Etiology and Occurrence.—This condition though rarely met with in the horse, is the result of violent strain upon the os calcis by the gastrocnemius and superficial flexor tendons in efforts put forth by animals in attempts to regain a footing when the hind feet slip forward under the body, or in jumping and in falls or direct contusion by heavy bodies. Hoare reports a case of a mare that had produced fracture in jumping.
Fracture of the other tarsal bones are very seldom observed but may be occasioned by contusions wherein multiple or comminuted fractures are produced, such as are to be seen in small animals. Fracture of the tibial tarsal bone (astragalus) is to be observed as a complication in luxations of the tarsal joint and, according to Cadiot, the other tarsal bones may likewise suffer fracture in luxations of the hock.
Symptomatology.—Great pain attends this accident according to the observations given in recorded cases. In the case cited by Hoare the animal evinced great pain and uneasiness; the hock was unduly flexed; the calcaneum was displaced forward; and marked crepitation was present. A portion of the body of the calcaneum was protruding through the perforated skin. The animal was destroyed and the bone was found broken in three pieces.
[Illustration: Fig. 54—Right hock joint. Viewed from the front and slightly laterally after removal of joint capsule and long collateral ligaments. T.t., Tibial tarsal bone (distal tuberosity). T.c., central tarsal bone. T.3. Ridge of third tarsal bone. T.f. Fibular tarsal bone (distal end). T.4. Fourth tarsal bone. Mt. III, Mt. IV. Metatarsal bones. Arrow points to vascular canal. (From Sisson’s “Anatomy of the Domestic Animals.")]