1.5-year-old Quarter Horse colt

• In this case 3 standard projections of the equine stifle were initially provided.
• All candidates identified soft tissue distention of the stifle joint; however, approximately one-half of the candidates failed to remember the different pouches of the equine stifle joint (distinguishing it from the canine stifle).
• Most successful candidates recognized and described specific femoropatellar pouch effusion which led them to more closely examine the patella.
• Almost all candidates described an angular projection of bone extending from the distal border of the patella, though unsuccessful candidates eventually concluded that this was osteophyte production.
• The incongruent articular margins of the patella on the caudolateral-craniomedial oblique projection were not noticed by most candidates.
• Successful candidates either focused on the patella due to femoropatellar pouch effusion or the distal border projection of bone – ultimately requesting a skyline (cranioproximal-craniodistal oblique) of the patella.

• Once supplied, all candidates recognized the sagittal patellar fracture.  The apparent rounding of the fracture margins made some candidates question the chronicity of this fracture but did not affect successful case diagnosis.

This case differentiated between candidates who were familiar with the equine stifle and could follow radiographic signs to request a necessary additional projection, and those who could not. Successful candidates (approximately 2/3) earned almost all case points while unsuccessful candidates (approximately 1/3) earned almost none.

When unsuccessful candidates failed to quickly identify a definitive lesion, most focused on the appearance of the tibial tuberosity apophysis or its adjacent physis.  Most described aggressive lysis or abnormal separation, ultimately diagnosing septic arthritis or tibial tuberosity avulsion.  Some candidates described the extensor fossa of the lateral tibial trochlea and diagnosed this as an osteochondrosis lesion.