Inhibition of dynamic thigh muscle contraction by electrical stimulation of the posterior cruciate ligament in humans

We investigated the influence of electrical stimulation of the posterior cr uciate ligament (PCL) on the motoneuron pool of the thigh muscle during vol untary static and dynamic muscle contraction. The study group comprised nin e young men with no history of injury to the knee joints. Multistranded Tef lon-insulated stainless-steel wires were inserted into the PCL guided by ul trasound. In three subjects wires were also inserted into the fat pad of th e knee. The PCL was electrically stimulated during static, concentric, or e ccentric muscle contraction with a constant load of 20% of the maximal volu ntary contraction of either the quadriceps or the hamstrings. Electromyogra phic signals were recorded with bipolar surface electrodes placed over the vastus medialis, rectus femoris, vastus lateralis, biceps femoris caput lon gum, and semitendinosus muscles. The stimuli consisted of four pulses deliv ered at 200 Hz; the stimulus amplitude was two to three times the sensory t hreshold. The electrical stimulation of the PCL inhibited the ongoing muscl e activity in both the quadriceps and hamstrings with latencies of 114-150 ms and 99-130 ms, respectively. Stimulation of the fat pad of the knee did not influence the muscle activity. The study suggests that the mechanorecep tors in the PCL are involved in controlling muscle activity during both sta tic and active muscle contractions. The relative long latency of the reflex makes it unlikely that it can serve as a directly protective reflex for th e cruciate ligaments. (C) 2001 John Wiley & Sons, Inc.