The Tarsus (Hock)



Incomplete Ossification of the Tarsal Bones

Another condition that can produce radiographic abnormalities of the tarsus obtained during the purchase exam is incomplete ossification of the tarsal bones. Incomplete ossification of the tarsal bones is most frequently associated with a premature birth or the result of twinning. When the foal is born normally all of the bones of the tarsus and carpus are completely ossified. If the foal is premature or one of a pair of foals, some of these bones might not be completely ossified. Since the foal gets up and is ambulatory shortly after birth, if the bones are not completely ossified they will collapse under the weight of the foal. Figures 73, 74, 75, 76, and 77 demonstrate the incomplete ossification in individual bones and the resulting abnormalities that can develop in the tarsus. Due to incomplete ossification and the resulting collapse of the tarsal bones, a major sequelae to this phenomenon is Degenerative Joint Disease. The veterinarian needs to be cautious about his or her recommendations due to the DJD that can frequently accompany this problem.
Figure 73. Figure 74.
Lateral radiographs of the tarsi with incomplete ossification of the third tarsal bone as seen in a premature foal. Postmortem radiographs of a disarticulated tarsus demonstrating incomplete ossification of the third tarsal bone as seen in a premature foal.


Figure 75. Figure 76.
Lateral radiograph of the tarsus demonstrating incomplete ossification of the third tarsal bone as a result of a premature birth with cranial displacement of the incompletely ossified third tarsal bone. Lateral radiograph of the tarsus demonstrating incomplete ossification of the third tarsal bone as a result of a premature birth with cranial displacement of the incompletely ossified third tarsal bone.


Figure 77. Lateral radiograph of the tarsus demonstrating incomplete ossification of the third tarsal bone as a result of a premature birth with cranial displacement of the incompletely ossified third tarsal bone.