The Tarsus (Hock)



Degenerative Joint Disease (Spavin)

One of the more common problems seen in the hock that can significantly interfere with a horse's future soundness is Degenerative Joint Disease, commonly known as Spavin. Two types of lesions are associated with Degenerative Joint Disease (DJD) - osteolytic and proliferative bone changes.

Figure 52 is an anterior posterior radiograph of the tarsus demonstrating early osteolytic changes along the medial aspect of the distal intertarsal articulation. Figures 53 and 54 also demonstrate similar osteolytic changes in the hock. Figure 54 demonstrates more advanced osteolytic changes.

All of the changes seen in the above figures are considered to be radiographically significant. Changes such as these are an indication that there are active and serious processes occurring in the affected joints. When these types of osteolytic changes are seen, they need to be considered as potential contributors of future unsoundnesses in a horse being considered for purchase. It should also be pointed out that although these types of changes are considered radiographically significant and can produce a future unsoundness; in many instances hock lameness can be treated and managed, and unsound horses can be returned to successful competition.

Figure 52. Figure 53.
Anterior Posterior radiograph of the tarsus demonstrating early osteolytic changes along the medial aspect of the distal intertarsal articulation. Lateral radiograph of the tarsus demonstrating significant osteolytic changes along the cranial aspect of the distal intertarsal articulation.


Figure 54. Anterior Posterior radiograph of the tarsus demonstrating significant osteolytic changes involving the medial aspect of the distal intertarsal articulation.

Osteolytic changes in the hock are associated with eventual loss of joint space. When destruction occurs between two bones, the joint space can disappear, and the two bones appear to be fused. Occasionally in a purchase exam, radiographs of the hock reveal that the third and central tarsal bones have completely fused together and appear as one large tarsal bone. The clinical examination may, however, reveal the horse to be sound. This radiographic change can be the result of a congenital fusion of the tarsal bones or previous DJD causing fusion of the joint. In these instances, if the horse is sound and has been in work for a significant length of time (six months or longer) and is not on medication, one could be optimistic about his future soundness. In reviewing the radiographs, the veterinarian must look carefully to be certain that there is no evidence of active osteolytic changes involving any of the joints. Figures 55 and 56 demonstrate complete loss of joint space involving the distal intertarsal articulation.

Figure 55. Figure 56.
Lateral radiograph of the tarsus with complete loss of joint space involving the distal intertarsal articulation. Lateral oblique radiograph of the tarsus demonstrating complete loss of joint space involving the distal intertarsal articulation.


The second type of degenerative joint change is proliferative new bone production. Figure 57 demonstrates proliferative bone changes involving the medial aspect of the tarsal metatarsal articulation. Bone bridging can be seen between the third tarsal bone and third metatarsal bone. This type of radiographic change has been called "bone spavin". Despite evidence of a bony proliferation as seen in Figure 57, if the radiograph shows no evidence of active osteolytic changes, the horse could be sound and remain sound. In general, the combination of both osteolytic and proliferative bone changes is not a good sign if the horse is expected to stay sound.

Figures 58, 59, and 60 demonstrate osteolytic and proliferative bone changes consistent with a radiographic diagnosis of degenerative joint disease. It is quite common to see this type of degenerative joint disease affecting the tarsalmetarsal joint in sound horses that remain sound. The tarsalmetatarsal joint is an unusual joint in this respect. As mentioned previously the combination of osteolytic and proliferative changes is usually not a good sign with respect to soundness, but this is not always true with the tarsalmetatarsal joint. Figures 58, 59, and 60 demonstrate the types of degenerative changes that could be seen in sound horses. In most instances these are older horses (greater than 10 years) that have been in work and are sound.

Figure 57. Figure 58.
Anterior Posterior radiograph of the tarsus with proliferative bone changes involving the medial aspect of the tarsometatarsal articulation. There is bone bridging between the third tarsal bone and third metatarsal bone. Medial oblique radiograph of the tarsus with evidence of osteolytic and proliferative bone changes involving the cranial and somewhat lateral aspect of the tarsometatarsal articulation consistent with a radiographic diagnosis of degenerative joint disease.


Figure 59. Figure 60.
Lateral radiograph of the tarsus with osteolytic and proliferative changes involving the cranial aspects of the tarsometatarsal articulation consistent with a radiographic diagnosis of degenerative joint disease. Lateral radiograph of the tarsus with osteolytic and proliferative changes involving the cranial aspects of the tarsometatarsal articulation consistent with a radiographic diagnosis of degenerative joint disease.


Figures 61 and 62 demonstrate bone spur formation present on the cranial and proximal aspect of the third metatarsal bone. This is a frequent radiographic finding as part of the purchase exam. It is often seen in sound horses that have been in considerable training for a significant period of time and have not demonstrated signs of lameness. It is important to point out these findings as an abnormality during the purchase evaluation, however, under these circumstances, I would be optimistic about the horse's future soundness.

Figure 61. Figure 62.
Bone spurs present along the proximal and cranial aspect of the third metatarsal bone in a sound horse. Bone spurs present along the proximal and cranial aspect of the third metatarsal bone and the cranial aspect of the third tarsal bone in a sound horse.


Figure 63 demonstrates complete loss of joint space between the tibia and tibial tarsal bones. This is a very serious condition and it would be very unusual for a horse with this degree of degenerative joint disease to be sound enough to evaluate performance on a purchase examination. If this degree of loss of joint space is detected, the examining veterinarian would have to be very pessimistic about the horse's future soundness.
Figure 63. Almost complete loss of joint space between the tibia and tibial tarsal bone. There is virtually no other evidence of degenerative joint disease.