Patella Luxation Flashcards
What is the extensor mechanism of the stifle composed of? (5)
Quadriceps m
Patella
Trochlea
Patellar ligament
Tibial tuberosity
What articulation facilitates stifle extension?
Femoropatellar articulation
What bone type is the patella?
Sesamoid bone
What tendon is the patella located within?
Insertion of the quadriceps m
What bone does the patella articulate with?
Femoral trochlea
What are present on each side of the patella which articulate with the trochlear ridges?
Parapatellar fibrocartilages
What is patellar luxation a result of?
Mal-allignment of the extensor mechanism, such that the tremendous force of the quadriceps causes abnormal “tracking” of the patella; leading to (sub)luxation
What “type” of condition is patella luxation?
Development
How common is traumatic patella luxation?
Rare
What primary abnormalities have been proposed? (2)
Altered angles of inclination and version of the femoral neck
Define anteversion
Leaning forwards e.g. femoral neck leaning forward
Coxa vara:
- What is the degree of anteversion?
- Which way does the patella luxate?
A) decreased. <120
B) Medial
What is the normal femoral neck angle?
120-135 degrees
Coxa valga:
A) What is the degree of anteversion?
B) Which way does the patella luxate?
A) >135
B) lateral (although one studied found medial risk)
During normal development, how does the patellar groove to deepen and widen.?
The presence of the patella normally exerts pressure on the trochlear groove while growing
If patella luxation is present from an early age, what is the result on the trochlea?
Hypoplastic + shallow
Or absent
(as the patella has not been exerting pressure)
What is the effect of recurrent luxation and reduction of the patella (instability) on the trochlea ridge?
What cartilage also erodes?
Erosion with shallowing –> easier luxation
Articular cartilage
Is external femoral torsion normally present with medial or lateral patellar luxation?
Medial
Is lateral bowing of the tibia normally present with medial or lateral patellar luxation?
Lateral
Is coxa vara normally present with medial or lateral patellar luxation?
Medial
Is internal rotation of the foot normally present with medial or lateral patellar luxation?
Medial
Is coxa valga normally present with medial or lateral patellar luxation?
Lateral
Is hypoplastic lateral femoral condyle normally present with medial or lateral patellar luxation?
Lateral
Medial patellar luxation:
A) Effect on distal femur?
B) General effect on legs?
C) Trochlear groove?
D) Medial trochlear ridge?
A) Medial bowing
B) Genu varum (bow legs)
C) Shallow
D) Poorly developed/absent
Medial patellar luxation:
A) Medial femoral condyle?
B) Effect on tibial tuberosity?
C) Effect on proximal tibia?
A) Hypoplastic
B) Medial displacement
C) Medial bow
Lateral patella luxation:
A) Effect on distal femur?
B) Femoral torsion?
C) General effect on legs/stifle?
D) Which trochlear ridge is poorly developed/absent?
A) Lateral bowing
B) Internal
C) Genu valgus (knock knees)
D) Lateral
Lateral patella luxation?
A) Effect on trochlear groove?
B) Which way does the tibial tuberosity displace?
C) Which way does the foot rotate?
A) Shallow
B) Laterally
C) External
What are the 3 types of patella luxation?
Medial
Lateral
Bidirectional
What is the most common breed patella luxation occurs in?
toy and miniature breeds of dogs (e.g. miniature poodle, Yorkshire terrier and Jack Russell terrier)
true or false
The incidence in patella luxation in the following breeds is increasing?
medium, large and giant breed dogs, such as cocker spaniel, Staffordshire bull terrier, French and English bulldogs, Labrador retrievers and Mastiffs
True
Is lateral or medial luxation more common?
Medial
Which breed of dog does lateral luxation most commonly happen in?
Large breed (although can happen in any)
At what age do most patients with congenital patellar luxation present?
6-12mo
What does the CE severity depedn on? (4)
Duration
Severity of deformity
Associated joint damage
Uni or bilateral
Why may congenital luxation present later in life? (3)
Progressive joint damage
OA
Developing cranial cruciate ligament dx
Before manipulating the patella, how should the CE be performed?
The patella should be lightly held between a thumb and forefinger whilst the other hand lifts the leg off the ground. The stifle should be put through its range of motion with flexion, extension and internal and external rotation. Whilst doing this patellar luxation may be felt.
Define a grade 1 luxation
The patella can be luxated manually when the stifle is extended but returns to normal position when released.
Define a grade 2 luxation
The patella luxates and reduces spontaneously during motion.
Define a grade 3 luxation
The patella is permanently luxated but can be manually reduced.
Define a grade 4 luxation
Permanent, irreducible luxation of the patella.
How can xrays be useful? (2)
- Direction of luxation
- Degenerative changes
What xray views should be performed?
