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Timing of knee swelling after injury

Last reviewed dd mmm yyyy. Last edited dd mmm yyyy

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Swelling of the knee is a common symptom. In patients following trauma, care should be taken to establish the time course of the swelling, as this helps to distinguish between a haemarthrosis and a post-traumatic effusion.

knee swelling after injury - was there swelling and how quickly did this occur?

  • an effusion that develops rapidly within a few hours, most likely indicates an haemarthrosis
    • source of bleeding may be from vessels in a ruptured cruciate ligament or fracture of bone within the joint capsule. In the latter scenario, a lipo-haemarthrosis may be seen on a supine lateral plain radiograph

  • an effusion developing more slowly or the following day is more likely to be a traumatic synovitis associated with meniscal tears and chondral pathology

  • assessment based on age of patient and chronicity of effusion:
    • if an acute effusion
      • if traumatic injury in young patient then most commonly is an anterior cruciate ligament tear, followed by meniscal tears and patellar subluxations
      • if traumatic injury in older patients then the causes include meniscal tears, tibial plateau fractures, aggravations of underlying arthritic processes, or ligament injuries

If a chronic effusion

  • in chronic effusions (including those with obvious trauma present) causes include an underlying osteoarthritic process, inflammatory process, infection, or tumour
  • joint warmth or redness may be indicative of an infection or an inflammatory process
    • aspiration of the affected knee may be indicated to evaluate the synovial fluid
  • bloody chronic effusions are more consistent with trauma or tumour (pigmented villonodular synovitis)
  • Baker's cyst may indicate swelling elsewhere within the joint and that this fluid has leaked out posteriorly in the knee in the space between the direct arm of the semimembranosus tendon and the medial head of the gastrocnemius tendon.


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