Osseous Cyst-Like Lesions in the Third Phalanx

Are Osseous Cyst-Like Lesions Significant?

It has been my experience that the location and size of osseous cyst-like lesions in the third phalanx are the most important features in evaluating their effect on soundness. The smaller the radiolucent defect and the further it is from the articular surface, the less likely it is to be of clinical significance. The lesion in Figure 20 is of concern because of its size, although it is located some distance away from the articular surface. The larger an osteolytic lesion, the greater the chance of a pathologic fracture through the defect. The lesions in Figures 21 and 22 were of concern because of their relation to the articular surface and because they were associated with clinical lameness; those seen in Figures 19 and 20 were not.
Figure 20. Figure 21.
Dorsoventral radiograph of the foot demonstrating a large, oval, osteolytic or cyst-like lesion in the middle portion of the third phalanx. Dorsoventral radiograph of the foot demonstrating an osseous cyst-like lesion close to the articular surface of the third phalanx.

Osseous cyst-like lesions or radiolucent areas in the third phalanx can be significant in relation to a horse's future soundness. While the cause of the lesion may vary and can include infection, a congenital vascular lake, an enlarging keratoma, or a simple, subchondral or aneurysmal bone cyst, the significance of the lesion depends primarily on its size and location.

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