Exam 1: Lecture 6 - Patellar luxation

Question 1

what is medial patellar luxation (MPL)

Answer 1

displacement of patella from trochlear sulcus (aka trochlear groove)

Question 2

what breed is MPL most commonly the cause of lameness in

Answer 2

small breed dogs…can occur in large but is uncommon

Question 3

what are the associated musculoskeletal abnormalities in patients with patellar lux

Answer 3

1. medial displacement of quadriceps muscle group (lateral torsion of distal femur or lateral bowing of distal 1/3 of femur)
2. femoral epiphyseal dysplasia
3. rotational instability of stifle joint
4. tibial deformity

Question 4

what is this picture showing

Answer 4

the displacement of the quadriceps apparatus and how it rotates and bows the leg

Question 5

what happens with femoral deformities that have pressure on the medial aspect of distal femoral physis

Answer 5

greater pressure on medial aspect = less growth

Question 6

what happens with femoral deformities that have pressure on the lateral aspect of distal femoral physis

Answer 6

decreased pressure on lateral aspect = accelerated growth

Question 7

how do we get lateral bowing of distal femur

Answer 7

when there is decreased length of medial cortex relative to increased length of lateral cortex

Question 8

Degree of lateral bowing depends on the ___1___ of patellar luxation and patients ___2____ at luxation

Answer 8

1. severity
2. age

Question 9

what happens with mild luxations of quadriceps apparatus

Answer 9

1. quadriceps rarely displaced medially
2. minimal effect on distal femoral physis

Question 10

what happens with severe luxations of quadriceps apparatus

Answer 10

1. quadriceps medially displaced all times
2. maximal effect on distal femoral physis to cause severe lateral bowing of distal femur in young patients

Question 11

T/F: A severe luxation is extremely difficult to correct

Answer 11

true!

Question 12

why do we see tibial deformities with medial displacement of quadriceps apparatus

Answer 12

because of the results of an abnormal force on proximal and distal physis of tibia

Question 13

what are the 3 tibial deformities we can see with medial displacement of quadraceps

Answer 13

1. medial displacement of tibial tuberosity
2. medial bowing (varus deformity) of proximal tibia
3. lateral torsion of distal tibia

Question 14

T/F: Dogs with MPL do not have an abnormal development of the trochlear groove

Answer 14

false, they do! it does vary from near-normal to absent trochlear groove

Question 15

what happens with femoral epiphyseal dysplasia

Answer 15

articular cartilage is the “physis” for epiphysis and responds to increased or decreases pressure as with metaphyseal physis

Question 16

how does the articulation of the patella within the trochlear groove impact the articular cartilage

Answer 16

it puts a physiological pressure which retards cartilage growth

Question 17

T/F: pressure by patella is responsible for development of normal depth of trochlear groove

Answer 17

true!!

Question 18

what happens if the physiologic pressure exerted by the patella is not present

Answer 18

the trochlea fails to gain proper depth

Question 19

T/F: Immature patients with mild luxation show a great loss of depth to trochlear groove

Answer 19

false, they show minimal loss of depth

Question 20

T/F: Immature patients with severe luxations have no trochlear groove

Answer 20

true!! normal pressure that is responsible for growth not present

Question 21

what is grade I of patellar luxation

Answer 21

patella in groove, can be forced out but comes back in immediately

Question 22

what is grade II of patellar luxation

Answer 22

patella in groove, sometimes comes out but comes back in every time

Question 23

what is grade III of patellar luxation

Answer 23

patella is NOT in groove, can be forced in but comes out again almost immediately

Question 24

what is grade IV of patellar luxation

Answer 24

patella not in groove, cant be moved back in without sx

Question 25

what is the signalment we see in patients with MPL

Answer 25

no age, breed, or gender predisposition....but small and toy breed dogs most often affected

Question 26

T/F: lateral patellar luxation is more common than medial patellar luxation in large breed dogs

Answer 26

false! MPL is more common BUT large breed dogs get LPL more than small breed (small breed almost never get LPL)

Question 27

what is the usual history for patellar lux

Answer 27

intermittent weight bearing lameness, dog occasionally holds leg in flexed position for 1-2 steps

Question 28

T/F: Dogs with grade IV patellar lux have severe lameness and gait abnormalities

Answer 28

true!

Question 29

how do we diagnose MPL

Answer 29

based on finding or eliciting mpl during PE

Question 30

what do we see on PE for grade I patella lux

Answer 30

no lameness, usually incidental finding on PE

Question 31

what do we see on PE for grade II patella lux

Answer 31

occasional skipping when walking or running and occasionally stretch lateral retinacular structures and develop NWB lameness

Question 32

what do we see on PE for grade III patella lux

Answer 32

varying lameness with occasional skipping to weight bearing lameness

Question 33

what do we see on PE for grade IV patella lux

Answer 33

walk with rear quarters in crouched position, patella is hypoplastic, and patella found displaced medially alongside femoral condyle

Question 34

what do we see on rads with grade I or II lux

Answer 34

patella within trochlear sulcus or displaced medially

Question 35

what do we see on rads with grade III or IV patella lux

Answer 35

standard craniocaudal and medial-lateral rads show patella displaced medially

Question 36

what can happen with poor radiograph positioning?

Answer 36

can get a false positive limb deformity!!

