Patellar Luxation (6) - End E1 Flashcards
Dr. Gilley
What is a medial patellar luxation?
displacement of the patella from the trochlea sulcus
What is the signalment of a medial patellar luxation?
small and toy-breed dogs
What are some other common abnormalities relating to medial patellar luxation?
- medial displacement of quadriceps muscle groups
- femoral epiphyseal dysplasia
- rotational instability of the stifle joint
- tibial deformity
What happens with medial displacement of the quadriceps regarding medial patellar luxation?
lateral bowing of distal 1/3 of femur
lateral torsion of distal femur
How do femoral deformities occur with medial displacement of the quadriceps apparatus?
produces pressure differences on distal femoral physis —> medial: less growth, lateral: more
decreased length of medial cortex relative to increased length of lateral cortex —> lateral bowing of distal femur
abnormal growth continues while quadriceps displaced medially and physics active
How does lateral bowing of the distal femur occur?
decreased length of medial cortex relative to increased length of lateral cortex
What does the degree of lateral bowing of the femur depend on?
the severity of patellar luxation and patient’s age at luxation
abnormal growth continues while quadriceps displaced medially and phases active
What are the characteristics of mild luxations regarding medial displacement of the quadriceps apparatus?
- quadriceps rarely displaced medially
- minimal effect on distal femoral physis
What are the characteristics of severe luxations regarding medial displacement of the quadriceps apparatus?
- quadriceps medially displaced all times
- maximal effect on distal femoral physis
How can there be tibial deformities seen with medial displacement of quadriceps apparatus?
results of abnormal forces on proximal and distal physes of tibia
What are the tibial effects with medial displacement of quadriceps apparatus?
- medial displacement of tibial tuberosity
- medial bowing (varus deformity) of proximal tibia
- lateral torsion of distal tibia
What happens with femoral epiphyseal dysplasia?
articular cartilage is “physis” for epiphysis
- responds to increased or decreased pressure as with metaphyseal physis
Increased pressure [accelerates/retards] growth
retards
Dogs with medial patellar laxations have abnormal development of the _____
trochlear groove
What is the pathophysiology of femoral epiphyseal dysplasia?
- articulation of patella within trochlear groove puts physiologic pressure on articular cartilage
- pressure by patella responsible for the development of normal depth of trochlear groove
- if physiologic pressure exerted by patella is not present on trochlear articular cartilage - trochlea fails to gain proper depth
Why does the trochlea fail to gain proper depth with femoral epiphyseal dysplasia?
if physiologic pressure exerted by patella is not present on trochlear articular cartilage
Severe luxations affect the trochlear groove how?
have no trochlear groove - the normal pressure that is responsible for groove development is not present
What is Grade I of patellar luxations?
patella in groove - can be forced out but comes back immediately
What is Grade II of patellar luxations?
patella in groove, but sometimes comes out but comes back in every time
What is Grade III of patellar luxations?
patella NOT in groove - can be forced in but comes out again almost immediately
What is Grade IV of patellar luxations?
patella NOT in groove - can’t be moved back in without surgery!
Which patellar luxation is more common large dogs?
lateral luxations
What is the history of medial patellar luxations?
- intermittent weight-bearing lameness
- dog occasionally holds leg in flexed position for 1 or 2 steps
- grade IV: severe lameness and gait abnormalities
How do you diagnose MPL?
based on finding or eliciting MPL during physical exam
What do you see on physical exam grade II?
occasional skipping when walking or running
What are physical exam findings of a grade IV luxation?
walk with rear quarters in a crouched position: inability to extend stifle joints fully
patella hypoplastic
patella found displaced medially alongside femoral condyle
How does a grade I or II MPL appear on diagnostic imaging?
- patella within trochlear sulcus or displaced medially
- care taken to properly position limb
How does a grade III or IV MPL appear on diagnostic imaging?
standard craniocaudal & medial-lateral radiographs
show patella displaced medially
What can lead to a false positive regarding MPLs?
poor positioning
Issue here?
medial patella luxation
When is surgery recommended for MPLs? When is it not?
recommended: young animals or if lame
not: in asymptomatic older patients
When do you treat MPLs surgically?
