Patellar Luxation Flashcards
Patellar Luxation pathophysiology
- what is the patella?
- alignment?
- Patella is the sesamoid for the quadriceps muscle group
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Quadriceps mechanism - Pelvis
- Rectus Femoris (+ other quadriceps)
- Patella
- Patellar tendon
- Tibial tuberosity
Must align with trochlear groove
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Congenital patellar luxation results from a misalignment of the quadriceps mechanism but involves anomalies of the entire limb.
Patellar Luxation
- congenital vs traumatic
> which is more common?
> development and signs
Congenital: By far the most frequent!
* Hereditary
* Develop w/i first few months of life
* Multiple bone and soft tissue deformations
> Sometimes visible, sometimes not
* Mild to no pain
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Traumatic: Extremely rare!
* Rare (may result from failed stifle surgery)
* VERY Painful
* Violent trauma
* Severe swelling
Congenital Patellar Luxation
- uni or bilateral?
- who is susceptible?
> medial or lateral?
- Often Bilateral
- Medial or lateral
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Small breed dogs - 98% medial and 2% lateral
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Large breed dogs - 80% medial and 20% lateral
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Giant breed dogs - 70% medial and 30% lateral
Lateral Patellar Luxation
- small vs large breed?
- etiology
- clinical signs
- treatment
- Large breed dogs > small breed dogs
- Heritable
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Clinical Signs: - Dogs walk with hock inward and paws outward
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Treatment: - Similar to MPL (reversed)
- Severity of deformities and size of dogs = decreased prognosis
Frequent Malformations with Congenital Patellar Luxations
- Medial
- Medial bowing of femur (Varus)
- External torsion of femur
- Internal torsion of tibia
- Lateral bowing of tibia
- Coxa vara
- Excessive femoral head and neck retroversion
- Medial condylar hypoplasia, genu varum
- Medial displaced tibial tuberosity
- Medial displaced rectus femoris
- Joint capsule and ligament laxity
Frequent Malformations with Congenital Patellar Luxations
- Lateral
- Lateral bowing of femur (valgus)
- Internal torsion of femur
- External torsion of tibia
- Medial bowing of tibia
- Coxa valga
- Excessive femoral head and neck anteversion
- Lateral condylar hypoplasia, genu valgum
- Lateral displacement of the tibial tuberosity
- Hypoplasia of vastus medialis
- Joint capsule and ligamentous laxity
patellar luxation grading
Grade 1
- The patella is IN the trochlear groove
- Can be manually luxated
- Pressure released – patella returns IN
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Grade 2
- The patella is IN the trochlear groove
- Can be manually luxated
- Pressure released – patella stays OUT
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Grade 3
- The patella is OUT of the trochlear groove
- Pressure applied – patella moves IN
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Grade 4
- The patella is OUT of the trochlear groove
- Pressure applied – patella stays OUT
luxating patella
- clinical signs
- progression
- what if it suddenly worsens?
Variable:
* Depends on the grade
* From none to severe disability
* Intermittent to permanent lameness
* “Skipping” steps
* Generally NON progressive after 1 year of age
> Mild progression due to slow increase in DJD
> Grade of luxation does not change
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* Large breed dogs have a more pronounced lameness than small breed dogs
* If suddenly worsens, suspect cruciate rupture!
patellar luxation diagnostic imaging
- purpose
- what we can see on radiographs and CT
- Rule out other diseases
- Radiographs
> Inexpensive
> Poor at determining cause of luxation (Severe positional artefacts) - CT
> Allows accurate measurements
> Expensive
luxating patella surgical decisons based on grade
Grade I
* Surgical correction rarely required
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Grade II
* Surgical correction is +/- recommended
* Surgical techniques depend on abnormalities
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Grade III
* Surgical correction is recommended
* Bone deformities more obvious
* Increased risk of CrCL rupture
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Grade IV
* Surgical correction if possible is recommended
* Extensive corrective osteotomies may be required
surgical strategy for luxating patella
1) Realign the quadriceps mechanism
* Tibial Tuberosity Transposition
* Corrective osteotomies
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2) Deepen the trochlear groove
* Trocheoplasty
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3) Tighten/loosen the Joint capsule
* Joint imbrication (+/- release)
Tibial Tuberosity Transposition (TTT) - what do we do?
- Osteotomy of tuberosity
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Transposed - Laterally for medial luxations
- Medially for lateral luxations
- Re-attach with pins (& wire)
Corrective Osteotomy - when is this recommended
- what is needed for measurements?
Should be recommended when significant deformities are identified
* Bowing of femur (varus)
* Torsional deformities
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CT is required for measurements
* Positional artifact
* Torsional deformities
Trochleoplasty
- when to perform
- why we have a problem with the trochlea in the first place?
- techniques?
- Trochleoplasty should be performed if groove shallow > 50% should sit in the groove
- Shallow trochlear groove is likely a SECONDARY change
> Requires patella to be in the groove for development
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Trochleoplasty techniques - Wedge
- Block
- Trochlear chondroplasty
- Trochlear sulcoplasty
Retinacular Release and Imbrication
- how is this technique used? along with what?
- what is it? how do we do it?
- Never used alone
- Always used in combination with re- alignment of quadriceps mechanism
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Retinacular release - Release incision (joint capsule)
- On the side of luxation (grade 3 or 4)
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Retinacular imbrication - Overlap and tightening of joint capsule and fascia lata on side opposite to luxation