Question 37

what are the lab findings with patella lux

Answer 37

consistent abnormalities are not really seen

Question 38

how do we decide if we treat MPL conservatively or surgically

Answer 38

depends on history, PE, frequency of lux, and patient age

Question 39

when is sx not warranted for MPL

Answer 39

in asymptomatic older patients

Question 40

when is sx recommended for MPL

Answer 40

in young animals or if lame

Question 41

when is surgical treatment of MPL strongly advised

Answer 41

in patients with active growth plate

Question 42

T/F: We should surgically treat MPLs for any age patients with lameness

Answer 42

true!! age is not a disease

Question 43

What is important to tell owners of dogs with bilateral grade IV MPLs

Answer 43

they likely need multiple surgeries and probably will have continued lameness even with successful sx

Question 44

what are the 4 most COMMON ways to surgically treat MPL

Answer 44

1. tibial tuberosity transposition (TTT) 2. medial restraint release 3. lateral restraint reinforcement 4. trochlear groove deepening

Question 45

what happens during the trochlear groove deepening sx

Answer 45

trochlear wedge or block recession and abrasion trochleoplasty or chondroplasty

Question 46

what happens during the medial retinaculum release (desmotomy)

Answer 46

stabilize patella in deepened trochlear groove

Question 47

what happens during the tibia crest transposition

Answer 47

realigns mechanical forces of extensor muscles

Question 48

of the 4 most common MPL procedures, what ALWAYS SHOULD be done

Answer 48

tibial crest transposition

Question 49

what happens during lateral retinaculum reinforcement

Answer 49

imbricate joint capsule with sutures, place fascia lata graft fabella to parapatellar fibrocartilage, and excision of redundant retinaculum

Question 50

T/F: combination of techniques are required for surgical treatment of MPL

Answer 50

true!!

Question 51

What happens if we only do the deepening of trochlear groove, capsule and fascial release, and imbrication

Answer 51

correction is PRONE TO FAIL WITHOUT TTT!!!

Question 52

Important!! What should we ALWAYS DO when surgically treating MPL

Answer 52

do the tibial tuberosity transposition!!

Question 53

T/F: reinforcement techniques alone are not adequate to prevent reluxation premanently

Answer 53

true!! it stretches eventually

Question 54

when should we do an osteotomy of the femur

Answer 54

when there is severe skeletal deformity

Question 55

what are the deformities we should do an osteotomy of the femur for

Answer 55

varus bowing of distal femur and medial torsional deformity of proximal tibia

Question 56

what is the goal of osteotomy of femur

Answer 56

to realign stifle joint in the frontal plane

Question 57

what does the osteotomy of the femur require preoperatively

Answer 57

measurement and wedge osteotomy of the main 4!! (deepen trochlear groove, medial restraint release, transposition of tibial crest, and lateral retinacular reinforcement)

Question 58

what does osteotomy of the femur REQUIRE

Answer 58

special equipment and training

Question 59

what happens with chronic patella lux

Answer 59

increased stress on cranial cruciate ligament and eventual rupture

Question 60

what are the extensor mechanisms of stifle joint

Answer 60

quadriceps muscle group, patella, trochlear groove, and straight patellar ligament

Question 61

what do the quadriceps muscle group do

Answer 61

extend the stifle joint, aids in stabilizing stifle joint, converges as patellar tendon on proximal patella, and continues distally as straight patellar ligament

Question 62

what is the patella an essential component for

Answer 62

a functional mechanism of extensor apparatus

Question 63

T/F: alignment of quadriceps, patella, trochlea, patellar lig, and tibial tuberosity must be normal for proper function

Answer 63

true!!

Question 64

what happens if there is mal-alignment in the quadriceps, patella, trochlea, patellar lig, or tibial tuberosity

Answer 64

may lead to patellar lux!

Question 65

what MUST you ID before making parapatellar incision

Answer 65

the patellar lig!!

Question 66

why is dorsal recumbency the best position for MPL correction

Answer 66

1. allows visualization of unrestrained extensor mechanism deviation 2. maximum manipulation of limb to evaluate patellar stability

Question 67

what is this picture showing

Answer 67

trochlear wedge resection

Question 68

what is being shown

Answer 68

trochlear block resection

Question 69

what is being shown here

Answer 69

tibial crest transposition

Question 70

T/F: For lateral patellar luxatons you transpose tibial crest the same for medial

Answer 70

FALSE, you transpose tibial crest medially!!

Question 71

T/F: Medial joint capsule is thicker than normal and contracted with grade III or grade IV MPL

Answer 71

true!!!

Question 72

T/F: medial joint capsule and retinaculum release does not allow lateral placement of patella

Answer 72

false, it does!

Question 73

T/F: we want to close the tissue gap in the release of medial joint capsule

Answer 73

false, we do not close the tissue gap

Question 74

With ___1__ luxations = redundant __2__ retinaculum

Answer 74

1. medial lux 2. lateral retinaculum

Question 75

what is the suture pattern we close retinaculum with

Answer 75

vest-over-pants suture pattern

Question 76

what type of suture pattern

Answer 76

vest-over-pants

Question 77

what do we use to do the trochlear wedge/block recession

Answer 77

fine tooth saw or sagittal saw

Question 78

what do we use to do the block recession

Answer 78

osteotome

Question 79

what do we use to do the TTT

Answer 79

osteotome and mallet, k-wires or lag screw, orthopedic wire, and hand chuck or drill to secure tibial crest

Question 80

what is the post op care for MPL correction

Answer 80

1. activity restricted to leash walks for 6-8 weeks 2. gradually returned to normal activity over 6-week period 3. radiographs done 6-8 weeks to eval healing of TTT