Mediolateral and caudocranial projections of the entire limb including coxofemoral and tarsal joints should be obtained to assess for femoral and tibial deformities.
What xray view of the femur can assess depth of patellar groove?
Skyline
What imaging is more precise than radigraphs and can be used for improved quantification of angles of varus or valgus, as well as for the presence of torsional deformities.?
Computed tomography with 3D reconstructions
What is used to decide on whether conservative or surgical is the best plan (2)
- Grading of luxation
- severity of signs
When/who is non surgical management an option for?
small dogs with no or mild clinical signs. Many small dogs can live with a mild degree of luxation with no effect on their activity levels.
What grade is surgery is generally warranted early in the course of the disease to mitigate progressive angular and torsional deformities and osteoarthritis?
3 or 4
What option is best for a grade 2 with mild/occasional lameness
Decision isn’t straight forward
- If the clinical signs are non-progressive and the patient is exercising normally, non-surgical management with regular re-evaluations can be recommended.
- If lameness, pain or osteoarthritis are, or become, progressive surgery should be opted.
Why should surgery be carefully considered in the very young patient? Why?
Bone reconstructive techniques could cause significant damage to the physes and these should be avoided until at least the majority of growth has been completed.
In the very young patients, what is the “two stage” repair approach?
starting with soft tissue reconstruction and trochlear chondroplasty to minimise progressive deformities.
Young patients have significant remaining growth potential and the mal-aligned A) mechanism could act as a B) and significantly worsen the angular and rotational deformities to a point where surgical correction is not possible.
A) quadriceps
B) bow string
What surgical procedures are likely to be needed in young luxation once skeletal maturity reached? (2)
Tibial tuberosity transposition
Femoral corrective osteotomy
What is primary aim of surgical treatment?
Restoring functional alignment of the quadriceps mechanism
What are the possible surgical approaches to a luxating patella (3)
Tibial tuberosity transposition (see operative technique)
Distal femoral corrective osteotomy
Proximal tibial corrective osteotomy (rarely required)
What are the 3 types of Distal femoral corrective osteotomy?
Closing wedge ostectomy
Opening wedge ostectomy
Derotational osteotomy
TTT:
If using a hacksaw, which way is it passed and directed?
Passed caudal to the patellar ligament, and directed distally
TTT:
What happens if the pins extend too far beyond the far cortex?
Irritate soft tissue
TTT: When cutting wires before twisting; what length should be left?
1.5cm-2cm
TTT: The wires must be twisted AROUND each other symmetrically; why is this?
An incorrectly twisted knot does not hold under load.
How many twist knots are best with TTT?
2 to improve tension distribution
Which of the following is not a typical skeletal deformity described to be associated with the development of medial patellar luxation?
Genu valgum
Coxa vara
Femoral varus
Proximal tibial varus
Genu valgum
TTT:
On the approach, what should be inspected?
Inspect the joint to identify any abnormalities of the cruciate ligaments and menisci.
TTT: The Osteotomy site shouldn’t be too far caudally - why?
Prevent tibial #
On the approach to a TTT, the joint should be inspect for?
Abnormalities of cruciate and menisci
TTT:
Which way is the tibia transposed in medial patellar luxation?
Laterally
TTT:
Which way is the tibia transposed in lateral patellar luxation?
Medially
TTT:
What does the degree of transposition based on? (3)
Realignment of the tibial tuberosity
Femoral trochlea
Quadriceps mechanism.
TTT - how is the tibial tuberosity stabilised with lateral transposition?
Stabilisation of the tibial tuberosity in its new position with two K-wires directed caudomedially
Following tibial tuberosity stabilisation with a TTT; what is drilled?
Drill a bone tunnel distocaudal to the osteotomy (appr 3-5mm distance).
What is placed following tibial tuberosity stabilisation and osteotomy?
Tension band wire
What are the possible adjunct procedures to a TTT? (6)
1 Trochleoplasties
2 Patelloplasty
3 Soft tissue release (on the side of patellar luxation)
4 Soft tissue tightening (imbrication: on the opposite side to patellar luxation)
5 Rectus femoris muscle release / transposition (rarely performed)
6 Anti-rotational suture
Are trochleoplasties performed before or after tibial tuberostiy transpositions?
Before or after
Which saw is used in a wedge trochleoplasty?
Fine tip crab saw
The osteotomies can be made with fine a toothed saw (eg. X-acto saw) or an oscillating saw.
Which of the following are often considered to be the underlying skeletal abnormality associated with patellar luxation?
Coxa valga and femoral varus
Coxa vara and femoral valgus
Coxa vara and femoral varus
Coxa valga and femoral valgus
Coxa vara and femoral varus
Wedge trochleoplasty:
The osteotomies are outlined on the articular Cartlidge of trochlea - where?