- any age in patients with lameness
- patients with active growth plates
How do you deal with bilateral grade IV MPL cases?
likely need multiple surgeries
probable continued lameness even with successful surgery
- due to severity of long-bone abnormalities
What are the surgical techniques for restraining patella within the trochlear groove?
- tibial tuberosity tranposition
- medial restraint release
- lateral restraint reinforcement
- trochlear groove deepening
Which MPL technique should always be done? Why?
tibial crest transposition
realigns mechanical forces of extensor mechanism
… unless major corrections of femoral and tibial deformity performed (corrective osteotomy)
What is the surgical treatment of MPL?
When do you perform an osteotomy of the femur?
use with severe skeletal deformity
varus bowing of distal femur and medial torsional deformity of proximal tibia - closing wedge osteotomy on lateral aspect of femur helps realign things
What is the goal of osteotomy of the femur?
realign stifle joint in frontal plane - make transverse axis of femoral condyles 90 degrees to longitudinal axis of femoral diaphysis
What does anosteotomy of the femur require?
preoperative measurement and wedge osteotomy of the femur with the 4:
- deepen trochlear groove
- medial restraint release
- transposition of tibial crest
- lateral reticular reinforcement
What is a common sequela to MPLs?
cranial cruciate rupture and patellar luxation
What is part of the extensor mechanism of the stifle joint?
- quadriceps muscle group
- patella
- trochlear groove
- straight patellar ligament
What are the properties of the quadriceps muscle group?
- extends stifle joint
- aids in stabilizing stifle joint
- converges as patellar tendon on proximal patella
- continues distally as straight patellar ligament
What are the properties of the patella?
normal gliding articulation of patella and trochlea needed for nutrition of trochlear and patellar articular surfaces
Why is the patella so important?
essential component of functional mechanism extensor apparatus
maintains even tension when stifle is extended
Malalignment of what 5 things may lead to patellar luxation?
- quadriceps
- patella
- trochlea
- patellar ligament
- tibial tuberosity
What should you identify before making the parapatellar incision to enter the joint?
patellar ligament - location changes when deformed, comes across instead of straight down
How is the patient positioned for an MPL and why?
- dorsal recumency at end of table with leg hanging over table end
allows visualization of unrestrained extensor mechanism deviation
maximum manipulation of the limb to evaluate patellar stability
How can you deepen the trochlear groove?
trochlear wedge recession
trochlear block recession
Which side of the trochlear groove do you remove more of?
lateral side
medial side wears down more because of the patellar luxation
How do you perform a trochlear wedge resection?
How do you perform a trochlear block resection?
How do you perform a tibial crest transposition?
A. transpose tibial crest laterally
B. place osteotome beneath patellar ligament
C. stabilize tibial tuberosity with 1 or 2 small K-wires
How do you perform a lateral patellar luxation tibial crest transposition?
How do you release the medial joint capsule in a MPL procedure?
What is lateral imbrication with a MPL?
lateral reinforcement of the retinaculum
place suture through femoral-fabellar ligament & lateral parapatellar fibrocartilage
Where do you place lateral imbrication with a MPL surgery?
place imbrication sutures through fibrous joint capsule and lateral edge of patellar ligament
- with leg slight flexion
If the patella is a grade III or IV, how is the retinaculum affected?
retinaculum opposite side of the luxation is stretched
with medial luxations = redundant lateral retinaculum
What is the vest-over-pants suture pattern?
interrupted horizontal mattress pattern
tissues sutured overlapped instead of meeting end to end - sutures pass through both layers at both edges
What is post-op care and assessment for MPLs?
- activity restricted to physical rehab exercises
- gradually return to normal activity over 6 week period
- radiographs done 6 to 8 weeks to evaluate healing of TTT
