Robot-Aided Off-Axis Neuromuscular Training for Knee OA

Although the primary knee motion occurs in flexion/extension, the frontal and transverse (off-axis) knee motions are smaller but crucial for maintaining joint stability and normal knee loading. Altered kinematics and neuromuscular control in off-axis knee motions have been reported in patients with knee osteoarthritis (OA), which are associated with excessive knee loading and the progression of knee OA. However, traditional rehabilitative treatments for people with knee OA and existing exercise equipment often focus on sagittal plane movement. Probably due to the technical limitations, there is a lack of convenient and effective equipment/method to train patients with knee OA in off-axis (frontal and transverse) planes. The purpose of this study is to use a robot-aided elliptical training device to measure knee neuromechanical properties and to improve neuromuscular control in off-axis knee motions, aiming for joint de-loading and pain reduction for individuals with knee OA.

The device used in this study is provided by Rehabtek LLC, which has received U.S. federal grants to develop and commercialize this device. Eligible knee osteoarthritis (OA) patients will be randomly assigned to three groups: (A) evaluation-based, progressive, neuromuscular training group; (B) traditional regular stepping group. Participants in both groups will undergo 3 assessments. Once the participants have consented, the first assessment visit will be scheduled before the training, which includes the neuromechanical and clinical assessments: 1. The neuromechanical assessments involve the off-axis knee moments and instability during the free-speed stepping and fast stepping tasks on the elliptical machine to see which off-axis directions (knee valgus, varus, internal rotation, and/or external rotation) or combination of directions show excessive moments. Off-axis instability, muscle strength, range of motion, stiffness, proprioception acuity, and knee moments during stepping will also be evaluated. A. Knee frontal-plane neuromechanical properties. * The participants sit with their knees in 0 degrees flexion. A fixture is used to hold the thigh near the femoral condyles steadily. The footplate is moved by a linear motor mediolaterally in the frontal plane, a 6-axis force sensor underneath the footplate, and a 6-DOF(degree of freedom) goniometer on the knee is used to measure knee motions. With the knee joint perturbed in varus-valgus motion, varus-valgus angle and torque can be determined. * With the participants in the seated position and relaxed, the participants' knee varus-valgus laxity and passive range of motion (ROM) will be determined when a specific passive resistance torque is reached at varus or valgus direction. * Knee varus-valgus proprioceptive acuity is measured by the threshold to detection of a passive movement in the respective varus and valgus directions. From the neutral position, the knee is randomly moved into either varus or valgus direction by the linear motor at a constant, slow speed. The blindfolded participant is instructed to push a trigger and report the direction of motion when he/she first sense which direction the knee is moving into. The motor stops the movement once the trigger is activated. Each participant completes 8 trials without complaints of pain or discomfort. * Tibial varus-valgus pain threshold is measured by the threshold to feel pain in the respective tibial varus-valgus directions. While the participant is seated relaxed, the footplate moves in varus-valgus direction. This movement occurs at a constant speed. The participant is asked to push a trigger and report the direction of pain when he/she first senses and the motor would stop and move back to the initial position. * For the active muscular contribution to varus-valgus stiffness, with the subject seated at 0 deg knee flexion, participants' ability to actively stabilize the lower leg against perturbations in varus-valgu trial.show_full_description

Inclusion Criteria: * Age 45 - 85 years. * Meets the ACR classification criteria for knee OA (clinical + radiographic criteria); Kellgren-Lawrence grade I-III. * Persistent knee pain ≥ 3 months. * Able to independently complete elliptical training (6 minutes without interruption). Exclusion Criteria: * Other inflammatory joint diseases (e.g., rheumatoid arthritis). * Knee trauma, surgery, or intra-articular injections within the past year. * History of knee or hip replacement. * Cardiovascular disease or uncontrolled hypertension contradict to exercises. * Cognitive impairment (Montreal cognitive assessment \< 22). * Currently participating in another interventional study for the lower limb. * Neurological impairment (e.g., stroke, Parkinson's disease, radicular pain).