Decision Making in the Treatment of Canine Medial Patellar Luxation

Wheat Ridge 

Veterinary Specialists 

EXPERTISE YOU CAN TRUST. 

“Skipping to a Solution”: 

Decision Making In Canine 

Patellar Luxation 

Cory Pinel, DVM, DACVS-‐SA 

Associate Surgeon -‐ WRVS 

Coors Field Symposium -‐ 2013 

Tuesday, September 24, 13

Outline 

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Overview 

Etiopathogenesis 

Anatomy and 

biomechanics 

History 

Physical exam 

Diagnostics 

Case selection 

Surgical planning 

Surgical execution 

2 


Functional Anatomy 

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Patella is sesamoid bone/ 

ossification in quadriceps 

femoris tendon of 

insertion 

Functions with the 

trochlea as a pulley 

Redirects the pull of the 

quadriceps to center over 

the stifle 

3 


Functional Anatomy 

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Extensor mechanism 

originates with the rectus 

femoris 

Ventral ilium, cranial to 

acetabulum 

Alignment critical 

Quad, femur, trochlea, 

patella, tibial tuberosity 

Main stabilization 

Secondary stabilization 

Femoropatellar ligaments 

Joint capsule 

4 



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Developmental disease; rarely 

traumatic 

Have predisposition at birth (don’t 

breed) 

Coxa vara & relative retroversion 

underlying 

Medialization of extensor apparatus 

Femoral varus 

Genu varum (bowleg) 

Shallow trochlear groove 

Medial femoral hypoplasia 

Medial tibial tuberosity 

Proximal internal tibial rotation 

Proximal tibial varus/valgus (comp.) 

Distal tibial external torsion 

Internal rotation of the foot 

5 



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Primary bony underlying 

abnormalities 

Extensor apparatus 

medialization 

Reduced axial retropatellar 

pressure +/-‐ repeated 

luxation 

Medial ridge wear 

Trochlear hypoplasia 

Capsular stretching and 

tension 

6 


Epidemiology 

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82% developmental 

Small breeds: 

95-‐98% medial 

2-‐5% lateral 

Medium breeds -‐ 81% MPL 

Large breeds -‐ 83% MPL 

Giant breeds -‐ 67% MPL 

Bilateral 50-‐65% 

Increasing incidence in 

large breeds? 

7 


Differential Diagnoses 

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Avascular necrosis of femoral 

head and neck (small breed) 

Hip dysplasia 

Cranial cruciate ligament 

disease 

Osteochondrosis 

Hypertrophic 

osteodystrophy/Panosteitis 

Neoplasia 

Inflammatory arthritis 

8 


Grading 

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Grade 1: In when palpated, can luxate in full 

extension 

 

 

No growth deformity 

Typically no clinical signs 

Grade 2: In when palpated, easily luxated 

 

 

spontaneous luxation (skipping) 

Mild deformity 

Can progress to grade 3 

Grade 3: Out when palpated, manually reduced 

 

More severe deformities 

Lameness, crouched posture 

Grade 4: Out when palpated, cannot be 

manually reduced 

 

 

 

Severe deformity with significant medial tibial 

rotation 

Should be corrected as early as possible 

Very challenging, complex cases 

9 


History 

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Incidental finding 

Skipping 

Crouched/semiflex/ 

internally rotated 

Acute onset of lameness 

should raise suspicion for 

concurrent cruciate 

ligament disease 

Recent cruciate surgery? 

More likely associated 

with tibial osteotomy 

10 


Physical Exam 

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Palpation throughout range of 

motion 

Internal rotation at foot 

Patella hard to locate 

Find tuberosity, follow tendon 

proximally 

Crepitus more likely with higher 

grades 

Genu varum (MPL) vs genu valgum 

(LPL) 

Crab like posture, poorly 

ambulatory (grade IV) 

Cranial drawer with patella reduced 

Stifle effusion, pain on 

hyperextension -‐ CCLD 11 


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ecision Making - Rule of 3’s 

Grade 3 or higher 

Progression to grade 4 

Osteoarthritis 

progression 

CCL rupture 

predisposition? 

Lame (significant) for 3 

weeks or longer 

Three days of lameness 

in a short time frame 

Concurrent cruciate 

disease 12 


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Decisions - Young Patient 

Severely affected/high grade 

Almost always associated 

with skeletal deformity 

Rarely traumatic 

Osteotomy risks injury to 

physes 

Two stage approach 

Soft tissues (trochlear 

chondroplasty as well) 

Bony manipulation when 

skeletally mature 

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Trochlear Chondroplasty 

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Patients

Imaging - Small Breeds 

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VD pelvis to assess for 

AVN and hip dysplasia 

Orthogonal stifles 

Assess degree of OA 

Stifle effusion 

(CCLD, IMPA) 

Cranial drawer 

Pre-‐op planning 

Degree of varus/ 

valgus, subjective 

Skyline can assess 

trochlear groove depth 

15 


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Imaging - Proximal Tibial Lucency 

