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 3 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 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 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 2 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 4 to 5 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 picture. 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, and at the veterinary college
this was removed and a plate 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 with his 8 international
championships and lady-Shiba visitors, though he still thinks we're
going to a dog show when he sees his crate and my suitcase together!
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.
COPYRIGHT 1995 Fred Lanting
Used with permission