Patellar Fracture

Ovid: 5-Minute Orthopaedic Consult

Editors: Frassica, Frank J.; Sponseller, Paul D.; Wilckens, John H.
Title: 5-Minute Orthopaedic Consult, 2nd Edition
> Table of Contents > Patellar Fracture

Patellar Fracture
John H. Wilckens MD
  • Fracture of the patella (knee cap)
  • Loss of extensor mechanism
  • Classification: by pattern of fracture (1):
    • Vertical
    • Transverse
    • Stellate
    • Polar
  • In children, the most common fracture pattern is the “sleeve” fracture (2).
    • The sleeve of periosteum is pulled off the bone.
    • Radiographs reveal patella alta, and the injury may be missed.
Affects all ages and both genders
1% of all fractures (3)
Risk Factors
  • Blunt trauma
  • Dashboard injury
  • ACL reconstruction with patellar graft (4)
  • Direct blow to the patella of a flexed knee, as occurs during a traffic accident in which the flexed knee hits the dashboard
  • The exact angle of the applied force directly influences the pattern of injury to the patella (5).
  • Sudden powerful quadriceps muscle eccentric contracture
  • Fractures may happen after knee replacement secondary to osteolysis of the bone or direct trauma (6).
Associated Conditions
  • Femoral shaft fracture
  • Knee ligament injury
Signs and Symptoms
  • Acute knee pain and swelling after trauma
  • Inability to extend or straighten the injured knee
Physical Exam
  • Localized pain or swelling in the injured knee
  • Patient inability to perform a straight-leg raise
  • Visible or palpable defect of the extensor mechanism
  • Radiography:
    • AP and lateral views
    • Axial and tangential (“sunrise”) views are helpful with longitudinal fractures.
  • CT/MRI are rarely indicated for isolated patellar fractures.
Pathological Findings
  • Hemarthrosis
  • Interruption of extensor mechanism
Differential Diagnosis
  • Distal femoral or tibial plateau fracture
  • Collateral ligament tear
  • OSD tear
  • Quadriceps tendon or patellar ligament rupture
General Measures
  • Nondisplaced fractures:
    • Only patellar fractures amenable to nonoperative treatment (casting or splinting the knee in full extension)
    • Close follow-up is required because nondisplaced fractures may displace.
  • Displaced fractures:
    • Best managed with open reduction and internal fixation:
      • Allows for anatomic reduction
      • Allows early ROM and reduced immobilization
Special Therapy
Physical Therapy
  • Nonsurgical patients may bear weight as tolerated in the cast or splint.
  • Patients may resume active ROM exercises once the cast is removed.
First Line
  • Acetaminophen
  • NSAIDs after 6 weeks (healed fracture)
Second Line
Surgery (7)
  • All displaced fractures should undergo open reduction and internal fixation.
    • Parallel Kirschner wires with tension band wiring is adequate for most transverse fractures (8).
    • Tension band wiring also can be accomplished using parallel cannulated screws (9).
  • Stellate fractures may require additional cerclage wiring.
  • Distal pole fractures can be excised, and the patellar tendon can be repaired to the proximal fragment (10).
  • Patellectomy is used only for the most comminuted fractures that cannot be stabilized.


  • Nondisplaced patellar fractures have a good prognosis with nonoperative treatment.
  • Well-aligned and stabilized fractures have a good prognosis.
  • Even in elderly patients, surgery gives better results than nonsurgical treatment of displaced fractures (11).
  • Open fractures should be managed with débridement and fixation, with an attempt to preserve as much bone as possible (12).
  • Fracture nonunion/malunion (13)
  • Refracture
  • Need for hardware removal (14)
  • Arthritis
  • Extensor mechanism weakness:
    • As comminution and loss of articular
      surface of the patella increase and as more of the patella is excised,
      extensor mechanism strength decreases.
Patient Monitoring
Serial radiographs are obtained at 4-week intervals until healing.
1. Carpenter JE, Kasman R, Matthews LS. Fractures of the patella. J Bone Joint Surg 1993;75A: 1550–1561.
2. Hunt DM, Somashekar N. A review of sleeve fractures of the patella in children. Knee 2005; 12:3–7.
3. Bostrom A. Fracture of the patella. A study of 422 patellar fractures. Acta Orthop Scand Suppl 1972;143:1–80.
4. Stein
DA, Hunt SA, Rosen JE, et al. The incidence and outcome of patella
fractures after anterior cruciate ligament reconstruction. Arthroscopy 2002;18:578–583.
5. Atkinson PJ, Haut RC. Injuries produced by blunt trauma to the human patellofemoral joint vary with flexion angle of the knee. J Orthop Res 2001;19:827–833.
6. Ortiguera CJ, Berry DJ. Patellar fracture after total knee arthroplasty. J Bone Joint Surg 2002;84A: 532–540.
7. Cramer KE, Moed BR. Patellar fractures: contemporary approach to treatment. J Am Acad Orthop Surg 1997;5:323–331.
8. Chen
A, Hou C, Bao J, et al. Comparison of biodegradable and metallic
tension-band fixation for patella fractures. 38 patients followed for 2
years. Acta Orthop Scand 1998;69:39–42.
9. Berg
EE. Open reduction internal fixation of displaced transverse patella
fractures with figure-eight wiring through parallel cannulated
compression screws. J Orthop Trauma 1997;11: 573–576.
10. Kastelec M, Veselko M. Inferior patellar pole avulsion fractures: osteosynthesis compared with pole resection. J Bone Joint Surg 2004;86A: 696–701.
11. Shabat S, Mann G, Kish B, et al. Functional results after patellar fractures in elderly patients. Arch Gerontol Geriatr 2003;37:93–98.
12. Catalano JB, Iannacone WM, Marczyk S, et al. Open fractures of the patella: long-term functional outcome. J Trauma 1995;39:439–444.
13. Klassen JF, Trousdale RT. Treatment of delayed and nonunion of the patella. J Orthop Trauma 1997;11:188–194.
14. Smith ST, Cramer KE, Karges DE, et al. Early complications in the operative treatment of patella fractures. J Orthop Trauma 1997;11: 183–187.
822.2 Patellar fracture
Patient Teaching
  • Injury to the cartilage and bone is typical in patellar fractures.
  • The risk of future knee pain and arthritis exists.
  • Full recovery can take up to 1 year.
Q: How soon can a patient walk after open reduction and internal fixation of the patella?
If the fracture is well reduced and stabilized, the patient can begin
weightbearing as tolerated with the leg locked straight. The patient
also may begin early ROM.
Q: Does the hardware (screws, pins, and wires) need to be removed after fracture healing?
If the hardware is asymptomatic, it usually does not need to be
removed. However, because little soft tissue covers the patella, the
hardware usually irritates the quadriceps and patellar tendons and
should be removed.

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