This randomized, double-blind clinical trial aims to evaluate the effect of high-intensity pulsed electromagnetic field therapy (HI-PEMF) applied either exclusively on the knee joint or bimodally on the knee and quadriceps, in older adults with knee osteoarthritis. Both groups will also receive a structured home-based exercise program. The primary outcome is pain reduction, and secondary outcomes include functional performance.

Knee osteoarthritis (OA) is a highly prevalent and disabling condition in older adults. It often coexists with quadriceps muscle weakness, sarcopenia, and frailty, all of which contribute to pain, functional decline, and loss of independence. Pulsed electromagnetic field therapy (PEMF) has emerged as a non-invasive alternative for pain relief in OA, with growing interest in its application at both articular and muscular levels.

High-intensity pulsed electromagnetic field (HI-PEMF) therapy-also known as the super inductive system-generates magnetic fields up to 2.5 Tesla, capable of stimulating both joint structures and skeletal muscle via deep tissue electric induction. HI-PEMF has shown promising results for pain reduction, anti-inflammatory modulation, and muscle bioactivation, particularly when applied over the quadriceps.

This randomized, double-blind, parallel-assignment clinical trial aims to compare the effects of two HI-PEMF treatment modalities in older adults with moderate to severe knee OA (Kellgren-Lawrence grade II-IV):

• Group A: HI-PEMF applied exclusively over the symptomatic knee.
• Group 2: HI-PEMF applied both over the knee and the quadriceps (bimodal). Both groups will also perform a standardized home-based strengthening and mobility exercise program.

A total of 64 participants (32 per group) will receive 9 sessions of HI-PEMF (2 per week for 5 weeks), using the BTL-6000 Super Inductive System. Outcomes will be assessed at baseline and post-intervention. The primary outcome is change in pain intensity using the Numeric Analog Scale (NAS). Secondary outcomes include functional tests (Timed Up and Go and 5-times Sit-to-Stand), and paracetamol use. Exploratory subgroup analyses will assess associations with frailty status (FRAIL), probable sarcopenia (SARC-F), and radiological OA grade.

This study seeks to generate evidence on the potential synergistic benefits of combining articular and muscular HI-PEMF therapy in geriatric rehabilitation. It is designed for implementation in a public hospital setting in Mexico, with minimal risk and high feasibility. All procedures follow ethical guidelines and have received institutional review board approval.

Inclusion Criteria:

• Age ≥ 60
• Clinical and radiological diagnosis of knee OA grade I-IV
• Pain ≥ 3 on Numeric Analog Scale for >6 months
• Can walk (with/without aid)
• Cognitive ability to follow instructions
• Signed informed consent
• Availability for 9 treatment sessions and home exercise Exclusion Criteria
• Prior total knee arthroplasty (unilateral or bilateral)
• Neurological disorders affecting motor function or cognition (e.g., Parkinson's disease, stroke, moderate to severe dementia)
• Active inflammatory rheumatic diseases (e.g., rheumatoid arthritis, lupus)
• Presence of pacemakers, implantable defibrillators, or metallic implants near the treatment area
• Current use of other physical therapy modalities for pain (e.g., electrotherapy, ultrasound, TENS) outside the study protocol
• Participation in another clinical trial within the past 3 months
• Current use of NSAIDs or systemic/local corticosteroids (including intra-articular injections)
• Open wounds or active infections at the treatment site
• Decompensated cardiac conditions or medical contraindication to exercise
• Vestibular disorders that affect balance and interfere with functional assessments
• Uncorrected visual impairment interfering with gait or balance (visual acuity worse than 20/60 in the better eye, assessed by Snellen chart)

Withdrawal Criteria:

• Participants who complete fewer than 7 out of the 9 planned intervention sessions (i.e., less than 80% adherence)
• Occurrence of serious adverse events related to the intervention that contraindicate continuation
• Repeated non-compliance with the home exercise program, documented in at least two consecutive weekly follow-up reports
• Voluntary withdrawal of consent at any time during the study

The individual participant data (IPD) will not be shared because the study is conducted within a public hospital setting without external funding, and there is no current plan or infrastructure to support secondary data sharing. Data will be used exclusively for the primary objectives outlined in the approved protocol.

Participants were informed that the intervention would be applied to the lower limb without specifying the anatomical region. The HI-PEMF equipment produces no perceptible sensations, aiding participant blinding. Outcome assessors were independent and unaware of group assignment. Care providers administering the intervention were not blinded.