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Patellar Fracture

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Other Names

  • Patella Fracture
  • Knee Cap Fracture
  • Patella sleeve fracture
  • Bipartite Patella
  • Tripartite Patella


  • This page refers to fractures of the Patella



  • Represents ~1% of all fractures (need citation)
  • Most commonly occur in ages 20 to 50 years[1]
  • Incidence in men is twice that of women[2]
  • Majority are closed, up to 7% are open
  • Periprosthetic fractures are a known complication of total knee arthroplasty[3]
    • incidence of 0.68% in unresurfaced patellae and up to 21% resurfaced patellae


Lateral radiograph of the with a mid body patella fracture. Note the two fragments are being pulled proximally and distally by their respective tendons.[4]
  • Fracture Patterns
    • Simple 2-part caused by direct blow is most common
  • The majority of patellar fractures are closed


  • Majority of cases due to direct trauma to flexed knee[5]
    • MVC represent 78.3% of cases
    • Work-related 13.7%
    • Domestic accidents 11.4%
    • Sports related fractures are uncommon
  • Indirect injury
    • Rapid knee flexion against contracted quad muscle leads to eccentric contraction, failure
    • In pediatrics, can see patellar sleeve fracture

Associated Injuries


Risk Factors

  • Unknown

Differential Diagnosis

Clinical Features

  • History
    • Some traumatic mechanism should be apparent
    • Patient will endorse knee pain
    • Painful knee extension and possibly inability to extend
  • Physical Exam: Physical Exam Knee
    • Inspection will likely reveal significant swelling and joint effusion, be sure to note any skin abrasions
    • There may be an obvious defect depending on the fracture pattern
    • The distal and proximal fragments may be seperated
    • There is typically a palpable defect on the bone
    • Inability to actively extend knee
  • Special Tests


This AP view shows a well rounded, corticated bony fragment in the superlateral patella, aka a bipartite patella[7]


  • Standard Radiographs Knee
    • Typically sufficient to identify injury
    • AP, Lateral, Sunrise
  • Findings
    • Lateral is best view for transverse
    • Sunrise is best for vertical fracture
    • If patella baja or alta is present, consider quadriceps or patellar tendon rupture
  • Bipartite Patella
    • Can be mistaken for fracture
    • Most individuals have 1 ossification center, however up to 23% have accessory ossification center(s)
    • Bipartate patella represents failure of second ossification center to fuse
    • Typically seen in superolateral position
    • Occurs in about 2% of individuals, and 50% of patients are bilateral
    • Tripartite Patella similarly, failure of 2 accessory ossification centers to fuse


  • Indicated for surgical decision making in unclear or complex fracture patterns
  • May be helpful for stress fracture, nonunion or malunion


  • Indicated if soft tissue injuries are suspected
  • In children, can be used instead of CT


AO/ASIF Classification

  • Extra-articular
    • 34-A1: Avulsion
    • 34-A2: Isolated body
  • Partial articular
    • 34-B1: vertical, lateral
    • 34-B2: vertical, medial
  • Complete articular
    • 34-C1: transverse
    • 34-C2: transverse plus second fragment
    • 34-C3: complex



  • Goals of treatment
    • Maintain extensor mechanism
    • Maintain anatomic alignment of patellofemoral articulation
  • Overall paucity of data on outcomes
    • Most experts agree non- or minimally displaced transverse fractures managed conservatively have the best outcomes
  • Comminuted fractures have thw worst outcomes
    • 30-50% suffer from persistent anterior knee pain, 15-30% from functional impairment[8]
  • Lazaro et al study of 30 patients who underwent ORIF of patella fracture[9]
    • 80% of patients reported persistent anterior knee pain
    • Despite radiographic healing, near anatomic reduction, reliable reconstruction of extensor mechanism and physical therapy
  • LeBrun et al studied long term surgical outcomes at median of 6.5 years[10]
    • 52% of patients required hardware removal, 28% reported implant-related pain
    • 15% of patients lacked 5° of extension, 38% of patients lacked some flexion
    • Mean extension deficit of 26%, loss of power was 30%


  • Indications
    • Only if the extensor mechanism is intact (can perform straight leg raise)
    • Typically includes stable, non-displaced fractures
    • Vertical fracture patterns
  • Stress views
    • Consider stressing under 60° of flexion to confirm stability
  • Immobilization
  • Early mobility
    • Start at 2-3 weeks, allow up to 40° flexion
  • Early weight bearing in full extension


  • Indications
    • Preserve patella whenever possible
    • Extensor mechanism failure (unable to perform straight leg raise)
    • Open fractures
    • Fracture articular displacement >2 mm
    • Displaced patella fracture >3 mm
    • Patella sleeve fractures in children
  • Technique
    • ORIF with tension band construction
    • Partial Patellectomy (only if ORIF not possible)
    • Total patellectomy (rare)

Rehab and Return to Play


  • Needs to be updated

Return to Play

  • Needs to be updated


  • Loss of extensor mechanism
  • Anterior knee pain
  • Symptomatic hardware (up to 50%)
  • Hardware Migration
  • Hardware failure
  • Weakness
  • Loss of reduction (22%)
  • Nonunion (<5%)
  • Osteonecrosis
  • Infection
  • Stiffness
  • Patellofemoral Pain Syndrome
  • Nonoperative risks
    • Loss of full extension due to non-union
    • Stiffness
    • Incongruity of patellofemoral articulation

See Also


  1. Wild, M., J. Windolf, and S. Flohé. "Patellafrakturen." Der Unfallchirurg 113.5 (2010): 401-412.
  2. Boström A. Fracture of the patella. A study of 422 patellar fractures. Acta Orthop Scand Suppl. 1972;143:1–80
  3. Märdian S, Wichlas F, Schaser KD, Matziolis G, Füchtmeier B, Perka C, Schwabe P. Periprosthetic fractures around the knee: update on therapeutic algorithms for internal fixation and revision arthroplasty. Acta Chir Orthop Traumatol Cech. 2012;79(4):297–306.
  4. Case courtesy of Dr Jeremy Jones, Radiopaedia.org, rID: 6461
  5. Nummi J. Fracture of the patella. A clinical study of 707 patellar fractures. Ann Chir Gynaecol Fenn Suppl. 1971;179:1–85.
  6. Catalano JB, Iannacone WM, Marczyk S, Dalsey RM, Deutsch LS, Born CT, Delong WG. Open fractures of the patella: long-term functional outcome. J Trauma. 1995 Sep;39(3):439–444.
  7. Case courtesy of Dr Mostafa El-Feky, Radiopaedia.org, rID: 22347
  8. Levack B, Flannagan JP, Hobbs S. Results of surgical treatment of patellar fractures. J Bone Joint Surg Br. 1985 May;67(3):416–419.
  9. Lazaro LE, Wellman DS, Sauro G, Pardee NC, Berkes MB, Little MT, Nguyen JT, Helfet DL, Lorich DG. Outcomes after operative fixation of complete articular patellar fractures: assessment of functional impairment. J Bone Joint Surg Am. 2013 Jul;95(14):e96
  10. LeBrun CT, Langford JR, Sagi HC. Functional outcomes after operatively treated patella fractures. J Orthop Trauma. 2012 Jul;26(7):422–426.
Created by:
John Kiel on 7 July 2019 06:17:40
Last edited:
4 October 2022 15:44:16
Knee | Lower Extremity | Trauma | Fractures | Acute