Effect of knee joint effusion on quadriceps and soleus motoneuron pool excitability

Purpose: To examine changes in quadriceps and soleus MN pool activity resul ting from knee joint effusion over a 4-h period and assess the relationship between the muscles. Methods: A repeated measures before-after trial desig n was used for this study. Eight, neurologically sound Volunteers (age 23.3 +/- 2.1 yr, height 171.8 +/- 15.9 cm, mass 65.5 +/- 17.7 kg) participated in this study. An area superomedial to the patella was cleaned and anesthet ized, and 30 mt of sterile saline was injected into the knee joint capsule to mimic mechanical joint effusion. The Hoffman reflex CH-reflex) was elici ted by applying a percutaneous stimulus to the appropriate nerve and record ing the response through surface electromyography. Soleus and vastus medial is H-reflex measures were collected from each volunteer before, at 30 min, 90 min, 150 min, and 210 min intervals over a 4-h period after knee effusio n. Results: All soleus H-reflex measures after effusion (30 min 5.89 +/- 0. 92 V; 90 min 6.16 +/- 0.48 V; 150 min 6.59 +/- 0.50 V; 210 min 6.70 +/- 0.5 6 V) were increased in relation to the preeffusion measure (5.01 +/- 0.79 V ). All vastus medialis H-reflex measures after effusion (30 min 4.23 +/- 0. 94 V; 90 min 4.15 +/- 1.11 V; 150 min 4.16 +/- 0.57 V; and 210 min 4.99 +/- 1.23) were decreased in relation to the preeffusion measure (5.88 +/- 1.44 VI P less than or equal to 0.05). Conclusions: Afferent activity from the knee joint capsule resulted in an inhibitory effect on the vastus medialis and a facilitatory effect on the soleus. Facilitation of the soleus in coop eration with other lower extremity musculature could be a mechanism for com pensation of the inhibited quadriceps to maintain lower kinetic chain funct ion.