Slightly axial to the trochlear ridge
Wedge trochleoplasty: The osteotomies should insect where:
A) Distally?
B) Proximally?
A) Intercondylar notch
B) Doral edge of trochlea articular cartilage
Wedge trochleoplasty:
The wedge is removed, how is the recession deepened?
Removing additional bone from one or both sides of the femoral groove
With a wedge trochleoplasty, when is the osteochondral wedge replaced?
When the depth of the groove is sufficient to house 50% of the height of the patella.
During a wedge trochleoplasty, if the wedge needs to be remodelled. What can be used?
Ronguer or rasp
Block trochleoplasty
Crab saw makes the 2nd side of block.
How far proximally?
Proximal enough to ensure proximal groove deepend
During a block trochleoplasty - what is used to elevate the block?
Osteotome
Block trochleoplasty - what can be done to ensure adequate block recession?
Base can be cut
During wound closures of trochleoplastys what should be regularly evaluated during wound closure?
Patellar tracking and stability
Which of the following are recognised as advantages of a block recession sulcoplasty over a wedge recession sulcoplasty (multiple answers apply)?
A) Ease of the technique
B) Increased patellar articular contact
C) Greater resistance to patellar luxation in and extended stifle position
D) Increased proximal patellar grove depth
B) Increased patellar articular contact
C) Greater resistance to patellar luxation in and extended stifle position
D) Increased proximal patellar grove depth
Wedge trochleoplasty:
A) What angle?
B) How deep?
A) 10 degrees axially
B) 2-6mm
Wedge trochleoplasty- where is the osteotomy extended to and from
TO: Intercondyler fossa
FROM: Proximal trochlea
How many osteotomy sites are there in a wedge trochleoplasty?
3
Wedge trochleoplasty:
The trochlear recession is deepened how? and how much?
by removing additional cancellous bone from the base of the groove or the base of the block so that 50% of the height of the patella is covered.
When is patellar groove replacement indicated?
If there is significant damage to trochlear groove
What is the major problem of patellar groove replacements?
Revision options limited if there are major complications e.g. fracture or infect
Delayed union is a complication associated with what surgical technique?
TTT
of trochlear ridges is a complication associated with what surgical technique?
Trochleoplasty
Implant failure is a complication associated with what surgical technique?
TTT
OA is a complication associated with what surgical technique?
Trochleoplasty
Septic arthritis is a complication associated with what surgical technique?
Trochleoplasty
Implant associated infect is a complication associated with what surgical technique?
TTT
Complications of a TTT? (8)
*Implant failure
*Loss of reduction of tibial tuberosity
*Non-union
*Mal-union
*Delayed union
*Implant associated infection
*Fracture of the tibial tuberosity or tibia
*Recurrent patellar luxation.
Possible complications of trochleoplasty? (6)
*Pain
*Loss of reduction of autograft
*Septic arthritis
*Fracture of trochlear ridges
*Recurrent patellar luxation
*Osteoarthritis.
What weight dog has a higher patella surgery risk?
> 20kg
Prognosis following patella surgery is grade 2/3?
Good
Prognosis for surgery following patella surgery if grade 4?
Fair to good?
Prognosis in grade 4 luxations with severe deformities, osteoarthritis, cartilage loss and muscle atrophy.
Poor - grave
What type of condition is patella luxation in cats?
Developmental
In cats which way is the patella more likely to luxate?
Medially
In cats patella luxation - one or both joints?
Both
In unaffected cats how mobile is the patella compared to dogs?
More mobile
Clinical signs of luxation in cats? (3)
Often mild:
inactivity,
unwillingness to jump
crouched gait.
What is a thought to be a contributing factor in cats?
HD
In cats - when is surgery advised?
If pain/almeness present
What surgical approach is normally sufficient in cats?
TTT with or without trochleoplasty
True or false:
Small dogs can occasionally cope with subclinical medial patellar luxation well for years and cranial cruciate ligament disease could be the reason for onset of clinical signs in middle aged to older dogs.
True
What may occur with cranial cruciate dx which could mean surgical correction of the luxating patella might then also need to be carried out concurrently or as staged procedures.?
Increased internal tibial rotation
Possible treatment options for those needing cruciate AND patella luxation surgery?
(although There is an increased risk of complications due to the increased complexity of these procedures. These cases can be challenging to treat and referral should be considered.)
Lateral fabellotibial sutures
Tibial tuberosity transposition / advancement (TTT/A),
TPLO with medialisation of the proximal fragment
A combined CCWO with tibial tuberosity transposition
A combined tibial osteotomy for CCL disease with a distal femoral corrective osteotomy.
TPLO with patellar groove replacement can result in successful outcomes as well as a routine cruciate stabilisation procedure along with an appropriate recession suclopasty.
