested to better evaluate the condyles, including a flexed lateral and the 125-degree dorsopalmar metacarpal skyline projection (125″ DPMS) (see reference). The lesion was not seen on either of these views. The next suggestion was cross sectional imaging. On CT, there was marked sclerosis of the dorsal distal medial metacarpal condyle and an impressive defect in the subchondral bone.
Discussion points included the anatomy of the fetlock joint. There are really two articulations, MTIII cranially articulates with P1 and MTIII caudally articulates with the sesamoid bones. The 125-degree dorsopalmar metacarpal skyline projection (125″ DPMS) was designed to highlight the caudal aspect of the joint, or the articulation with the sesamoids. The fact that the lesion was not seen on this view meant that it had to be involving the cranial portion of MTIII. This was confirmed with the CT scan.
Additional comments were that you could see this area of the fetlock with ultrasound, holding the limb in a flexed position. The lesions would be visible and the images would provide very valuable information.
The special projection article is worth a look, there are great diagrams of the angled projections of the fetlock. ACVR members have access through the ACVR website.
Hornof WJ, O’Brien TR. Radiographic evaluation of the palmar aspect of the equine metacarpal condyles: a new projection. Journal – American Veterinary Radiology Society 1980;21:161-167.
Case 2
5 year old Quarter Horse mare with mandibular swelling. Two oblique lateral projections of the skull showed a marked thickening of the mandible ventral to the right third premolar. The roots of the premolar were blunted and irregular, with areas of increased and decreased lucency superimposed. The periodontal ligament was absent ventral to the roots but was of normal width adjacent to the tooth. Differential diagnoses included a tooth root abscess, possibly caused by trauma or a developmental anomaly since the horse was so young. It also may have been abnormal tooth root development post-trauma. The opposite maxillary tooth was overgrown. A CT showed the marked mandibular thickening, and a hook-shaped tooth root oriented medially at a 90 degree angle. The tooth was extracted and was not infected. Comments included that the normal width of the periodontal ligament indicated infection was unlikely; it tends to widen with inflammation.
Case 3
The first image in this case was nuclear scintigraphy of the carpus. There was marked increase in uptake in the proximal metacarpus that extended from the dorsal to palmar surface on the lateral projection. There was also mild uptake in the proximal left metacarpus. Differentials included suspensory ligament desmitis or avulsion, and radiographs were requested. There were two faintly visible vertical, radiolucent lines in the proximal right metacarpus along with sclerosis. A collimated view was requested but it did not enhance visibility of the lesions. Diagnosis – proximal metacarpal fracture.
During the discussion, several good points came out. First, a pure suspensory desmitis should not cause increased uptake in the entire proximal metacarpus. It should be limited to the caudal aspect. Second, additional oblique DP radiographs with very small angle increments can often reveal the fractures when the x-ray beam lines up with them. No cross-sectional imaging was recommended for this horse because of the risk of catastrophic fracture during anesthesia.
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