II. Epidemiology

  1. Uncommon Fracture (<1% of all Fractures)
  2. Rare in children

III. Mechanism

  1. Direct blow to anterior, flexed knee (direct injury)
  2. High force injury associated with Femur Fracture, Hip Dislocation or Knee Dislocation (secondary Patella Fracture)
  3. Rapid knee flexion against a eccentrically contracting quadriceps (uncommon, indirect injury)
    1. May result in sleeve Fracture as below

IV. Types

  1. Stellate Fracture
    1. Direct blow to Patella
  2. Sleeve Fracture
    1. Distal Patella Fracture due to quadriceps Muscle Contraction against a fixed lower leg

V. Exam

  1. Tenderness, swelling, Ecchymosis overlying the Patella
  2. Evaluate for breaks in the skin overlying the Patella
    1. Suggests Traumatic Arthrotomy (open Fracture)
  3. Evaluate extension mechanism
    1. Ability to extend knee suggests intact quadriceps tendon and Patellar tendon
    2. Vertical Fracture lines are less likely to result in extensor mechanism disruption
    3. High riding Patella (Patella alta) suggests Patellar tendon disruption
    4. Low riding Patella (Patella baja) suggests quadriceps tendon disruption

VI. Imaging

  1. Knee XRay (esp. lateral Knee XRay and sunrise view)
    1. Evaluate for pneumoarthrosis (air within joint), suggesting a Traumatic Arthrotomy (open Fracture)
  2. Knee CT without contrast Indications
    1. Non-diagnostic Knee XRay (e.g. suspected Tibial Plateau Fracture)
    2. Surgical planning (or MRI Knee)
    3. Suspected Traumatic Arthrotomy (open Fracture)
      1. Test Sensitivity and Test Specificity approaches 100% (better than saline load test)
      2. Konda (2013) J Orthop Trauma 27(9): 498-504 [PubMed]

VII. Differential Diagnosis

  1. Bipartite Patella (2% of uninjured patients)
    1. Congenital Ossification Center that failed to fuse
    2. Consider Bilateal Knee XRay (expect both Patellas to be bipartite in 50% of cases)

VIII. Management: Surgical versus non-surgical management

  1. Surgical indications
    1. Traumatic Arthrotomy (open Fracture) requires emergent Consultation
      1. Initiate antibiotics, Tetanus Prophylaxis and send to operating room
    2. Fracture step-off of >2 mm on articular surface
    3. Fracture separation of >3 mm
      1. Associated with Retinacular disruption and active knee extension loss
  2. Non-surgical Indications
    1. Non-displaced Patella Fracture with intact articular surface
    2. Active knee extension against gravity intact
    3. Minimal Patella Fracture fragment displacement
    4. Articular surface with minimal involvement

IX. Management: General

  1. Acute management (for first week)
    1. Knee Immobilizer (knee in full extension)
    2. Non-weight bearing (Crutches)
    3. Ice and elevation
  2. Non-surgical management
    1. Week 1
      1. Start immobilization for 4-6 weeks
        1. Cylinder cast from groin to above ankle (with knee in full extension) OR
        2. Knee Immobilizer brace worn at all times except bathing (in highly compliant patients)
      2. Weight bearing
      3. Straight leg Exercises
    2. Week 2
      1. Repeat Knee XRay and confirm Fracture stable without displacement
      2. Continue knee immobilization
    3. Weeks 4-6
      1. Repeat Knee XRay and exam
      2. Continue knee immobilization until XRay demonstrates radiographic union
    4. Weeks 6-10
      1. Physical therapy for knee range of motion and quadriceps strengthening
      2. Repeat exam every 3-4 weeks until fully healed (typically 8-10 weeks from start of immobilization)

X. Complications

  1. Inability to extend knee
    1. Disrupted knee extension mechanism (Patellar tendon or quadriceps tendon)
  2. Premature Knee Osteoarthritis
    1. Related to articular surface defects (osteochondral defects)

XI. References

  1. Eiff (1998) Fracture Management for Primary Care, W.B. Saunders, p. 179-83
  2. Kiel (2022) Crit Dec Emerg Med 36(7): 18
  3. Spangler and Tollefson (2014) in Herbert 14(6): 9-11

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Related Studies

Ontology: Fracture of patella (C0159849)

Concepts Injury or Poisoning (T037)
ICD9 822
ICD10 S82.0
SnomedCT 157237006, 208607004, 51037009
English Fracture of patella, NOS, fracture of patella (diagnosis), fracture of patella, Broken knee cap, Patella fracture, fracture patella, patella fracture, fracture patellar, Fracture;patella, fracture knee cap, fractures patellar, fracture knee-cap, fractures patella, patellar fracture, broken knee cap, knee-cap fracture, Fracture of patella, NOS (disorder), Fracture of patella, Fracture of knee-cap, Fracture of patella (disorder), fracture; knee cap, fracture; patella, knee cap; fracture, patella; fracture, fractured patella
Italian Frattura della rotula
Dutch breuk van knieschijf, gebroken knieschijf, fractuur; knieschijf, fractuur; patella, knieschijf; fractuur, patella; fractuur, Fractuur van patella, knieschijfbreuk
French Rotule cassée, Fracture de la rotule
German gebrochene Kniescheibe, Fraktur der Patella, Patellafraktur
Portuguese Rótula partida, Fractura da rótula
Spanish Rótula rota, fractura de la rótula, fractura rotuliana, SAI (trastorno), fractura de rótula (trastorno), fractura de rótula, fractura de la rótula (trastorno), fractura rotuliana, SAI, Fractura de rótula
Japanese 膝蓋骨骨折, シツガイコツコッセツ
Czech Zlomenina čéšky, Zlomenina pately
Korean 무릎뼈의 골절
Hungarian Patellatörés, Törött térdkalács