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 n eurosensory reflex are from mechanoreceptors in human collateral ligam ents and joint capsule to knee muscles and to determine if these muscl es could be selectively activated as varus or valgus stabilizers using randomized trials. All studies were performed in the research departm ent laboratories. Eleven subjects were recruited from the university s taff and students based on no prior history of knee ailments. Subjects laid supine on an experimentation table as a current-modulated electr ical stimulation was provided through the medial (MCL) or lateral coll ateral (LCL) knee ligaments. Latency of activation was measured for se ven muscles, four by surface electrodes (semitendinosus, biceps femori s long head, vastus medialis, and lateralis), and three by intramuscul ar electrodes (sartorius, gracilis, tenser fascia lata), In the protoc ol, selective activation was defined as the relative increase in the a ctivity of four muscles with medial moment arms following MCL stimulat ion compared with corresponding activity following LCL stimulation. Fo r lateral muscles, the opposite was assumed the, that more activity wo uld follow LCL than MCL stimulation). Monte Carlo simulations were per formed on the data to determine significant selective muscle activatio n (p < .05). Statistically significant increases in activation were ob served, most consistently, in the vastus medialis following MCL stimul ation and in the vastus lateralis following LCL stimulation. These res ults suggest that a neurosensory reflex are from ligament mechanorecep tors may provide varus and valgus stabilization and knee muscles may b e selectively activated to counter varus or valgus loads. (C) 1995 by the American Congress of Rehabilitation Medicine and the American Acad emy of Physical Medicine and Rehabilitation