Vet Radiol Ultrasound 

2013 

675 dogs evaluated, 145 

proximal tibial 

lucencies 

More common in small 

and toy breeds 

Higher incidence of 

MPL 

Lower incidence of 

CCLD 

Retained cartilage core 

on histopathology 

16 


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2013 



lucencies 




MPL 


CCLD 



16 


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2013 



lucencies 




MPL 


CCLD 



16 


Surgical Management 

- Small Breeds 

Re-‐alignment of the extensor 

mechanism and soft tissue 

balance 

Dorsal recumbency 

Lateral approach to the stifle, 

distal femur, proximal tibia 

Careful exploration of the 

stifle 

Probing of the cruciate 

ligament, meniscus 

Trochlea, re-‐alignment, soft 

tissues 

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17 


Trochleoplasty 

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Deep enough and wide 

enough such that 50% of 

the patella protrudes 

Typically osteoarthritis is 

mild and cartilage damage 

minimal 

Preserve hyaline cartilage 

whenever possible 

18 


Abrasion Sulcoplasty 

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Simplest technique 

Rongeurs, rasp, bur 

Remove articular 

cartilage and 

subchondral bone 

(few mm) 

Defect fills with 

fibrocartilage in few 

weeks 

Atrophy, patellar 

cartilage erosion, 

crepitus, slower 

return to function 

19 


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Trochlear Wedge Recession 

Similar triangle theory 

Flex stifle and luxate 

patella 

Outline wedge with No. 

15 scalpel blade 

Create osteochondral 

wedge with convergent 

lines 

Remove taco shell or 

bone from lateral wedge 

Wedge is viable 

Retropatellar pressure 

maintains stability 

20 


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Wedge Recession Modified 

Vet Surg 2013 -‐ 

Clinical evaluation 

in 5 dogs 

Medial ridge 

elevation 

Asymmetrical 

wedge osteotomy 

The “Flip” 

Small K-‐wire 

required for 

stabilization 

Tuesday, September 24, 13 

21

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Trochlear Block Recession 

Similar approach to the above 

Outline osteotomy with No. 15 blade 

Abaxial margins are angled in by 10 degrees 

Press-‐fit 

Proximal from suprapatellar; distal to intercondylar fossa 

Start osteotomy perpendicular and then slowly level out 

parallel to the trochlea 

Width of osteotomy = width of the osteotome 

Need wide variety and they need to be SHARP 

Avoid levering and fracture 

Deepen the groove with a thin osteotome (~4 mm) 

Resect the base of the fragment with fine rongeurs 22 


Trochlear Block Recession 

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Block Vs Wedge 

Block more technically 

demanding 

Block advantages 

Increased PROXIMAL 

patellar depth 

Increased patellar 

articular contact within 

recession 

Greater resistance to 

luxation in stifle extension 

Articular Surface (oval) 

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24 


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Tibial Tuberosity Transposition 

Most important procedure 

Often times make or break 

Most likely to have 

complications 

Fracture 

Implant issues 

Non-‐union 

Degree of lateralization is 

animal and experience 

dependent 

25 


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Assessment at end of table 

Neutral hip, stifle, hock 

Reduce the patella 

Place stifle through range 

of motion 

Typically oblique patellar 

ligament 

Proximolateral to 

distomedial 

26 


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Pre-‐op radiographs to measure the length 

and depth of osteotomy 

 

 

1/2 depth of the tuberosity 

Big enough for implants 

Insertion of the patellar tendon identified 

 

 

Bony prominence 

Osteotomy 3-‐4 mm proximal 

Osteotome greater than the width of the 

tuberosity 

Saggital saw, bone cutting forceps 

Leave distal periosteal attachment intact 

(unless require proximal/distal 

transposition) 

Prefer two wires (0.035-‐0.062) proximal 

and distal 

Tension band if not toy breed 

May need to prepare recipient bed 

TEST STIFLE with joint open! 27 


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Soft-tissue Balance - Release 

Palpation of medial joint 

capsule 

Aggressive medial release 

(joint capsule, retinaculum) 

Avoid parapatellar cartilage 

(6-‐8 mm medial to border of 

patella) 

Proximodistal borders 

animal dependent 

Mobilize entire quadriceps 

as needed 

Leave open if necessary 

28 


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Soft-tissue Balance - Imbrication 

“To tighten by overlap” 

Any everting pattern will 

do 

Horizontal mattress 

Vest-‐over-‐pants (modified 

Mayo) 

Long lasting monofilament 

absorbable (Maxon, PDS) 

Resection of redundant 

capsule and apposition 

Tuesday, September 24, 13 

29

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Anti-rotational Techniques 

Especially important with 

MPL and CCLD 

Loss of internal rotation 

stability with CCLR 

Lateral fabellotibial suture 

Fibular head transposition 

TightRope, etc. 

