Muscle reflexes during gait elicited by electrical stimulation of the posterior cruciate ligament in humans

We investigated the influence of electrical stimulation of the posterior cruciate ligament (PCL) on the motoneuron pool of the thigh and calf muscle during gait. The study group comprised eight young men without any history of injury to the knee joints. Multistranded teflon-insulated stainless steel wires were inserted into the PCL guided by sonography and in four subjects also into the fat pad of the knee. The PCL was electrically stimulated during gait on a treadmill at heel strike and 100 ms after heel strike. Electromyographic signals were recorded with bipolar surface electrodes placed over the vastus medialis, rectus femoris, vastus lateralis, biceps femoris caput longum, and semitendinosus muscles. The stimuli consisted of four pulses delivered at 200 Hz; the stimulus amplitude was two to three times the sensory threshold. The electrical stimulation of the PCL inhibited the ongoing muscle activity in both the quadriceps and the hamstrings. The latency of the inhibition ranged between 78 and 148 ms in the quadriceps, between 88 and 110 ms in the hamstrings and between 189 and 258 ms in m. gastrocnemius. Stimulation of the fat pad of the knee did not influence the thigh and calf muscle motoneuron pool as evidenced by electromyography. The response elicited from the stimulation of the PCL was not limited to a specific muscle group but depended on ongoing muscle contraction, which suggests that the mechanoreceptors in the PCL are involved in the control of all muscles acting on the knee joint during gait.