Thanks for the query to H.C.M. Forum.
Any way I will not say any thing about chiropractor .
The swelling behind ( posterior ) knee joint may be due to osteoarthritis
,the most probable cause .
2nd reason may be tuberculosis
of this joint .
In both situation you should get in X RAY
of effected part with C T scan .
After this consult an Orthopaedician and get his opinion and treatment .
Once , if due to negligent conduct synovial fluid
get infection then condition will worse, so in my opinion take a proper and scientifically proven treatment .