An experimental knee joint effusion does not affect plasma catecholamine concentration in humans.

Knee joint effusion causes quadriceps inhibition and is accompanied by increased soleus muscle excitability. In order to reverse the neurological alterations that occur to the musculature following effusion, we need to understand the extent of neural involvement. Ten healthy adults were tested on two occasions; during one session, subjects had their knees injected with saline and in the other admission, they did not. Soleus Hmax, Mmax, plasma epinephrine, and norepinephrine concentrations were obtained at five intervals. Results showed that Hmax increased following the effusion, while norepinephrine and epinephrine levels were not altered. We suggest that the soleus facilitation seen following knee effusion results from stimulation of joint mechanoreceptors and removal of descending spinal and supraspinal inhibition and is not the result of a sympathetic response.