Patella Luxation

Description & Cause
The patella, or kneecap, is part of the stifle joint (knee). In patella luxation, the kneecap luxates, or pops out of place, either in a medial or lateral position.


Symptoms
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 patella luxation.

Symptoms vary dramatically with the degree of luxation.
In grade 1 dogs may not show symptoms early on, but older animals may exhibit sudden signs of lameness.

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.

In grades 3 and 4 puppies may show signs of abnormal hind-leg carriage and function from the time they start walking. Grade 3 and 4 animals exhibit a crouching, bowlegged stance with the feet turned inward and with most of the weight transferred to the front legs.

Pain is present in some cases. Most animals; however, seem to show little irritation.

Lateral luxation in small breeds is most often seen late in the animal's life, from 5 to 8 years of age. 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. In mature animals, signs may develop rapidly and may be associated with minor trauma or strenuous activity.


Diagnosis
Physical examination.

Severity of Luxating Patella is determined by palpation of the knee joint and is classified from 0 (normal) to 4 (severely affected) as follows;

Grade 0 : Normal
Grade 1: The patella can be pushed out of the groove but spends most of time in the groove
Grade 2: The patella approximately half the time in the groove and half the time out of the groove. It can easily be manipulated in or out but has no tendency to stay in either position.
Grade 3: The patella spends almost all the time outside the groove and with pressure can be pushed back into the groove.
Grade 4: The patella spends all the time outside the groove and even with pressure the patella cannot be pushed back into the groove.

Treatment & Prognosis The prognosis for a Grade I patella luxation is very good. These dogs may not need surgery. However close observation for signs of worsening is important. If surgery is indicated and performed early on, most animals regain normal functionality. The prognosis for Grades 2 and 3 depends on how much arthritis and malformation have occurred. If caught and treated early, both have a good to excellent prognosis. If there is significant bony malformation or arthritis, the prognosis is guarded to fair. The prognosis for Grade 4 patella luxation is guarded. Most of these animals have moderate to severe bony malformations and significant arthritis. If correction is performed, it is important to initiate early physical therapy to help restore function. Inheritance Patella luxation should be considered an inherited disease. Trauma or injury can also cause patella luxation.