Patellofabellar suture 

Ancillary support 

30 


Large Breed Luxations 

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50% incidence of concurrent 

CCLD 

Labradors most common breed 

Tibial varus and femoral varus -‐ 

genu varum 

Correct only femur 

Tibial valgus and femoral varus -‐ 

normal appearance 

Correct femur and tibia 

Post-‐op CCL surgery 

Labradors most common 

0.018% of all CCL surgery 

31 


Patellar Positioning 

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Patellar ligament length (L) 

to patellar length (P) 

Medium to giant breed 

dogs with a L:P ratio of 

greater than 1.97 = patella 

alta 

Abnormally proximal 

patellar location 

vs/ patella baja 

Increased incidence of 

MPL 

32 


Patellar Lateralization and Distalization 

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Imaging Large Breeds 

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Accurate radiographic 

assessment is exceptionally 

challenging 

General anaesthesia (or 

the dexmedetomidine 

equivalent) 

Ideally image the hip, 

femur, stifle, tibia, & tarsus 

all in one view 

CT ideal 

34 


Radiographs 

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Lateral 

Can identify 

femoral 

deformity 

Cannot quantify 

Double condyle 

sign 

 

 

Cranial/caudal = 

torsion 

Distal/proximal 

= angular 

Torsion 

Varus 

(Lat) 

35 


Radiographs cont’d 

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Craniocaudal most 

important for 

quantification & 

planning 

Femur parallel; beam 

perpendicular to the 

detector/cassette 

CR and plain > DR 

Angled, elevated, 

horizontal 

36 



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Fabella bisecting cortices 

Parallel walls of 

intercondylar notch 

Barely visible lesser 

trochanter 

Nutrient foramen near 

middle of the femur 

Trochlea not proximal to 

condyles 

Measure “normal” 

Or use reference indices 

37 



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trochanter 




condyles 



37 



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trochanter 




condyles 



37 



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trochanter 




condyles 



37 



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trochanter 




condyles 



37 



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trochanter 




condyles 



37 



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trochanter 




condyles 



37 



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trochanter 




condyles 



37 


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Radiographs Measurements 

Anatomic lateral distal femoral 

angle 

aLDFA 

Intersection of the femoral 

anatomic axis and the distal 

joint reference line 

Center of femur at 33% and 

50% 

Line connecting medial and 

lateral condyles 

97º in “normal” Labradors 

97 Golden, 94 GSD, 98 Rotties 

38 



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The aLDFA defines 

the center of 

angulation of rotation 

(CORA) in cases with 

distal femoral varus 

Intersection of the 

proximal and distal 

anatomic axes of the 

femur 

Measured on CT or 

radiographs 

FVA = femoral varus 

angle 39 


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•CT less affected 

by positioning 

artifacts 

Oxley, et al. 2013 



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Femoral torsion requires an axial/skyline view of the femur 

Dorsal recumbency with the hip flexed and cassette under the joint 

Mean angle is ~27º (range 12-‐40º) 

If 27 as may make MPL worse! 

41 


Radiographic Artifact 

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Jackson, 2012 

Artifactual aLDFA created 

with elevation from the 

table 

Difference significant for 

all elevations >5º 

At 45º elevation, the 

difference was only 3º 

42 


Treatment Options 

If distal femoral varus is 

significant (typically >5º; i.e. 

aLDFA >102º) and/or torsion 

consider femoral corrective 

osteotomy 

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All other options also present 

Patellar distalization, more 

robust transposition 

Cruciate treatment 

14 of 30 stifles in one study 

Increased internal rotation/ 

torsion 

43 


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Femoral Corrective Osteotomy 

Identify CORA 

Quantify the magnitude of 

varus and torsion 

Laterally based closing 

wedge ostoeotmy 

Biomechanically stable 

Laterally applied plate 

LC-‐DCP, LCP, DFO plate 

Morselized osteotomy 

segment as graft 

44 


Combined MPL/CCL 

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Lateral suture -‐ 

antirotational 

TPLO -‐ allows 

corrective osteotomy 

of tibial torsion/ 

internal rotation 

TTA -‐ allows 

transposition of the 

tibial tuberosity 

Preferred for grades 

1-‐2 

45 



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1-‐2 

45 



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1-‐2 

45 



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1-‐2 

45 


Lateral Patellar Luxation 

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Typically genu valgum 

(knock kneed) 

Treatments are reversed 

Lateral approach with 

medial based closing 

wedge 

Tibial tuberosity 

medialization 

Correct torsion if 

GREATER than 27 º 

Similar prognosis 

46 


Outcomes 

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Low incidence of reluxation with DFO 

in large breed dogs and distal femoral 

varus 

Up to 50% reluxation rate historically 

reported 

 

Often times grade I -‐ no surgery 

Recent report: 

 

 

8% overall reluxation 

Reluxation higher in dogs >20kg 

Osteotomy procedure predictive of 

good outcome 

JAVMA 2011 7% without trochleoplasty 

Grade IV can be very challenging 

OA progression, but

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On the Horizon - 

Patella Groove Replacement 


Summary 

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Patient assessment is 

critical 

Surgical management is 

patient dependent 

Need LOTS in the tool box 

Correction of underlying 

skeletal abnormalities is the 

most important factor in 

success 

CT assessment is easiest 

and most accurate 

49 


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Decision Making in the Treatment of Canine Medial Patellar Luxation

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