Patellar Instability

Question 1

types or classification of patellar instability

Answer 1

• acute traumatic
  
  • occurs equally by gender
  • may occur from a direct blow (ex. helmet to knee collision in football)
• chronic patholaxity
  
  • recurrent subluxation episodes
  • occurs more in women
  • associated with malalignment
• habitual
  
  • usually painless
  • occurs during each flexion movement
  • pathology is usually proximal (e.g. tight lateral structures - ITB and vastus lateralis)

Question 2

risk factors

Answer 2

• ligamentous laxity (Ehlers-Danlos syndrome)
• previous patellar instability event
• “miserable malalignment syndrome”
  
  • a term named for the 3 anatomic characteristics that lead to an increased Q angle
    
    • femoral anteversion
    • genu valgum
    • external tibial torsion / pronated feet

Question 3

pathoanatomy

Answer 3

• osseous
  
  • patella alta
    
    • causes patella to not articulate with sulcus, losing its constraint effects
  • trochlear dysplasia
  • excessive lateral patellar tilt (measured in extension)
  • lateral femoral condyle hypoplasia
• muscle
  
  • dysplastic vastus medialis oblique (VMO) muscle
  • overpull of lateral structures
    
    • iliotibial band
    • vastus lateralis

Question 4

biomechanical or the anatomic stability of patellofemoral joint

Answer 4

• Passive stability
  
  • medial patellofemoral ligament (MPFL)
    
    • femoral origin-insertion is between medial epicondyle and adductor tubercle
      
      • is usual site of avulsion of MPFL
    • is primary restraint in first 20 degrees of knee flexion
  • patellar-femoral bony structures account for stability in deeper knee flexion
    
    • trochlear groove morphology, patella height, patellar tracking
• Dynamic stability
  
  • provided by vastus medialis (attaches to MPFL)

Question 5

Radiographic Assessment in patellar instability

Answer 5

• rule out fracture or loose body
  
  • medial patellar facet (most common)
  • lateral femoral condyle
• AP views
  
  • best to evaluate overall lower extremity alignment and version
• lateral views<
  
  • ​best to assess for trochlear dysplasia
  • crossing sign
    
    • trochlear groove lies in same plane as anterior border of lateral condyle
    • represents flattened trochlear groove
  • double contour sign
    
    • anterior border of lateral condyle lies anterior to anterior border of medial condyle
    • represents convex trochlear groove/hypoplastic medial condyle
  • supratrochlear spur
    
    • arises in proximal aspect of trochlea
  • evaluate for patellar height (patella alta vs. baja)
    
    • Blumensaat’s line should extend to inferior pole of the patella at 30 degrees of knee flexion
    • Insall-Salvati method
      
      • normal between 0.8 and 1.2
    • Blackburne-Peel method
      
      • normal between 0.5 and 1.0
    • Caton Deschamps method
      
      • normal between 0.6 and 1.3
    • Plateau-patella angle
      
      • normal between 20 and 30 degrees
• Sunrise/Merchant views
  
  • best to assess for lateral patellar tilt
  • lateral patellofemoral angle (normal is an angle that opens laterally)
    
    • angle between line along subchondral bone of lateral trochlear facet + posterior femoral condyles
    • normal > 11°
  • congruence angle (normal is -6 degrees)
• CT scan
  
  • TT-TG distance
    
    • measures the distance between 2 perpendicular lines from the posterior cortex to the tibial tubercle and the trochlear groove
    • >20mm usually considered abnormal
• MRI
  
  • help further rule out suspected loose bodies
    
    • osteochondral lesion and/or bone bruising
    • medial patellar facet (most common)
    • lateral femoral condyle
  • tear of MPFL
    
    • tear usually at medial femoral epicondyle

Question 6

non operative treatment in adult

Answer 6

NSAIDS, activity modification, and physical therapy

• indications
  
  • mainstay of treatment for first time patellar dislocator
    
    • without any loose bodies or intraarticular damage
  • habitual dislocator
• techniques
  
