Incomplete ossification of the central and third tarsal bones is most common in premature or twin foals and is characterized by a “sickle-hock” appearance. It may occur unilaterally or bilaterally. Radiologically, the partially ossified cuboidal bones appear smaller and more rounded than normal. Early recognition and treatment are important to prevent crushing of the bones and resultant progressive osteoarthritis. Cylinder tube casts can be used with good results to protect the immature bones until they have ossified.