Patellar luxation is the dislocation (slipping) of the
patella (kneecap). In dogs the patella is a small bone that shields
the front of the stifle joint. This bone is held in place by ligaments.
As the knee joint is moved, the patella slides in a grove in the femur.
The kneecap may dislocate toward the inside (medial) or outside (lateral)
of the leg. This condition may be the result of injury or congenital
deformities (present at birth). Patellar luxation can affect either
or both legs.
The most common occurrence of luxating patella is the
medial presentation in small or miniature dog breeds. Shallow femoral
groove, weak ligaments and malalignment of the tendons and muscles that
straighten the joint are all conditions that will predispose a dog toward
Indications of patellar luxation are; difficulty in straightening
the knee, pain in the stifle, limping, or the tip of the hock points outward
while the toes point inward.
The diagnosis of this condition can usually be confirmed
(by a veterinarian) by manipulating the stifle joint and pushing the patella
in and out of position.
fall into several categories:
luxation; toy, miniature, and large breeds.
luxation; toy and miniature breeds.
luxation; large and giant breeds.
induced luxation; various breeds
Categories 1, 2, and 3 are either
hereditaryor strongly suspected of being inheritable.
Beyond the categorization of patellar luxation there
are 4 grades of deviation for this condition:
Intermittent patellar luxation - occasional carrying
of the affected limb. The patella can easily be manually luxated
at full extension of the stifle, but returns to proper position when pressure
Frequent patellar luxation - in some cases luxation is
more or less permanent. The affected limb is sometimes carried, although
the dog may walk with the stifle slightly flexed.
Permanent patellar luxation - even though the patella
is luxated; many animals will walk with the limb in a semi-flexed position.
Permanent patellar luxation - the affected limb is either
carried or the animal walks in a crouched position, with the limb partially
Medial Luxation in Toy, Miniature, and Large Breeds
Termed "congenital" because the luxations occur early
in life and are not trauma associated.
1) Neonates and older puppies - display clinical signs
of abnormal leg carriage and function from the time they start walking.
These cases are generally grades 3 or 4.
2) Young to mature animals - usually exhibit intermittently
abnormal or abnormal movement all their lives. Generally evaluated
when the symptomatic gait worsens. Most often grade 2 or 3.
3) Older animals - may exhibit sudden lameness.
Usually due to further breakdown of soft tissues or the degenerative nature
of joint disease. These cases are usually grade 1 or 2.
Lateral Luxation in Toy and Miniature Breeds
Lateral luxation in small breeds is most often seen in
dogs between 5 to 8 years of age. The skeletal abnormalities in these
cases is most often obscure. Most of these cases are grade 1 or 2
and the dog tends to exhibit a more functional disability.
Lateral Luxation in Large and Giant Breeds
Animals usually appear to be affected by 5 to 6 months
of age, with bilateral involvement being the most common presentation.
The most noticed symptom is a knock-knee stance. The patella is usually