  • short-term immobilization for comfort followed by 6 weeks of controlled motion
  • emphasis on strengthening
    
    • closed chain short arc quadriceps exercises
    • Quad strengthening
    • core and hip strengthening to improve limb positioning and balance (hip abductors, gluteals, and abdominals)
  • patellar stabilizing sleeve or “J” brace
  • consider knee aspiration for tense effusion
    
    • positive fat globules indicates fracture

Question 7

list the operative treatment in adult

Answer 7

1. Arthroscopic debridement (removal of loose body) vs Repair with or without stabilization
2. MPFL repair
3. MPFL reconstruction with autograft vs allograft
4. Fulkerson Osteotomy (anterior and medial tibial tubercle transfer)
5. tibial tubercle distalization
6. lateral release
7. trochleoplasty

Question 8

discuss operative treatment in adult

Answer 8

• Arthroscopic debridement (removal of loose body) vs Repair with or without stabilization
• indications
  
  • displaced osteochondral fractures or loose bodies
  • may be an indication for operative treatment in a first-time dislocator
• techniques
  
  • arthroscopic vs open removal versus repair of the osteochondral fragment
  • primary repair with screws or pins if sufficient bone available for fixation
• MPFL repair
  
  • indications
    
    • acute first time dislocation with bony fragment
  • techniques
    
    • direct repair when surgery can be done within first few days
      
      • no clinical studies support this over nonoperative treatment
• MPFL reconstruction with autograft vs allograft
  
  • indications
    
    • recurrent instability
    • no significant underlying malalignment
  • techniques
    
    • gracilis or semitendinosus commonly used (stronger than native MPFL)
    • femoral origin can be reliably found radiographically (Schottle point)
• Fulkerson-type osteotomy (anterior and medial tibial tubercle transfer)
  
  • indications
    
    • may be used in addition to MPFL or in isolation for significant malalignment
    • TT-TG >20mm on CT
  • techniques
    
    • anteromedialized displacement of osteotomy and fixation
    • correct TT-TG to 10-15mm (never less than 10mm)
• tibial tubercle distalization
  
  • indications
    
    • patella alta
  • techniques
    
    • distal displacement of osteotomy and fixation
• lateral release
  
  • indications
    
    • isolated release no longer indicated for instability
    • only indicated if there is excessive lateral tilt or tightness after medialization
  • technique
    
    • arthroscopic
• trochleoplasty
  
  • indications
    
    • rarely addressed (in the USA) even if trochlear dysplasia present
    • may consider in severe or revision cases
  • techniques
    
    • arthroscopic or open trochlear deepening procedure

Question 9

nonoperative treatment in children and adolescent

Answer 9

standard of care unless there is one of the following

1. osteochondral fragment (≥ 5 mm)
2. osseous avulsion of the MPFL
3. meniscus tear

Nonoperative protocol:

1. full recovery time traditionally takes 3 months
2. The initial aim after the acute dislocation is to decrease swelling and pain, strengthen the vastus medialis and gluteal muscles
3. immobilizes the patient for 3 weeks in a lateral J type brace and then focuses on increasing mobility (regressive immobilization)
4. Physical therapy emphasizes isometric quadriceps strengthening, specific VMO strengthening, and progression to more dynamic exercises involving the core and gluteal muscles

Question 10

operative treatment in kids

Answer 10

Proximal Realignment

• MPFL repair
• Medial Patellofemoral Reconstruction
  
  • hamstring autograft
  • various allografts (gracilis, semitendinosus, tibialis anterior, tibialis posterior)
  • nonanatomic like quadriceps turn down, adductor sling
  • various forms of fixation (suspensory, interference screw, suture anchor)

Distal Realignment

• Patients with patella alta or increased TT-TG distances
• Galeazzi procedure
  
  • semitendinosus tendon is harvested from its distal insertion and secured to the medial patella in an oblique manner