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Orthopedic Problems
In Hocks |
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(originally published in the Mastiff Reporter, 1995) |
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
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
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.
