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DP of the left metacarpophalangeal jointcaption
Lateral of the left metacarpophalangeal jointcaption
DMPLO of the left metacarpophalangeal jointcaption
DLPMO of the left metacarpophalangeal jointcaption
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  • Mild intracapsular soft tissue in the metacarpophalangeal joint
  • Seen only on the DP projection, thin distinct radiolucent line in the sagittal groove of the proximal aspect of the first phalanx, extending from the subchondral bone (ie. articular) into the metaphysis
  • Smooth remodeling and equivocal rounded vascular channels on medial sesamoid (not consistent with sesamoiditis)


  1. Incomplete, non-displaced, articular, sagittal fracture of left fore proximal phalanx.
  2. Mild metacarpophalangeal synovial effusion/proliferation
  • Flexed DP or 125° DP (Hornof projection)
  • Additional oblique projections slightly off DP, since not seen on provided obliques or CT

In a young thoroughbred, fractures of this nature should be considered with the development of lameness and this clinical presentation.  Incomplete, non-displaced fractures are frequently very subtle on routine radiographic projections.  It is necessary to have a suspicion and investigate with additional projections to confirm or completely rule out this possibility.   The flexed DP or 125° DP are considered standard projections, for some, in young racing horses because of the increased detection rate of these projections for incomplete articular fractures of the metacarpophalangeal joint.   Thorough evaluation of the subchondral bone in racing animals is critical to avoid catastrophic breakdown if the fracture becomes complete.

Candidates that did well on this case recognized and appropriately described the fracture as being localized to the first phalanx.  Strong candidates further distinguished the dorsal and palmar contours of P1 on the DP projection.  These candidates also described the medial sesamoid changes as mild or more likely chronic, and concluded this was of doubtful significance.

Candidates doing poorly on this case mostly failed to identify the fracture; others diagnosed a concurrent fracture in the sagittal ridge of the 3rd metacarpal bone. The fracture was the main finding of this case and obviously the finding with the greatest clinical impact since missing it could lead to catastrophic breakdown.

In general, it was unsettling how rarely candidates recommended additional radiographs.  Better definition of the fracture prior to the patient leaving radiography would be important to clinicians in determining the immediate need for casting.   Additional projections are more common in the clinical equine practice and there numerous possible projections that would better define the extent of the lesion.  CT was more commonly recommended.  Candidates were not provided the 5th radiograph, even if requested, but it nicely shows the extent of the fracture and that is more extensive than assessed on the initially provided images.

Additional DP - not shown unless requestedcaption