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What musculature is involved with the anatomy of the patellar mechanism? Describe how they form the patellar mechanism.
- rectus femoris
- vastus lateralis, intermedius, and medius
- all the muscle converge on the patella and continue as the patellar ligament, which inserts on the tibial tuberosity
- this is an EXTENSOR apparatus
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What structures add secondary support to the patellar ligament?
joint capsule, femoropatellar ligaments
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For a stable patella, the extensor apparatus must...
have all elements (musculature, ligaments) align along the femoral shaft, trochlear grove, and tibial tuberosity
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Most patellar luxations are __________, ____________, and __________ and occur due to...
congenital; bilateral; medial; malalignment of the quadriceps due to anatomical deformation
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Describe the etiology of patellar luxation.
- abnormal femoral neck angle- either coxa vara (decreased femoral neck angle) or coxa valga (increased femoral neck angle)
- femoral varus/ valgus
- quadriceps pulls tibial crest medial or lateral
- trochlear groove doesn't develop or becomes too shallow
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Describe the grades of patellar luxation.
- Grade I: minimal malalignment, patella wants to ride in grove but can be luxated by force, asymptomatic, no txt
- Grade II: luxation occurs intermittently, patella wants to ride in the grove but luxates easily, often young animals, sx indicated if painful and progressive lameness
- Grade III: permanent luxation but patella can be reduced into the groove, significant lameness, often young animals, surgery indicated
- Grade IV: permanent luxation, patella cannot be reduced, trochlear groove not developed, severe gait abnormalities, very young animals (congenital), surgery indicated
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What are clinical signs of patellar luxation? (11)
- may be asymptomatic
- skipping steps, knee may lock then go back to normal
- lameness
- pain
- abnormal gait
- abnormal stance
- mechanical lameness (quads needed for extension)
- lameness due to pain
- joint capsule stretching
- abrasion of articular cartilage
- concurrent cruciate tear is very common
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How is patellar luxation diagnosed? (4)
- palpation standing- dynamic
- palpation recumbant- passive
- internal or external rotation of tibia
- radiographs- assess DJD
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Describe how you palpated medial versus lateral patellar luxation.
- Medial: stifle fully extended, internal rotation of tibial, push patella medially
- Lateral: stifle partially flexed, external rotation of tibia, push patella laterally
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For what patellar luxations is surgery indicated?
- some grade II
- all grade III and IV
- when there is pain from bone on bone contact
- when there is mechanical lameness
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Describe methods of stifle joint bone correction. (2)
- Deepen trochlear groove (trochleoplasty)
- Realign quadriceps mechanism
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Describe trochleoplasty.
- wedge or block resection
- chondroplasty
- abrasion sulcoplasty
- patellar groove replacement
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How is surgical realignment of the quadriceps mechanism achieved?
- tibial tuberosity transposition
- anti-rotation suture (tibio-fabellar suture)
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Describe the surgical approach to the stifle.
- standard craniolateral stifle arthrotomy- incision from proximal to the patella to distal to the tibial tuberosity
- joint exploration- assess cruciates, flip patella over and assess cartilage, assess cartilages of femur
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Describe the surgical aspects of trochlear wedge resection.
- deepen groove until ~50% of the patella is recessed below the trochlear ridges
- "V-shaped" wedge
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What are the pro and con of trochlear wedge resection?
- Pro- maintains hyaline cartilage
- Con- can be difficult to deepen the most proximal and distal aspects of the groove
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Describe the surgical aspects of trochlear block resection.
deepen groove as a rectangle instead of a "V-shape"
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What are the pros and con of trochlear block resection?
- Pros- maintains hyaline cartilage, great in large dogs b/c they have more bone, better recession proximal and distal in groove
- Con- not good in small dogs with small bones
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Describe the surgical aspects of trochlear resection and abrasion sulcoplasty.
- rasp, rongeur, or burr to create the groove
- defect fills with fibrocartilage and patella fixes to it
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What are the pros and con of trochlear resection and abrasion sulcoplasty?
- Pros- easy to perform, can create custom groovedefect fills in with fibrocartilage
- Con- removes normal hyaline cartilage
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Describe the surgical aspects of chondroplasty.
- performed in immature animals only (<6 months old), before the cartilage attachment is very strong
- peel up cartilage
- remove subchondral bone to deepen groove
- replace cartilage flap
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What is the goal of the tibial tuberosity transposition?
align quadriceps mechanism
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Describe the surgical aspects of tibial tuberosity transposition.
- cut tibial tuberosity with osteotome, sagittal saw, or bone cutters
- transpose it laterally for medial luxation or medially for lateral patellar luxation
- affix tuberosity with K-wires/ pins/ tension band wire- aim K wire parallel to joint, place proximally in widest portion of tuberosity
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What is the goal of placing anti-rotational suture?
rotate tibia laterally (externally) to align the quadriceps
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Describe the surgical aspects of anti-rotational suture.
- suture placed from lateral fabella to tibial crest (same as lateral suture)
- used in dogs with CCL tear or if the tibial tuberosity transposition is problematic
- provides ancillary support only!! not a sole correction
- changes joint configuration
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What soft tissue changes occur with correction of patellar luxation?
soft tissue adapt to position of patella over time- contracts on luxated side, stretched on non-luxated side
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What soft tissue release can be done after surgically correcting patellar luxation? (3)
- incise joint capsule on side of luxation (capsulotomy)
- release retinaculum on side of luxation- start proximal to tibial attachment of patellar tendon, continue to level of patella as necessary
- muscle release- quadriceps femoris
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Describe soft tissue imbrication after surgical correction of patellar luxation.
- Remove excess soft tissue on side opposite of luxation (joint capsule, fascia- not too much!)
- imbrication on side opposite luxation- close capsule with appositional pattern or imbrication with horizontal mattress, retinaculum with mayo-mattress suture pattern
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What are complications of surgical correction of patellar luxation? (5)
- overcorrection
- undercorrection
- pin-related issues (too far into soft tissue, pin migration, broken pins)
- delayed healing of osteotomy or failure of TTT
- fracture of distal femur, patellar tendon laceration
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What is the prognosis with patellar luxation?
- good to excellent for low-grade luxations
- fair to good with higher grades
- warn owners about 10% relaxation rate
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