Patellar Luxation in Small Breed Dogs
More Patellas - OFA Certification for Dogs with Normal Patellas
Patellar Luxation in Small Breed Dogs
Teri Dickinson, DVM
Luxated patellas or "slipped stifles" are a common orthopedic
problem in small dogs. A study of 542 affected individuals revealed
that dogs classified as small (adult weight 9 kg (20 lbs) or less)
were twelve times as likely to be affected as medium, large or giant
breed dogs.(1) In addition, females
were 1.5 times as likely to be affected.1 Some researchers
have
suggested a recessive method of inheritance,(2),(3) and
the higher incidence in females could possibly be related to
X-linked(4) factors or hormonal influences.
Luxated patellas are a congenital8 (present at birth) condition. The
actual luxation may not be present at birth, but the structural changes which
lead to luxation are present. Most researchers believe luxated patellas to be
heritable (inherited) as well, though the exact mode of inheritance is not known.
The condition is commonly seen in Italian Greyhounds, although no published data
regarding the incidence in IG's exists at this time. Researchers1 have
suggested that due to the high risk factor in toy breeds, breeding trials or
retrospective pedigree analyses should be undertaken by national breed clubs
to answer some of these questions.
The
stifle is a complicated joint(5) which is the
anatomical equivalent of the human knee. The three major components involved
in luxating patellas are the femur (thigh bone), patella (knee cap), and tibia
(calf or second thigh). See drawing A. In a normal stifle, the femur and tibia
are lined up so that the patella rests in a groove (trochlea) on the femur, and
its
attachment (the patellar tendon) is on the tibia directly below the trochlea.
Drawing A
The function of the patella is to protect the large tendon of the quadriceps
(thigh) muscle as it rides over the front of the femur while the quadriceps is
used to extend (straighten) the stifle joint. Placing your hand on your patella
(knee cap) while flexing and extending your stifle (knee) will allow you to feel
the normal movement of the patella as it glides up and down in
the trochlea.
Luxation
(dislocation) of the patella occurs when these structures are not in
proper alignment.(6) Luxation in toy
breeds most frequently occurs medially (to the inside of the leg).
See drawing B. The tibia is rotated medially (inward) which allows
the patella to luxate (slip out of its groove) and ride on the inner
surface of the femur.
Drawing B
While the patella is luxated, the quadriceps is unable to properly extend the
stifle, resulting in an abnormal gait or lameness. In addition, the smooth
surface of the patella is damaged by contact with the femur, rather than the
smooth articular (joint) cartilage present in the trochlea. With time this
rubbing will result in degenerative joint disease (arthritis). Furthermore,
while the patella is luxated, the quadriceps puts a rotational force on the
tibia, which over time will increase the rotation of the tibia, thereby increasing
the severity of the problem. The additional strain caused by the malformation
of the bones may also lead to later ligament ruptures. Many individuals are
affected bilaterally (both legs).
Signs of luxation may appear as early as weaning or may go undetected until
later in life. Signs include intermittent rear leg lameness, often shifting
from one leg to the other, and an inability to fully extend the stifle. The
leg may carried for variable periods of time. Early in the course of the disease,
or in mildly affected animals, a hopping or skipping action occurs. This is
due to the patella luxating while the dog is moving and by giving an extra
hop or skip the dog extends its stifle and is often able to replace the patella
until the next luxation, when the cycle repeats.
Several grades of luxation have been defined(7),5.
In simple terms they are:
- Grade I. Patella can be luxated manually (by the examiner) but
returns to the trochlea when released. Occasional luxation occurs
causing the animal to temporarily carry the limb. Tibial rotation
is minimal
- Grade II. Patella can be easily luxated manually and remains luxated
until replaced. Luxation occurs frequently for longer periods of
time, causing the leg to be carried or used without full extension.
Tibial rotation is present.
- Grade III. The patella is permanently luxated, but can be replaced
manually. The dog often uses the leg, but without full extension.
Tibial rotation is marked.
- Grade IV. The patella cannot be replaced manually, and the
leg is carried or used in a crouching position. Extension of
the stifle
is virtually impossible. Tibial rotation is quite severe, resulting
in a "bow legged" appearance.
While no data has been published, personal observation reveals most
affected IG's appear to have Grade I or II luxations. I have also encountered
puppies born with no trochlea and severe tibial rotation causing permanent
luxation from birth (Grade IV), and adult dogs so severely affected
they were non-weight bearing in both hind legs and merely dragged their
rear legs along in a frog-like position (Grade IV).
Diagnosis is relatively simple for a veterinarian familiar with orthopedics.
It involves palpation of the joint and manual luxation of the patella. X-rays
may also be used to determine the degree of rotation. Motivated owners may
be trained by veterinarians to palpate the stifles, but care must be exercised
in order to avoid injuring the joint, or making an incorrect diagnosis.
Diagnosis in severe cases may be possible at weaning, but in most cases the
joints should be tight enough at 4 to 6 months(8) to
allow reliable palpation. Screening of puppies at this age will help prevent
large expenditures training and showing dogs which later prove unsound. Screening
of breeding stock and culling of affected individuals should, over time, reduce
the incidence of the condition.
Treatment involves surgical correction of the deformities. Many techniques
are available depending on the severity of the condition.(9) Satisfactory
results are usually obtained if the joint degeneration has not progressed too
far. Once the condition is repaired, most affected individuals make satisfactory
pets.
Bibliography
1. Priester WA: Sex, Size and Breed as Risk Factors
in Canine Patellar Luxation. J Am Vet Med Assoc. 160:740, 1972.
2. Hutt FB: Genetic Defects of Bones and Joints
in Domestic Animals. Cornell Vet. 58:104, 1968.
