Hocks

Osteochondrosis is a term applied to a number of similar disorders of the joints where bone (osteo-) and cartilage (chondro-) are involved. If they are inflamed we use the term osteochondritis. It is now a fairly common diagnosis in young limping dogs, the defects being found in one or more of those joints I named above. The hock joint is what corresponds to our ankle and first short bones in the foot, though the dog does not walk on the heel as we do. In the hock, the large bone of the lower thigh (tibia) rests mainly on the tibial tarsal bone, also known as the talus. The common specific expression of osteochondrosis in the hock is OCD (osteochondritis dissecans) which means, as it does in the shoulder and the elbow, a small piece of cartilage or bone has come loose in the joint of a young dog and is causing irritation and inflammation.

INCIDENCE

Sweden's Dr. S. E. Olsson reported on 51 dogs with hock ailments, 48 of which had a diagnosis of OCD of the hock, and the other three having osteoarthritis in the joint but no real sign of OCD. In all but one of the 48, the site of this osteochondrosis defect was associated with the rear part of the medial (toward the middle) ridge of this bone. Labrador Retrievers made up 23 of these dogs in Olsson's 1984 group, with 10 Rottweilers, 6 Golden Retrievers, and smaller numbers of Beagle, Newfoundland, Schnauzer, GSD, Bouvier, and Welsh Springer also being included. Ten had lesions in both hocks. About half the flaps or mice were all cartilage, and 25% each were bone or both, the bone sometimes being formed by ossification rather than being pulled off. As in OCD of the other joints, this one begins with a defect in cartilage rather than a fissure in bone. In conversations with radiologists at Auburn University, I was told that they see tibial-tarsal OCD most predominantly in Rottweilers, a breed they also connect frequently with OCD of the humeral head and even panosteitis. In Australia, OCD of the hock is also seen in Bull Terriers.

In a later study of 89 dogs, Olsson concluded that "osteochondrosis of the hock does not show the same preponderance for the male sex" as seen in other joints. He surmised that this difference was connected with the fact that the hock lesions are much more associated with a history of trauma. Heritability, therefore, may be lower for this ailment than for others. However, before you get confused between heritability and inheritance, you may want to read my new book on orthopedic disorders, unfortunately not yet in print as of the time of this article's publication. For now, suffice it to say that they are not the same: heritability is a description of how environment can influence the expression of genes, and inheritance refers to the actual chemical structures we call genes being replicated and passed along in the formation of sperm and egg cells.

TREATMENT

Prompt surgical treatment is as much recommended in the hock as it is in the elbow. If surgery is delayed until severe DJD (degenerative joint disease) has started, permanent lameness is very likely even after surgery to remove calcium deposits or particles. Even if diagnosed early, a few cases will have a poor prognosis for recovery and freedom from limping and DJD.

GENETICS

Mason and Lavelle in 1979 found a familial characteristic in Australian Cattle Dogs. (Remember the early historical connection between this breed and the Shiba through the southern Asia Dingo.) A year later they and a couple more colleagues studied 68 dogs, half of which were Labrador Retrievers, bred by the National (Australian) Guide Dogs Association. When the pedigrees of the Labs were analyzed, it was discovered that most of them went back to one foundation bitch, and that the odds of any of these dogs developing osteochondrosis were greatly increased if both parents had that bitch in their pedigrees.

ADDITIONAL COMMENTS ON OCD OF THE HOCKS

In the 1970s, Olsson reported a number of observations which are presented in the following two paragraphs, copied from his contribution to my 1981 HD book:
"OCD of the hock may not be as common in your breed as in Labs, Rotts, and Goldens, but it is found in individuals of many breeds and it is wise to give attention to its possibility in cases of slight to severe lameness in the hind legs of young dogs. The clinical signs usually begin at four to five months and are usually very vague. The lesion is more often unilateral than OCD in other joints. The most typical findings are a slightly shorter step than normal on the affected leg and pain on extension and flexion of the hock. Rather early, the range of flexion is decreased. In some dogs there is obvious joint effusion (swelling). As in OCD of other joints, the radiographic examination (x-rays) provides the diagnosis. The lesion is located to the medial ridge of the talus and is best demonstrated as a defect in this ridge on an anterioposterior film. A fragment can often be seen because it is calcified or ossified. In old cases the fragments can be very large in size. Sometimes a lateral radiograph with the hock joint in as much flexion as possible is useful.

A rather high percentage of loose bodies removed from hock joints contain bone. This is in contrast to OCD in other joints of the dog, where such ossicles are extremely rare. Surgery is the treatment of choice. With the leg in flexion, the loose bodies easily can be removed. Prognosis is good if surgery is performed early."

A SIMILAR CONDITION

Stress fractures of the hock have been well known in racing Greyhounds for many years. However, these can and do occur very occasionally in other breeds. It is bittersweet irony that it should have first been reported in a Shiba belonging to the author of the book on orthopedic disorders, namely me. The day after winning another Best in Show, my male suffered a very painful fracture in the hock as a result of jumping into a jumble of large rocks. "Track" Greyhounds avulse (tear off) a fragment of bone when they exert those tremendous and sudden tensile forces in racing. My Shiba did the same thing, apparently when bouncing out of a crevice between rocks while the hock was twisted. This severe trauma can be (and was, in this case) accompanied by the creation of a slight but significant subluxation between the talus and the several tarsal bones below it, adding to the pain. Surgery about a week after the injury was followed by hydrotherapy and restricted free exercise, and recovery was apparent, but occasional limping was still seen, thought at the time to be due to intermittent arthritis. Arthritis, consisting of swelling and usually some extra bony ("calcium") deposits is a natural result of injury to a joint. However, when the limp returned a year later, further radiography revealed a previously-undetected avulsed fragment, affixed with pins. Since he had normal gait most of the time, I "brought him out" for a short series of shows, but following Murphy's Law, he limped at those shows. Since then he's been happily retired.

Stress fractures (acquired, environmental) can be differentiated from genetic OCD mainly by the age of onset, the former occurring after full skeletal maturity has been reached and at an age when the dog is in top muscular condition. They are brought on suddenly, like a muscle strain or a bone broken in a fall. OCD of the hock occurs in young pups whose joints have bones that are still ossifying (turning to bone from cartilage and connective tissue) and thus in a very "plastic" form, easily distorted by less severe but constant stress. Minor subluxation may accompany stress fracture, while subluxation can range from minor to severe in congenital-developmental joint disorders. The OCD lesion is found on the top end of the talus, while the stress fracture avulsed piece is torn off the bottom. Stress fractures almost always show an obvious bone fragment on the x-ray picture, but more often than not, the OCD lesion is either all cartilage or hard to find on film, sometimes because bone has been partly or completely resorbed. The occurrence of stress fracture in the Shiba is probably very rare (mine is the only case I know of so far), while hereditary OCD of the hock is common enough so that an owner of a dog with rear-leg lameness should have this possibility checked by a team of radiologist and orthopedist, probably at a veterinary college.

(Fred Lanting is an AKC judge, breeder of German Shepherds, the au-thor of "Canine Hip Dys-plasia" and the soon-to-be published "Canine Or-thopedic Prob-lems.")