Diagnosis

Extraarticular avulsion fracture (AO/OTA 34A1)

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General considerations
Patellar fractures are some of the most difficult fractures to treat. The surgeon will often underestimate the complexity of the injury and will therefore not be prepared for a very challenging osteosynthesis. The articular injury is usually much more severe than predicted from the radiographs. In addition, multiple small articular fragments may be difficult to bring together. Patellar fractures are important for two reasons: 

  1. they generally disrupt the extensor mechanism and
  2. they are associated with a significant articular injury to the patellofemoral joint

 

Clinical examination: straight leg raise test
Injury to the patella may disrupt the extensor apparatus of the knee and the patient may be unable to perform an active straight leg raise. Untreated, displaced patellar fractures may lead to marked difficulty with normal gait. If there is clinical uncertainly about the correct diagnosis of disruption of the extensor apparatus of the knee, an ultrasound scan, or MRI, of the extensor apparatus, including the quadriceps tendon and patellar tendon should be obtained, in order to elucidate the correct diagnosis.

Extraarticular avulsion fracture 

Extraarticular avulsion fractures generally occur in adolescents, or young adults. They may be due to hyperflexion of the knee.

These are classified by AO/OTA as 34A1.

Occasionally a thin shell of bone may be avulsed from the distal patella together with the patellar tendon (“sleeve” fracture). This may be subtle on the radiographs. A clue to the injury may be found by detection of a high-riding patella (see Insall-Salvati index ).