3. Kodituwakku GE: Luxation of the Patella in the
Dog. Vet. Rec. 74:1499, 1962.
4. present on the X chromosome, of which females
have two, XX and males one, XY
5. Miller, ME: Anatomy of the Dog. WB Saunders
Co., Philadelphia, PA 1964.
6. Putnam RW: Patellar Luxation in the Dog. M.Sc.
Thesis. Presented to the faculty of graduate studies, University of
Guelph, Ontario, Canada, January 1968.
7. Singleton WB: The Surgical Correction of Stifle
Deformities in the Dog. J Small An Pract 10:59, 1969.
8. Archibald J: Canine Surgery. American Veterinary
Publications, Santa Barbara, CA, 1974.
9. Brinker WO: Handbook of Small Animal Orthopedics & Fracture
Treatment. WB Saunders Co., Philadelphia, PA, 1990.
(Up to page menu)
A Little More About Patellas
Teri Dickinson, DVM
In the last issue of this magazine (Volume XXXIX Number 1) we reprinted
an article about luxated patellas which had been previously published.
The information in the original article is still relevant, as the disease
process itself has not changed. At this time, I would like to add a
little updated information on the topic.
The previous article stated that no data existed about the incidence of luxating
patellas in Italian Greyhounds. While no serious scientific study has even been
undertaken, the Italian Greyhound Club of America did conduct a health survey
in 1993. A total of 2174 adult dogs were included in the survey, and of those,
38 (1.75%) were reported as afflicted with luxating patellas. In reality, the
percentage of affected dogs may well be higher than that, as affected dogs may
go undiagnosed.
The Orthopedic Foundation for Animals (OFA) has begun a registry to certify the
patellas of dogs which are not affected with luxating patellas. The procedure
is quite simple. A veterinarian must palpate the dog's patellas and fill out
a form indicating that the patellas do not luxate. During the exam, the veterinarian
will extend (straighten) the stifle joint, and attempt to luxate (dislocate)
the patella. If the patella luxates (leaves the groove) the veterinarian will
assess what degree of luxation is present. The OFA recognizes and describes in
their written material the four grades of
luxation presented in the last article.
The DVM will then fill out the OFA form indicating that either the dog's patellas
do not luxate, or that they do luxate, and to what degree. The OFA will issue
a registry number only to dogs whose patellas do not luxate.
If you are interested in having your dogs certified by the OFA, you can download
the necessary forms from the OFA web site www.offa.org. Any
licensed veterinarian can perform the evaluations. If you, or your veterinarian,
are not comfortable having a general practitioner evaluate your dogs, then ask
to be referred to a board certified orthopedic specialist. If you live in an
area where there are no board certified specialists, there still may be a veterinarian
in your area who is particularly interested in this field, and may have a lot
of experience in orthopedics. Many IG owners already have the name of someone
who specializes in this field, in the event they have a dog suffer a broken leg.
Generally speaking, these veterinarians should be good candidates to evaluate
patellas.
The OFA requires that a dog be 12 months of age or older in order to be entered
in the breed registry. There is a $15.00 charge.Veterinarians are encouraged
to submit the results of all evaluations, whether normal or abnormal, for the
purpose of completeness of data. There is NO FEE for entering an abnormal evaluation
of the patella in the data base.
As a review of the symptoms one might see with an affected dog, I've included
an excerpt from the OFA publication.
The following descriptions were written by Donald
L. Piermatti, DVM,
PhD
and
Steven Arnoczky, DVM and
obtained with permission from "OFA Patellar Luxation Registry: General Procedures."
MEDIAL LUXATION IN TOY, MINIATURE, AND LARGE BREEDS
These luxations are often termed "congenital" because they occur early
in life and are not associated with trauma. Although the luxation may not be
present at birth, the anatomical deformities that cause these luxations are present
at that time and are responsible for subsequent recurrent patellar luxation.
Patellar luxation in these breeds should be
considered an inherited disease.
Medial (to the inside) luxation is far more common than lateral (to the outside)
luxation in all breeds, representing 75 to 80 percent of cases, with bilateral
(both legs) involvement seen 20 to 25 percent of the time.
CLINICAL SIGNS
Three classes of patients are identifiable:
1. Neonates and older puppies often show clinical signs of abnormal hind-leg
carriage and function from the time they start walking, these generally present
with grades 3 and 4.
2.Young to mature animals with grade 2 to 3 luxations usually have exhibited
abnormal or intermittently abnormal gaits all their lives but are presented when
the problem symptomatically worsens.
3. Older animals with grade 1 or 2 luxations may exhibit sudden signs of lameness
because of further breakdown of soft tissues as result of minor trauma, or because
of worsening of degenerative joint disease pain.
Signs vary dramatically with the degree of luxation. In grades 1 and 2,
lameness is evident only when the patella is in the luxated position. The leg
is carried with the stifle joint flexed, but may be touched to the ground every
third or fourth step. Grade 3 and 4 animals exhibit a crouching , bowlegged stance
(genu varum) with most of the weight
transferred to the front legs.
LATERAL LUXATION IN TOY AND MINIATURE BREEDS
Lateral luxation in small breeds is most often seen late in the animal's life,
from 5 to 8 years of age. The heritability is unknown. Skeletal abnormalities
are relatively minor in this syndrome, which seems to represent a breakdown in
soft tissue in response to, as yet, obscure skeletal derangement. Thus, most
lateral luxations are grades 1 and 2, and the bony changes are similar, but opposite
to those described for medial luxation. The dog has more functional disability
with lateral luxation than with medial luxation.
Copyright The Italian Greyhound
(Up to page menu)
