Radiographic detection and characterization of palmar lesions in the equine fetlock joint.

Subchondral lesions were identified in the distal palmar region of the third metacarpus in 21 fetlock joints of 15 Thoroughbred horses. The lesions were more commonly identified on the lateromedial and flexed lateral projection, with the flexed lateral projection permitting optimal visualization of the lesion. Lesions appeared as poorly marginated, radiolucent defects and were located at the level of the base of the proximal sesamoid bones. The shape and distribution of the radiolucent defects were: crescent, 4; flattened, 4; shallow concavity, 5; deep concavity, 3; oval, 3; and circular, 2. Secondary joint disease was commonly identified in joints with these lesions and was more severe when the lesions increased in size and were irregular at the subchondral bony surface. Three horses with the palmar lesions were rested and re-examined after 16, 40, or 56 weeks. The lesions appeared smaller and less distinct on a subsequent examination for 2 horses, but the degree of secondary joint disease had increased in all 3 horses. Identification of palmar lesions when small seems important for the successful return of the Thoroughbred to racing soundness.