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Updated: 10/12/2022

Bipartite Patella

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Images 1.jpg 2.jpg type iii xr.jpg prone.jpg
  • summary
    • Bipartite Patella is a congenital knee condition caused by the failure of the patella to fuse and is often an incidental finding on radiographs.  
    • Diagnosis is confirmed radiographically with most commonly an unfused patella at the superolateral pole. 
    • Treatment is observation and most often does not require treatment as the condition is typically asymptomatic.
  • Epidemiology
    • Incidence
      • 2-3% of the population
    • Demographics
      • no notable sex predilection
    • Anatomic location
      • most often found in the superolateral region (Type III)
      • bilateral in 50%
  • Etiology
    • Etiology
      • Normal patella variant representing a failure of fusion
        • often confused with patella fractures
    • Pathophysiology
      • considered a developmental variation of ossification
      • painful bipartite patella following injury
        • direct or indirect injury results in disruption of the fibrocartilaginous zone between the main patella and accessory fragment
        • fibrocartilaginous zone cannot heal by bony union, resulting in persistent pain
          • lack of arterial penetration from patella to osteochondral fragment
          • vastus lateralis contributes to traction force in fragment separation and nonunion
    • Associated conditions
      • nail-patella syndrome
      • patella fracture
        • compared with patella fractures, bipartite patellas:
          • are located superolaterally
          • have smooth, rounded borders
          • may have similar findings on contralateral knee radiographs (50%)
  • Anatomy
    • Osteology
      • the patella is the largest sesamoid bone
      • arises from a single ossific nucleus
      • ossification
        • males at 4-5 years old
        • females at 3 years 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
          • anterior tibial recurrent artery
  • Classification
      • Saupe Classification
      • Type
      • Incidence
      • Location
      • 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 overuse injuries (e.g. cycling, hill climbing)
          • aggravated by squatting, jumping, climbing stairs
        • giving way
    • Physical exam
      • localized tenderness over accessory fragment (typically superolateral patella)
      • hematoma
      • quad 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-weight-bearing)
          • squatting position (weight-bearing)
            • may show displacement of the accessory fragment
        • consider radiographs of the contralateral knee for comparison
      • findings
        • smooth edges (helps differentiate from fracture)
        • weight-bearing skyline (squatting) view demonstrates increased separation of fragments compared with non-weight views (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 may indicate that it is the cause of symptomatic knee pain
    • Bone scan
      • indications
        • equivocal radiographs with high suspicion for symptomatic bipartite patella
      • findings
        • increased uptake along superolateral aspect
      • utility somewhat controversial
    • CT scan
      • will clearly demonstrate fragment, but does not demonstrate edema
  • Studies
    • Histology
      • interposed tissue between accessory and main fragment
        • composed of fibrocartilage > fibrous > hyaline cartilage
        • avascular
      • adjacent bone
        • scalloped surface with numerous osteoclasts
        • well-vascularized
  • Treatment
    • Nonoperative
      • rest, immobilization, NSAIDS, and physical therapy
        • indications
          • generally, non-operative, symptomatic management is indicated for bipartite patella for at least 6 months
        • modalities
          • rest and restriction of sports activities
          • NSAIDs
          • isometric quadriceps strengthening exercises
          • immobilization with the knee braced in 30Ā° of flexion
          • local corticosteroid injections
        • non-operative management may be less successful in younger, athletic patients, possibly due to non-compliance
    • Operative
      • open excision of the accessory fragment
        • indications
          • failed nonoperative treatment >6 months or in cases of a displaced fragment requiring reduction, direct trauma resulting in the onset of pain, or significant impairment in daily activities
        • most common treatment technique, typically good results
          • may lead to poor results if large, articular fragment due to patellofemoral incongruity
      • arthroscopic excision
        • thought to lead to expedited recovery and avoids disrupting the quad tendon
        • limited evidence to support but good results in case reports
      • lateral retinacular release
        • indications
          • superolateral fragment (to remove the traction force of the vastus lateralis on the fragment)
      • vastus lateralis release (subperiosteal)
        • indications
          • superolateral fragment
          • to avoid long lateral retinacular release
        • open vs arthroscopic
          • quicker recovery and less effusion noted in arthroscopic patients
      • ORIF
        • indications
          • for large fragments
          • limited support in the literature, controversial
  • Complications
    • Patellofemoral maltracking
      • due to excision of a large fragment or lateral retinacular release
      • may lead to patellofemoral degenerative changes
    • Effusion
      • may require arthrocentesis following fragment excision
    • Persistent knee pain
      • may see following lateral retinacular release
    • Quadriceps weakness
    • Osteonecrosis
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Questions (3)
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(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?

QID: 4402

Figure A



Figure B



Figure C



Figure D



Figure E



L 1 B

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(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.

QID: 4505

Magnetic resonance imaging (MRI) for ligament reconstruction planning



Immobilize in 120 degrees of knee flexion for 24 hours and return-to-play in 2 weeks



Open reduction and internal fixation with interfragmentary screws with return-to-play in 5 months



Symptomatic treatment with return-to-play as tolerated



Long leg cast for 6 weeks with toe-touch weightbearing precautions with return-to-play in 2 months



L 2 B

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Evidence (3)
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