Selective muscle activation following electrical stimulation of the collateral ligaments of the human knee joint.

The objective of this study was to establish the presence of a local neurosensory reflex are from mechanoreceptors in human collateral ligaments and joint capsule to knee muscles and to determine if these muscles could be selectively activated as varus or valgus stabilizers using randomized trials. All studies were performed in the research department laboratories. Eleven subjects were recruited from the university staff and students based on no prior history of knee ailments. Subjects laid supine on an experimentation table as a current-modulated electrical stimulation was provided through the medial (MCL) or lateral collateral (LCL) knee ligaments. Latency of activation was measured for seven muscles, four by surface electrodes (semitendinosus, biceps femoris long head, vastus medialis, and lateralis), and three by intramuscular electrodes (sartorius, gracilis, tensor fascia lata). In the protocol, selective activation was defined as the relative increase in the activity of four muscles with medial moment arms following MCL stimulation compared with corresponding activity following LCL stimulation. For lateral muscles, the opposite was assumed (ie, that more activity would follow LCL than MCL stimulation). Monte Carlo simulations were performed on the data to determine significant selective muscle activation (p < .05). Statistically significant increases in activation were observed, most consistently, in the vastus medialis following MCL stimulation and in the vastus lateralis following LCL stimulation. These results suggest that a neurosensory reflex are from ligament mechanoreceptors may provide varus and valgus stabilization and knee muscles may be selectively activated to counter varus or valgus loads.