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Baker’s cyst: a lump behind the knee

Bakers cyst
  • A Bakers Cyst is a collection of fluid in a bulge in the joint capsule. It causes a lump behind the knee, although this is typically not visible.
  • The average size of a Baker’s cyst varies depending on the amount of fluid and how long the knee had been swollen.
  • The cause of a Baker’s cyst is a separate injury in the knee which is causing fluid to accumulate inside the joint. This can include osteoarthritis, meniscal tears or cartilage defects.
  • How long a Baker’s cyst lasts for depends on whether the underlying injury is still producing fluid. It’s worth noting that anti inflammatory medication will stop or reduce further fluid accumulation but won’t get rid of the existing fluid.
  • It causes localised pain behind the knee and restriction to movement with bending and straightening. It can feel like a muscle knot behind the knee.
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TIPS

  • Baker’s cyst management involve two approaches:
    • Reduce the amount of new fluid being added to the knee with ice or anti inflammatory-meds
    • Use a compressive neoprene brace with adjustable pressure, such as this one, to speed up resolution of existing swelling
  • Management guidelines include avoiding exercises involving compressive or twisting positions, such as crouching or pivoting, to reduce the pain and limit new fluid accumulating
  • Baker’s cyst rupture causes a sudden rush of fluid into the calf along with sudden pain and tightness.
    • This is often misdiagnosed as a calf tear. The ruptured cyst is usually not problematic and heals without intervention
  • It’s not critical to confirm a Baker’s cyst via ultrasound or MRI however it can be helpful for long term monitoring (see here for an MRI of a Baker’s cyst behind the knee)

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MYTHS

  • A compressive knee brace is only helpful when the level of fluid bulges past the bony edges of the joint. Otherwise it only exerts pressure on the bony bumps around the knee, not on the swelling
  • Draining a Baker’s cyst is not painful but it’s usually ineffective as the source of fluid in the knee remains and the fluid pressure rebuilds quickly
  • Stretching the muscles around the knee is counterproductive as, although the knee feels tight, stretching will increase the pressure inside the knee and aggravate the cyst
    • If the knee feels tight, gentle exercise like walking can help the Baker’s cyst