Patellar Luxation Flashcards
What 5 parts are pieces of the extensor mechanism of the stifle?
- quadriceps
- patella
- trochlea
- ligamentum rectum patellae
- tibial tuberosity
What signalments are most common with medial and lateral luxations?
MEDIAL = small breeds (Poodles, Yorkies, Pomeranians, Pekingese, Chihuahua, Boston Terriers)
LATERAL = large breeds (Newfoundlands)
(medial patellar luxations are more common than lateral luxations in BOTH small and large dogs)
What are 2 parts of the pathophysiology of patellar luxation?
- abnormal (usually S-shaped) deformation of the rear limb
- tension of the rectus femoris muscle
What 5 musculoskeletal abnormalities are commonly seen in patients with medial patellar luxations?
- medial displacement of quadriceps muscle group
- lateral torsion of the distal femur
- lateral bowing of the distal one third of femur
- femoral epiphyseal dysplasia
- rotational instability of the stifle joint or tibial deformity
Patellar luxation:
- curved tibia pulls extensors
- actual groove becomes shallow because the patella is no longer in place
Patellar luxation, radiographs:
Medial patellar luxation:
- bone curvature
- abnormal muscular pull
Lateral patellar luxation:
medial displacement of distal femur
How is patellar luxations diagnosed on physical exam? Why must radiographs be done carefully?
- gait: walks, hops a few steps, walks again (usually no pain) = intermittent lameness and skips
- cranial drawer
- tibial thrust
possible for false positive/negative if positioned incorrectly, may see a degree of degenerative changes
What are the 4 grades of medial patellar luxations?
- patella found in place, but can be luxated with stifle in extension only (with stress)
- patella found in place, but cam be luxated with stifle in flexion
- patella found luxated, but can be digitally reduced
- patella found luxated and cannot be digitally reduced
How are animals with possible patellar luxations palpated in standing position and in recumbency?
palpate both sides for atrophy
cranial drawer and tibial thrust —> best done under sedation
Do all patellar luxations need to treated?
no
- BUT - can be progressive, lead to cruciate tears, cause arthritis —> permanent changes!
What are 2 important aspects to the surgical repair of patellar luxations?
- restore joint function
- correct extensor mechanism
(bone and soft tissue reconstruction)
What 2 surgical repairs are performed for patellar luxations?
- tibial tuberosity transposition: osteotomy + lateral luxation, move medial / medial luxation, move lateral to line up insertion points
- trochleoplasty to deepen the groove
How is a tibial tuberosity transposition performed on a medial luxation?
goal is to transpose tibial crest laterally
- tibial crest osteotomy beneath the patellar ligament
- stabilize tuberosity in new lateral location with one or two small K wires
What is the purpose of performing a tibial tuberosity osteotomy in correcting patellar luxations?
osteotome is used to cut bone out and create a deeper groove for the patella to sit in
- typically bent and left attached +/- tension band to keep it in place
When is a tibial tuberosity osteotomy not performed?
in younger dogs with open physes
- osteotome and tension band would disrupt and compress the physis, resulting in closing the physis and growth defects
What are the 2 approaches to trochleoplasties based on age? What is the purpose?
- > 5 months = wedge/block resection sulcoplasty - more solid bone that a blade cannot cut
- < 5 months = subchondral sulcoplasty (cartilage flap) - soft, minimal arthritis with ability to lift up cartilage with a blade
patellar groove replacement
How are wedge resection sulcoplasties performed?
- resect an osteochondral wedge
- remove the bone and deepen the sulcus
- replace the osteochondral wedge
Wedge resection sulcoplasty:
How are block resection sulcoplasties performed?
- create two parallel cuts axial to both trochlear ridges
- elevate an osteochondral block from the patellar ridge
- remove the bone from the bottom of the incised block
- replace the osteochondral block
Subchondral sulcoplasty:
< 5 months
What material is used for a patellar groove replacement? When is it most commonly implemented?
smooth, low friction, titanium groove replacement placed on a plate at the smoothened patellar groove (along long digital extensor tendon to proximal trochlear groove) to tighten patella and deepen groove
breeds with increased recurrence
What are the 3 most common soft tissue reconstruction techniques used to correct patellar luxations? How are they utilized?
- imbrication away from defect +/- anti-rotational sutures
- desmotomy (retinaculum) release toward defect
- quadriceps release
(medial luxation = lateral imbrication, medial release)
in combination with bone reconstruction, NEVER alone
What post-operative management is recommended following patellar luxation repair?
- 2 weeks of rest
- physical therapy
- leash walking only for 6-8 weeks
- radiographic evaluation at 6-8 weeks
What is the prognosis of patellar luxation repair?
- recurrent luxation 50%, usually grade 1
- less favorable in larger dogs with LPL than smaller dogs with MPL
- progressive DJD common, but less severe compared to if it was not repaired
- grade 4 = guarded, sx not necessarily indicated
What patellar luxation is the most common?
medial luxation in small breeds
At what age are dogs able to receive a patellar groove replacement?
> 6 months
What is vital to ensuring the proper prosthesis choice for patellar groove replacements?
trial implants with patella reduction and stifle flexion and extension
- ensures a “snug” correct size is chosen with smooth tracking, and absence of a click or hitch
Is a patellar groove replacement a cure for patellar luxations?
NO - requires concurrent joint capsule release/imbrication, tibial tuberosity transposition, and distal femoral/proximal tibial corrective osteotomies
