Lecture 39: Medial patellar luxation

What are most patellar luxation?

Bilateral, most commonly medial

What is the most common patella luxation in small and large breed dogs?

Small breed → Medial patellar luxation

Large breed → Lateral patellar luxation

Musculature found around patellar?

• Quadriceps

  • Rectus femoris

  • Vastus lateralis, intermedius, medius

  • Insert on patella and continue as patella ligament

  • Inserts on a tibial tuberosity

• Bone embedded w/ a tendon

• Provides smooth surface for tendon to glide over moving joint

• Acts like pulley mechanism, changes the direction of the force. Magnifies the force w/ less effort

Patella/sessamoid bone

What is the normal patella mechanism?

• Extensor appartus of stifle must be properly aligned for normal function

• All elements must align with femoral shaft trochlear groove and tibial tuberosity for stable patella

• Luxations cause malignment of quadriceps mechanism

What common femoral malformations cause medial patellar luxation?

• Coxa cara

• Decrease angle of anteversion

• Distal external torsion

• Distal varus

• Hypoplasia of medial condyle

When should you decrease coxa vary?

Inclination of the femoral head angle

Femoral head <120 degrees

Coxa vara

Femoral head >135 degrees

Coxa valga

Angle formed by the axis of the femoral neck and the transcondylar axis. Basically the femoral neck leans forward w/ respect to the rest of the femur causing the limb to rotate internally so the knee and foot twist toward midline

Aneteversio angle

External rotation

Internal rotation

Distal femoral torsion

Distal femoral torsion

Distal femoral varus

When does hypoplasia of femoral condyles occur?

Secnodary to luxated patella during growth because there is no pressure on trochlear groove

What tibial malformations can cause MPL?

• medial displacement of tibial tuberosity

• Internal proximal tibial torsion

• Proximal tibial valgus

• Distal varus

Medial displacement of tibial tuberosity

Internal proximal tibial torsion

Proximal tibial valgus

Less common causes of MPL

Luxation secondary to trauma, patellar alta, tightness or atrophy of quads muscle complex

Common signalement of MPL

• Small breed dogs, usually detected in younger dogs w/out CCL tear

• Middle aged to older dogs MPL/CCL

• Usually no history of trauma

• Owner may be “skipping” hindlimb lameness

• Non-weight bearing lameness (NWB) can be indicative

Standing and walking with MPL

• Decreased to normal muscle mass hind limbs

• Decreased to normal weight bearing hindlimb

• Unilateral or bilateral skipping gait

• Lameness may come and go

• Dog may limp than extend leg which eliminates the limp and keep walking

Orthopedic exam findings with MPL

• Discomforta w/palpation and ROM

• Medially displaced patella, may feel grinding as patella move

• Stifle effusion

• Crepitus w/ROM

• Check for tibial thrust and or cranial drawer

• Minimal malalignment

• Patella wants to ride in the grove

• Can be luxated by force

• Asymptomatic

• Often incidental on PE

• No treatment necessary

Grade I MPL

• Luxation occurs intermittently

• On palpation, patella luxates easily but still wants to stay in groove

• In more than out

• Surgery indicated if CS or are progressive

Grade II MPL

• Patella permanently luxated

• Can be manually reduced, automatically re-luxates when releasing

• Significant lameness and gait abnormalities

• Surgery is indicated

Grade III MPL

• Permenant luxation

• Cannot be reduced manually

• Trochlear groove absent or severely eroded trochlear ridges

• Severe gait abnormalities

• Look for concurrent cruciate ligament tears

• Surgery indicated- prognosis is more guarded

Grade IV MPL

What cases should you select for surgical MPL repair?

Minimal limb deformaiites

• Hyaline cartilage preserving techiniques

  • Trochlear block resection

  • Trochlear wedge recession

• Abrasion sulcoplasty

Trohleoplasty

• Deepens the trochlear groove

• Preserves articular cartilage

• Narrows proximally and distally

• Wedge created w/ hobby saw or sagittal saw

Wedge trocheloplasty

How do you assess patellar stability?

Flex and extend the stifle, then again with both internal and external rotation of the tibia

Goal of tibial crest transposition

Realign quads, shifts insertion patellar ligament

Risk tibial crest transposition

• Create LPL

• Implant failure

• Tibial tuberosity avulsion fracture

Techniques for addressing ST aspects of MPL

• Releasing incision

• Retinacular imbrication

• Anti-rotational suture, concurrent CCLD

• Correct retinacular laxity

• Perform as final step of luxation correction

• Excessive tension predisposing to luxation in opposite direction

• Goal is the equal tension medial and lateral

Retinacular imbrication

Which of the following is the most common direction of patellar luxation overall? a) Lateral b) Medial c) Cranial d) Caudal

b) Medial

In which size category of dog are medial patellar luxations (MPLs) most prevalent, accounting for approximately 98% of patellar luxations in those breeds? a) Large breeds b) Medium breeds c) Toy and Miniature breeds d) Giant breeds

c) Toy and Miniature breeds

According to the sources, patellar luxation is considered a: a) Primarily traumatic injury b) Degenerative condition c) Genetic and heritable developmental disease d) Infectious disease

c) Genetic and heritable developmental disease

The patella is classified as what type of bone? a) Long bone b) Short bone c) Sesamoid bone d) Flat bone

c) Sesamoid bone

Which of the following best describes the function of the patella? a) It primarily provides structural support to the stifle joint. b) It acts like a hinge, allowing flexion and extension of the stifle. c) It provides a smooth surface for the tendon to glide over, acting like a pulley mechanism and magnifying force. d) It is the primary site of muscle attachment for the hamstring muscles.

c) It provides a smooth surface for the tendon to glide over, acting like a pulley mechanism and magnifying force.

