Patellar Fractures

Key Points:

  • Osseous patellar fractures are generally caused by direct blows, and are treated similar to adult patella fractures
  • Patellar sleeve fractures are generally caused by indirect mechanisms, and one needs a high level of suspicion to diagnose these injuries
  • Although only a small bony fragment is seen in patellar sleeve fractures, a significant cartilaginous component exists and operative fixation is generally recommended

Description:

The patella is the largest sesamoid in the body. Ossification typically begins by age 6 and continues into the second decade. Patella fractures are relatively rare. Osseous fractures caused by a direct blow typically result in adult type vertical or transverse fractures. Indirect fractures occur as a result of a forceful quadriceps contraction, and in skeletally immature patients, generally lead to patella sleeve fractures in which a small osseous fragment and sleeve of periosteum/perichondrium and cartilage is disrupted from the osseous patella.(Houghton 1979)

Epidemiology:

Patella sleeve fractures are most common in children aged 8-16 years, and are more likely to occur during adolescence. More than half of patella fractures in skeletally immature patients are patella sleeve fractures. (Hunt 2005) 

Clinical Findings:

Osseous fractures present with a knee effusion, point tenderness at the fracture site, and the inability to extend the knee fully without pain. Patella alta is frequently present as well. 

Imaging Studies:

AP/lateral radiographs demonstrate the fracture configuration. CT and MRI are generally not required, but may be useful in planning surgery for comminuted fractures or to detect osteochondral fragments. 

Etiology:

Treatment:

Treatment principles are similar to management of these fractures in adults. Fractures that are displaced require open (operative) management to restore function of the extensor mechanism.

 
14 yo fell onto knee one month prior to these Xrays


6 months after open reduction and internal fixation

 

Complications:

Patella Sleeve Fractures:

Clinical Findings 

Patients with patella sleeve fractures present with a hemarthrosis, the inability to extend the knee and bear weight, and either patella alta (inferior sleeve) or patella baja (superior sleeve). These fractures occur without an antecedent direct blow to the patella. A palpable defect is often present superior or inferior to the patella. With minimal displacement of the fracture, diagnosis may be difficult as patients may be able to extend their knee without an extension lag with internal rotation of the limb and utilization of the tensor fascia lata. (Hunt 2005) 

Imaging 

AP/lateral radiographs can be difficult to interpret if the reader does not actively look for a patellar sleeve, as the bony component of the fracture may be very small. As such, a high index of suspicion must be maintained by the examiner when evaluating patients in this population.  Significant patella alta or baja should prompt increased scrutiny of the radiographs. A slight anterior tilt of the superior pole of the patella can be present with superior pole sleeve fractures. (Maripuri 2008, Gettys 2010) Ultrasound and MRI imaging  may be useful to confirm the injury in unclear cases. Inferior pole fractures can be confused with Sinding Larsen Johanson disorder. (Grogen 1990) 

Classification 

Sleeve fractures can be classified by the direction of force acting on the patella into medial, lateral, superior and inferior. Inferior pole fractures are most common. (Grogen 1990) 

Treatment 

Displaced sleeve fractures have cartilaginous components which greatly exceed the small bony components seen on radiographs, and require open reduction and internal fixation with suture. Superior sleeve fractures require repair of the quadriceps tendon avulsion. Inferior sleeve fractures require repair of the patella tendon avulsion. Immobilization in a brace or cast is required post operatively. Non-operative management can be considered in non-displaced fractures (2mm or less), particularly if active knee extension is intact. 

Complications 

Complications related to both osseous and sleeve fractures include malunion, nonunion, an extension lag, arthrofibrosis, and painful implants. 

References:

  1. Gettys FK, Morgan RJ, Fleischli JE. Superior Pole Sleeve Fracture of the Patella. Am J Sports Med 38(11):2331-2336, 2010.
  2. Grogen DP, Carey TP, Leffers D, Ogden JA. Avulsion Fractures of the Patella. J Pediatr Orthoped 10: 721-730, 1990.
  3. Houghton GR, Ackroyd CE. Sleeve fractures of the patella in children. J Bone Joint Surg Br 61:165-168, 1979.
  4. Hunt DM, Somashekar N. A review of sleeve fractures of the patella in children. The Knee 12:3-7, 2005. 
  5. Maripuri SN, Mehta H, Mohanty K. Sleeve fracture of the superior pole of the patella with an intra-articular dislocation: a case report. J Bone Joint Surg Am 90(2):385-389, 2008. 

Top Contributors:

Kevin H. Latz, M.D.