Patellar Luxation

Question 1

patella

Answer 1

largest sesamoid bone

part of the EXTENSOR apparatus

insertion of the quadriceps tendon via the patellar tendon

Question 2

what are the muscles of the quadriceps and where do they originate

Answer 2

vastus lateralis (prox. femur)
vastus medialis (prox. femur)
vastus intermedius (prox. femur)
rectus femoris (ilium)

Question 3

patellar luxation

Answer 3

partial or intermittent displacement of the patella from its normal position in the cranial trochlear sulcus (patellar groove)

most common to luxate MEDIALLY

bilateral is common

Question 4

medial patellar luxation

Answer 4

malalignment of the quadriceps mechanism medial to the joint

Question 5

clinical signs of medial patellar luxation

Answer 5

decreased growth medially, normal growth laterally leading to “cowboy bowleg” appearance (genu varus)

tibia rotates internally

Question 6

lateral patellar luxation

Answer 6

malalignment of the quadriceps mechanism lateral to the joint

Question 7

clinical signs of lateral patellar luxation

Answer 7

normal growth medially, decreased growth laterally leading to “knock knees” appearance (genu valgum)

tibia rotates externally

Question 8

grade 1 luxation

Answer 8

no clinical signs

patella stays in position but can be manually pushed out

Question 9

grade 2 luxation

Answer 9

patella occasionally luxates causing intermittent lameness (“skipping steps”)

Question 10

grade 3 luxation

Answer 10

patella is always luxated causing continous lameness but can be manually pushed back in

Question 11

grade 4 luxation

Answer 11

patella is always luxated causing continuous lameness but can NOT be manually pushed back in

Question 12

clinical signs of patellar luxation

Answer 12

intermittent to continuous lameness
abnormal stifle joint function
genu varum or valgus
secondary angular limb deformities

Question 13

diagnosis of patellar luxation

Answer 13

• signalment
• PE
• orthopedic exam
• radiographs
• CT

Question 14

PE/orthopedic exam considerations

Answer 14

try manually luxating the patella medially and laterally

medial: place leg in extension and internally rotate foot, then push patella medially

lateral: place leg in flexion and externally rotate foot, then push patella laterally

Question 15

luxating patella on radiographs

Answer 15

displacement of patella relative to patellar groove
assess valgus/varum
look for OA in stifles/hips

Question 16

when should you CT luxating patellas

Answer 16

surgical planning for more advanced corrections

Question 17

luxating patella treatment

Answer 17

grade 1: none bc no clinical signs
grade 2: depends on age and frequency of luxation
grade 3: surgery

NOTE: if concurrent CCL tear then must repair

Question 18

4 in 1 surgical technique

Answer 18

1. ST release
2. ST imbrication
3. recession trochleoplasty
4. tibial tuberosity transposition

Question 19

ST release

Answer 19

loosening of the tight fascia on the side of the luxation

Question 20

ST imbrication

Answer 20

tightening of the loose fascia on the opposite side as the luxation

Question 21

recession trochleoplasty

Answer 21

deepening of the patellar groove to keep patella in place by removing articular cartilage, shaving down subchondral bone, then replacing the cartilage

Question 22

tibial tuberosity transposition (TTT)

Answer 22

realigning the quadriceps by cutting the tibial tuberosity and sliding sideways in the opposite direction as the luxation