Knee iSAWE 20

Question

A 15 year old basketball player has superolateral knee pain after a direct blow. The radiograph is shown.

Knee iSAWE 20, AP radiograph of the knee
AP radiograph of the knee. Image by Hellerhoff, Wikimedia Commons, CC BY-SA 3.0.
  1. What is the finding and how do you distinguish it from a fracture?
  2. Describe the classification.
  3. How is the painful lesion treated?

Answer

Finding

  • Separate ossicle at the superolateral pole of the patella
  • Bipartite patella, failed fusion of an accessory ossification centre
  • Present in about 2% and bilateral in about half
  • Smooth, well corticated edges distinguish it from a fracture
  • Image the opposite knee

Saupe classification

TypeLocationFrequency
IInferior poleAbout 5%
IILateral marginAbout 20%
IIISuperolateral poleAbout 75%

Treatment

  • Most are asymptomatic
  • Painful synchondrosis after trauma or overuse
  • Activity change, NSAIDs and physiotherapy
  • Brief immobilisation for acute pain
  • Excision of a small painful fragment
  • Lateral retinacular release of the vastus lateralis attachment
  • Fixation of a large fragment

Related pages

Author Contributions

Orthofracs team

Reviewed by Professor Phong Tran, Head of Orthopaedic Surgery, Western Health. Last updated 10 October 2026.