Immediate Effects of Low-Intensity Plantar Proprioceptive Stimulation of the Affected Limb on Stable Versus Unstable Surfaces on Modified Sit-to-Stand Time and Gait Following Total Knee Arthroplasty

Participants will perform low-intensity plantar proprioceptive stimulation while seated, with the operated foot placed on a balance pad. The intervention consists of repeated low-intensity pressing through the operated foot on an unstable surface.

Participants will perform low-intensity plantar proprioceptive stimulation while seated with the operated foot placed on a balance pad. They will apply low-intensity pressure through the operated foot for 5 seconds followed by 5 seconds of relaxation. The cycle will be repeated 12 times for approximately 2 minutes.

Participants will perform the same low-intensity plantar proprioceptive stimulation while seated, with the operated foot placed on a firm surface. The pressing procedure will be identical to that of the unstable-surface group except for the supporting surface.

Participants will perform the same low-intensity plantar proprioceptive stimulation while seated with the operated foot placed on a firm surface. They will apply low-intensity pressure through the operated foot for 5 seconds followed by 5 seconds of relaxation. The cycle will be repeated 12 times for approximately 2 minutes.

Time required to complete one modified sit-to-stand (mSTS) task will be measured in seconds. The task will be video-recorded using a smartphone at 60 frames per second and analyzed using Kinovea software. Time will be calculated from seat-off to attainment of a fully upright standing position. Participants will be allowed to use upper-extremity support as needed. Measurements will be performed before and immediately after the intervention. A shorter time indicates better sit-to-stand performance.

Pain intensity will be assessed using a 100-mm Visual Analog Scale (VAS), ranging from 0 mm (no pain) to 100 mm (worst imaginable pain). Participants will mark the point on the scale that best represents their current knee pain. The distance from the 0-mm anchor to the participant's mark will be measured in millimeters. Measurements will be performed before and immediately after the single-session intervention. A lower score indicates less pain.

Active knee flexion range of motion (AROM) of the operated limb will be measured in degrees using a standard goniometer with the participant in the supine position. Participants will be instructed to actively flex the operated knee as far as comfortably possible. Measurements will be performed before and immediately after the single-session intervention. A greater flexion angle indicates greater active knee flexion range of motion.

Walking performance will be assessed using the 4-Meter Walk Test (4MWT). Participants will be instructed to walk 4 meters at their usual comfortable walking speed. The time required to complete the 4-meter distance will be recorded in seconds. Participants may use their usual walking aid if required for safety. Measurements will be performed before and immediately after the single-session intervention. A shorter completion time indicates better walking performance.

Kinesiophobia will be assessed using the Tampa Scale for Kinesiophobia-11 (TSK-11), an 11-item self-reported questionnaire assessing fear of movement or reinjury. Each item is rated on a 4-point Likert scale. A higher total score indicates a greater level of kinesiophobia. The TSK-11 will be used as an exploratory psychological measure.