Patellar Luxation

Question 1

What is a grade 1 patellar luxation?

Answer 1

Can be luxated in normal motion or by hand but reduces when the pressure is removed

Question 2

What is a grade 2 patellar luxation?

Answer 2

Patella luxates with pressure or in flexion and remains luxated until the animal extends and derotates the tibia

Mild angular and torsional limb deformities may be present

Question 3

What is a grade 3 patellar luxation?

Answer 3

Patella remains luxated most of the time

The patella can be reduced but flexion causes re-luxation

There is medial displacement of the quadriceps group and abnormalities of the femur and tibia are present

Question 4

What is a grade 4 patellar luxation?

Answer 4

Permanently luxated and cannot be repositioned
The femoral trochlear groove is shallow/absent
May be medial rotation of the proximal tibial plateau
There is medial displacement of the quadriceps group and deformities of the femur and tibia are notable

Question 5

When is surgery warranted and what could occur if left untreated?

Answer 5

Gait abnormalities or lameness associated with luxation, especially in young or young adults because intermittent luxation can wear the articular cartilage of the patella. Abnormal quadriceps forces can cause angular limb deformities

Question 6

When is surgery not required?

Answer 6

Asymptomatic older patients

Question 7

Principles of surgical correction of medial patellar luxation

Answer 7

Trochlear groove deepened
Release of medial retinaculum to allow patella into trochlear groove
Tibial crest transposition to realign forces of extensors
Lateral retinaculum reinforced with sutures and imbrication of joint capsule

Question 8

Why does reinforcement alone fail?

Answer 8

The reinforced retinaculum stretches due to the extensor muscles pulling the patella out of the trochlear groove

Question 9

What can chronic patellar luxation lead to in an older dog?

Answer 9

Increased stress on the CCL and eventual rupture