Final Exam - Patellar Luxation

Question 1

what dog breeds are more commonly affected by patellar luxation?

Answer 1

toy breeds - chihuahua, pomeranians, mini poodles, & yorkies

Question 2

T/F: toy breeds are 12x more likely to be affected by patellar luxations than large breed dogs

Answer 2

true

Question 3

what is surgery considered to do for dogs with patellar luxation?

Answer 3

improve quality of life

Question 4

what is the cause of patellar luxation?

Answer 4

congenital/developmental - can be acquired but congenital is more common

Question 5

what direction is luxation most common?

Answer 5

medial - variable for lateral luxation

Question 6

what is included in the quadriceps mechanism?

Answer 6

quadriceps, patella, trochlea, straight patellar tendon, & tibial tuberosity

Question 7

quadriceps function depends on what?

Answer 7

femoral patellar articulation & alignment

proper development of trochlear groove & tibia

proper loading of distal femur

Question 8

what happens to the pelvic limb in cases of chronic patellar luxation?

Answer 8

medial displacement of quadriceps mechanism

external torsion deformity of the distal femur leading to lateral bowing of the distal femur lateral torsion of distal femur

medial displacement of tibial tuberosity

distal femoral varus & distal tibial valgus

Question 9

what anatomic changes are seen in a dog with chronic patellar luxation?

Answer 9

lack of extension of stifle, severe deformation of the femur & tibia, & contracted & fibrotic soft tissue changes medially

Question 10

what signs may be seen on gait & standing exam on a patient with luxating patellas?

Answer 10

may be lame

muscle atrophy, crouched stance with weight shifting & lack of hindlimb extension

lateral recumbency - to elicit luxation

Question 11

what is grade I patellar luxation?

Answer 11

intermittent luxation - manual dislocation in full distension

spontaneous reduction on release

Question 12

what is grade II patellar luxation?

Answer 12

occasional spontaneous luxation - doesn’t always reduce on its own

Question 13

what is grade III patellar luxation?

Answer 13

permanent luxation, manual reduction possible

reluxation on release

Question 14

what is grade IV patellar luxation?

Answer 14

permanent luxation - manual reduction is impossible

Question 15

what may be seen on radiographs of a patient with luxating patellas?

Answer 15

medialization of tibial crest - +/- internal rotation of the proximal tibia

shallow femoral trochlea +/- hypoplastic medial trochlear ridge

quadriceps displacement

use for assessment of angular limb & other skeletal abnormalities

Question 16

why is positioning critical for radiographic assessment of patellar luxation?

Answer 16

need to know if the distal femur or proximal tibia needs to be surgically corrected

Question 17

what is the proper positioning for radiographs of dogs with patellar luxation?

Answer 17

cranial/caudal view long pelvis - V/D hip to tibia

femur as a reference - parallel to spine, no abduction or adduction

max hip extension - parallel to cassette

no external or internal rotation

Question 18

what are the requirements of radiographic positioning for evaluating a patient with luxating patellas?

Answer 18

symmetrical appearance of pelvis & femur

sesamoids split by femoral cortices

only tip of lesser trochanter is visible

varus measurements are repeatable

Question 19

when should you recommend surgery for a dog with luxating patellas?

Answer 19

huge variety - recommend when there is a loss of quality of life & pain with any degree of luxation

Question 20

what are the surgical goals of luxating patellas?

Answer 20

restoration of limb alignment

restoration of femoropatellar articulation

soft tissue support

Question 21

what are the goals of trochleoplasty surgery?

Answer 21

50% of patellar thickness to sit in the groove

medial & lateral ridges cradle the patella

argument for necessity in all cases

Question 22

how is a trochleoplasty performed?

Answer 22

technique that deepens a shallow/absent/convex trochlea

articulation of patella provides physiologic pressure & retards cartilage growth - improper depth in cases with no patellar pressure & varies with degree of luxation

Question 23

what is recession in terms of trochleoplasty?

Answer 23

preservation of the articular surface

Question 24

what is resection in terms of trochleoplasty?

Answer 24

removal of articular cartilage & subchondral bone

Question 25

what is a trochlear wedge recession technique?

Answer 25

diamond shaped osteochondral wedge that maintains the articular surface with smooth arcs - width is consistent with patellar width

complete cut with a fine toothed saw - be conscious of depth & avoid long wedge length

Question 26

where are the cuts made in a trochlear wedge recession?

