Soleus Arthrogenic Muscle Response is Mediated by Pre- and Post- Synaptic Spinal Mechanisms

Abstract

1131 Knee joint effusion results in quadriceps inhibition and is accompanied by increased excitability in the soleus musculature. In order to develop an intervention that is successful in returning the musculature to its normal state we must understand what central mechanisms result in the soleus arthrogenic muscle response (AMR) seen following knee joint effusion. PURPOSE: To determine if soleus AMR is regulated by pre- or post-synaptic spinal mechanisms. METHODS: 10 healthy, physically active volunteers were admitted to the hospital on 2 separate occasions, during one admission subjects had their knees injected with 60mL of sterile saline and in the other admission they did not. Unconditioned and conditioned H-reflex amplitudes were elicited and recorded at 5 measurement intervals: baseline, post needle stick, post lidocaine, 25 minutes post effusion, and 45 minutes post effusion. Measures for the control condition were protocol matched to the effusion condition. Pre- and post-synaptic inhibition was calculated as the percent of the unconditioned reflex amplitude expressed as a percent change from the baseline value. A mixed effects model ANOVA for repeated measures was used for both dependent variables. RESULTS: The percent of the unconditioned reflex amplitude for recurrent inhibition (P< 0.0001) and reflex activation history (P< 0.0001) increased from baseline at 25 minutes and 45 minutes post effusion. No differences were noted at any time interval during the control admission (P > 0.05). CONCLUSION: Soleus AMR seen following knee joint effusion is mediated by both pre- and post-synaptic mechanisms. Supported in part by a grant from the National Institutes of Health to the University of Virginia General Clinical Research Center, number M01RR00847.