General Patellar Luxation Information
What is Patellar Luxation?
The patella, or kneecap, is part of the stifle joint (knee). In patellar
luxation, the kneecap luxates, or pops out of place, either in a medial
or lateral position.
Bilateral involvement is most common,
but unilateral is not uncommon. Animals can be affected by the time they
are 8 weeks of age. The most notable finding is a knock-knee (genu valgum)
stance. The patella is usually reducible, and laxity of the medial collateral
ligament may be evident. The medial retinacular tissues of the stifle
joint are often thickened, and the foot can be seen to twist laterally
as weight is placed on the limb.
Patellar Luxation Categories
Patellar luxations fall into several categories:
- Medial luxation; toy, miniature, and large breeds
- Lateral luxation; toy and miniature breeds
- Lateral luxation; large and giant breeds.
- Luxation resulting from trauma; various breeds, of no importance to
the certification process.
Numbers 1, 2 and 3 are either known to be heritable or strongly suspected.
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 should be
considered an inherited disease.
Clinical Signs
Three classes of patients are identifiable:
- Neonates and older puppies often show clinical signs of abnormal hind-leg
carriage and function from the time they start walking; these present
grades 3 and 4 generally.
- 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.
- Older animals with grade 1 and 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 at fast gaits. Grade 3 and 4 animals
exhibit a crouching, bowlegged stance (genu varum) with the feet turned
inward and with most of the weight transferred to the front legs.
Permanent luxation renders the quadriceps ineffective in extending the
stifle. Extension of the stifle will allow reduction of the luxation in
grades 1 and 2. Pain is present in some cases, especially when chondromalacia
of the patella and femoral condyle is present. Most animals; however,
seem to show little irritation upon palpation.
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.
Clinical Signs
In mature animals, signs may develop rapidly and may be associated with
minor trauma or strenuous activity. A knock-knee or genu valgum stance,
sometimes described as seal-like, is characteristic.
Sudden bilateral luxation may render the animal unable to stand and so
simulate neurological disease. Physical examination is as described for
medial luxation.
Also called genu valgum, this condition is usually seen in the large
and giant breeds. A genetic pattern has been noted, with Great Danes,
St. Bernards, and Irish Wolfhounds being the most commonly affected. Components
of hip dysplasia, such as coxa valga (increased angle of inclination of
the femoral neck) and increased anteversion of the femoral neck, are related
to lateral patellar luxation. These deformities cause internal rotation
of the femur with lateral torsion and valgus deformity of the distal femur,
which displaces the quadriceps mechanism and patella laterally.
Clinical Signs
Bilateral involvement is most common. Animals appear to be affected by
the time they are 5 to 6 months of age. The most notable finding is a
knock-knee (genu valgum) stance. The patella is usually reducible, and
laxity of the medial collateral ligament may be evident. The medial retinacular
tissues of the stifle joint are often thickened, and the foot can often
be seen to twist laterally as weight is placed on the limb.
Diagnosing Patellar Luxation
Examination and Certification
The dog is examined awake (chemical restraint is not recommended) and
classified by the attending veterinarian according to the application
and general information instructions. The veterinarian then completes
the application form indicating the the results
of the dog's patella evaluation.
The application and fee can then be mailed to
OFA. The attending veterinarian and owner is encouraged to submit all
evaluations, whether normal or abnormal, for the purpose of completeness
of data. There is no OFA fee for entering an abnormal evaluation of the
patella in the data bank.
A breed database number will be issued to all dogs found to be normal
at 12 months of age or older. The breed database number will contain the
age at evaluation and it is recommended that dogs be periodically reexamined
as some luxations will not be evident until later in life.
Preliminary Evaluations
Evaluation of dogs under 12 months of age is encouraged if the owner
desires to breed at this age. The most opportune time to gather breeding
data is at 6-8 weeks of age prior to the puppy's release to the new owner.
Grades of Patellar Luxation
The Patellar Luxation Database is for dogs 12 months and over. Examinations
performed on dogs less than 12 months will be treated as Consultations
and no OFA breed numbers will be assigned.
A method of classifying the degree of luxation and bony deformity is
useful for diagnosis, and can be applied to either medial or lateral luxations
by reversing the medial-lateral directional references. The position of
the patella can easily be palpated starting at the tibial tubercle and
working proximal along the patellar ligament to the patella.
Grade 1
Manually the patella easily luxates at full extension of the stifle joint,
but returns to the trochlea when released. No crepitation is apparent.
The medial, or very occasionally, lateral deviation of the tibial crest
(with lateral luxation of the patella) is only minimal, and there is very
slight rotation of the tibia. Flexion and extension of the stifle is in
a straight line with no abduction of the hock.
Grade 2
There is frequent patellar luxation, which, in some cases, becomes more
or less permanent. The limb is sometimes carried, although weight bearing
routinely occurs with the stifle remaining slightly flexed. Especially
under anesthesia it is often possible to reduce the luxation by manually
turning the tibia laterally, but the patella reluxates with ease when
manual tension of the joint is released. As much as 30 degrees of medial
tibial torsion and a slight medial deviation of the tibial crest may exist.
When the patella is resting medially the hock is slightly abducted. If
the condition is bilateral, more weight is thrown onto the forelimbs.
Many dogs with this grade live with the condition reasonably well for
many years, but the constant luxation of the patella over the medial trochlear
ridge of the trochlea causes erosion of the articulating surface of the
patella and also the proximal area of the medial lip. This results in
crepitation becoming apparent when the patella is luxated manually.
Grade 3
The patella is permanently luxated with torsion of the tibia and deviation
of the tibial crest of between 30 degrees and 50 degrees from the cranial/caudal
plane. Although the luxation is not intermittent, many animals use the
limb with the stifle held in a semi flexed position. The trochlea is very
shallow or even flattened.
Grade 4
The tibia is medially twisted and the tibial crest may show further deviation
medially with the result that it lies 50 degrees to 90 degrees from the
cranial/caudal plane. The patella is permanently luxated. The patella
lies just above the medial condyle and a space can be palpated between
the patellar ligament and the distal end of the femur. The trochlea is
absent or even convex. The limb is carried, or the animal moves in a crouched
position, with the limb flexed.
Tillbaka
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