Answer 26

distally at intercondylar notch

proximally at dorsal aspect of the articular cartilage

preservation of medial ridge

Question 27

what is the procedure of a block recession?

Answer 27

similar to wedge concept but deeper placement of patella proximally often used in large breed dogs to capture patella with full extension

vertical lines are consistent with patellar depth 3-4mm below the surface

osteotome advanced between vertical lines proximally to create rectangular block to cradle the patella

Question 28

what is the angle of the block, depth of recession, & length of recession in a block recession?

Answer 28

angle - parallel to femur

depth - 50% of patella

length - proximal margin of articular cartilage, intercondylar notch

Question 29

what is a trochlear resection?

Answer 29

removal of articular cartilage & subchondral bone with parameters similar to recession

Question 30

what is the minimum depth of a trochleoplasty?

Answer 30

at least 50% patella height

Question 31

if the patella doesn’t remain reduced through flexion/extension after transposition, what happens?

Answer 31

chance of luxation & revision post-surgery increases

Question 32

what is the Q angle in a tibial tuberosity transposition?

Answer 32

angle between the direction of force of the quads, patella, straight patellar tendon, & tibial tuberosity

if increased - denotes severity of medial patellar luxation

Question 33

what is a normal q angle?

Answer 33

10.5 degrees

Question 34

how is a tibial tuberosity transposition performed?

Answer 34

fascia is extended a few cm distally to the tuberosity - exposure is important for positioning the osteotome

release the crest with the osteotome/bone cutters/oscillating saw/gigli wire

place the osteotome caudal to the patellar tendon (size similar to the width of the tuberosity) & perpendicular to the bone & use the mallet to advance the osteotome distally

leave the distal periosteum intact

transpose adequately to assure patella in femoral trochlea & hold in place to create a bone platform

use k-wires to secure & avoid the joint

Question 35

what is the key to success in a tibial tuberosity transposition? what other considerations should be made?

Answer 35

alignment of the quadriceps mechanism

k wire size, length, & number used

Question 36

how is a medial release surgical procedure performed?

Answer 36

due to the medially luxated patella, the joint capsule & retinaculum on one side of the joint contracts & must be released to allow return to proper anatomic position

tissues broken down to mobilize patella - medial joint capsule, cranial belly of the sartorius, & vastus medialis - continues proximal to femoral triangle

medial parapatellar incision through full thickness tissues introducing instrument from lateral to medial - isolate the edge of the patella & straight patellar tendon prior to cutting & sharply cut over the instrument extending the incision from the patella to the proximal tibia & manually breakdown contracted tissues on the medial thigh

Question 37

what is the goal of the medial release technique?

Answer 37

free the quadriceps mechanism until you can luxate the patella both ways - closure with simple appositional sutures

Question 38

what is imbrication?

Answer 38

to overlay things so that they overlap in layers in a similar way to roof tiles

Question 39

what is a lateral imbrication?

Answer 39

reinforcement to the lateral retinaculum with control of tension best done with separation of tissue layers

Question 40

what is a biceps overlay?

Answer 40

form of imbrication - parapatellar fascia is tucked underneath lateral fascia in a vest over pants pattern - may trim excess biceps fascia to increase tension

use a monofilament - gauge is the most important decision, don’t under power

Question 41

what should you do after every 2-3 sutures in a lateral imbrication?

Answer 41

check the position & movement of the patella - may require replacing sutures

Question 42

what is the purpose of anti-rotational suture?

Answer 42

externally rotates the tibia & assists in quadriceps realignment - often done in conjunction with CCL repair

Question 43

what is the procedure of lateral imbrication?

Answer 43

intentional overlap of the fascia lata & lateral joint capsule used on the lateral parapatellar tissues during correction of medial patellar luxation resulting in a tightening of tissues to help maintain the patella’s position in the trochlear groove

Question 44

what is involved in true imbrication?

Answer 44

using 2 separate rows of sutures to advance the biceps femoris cranially & then the fascia lata is sutured caudally

Question 45

how are anti-rotational sutures placed for a medial luxation?

Answer 45

suture material is placed from the lateral fabella around the patella & back to the lateral fabella so when tied, the suture will help prevent medial luxation (can also place from the lateral fabella to the tibial crest)