38. Diseases of the stifle joint- patella luxation and fractures. Screening program and therapy. Radiological examination and assessment of the DJD in stifle joint.

What is the neutral position of the stifle joint in a dog?

120 degrees

What type of joint is the stifle?

Composite, incongruent hinge joint

Which two joints make up the stifle?

1. Femorotibial

2. Femoropatellar

What are the components of the femorotibial joint?

1. Menisci

2. Meniscal ligaments

3. Femorotibial ligaments

4. Fabellae

What are the menisci?

Menisci lateralis et medialis. Cartilage structures between the femoral condyles and tibia

Which ligaments attach the menisci to the tibia?

lig. meniscotibiale craniale/caudale

Which ligament attaches the meniscus to the femur, and which meniscus?

Lateral meniscus. lig. meniscofemorale

Which ligament attaches the anterior parts of the menisci?

lig. transversum genus

Which ligaments are part of the femorotibial joint?

1. ligs. collaterale laterale/medialeligs

2. ligs. cruciatum craniale/caudale

3. lig. popliteum obliquum

What are fabellae?

Sesamoid bones within the gastrocnemius muscle tendon

What are the components of the femoropatellar joint?

1. Patella

2. Ligaments

Where is the patella located?

In the trochlea of the femur

What is the function of the patella?

Acts as a pulley for the quadriceps, increases strength, protects tendons

Which ligaments are associated with the patella?

1. retinaculum patellae laterale/mediale (fibrous tissue on lateral/medial aspects of the patella; extension of m. vastus lateralis)

2. ligs. femoropatellare laterale/mediale

3. lig. patellae (apex patellae → tuberositas tibiae)

What is the function of the menisci?

Cushion the femoral condyles and tibia, distribute forces evenly

What is the composition of the menisci?

Cartilage (avascular), red zone has some vessels

Which muscles primarily act on the stifle joint?

1. Quadriceps (m. vastus lateralis/medialis/intermedius + rectus femoris)

2. m. popliteus

What is unique about the stifle joint capsule?

More than 25% is fat (more radiolucent, but makes arthroscopy difficult)

What is the goal for all stifle trauma?

Induce primary bone healing with rigid fixation, restore normal function

What is the consequence of non-surgical management of stifle trauma?

Secondary intention healing → increased risk of degenerative joint disease

What is Wolff's Law?

Bone remodels itself to become stronger with increased loading, weaker with decreased loading

(→ production of osteophytes → thickening of cortical bone & change of shape (ankyloses of bone))

What are examples of diseases of the stifle?

1. Patella luxation

2. Patellar fracture

3. DJD

Where is the physiological location of the patella?

Trochlear groove

What is patellar luxation?

Displacement of the patella from the trochlear groove

Which species is more susceptible to patellar luxation?

Dogs

What are the two types of patellar luxation?

Medial and lateral

Which breeds are more prone to medial patellar luxation?

Toy, miniature, and some large breeds

Which breeds are more prone to lateral patellar luxation?

Large and giant breeds, sometimes smaller breeds

What are the aetiologies of patellar luxation?

1. Shallow trochlear groove

2. Varus deformity of femur

3. Valgus deformity of tibia

4. "Misplaced" quadriceps pull

5. Trochanter damage

6. Femur bending

Which is the most common type of patellar luxation?

Medial

What are the characteristics of medial patellar luxation?

Damaged medial ridge → medial patellar luxation → inward tibial tuberosity rotation → weakened lateral tissues, contracted medial tissues

What are the clinical signs of patellar luxation?

Depend on severity: from asymptomatic to non-weight bearing lameness

• Grade 0: Physiological → no symptoms/normal - can move patellar but moves back to physiological position

• Grade 1: Asymptomatic - patella in physiological position but skips spontaneously

• Grade 2: Weight bearing lameness, skipping gait when walking - patellar permanently on side but can move back

• Grade 3 + 4: Intense non-weight bearing lameness - patellar permanently on side and ca/n move patellar back

How is patellar luxation diagnosed?

Physical exam (standing patient). X-ray/CT only used to assess the degree of changes

How is a physical exam for patella luxation performed?

Palpation of patella: find tuberositas + Patella ligament + Patella

W/ thumb & finger only slight movement to sides are normal. Palpate both in standing & lateral position: Palpate patella while moving leg in full range of motion. It is important to check the following structures for alignment & joint movement: Quadriceps femoris muscle, patella, patellar tendon, tibial tuberosity!!

What is the grading system for patellar luxation?

