Features

There will be either a history of

• a direct blow to the patella, or
• a fall, or a injury involving passive, forced flexion of the knee joint whilst the quadriceps muscles were contracted (1).

Fracture description should be done by

• fracture orientation and position - e.g. - transverse, inferior pole
• degree of comminution
• displacement (1)

In the paediatric population avulsion fractures (normally at the inferior pole of the patella) are often seen as patellar sleeve fractures while in the adults it is seen at the origin of the patella tendon and often results in disruption of the extensor mechanism (1).

Clinical examination may reveal:

• painful and swollen knee
• a gap between the fragments may be felt - in case of a transverse fracture
  • if a transverse fracture has occurred with a consequent gap between the fragments then the knee extension mechanism will not work.
• state of the extensor mechanism
  • to differentiate between disruption as opposed to pain-related guarding as the cause of the inability to extend the knee lidocaine could be injected to the knee (1)

Reference:

• (1) Scolaro J, Bernstein J, Ahn J. Patellar fractures. Clin Orthop Relat Res. 2011;469(4):1213-5.