Total knee arthroplasty (TKA) is a widely performed surgical procedure for patients with severe knee osteoarthritis. Following TKA, changes in lower extremity alignment and gait mechanics may influence the spinopelvic sagittal alignment, and postoperative rehabilitation programs traditionally focus on the knee joint without addressing the lumbopelvic chain.

This study aims to investigate whether adding paraspinal neuromuscular electrical stimulation (NMES) to a standard postoperative rehabilitation program (which includes quadriceps NMES) affects spinopelvic sagittal alignment parameters in patients undergoing TKA for primary knee osteoarthritis, compared with standard rehabilitation and quadriceps NMES alone.

In this single-center, prospective, randomized, single-blind (outcome assessor-blinded) controlled trial, eligible participants aged 40-80 years with primary knee osteoarthritis scheduled for TKA and with measurable spinopelvic malalignment will be randomly assigned in a 1:1 ratio to receive either standard rehabilitation with quadriceps NMES plus paraspinal NMES (intervention group) or standard rehabilitation with quadriceps NMES alone (control group) for 4 weeks (20 sessions).

The primary outcome is the change in radiographic spinopelvic parameters - including pelvic tilt, sacral slope, pelvic incidence, lumbar lordosis, sagittal vertical axis, and spinosacral angle - measured on standing lateral whole-spine radiographs at baseline (preoperative), before rehabilitation, after the 4-week intervention, and at 6-month follow-up. Secondary outcomes include knee and back pain (VAS), functional and quality-of-life measures (WOMAC, Knee Society Score, Forgotten Joint Score, Oswestry Disability Index, Nottingham Health Profile), performance-based tests (Timed Up and Go, 6-Minute Walk Test), and knee range of motion.

The investigators hypothesize that adding paraspinal NMES to standard rehabilitation will result in greater improvement in spinopelvic alignment parameters, and potentially in clinical/functional outcomes, compared with standard rehabilitation alone.