• 0: normal

• 1: Located in groove, but can be luxated. Immediately returns to groove after displacement. Asymptomatic. No surgery needed. <15° tibial rotation

• 2: Luxate w/ flexion, returns w/ extension / Luxates when walking. Mildly bow-legged.

  Intermittent non-weight bearing. Requires surgery. 15-30° tibial rotation

• 3: Permanently located medially, but able to push back to groove- will return immediately. Moderate bow-legged, flexed stifles. Frequently non-weight bearing. Requires surgery. 30-60° tibial rotation

• 4: Permanently luxated/medially, not possible to push back to groove. Severe bow-legged and flexed stifles. Requires surgery. 90° tibial rotation

What are the treatment options for patellar luxation?

• Grade 1 w/ CS: conservative (NSAIDs & chondroprotectives). No treatment needed if no CS

• Grade 2 depends on which side it leans to. If significant CS → surgery. If intermittent and non-progressive → conservative and re-evaluate

• Grade 3 & 4 surgical correction

What are examples of surgical treatments for patella luxation?

1. Combination therapy:

   1. Trochleoplasty: wedge or block resection to deepen the patellar groove

   2. Medial release: release medial tissue to relieve tension

   3. Lateral tightening: tighten lateral soft tissues (capsule and retinaculum)

   4. Tibial anti-rotation: non-absorbable suture material used to suture around fabella & through tibial tuberosity to get centred patella

2. Tibial tuberosity transposition: Resect tuberosity & move it until patella lies in patellar groove & patellar tendon is aligned perfectly & straight

3. Trochlear chondroplasty: up to 6 months

4. Trochlear wedge resection

5. Trochlear block resection

What is trochleoplasty?

Deepening the patellar groove

What are the methods of trochleoplasty?

• Trochlear wedge resection

• Trochlear block resection

What is tibial tuberosity transposition?

Moving the tuberosity to align the patellar tendon

Which type of patellar luxation is less common?

Lateral

Which breeds are primarily affected by lateral patellar luxation?

Large and giant breeds

What conformation is often associated with lateral patellar luxation?

Genu valgum ("knock-kneed")

Are patellar fractures common?

Rarely

What are the aetiologies of patellar fractures?

Direct or indirect trauma. Usually a complication of tibial plateau-levelling osteotomy (TPLO) surgeries

What are the types of patellar fractures?

Undisplaced fissure, transverse, multifragmentary

What are the clinical signs of patellar fractures?

Non-weight bearing lameness, pain and swelling of cranial surface, possible void in quadriceps mechanism. Usually no crepitus.

How are patellar fractures diagnosed?

Radiographs (craniocaudal/caudocranial & mediolateral)

When in conservative treatment for patellar fractures indicated?

Cats with minimal displacement of fractured segments

What are the surgical treatment options for patellar fractures?

1. Undisplaced fissure fracture: Wire through quadriceps tendon and patellar ligament. Wires tightened.

2. Transverse fracture: Krischner wire and tension band wire, second wire in larger dogs.

3. Multi-fragmentary fracture: Krischner wire and tension band wire

What are DJDs?

Degenerative joint diseases (osteoarthritis)

What are some radiographic signs of DJD in the stifle?

Osteophyte formation, fat pad sign, periarticular osteophytes, femoral subchondral sclerosis

Which radiographic views are used to assess the stifle for DJD?

Mediolateral (flexed 90 degrees) and caudocranial

What are the grading systems for DJD?

Usually 0-3 or 1-4

• Initial: reduced density of the infrapatellar fat pad (asterisk);

• Early: osteophytosis in the femoral ridge (left arrow) in the femur and tibia ligament insertion with osteophytosis in the femoral ridge (right arrow)

• Osteophytes become apparent in the patella insertions, in the mid-zone portion of the femoral condyle’s trochlear ridge and in the femoral sesamoids (arrows);

• Advanced: osteophytosis (arrow), enthesophytosis (asterisk), and calcification of the ligaments and meniscus (cross)

What often occurs prior to DJD?

Patella luxation or ruptured CCL

What are common signs of DJD in the stifle?

1. Osteophyte formation on patellar apex (& later patellar base is affected)

2. Fat pad sign – fat pushed out of joint capsule due to joint effusion

3. Periarticular osteophyte formation

4. Femoral subchondral sclerosis

What are some common sites for osteophyte formation in stifle DJD?

Patellar apex and base, femoral condyles, fabellae, proximal tibia, tibial plateau

What is the fat pad sign?

Displacement of the fat pad due to joint effusion

Where do periarticular osteophytes form?

On femoral condyles, fabellae, proximal tibia, tibial plateau