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Bipartite Patella

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Topic updated on 01/20/16 7:37pm
Introduction
  • Normal patellar variant representing a failure of fusion
    • often confused with patellar fractures
  • Epidemiology
    • incidence
      • 2-8% of the population
    • demographics
      • male:female ratio = 9:1
    • location
      • most often found in the superolateral region (Type III)
      • bilateral in 50%  
  • Pathophysiology
    • painful bipartite patella following injury
      • direct or indirect injury results in disruption in fibrocartilaginous zone between main patella and accessory fragment
      • fibrocartilaginous zone cannot heal by bony union, resulting in persistent pain
      • vastus lateralis contributes to traction force in fragment separation and nonunion
  • Associated conditions
    • nail-patella syndrome
    • patella fracture
      • compared with patellar fractures, bipartite patellas
        • are located superolaterally
        • have rounded borders
        • may have similar findings on a contralateral knee radiograph
Anatomy
  • Osteology
    • the patella is the largest sesamoid bone
    • ossification
      • males at 4-5 yrs. old
      • females at 3 yrs. old
      • accessory ossification center appears between 8-12 years 
      • separate fragment attached to patella by fibrocartilaginous tissue
  • Function
    • fulcrum for the quadriceps
    • protects the knee joint
      • articular cartilage of patella is thickest in body (up to 1cm)
    • enhances lubrication of the knee
    • see complete knee biomechanics 
  • Blood supply
    • blood supply to patella is predominantly from distal to proximal
    • 6 arteries contribute  
      • from popliteal artery
        • superior lateral geniculate artery
        • superior medial geniculate artery
        • inferior lateral geniculate artery
        • inferior medial geniculate artery
      • from superficial femoral artery
        • supreme geniculate artery
      • from anterior tibial artery
        • recurrent anterior tibial artery
Classification
 
Saupe Classification
Type Incidence Location
Image
Type I 5% Inferior pole
 
Type II 20% Lateral margin  
Type III 75% Superolateral pole  
 
Presentation
  • Symptoms
    • most are asymptomatic and discovered incidentally
    • only 2% become symptomatic
      • anterior knee pain from
        • direct trauma (e.g. fall, kick to the knee)
        • indirect trauma or repetitive, small injuries (e.g. cycling, hill climbing)
        • aggravated by squatting, jumping, climbing stairs
      • giving way
  • Physical exam
    • localized tenderness over accessory fragment
    • hematoma
    • quads inhibition
    • unusual patella prominence or palpable defect
    • larger than normal patella
Imaging
  • Radiographs
    • recommended views
      • AP knee radiograph  
        • best view to visualize bipartite patella
      • skyline view 
        • prone position (non-weightbearing)  
        • squatting position (weightbearing) 
      • radiograph of contralateral knee
    • findings
      • smooth edges (differentiate from fracture)
      • weightbearing skyline (squatting) demonstrates increased separation of fragments compared with non-weightbearing skyline (prone)
      • 50% have bilateral bipartite patella   
  • MRI 
    • indications
      • assessment of painful bipartite patella to determine if pain is attributable to the bipartite patella
    • findings
      • edema around the fragment  
  • Bone scan
    • indications
      • equivocal radiographs with high suspicion for bipartite patella
    • findings
      • increased uptake along superolateral aspect  
Studies
  • Histology
    • the interposed tissue between accessory and main fragment 
      • is composed of fibrocartilage > fibrous > hyaline cartilage
      • complete lack of blood vessels
    • adjacent bone
      • scalloped surface with numerous osteoclasts
      • numerous blood vessels in bone marrow
Treatment
  • Nonoperative
    • rest, immobilization, NSAIDS, and physical therapy  
      • indications
        • nonoperative symptomatic management indicated for bipartite patella for at least 6 months
      • modalities
        • rest and restriction of sports activities
        • NSAIDS
        • isometric strengthening exercises of the quadriceps muscle in extension
        • immobilization with the knee braced in 30° of flexion
        • local corticosteroid injection
  • Operative
    • open excision of the accessory fragment 
      • indications
        • failed nonoperative treatment >6mths
        • irregular articular surface of accessory fragment (on radiographs)
      • most common treatment technique
    • lateral retinacular release  
      • indications
        • superolateral fragment (to remove traction force of vastus lateralis on the fragment)
    • vastus lateralis release  
      • indications
        • superolateral fragment
        • to avoid long lateral retinacular release
    • ORIF  
      • indications
        • for large fragments 

 

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Qbank (2 Questions)

TAG
(OBQ12.42) A 19-year-old male complains of two week history of knee pain after falling during a college basketball game. Physical exam is unremarkable with no signs of effusion or focal tenderness. In this clinical scenario, which of the following radiographs would warrant continued reassurance and observation? Topic Review Topic
FIGURES: A   B   C   D   E  

1. Figure A
2. Figure B
3. Figure C
4. Figure D
5. Figure E

PREFERRED RESPONSE ▶
TAG
(OBQ12.145) A 14-year-old high school running back strikes his left knee on an opposing players helmet during practice. He is able to continue playing for 10 more minutes before seeking medical attention. On examination, he has soft tissue swelling at the anterior knee and early ecchymosis formation. His range of motion was full and no palpable crepitus over the patella was noted. His knee is stable to varus and valgus at 30 degrees. He has a grade one Lachman examination and the medial tibial plateau is anterior to the medial femoral condyle upon a posteriorly directed force on the proximal tibia. There is less than one-quartile of medial and lateral patellar translation with a negative "J" sign. Radiographs are shown in Figures A-C. What is the most appropriate next step in management. Topic Review Topic
FIGURES: A   B   C      

1. Magnetic resonance imaging (MRI) for ligament reconstruction planning
2. Immobilize in 120 degrees of knee flexion for 24 hours and return-to-play in 2 weeks
3. Open reduction and internal fixation with interfragmentary screws with return-to-play in 5 months
4. Symptomatic treatment with return-to-play as tolerated
5. Long leg cast for 6 weeks with toe-touch weightbearing precautions with return-to-play in 2 months

PREFERRED RESPONSE ▶




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