Stimulation of Peripheral Afferents to Reduce Muscle Inhibition at the Knee

Knee osteoarthritis affects more than 14 million adults in the United States and is a leading cause of disability. Its most disabling consequence is not joint degeneration alone but persistent quadriceps dysfunction. Afferent signals arising from the painful joint inhibit the descending motor drive that activates the muscle, so voluntary activation remains incomplete. Exercise therapy, the mainstay of care, therefore produces strength gains of only 10 to 20 percent against the 30 to 40 percent required for meaningful clinical benefit, and patients walk with rigid, co-contracted movement patterns that concentrate joint loading and accelerate degeneration. Existing interventions address either pain or motor retraining; none target the cortical circuits in which the two interact. This study tests whether paired-pulse electrical stimulation (ppES) of the tibial nerve can reduce that inhibition. ppES delivers two stimuli in rapid succession: the first activates sensory afferents projecting to the primary somatosensory cortex, and the second, delivered at a precisely timed interval, induces heterosynaptic depression of that transmission, in turn reducing sensory-driven inhibition of motor output. Applied at the tibial nerve, ppES acts on the sensorimotor integration that governs quadriceps activation during walking. Twenty adults with knee osteoarthritis will each complete two single-session visits separated by at least seven days, receiving active ppES at one visit and sham stimulation at the other in randomized order, with participants and outcome assessors blinded. At each visit, before intervention and again immediately and 30 minutes afterward, we will measure short-latency afferent inhibition of the quadriceps motor pathway and quadriceps-hamstrings co-contraction during treadmill walking, the two primary outcomes. Somatosensory evoked potentials and modular organization of gait will be measured as secondary outcomes. Aim 1 will determine whether ppES reduces sensorimotor inhibition and co-contraction relative to sham. Aim 2 will determine whether baseline pain sensitization, cortical sensory processing, and sensorimotor inhibition predict the magnitude and variability of individual response. Establishing that this circuit is modifiable would identify a rehabilitation target that current care does not address and would provide the mechanistic evidence and effect-size estimates required for a trial of ppES as an adjunct to exercise.