#punction

 A right doctor will recognize synovitis for knee joint as in first investigation as clinical picture is charactering. And knee joint is free for checking access and palpation and not hide behind massive soft tissues,as a hip joint.  As for diagnosis approving you are visiting for ultrasound test, MRT, CT, as these methods are right finding structure changing in joint tissue, define thickness and proliferation  for synovial membrane, as in a long chronic display having, to objective for enlarging a size for joint liquid and in not much abundant.

As importance here for diagnosis is joint punction and arthroscopic testing,as punction doing with a medic needle,which entering in joint cavity,and through a needle taking a joint liquid for testing a character for inflammation as serous, pus and bacteriologic analysis. As in norm a infection in a joint cavity is absences, joint liquid is sterility,thus and any microbes are meaning on the infection inflamation developing.And on  bacteriologic testing is a not just secreting and defining concrete agent and rating  his sensitiveness to antibiotics.