For normal patellar function, which of the following must be properly aligned? a) Femoral condyles and menisci b) Patella and cruciate ligaments c) Extensor apparatus of the stifle, femoral shaft, trochlear groove, and tibial tuberosity d) Fibula and tarsal bones

c) Extensor apparatus of the stifle, femoral shaft, trochlear groove, and tibial tuberosity

Malalignment of which mechanism is the underlying issue in patellar luxations? a) Hock joint b) Hip joint c) Quadriceps mechanism d) Elbow joint

c) Quadriceps mechanism

A veterinarian is examining a young Cavalier King Charles Spaniel presenting with intermittent hind limb lameness described by the owner as a "skipping" gait. Based on the signalment and history, which of the following is the most likely differential diagnosis? a) Cranial cruciate ligament tear b) Hip dysplasia c) Medial patellar luxation d) Elbow dysplasia

c) Medial patellar luxation

Coxa vara, a femoral malformation associated with MPL, is characterized by: a) A femoral head angle greater than 135 degrees. b) A normal femoral head angle between 120-135 degrees. c) A femoral head angle less than 120 degrees. d) An increased angle of anteversion.

c) A femoral head angle less than 120 degrees.

A decreased angle of anteversion of the femur can cause the limb to rotate: a) Externally b) Cranially c) Internally d) Caudally

c) Internally

Hypoplasia of the medial femoral condyle in MPL is often secondary to: a) Trauma to the stifle joint b) Infection within the joint c) Lack of pressure on the trochlear groove due to a luxated patella during growth d) Excessive weight bearing

c) Lack of pressure on the trochlear groove due to a luxated patella during growth

During an orthopedic exam for suspected MPL, what might a veterinarian palpate in the stifle joint? a) Increased range of motion b) A laterally displacing patella c) A medially displacing patella, possibly with a grinding sensation d) Decreased joint effusion

c) A medially displacing patella, possibly with a grinding sensation

A dog with Grade III medial patellar luxation is characterized by which of the following? a) The patella can be luxated with force but returns to the groove when released. b) The patella luxates intermittently but returns to the groove spontaneously. c) The patella is permanently luxated but can be manually reduced, although it re-luxates upon release. d) The patella is permanently luxated and cannot be manually reduced.

c) The patella is permanently luxated but can be manually reduced, although it re-luxates upon release.

A 5-year-old Pomeranian has a patella that can be easily luxated during a stifle examination but spontaneously returns to the trochlear groove when pressure is released. The dog is asymptomatic. What grade of patellar luxation is most likely? a) Grade I b) Grade II c) Grade III d) Grade IV

a) Grade I

Surgical intervention is generally recommended for which grades of MPL when clinical signs are present or progressive? a) Only Grade IV b) Grades I and II c) Grades II, III, and IV d) Only Grade III

c) Grades II, III, and IV

Which of the following surgical procedures aims to deepen the trochlear groove to provide better stability for the patella? a) Tibial tuberosity transposition b) Retinacular imbrication c) Trochleoplasty d) Capsulotomy

c) Trochleoplasty

Tibial tuberosity transposition (TTT) is a surgical technique used in MPL treatment to: a) Deepen the trochlear groove. b) Tighten the joint capsule. c) Re-align the quadriceps mechanism by shifting the insertion of the patellar ligament. d) Release tension on the lateral retinaculum.

c) Re-align the quadriceps mechanism by shifting the insertion of the patellar ligament.

During surgery for a Grade III MPL, the surgeon assesses the trochlear groove and finds it to be very shallow. Which surgical technique would be most appropriate to address this specific finding? a) Tibial tuberosity transposition b) Retinacular release c) Trochleoplasty d) Retinacular imbrication

c) Trochleoplasty

Retinacular imbrication is a soft tissue surgical technique performed on which side of the stifle joint relative to the direction of patellar luxation? a) The same side as the luxation b) The opposite side as the luxation c) Both sides of the luxation d) The cranial aspect of the stifle

b) The opposite side as the luxation

A Labrador Retriever presents with lateral patellar luxation. Based on the information in the sources, this is: a) The most common type of patellar luxation in all breeds. b) More common in small breeds. c) More common in large breeds compared to medial luxation in large breeds. d) Equally common as medial patellar luxation in large breeds.

c) More common in large breeds compared to medial luxation in large breeds.