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.
Main patellar luxation page | Diagnosing patellar luxation | Patellar
luxation grades | Patellar
luxation statistics | Patellar
luxation application |Patellar Luxation Number Key | Patellar Luxation Report Sample
|
Over 40 years of dedication to the advancement of canine health 
