When is a swollen knee a surgical problem, and when is it a medical problem?
Hey, if it’s my knee, I’d rather not get it scoped unnecessarily.
A large effusion without clear evidence of internal derangement (meniscal tear, bone bruise/fracture, hyaline cartilage damage, or tendon/ligament tear) is like a stop sign.
Stop and think about the possibility of an infectious or inflammatory cause. Possibilities include Lyme disease, crystal arthropathy, and other arthropathies.
A large effusion with a small meniscal tear should still make you do a double take, because small meniscal tears by themselves should not give rise to large effusions.
Here is a patient with a large knee effusion:
The only other finding was a small lateral meniscal tear (not shown). The patient was scoped, confirming the small lateral meniscal tear. There was also extensive crystal disease, which was the real cause of the effusion.