Pulsed Electromagnetic Field Therapy for Mild-to-Moderate Knee Osteoarthritis: A Double-Blind, Randomized, Placebo-Controlled Clinical Trial

Abstract

Background: Current treatments for knee osteoarthritis (OA) offer limited functional and structural improvements. Compared to age- and gender-matched controls, patients with knee OA show a higher prevalence of muscle weakness, which negatively affects their ability to exercise-a key factor in enhancing physical mobility and delaying disease progression. Pulsed electromagnetic field (PEMF) therapy shows promise in promoting myogenesis and chondrogenesis in pre-clinical studies. However, its effects on muscle strength and size, cartilage deterioration and overall physical function in knee OA patients remain unclear. This randomized placebo-controlled trial aimed to evaluate the impact of PEMF therapy on knee muscle power, lean muscle mass, femoral cartilage thickness, minimum joint space width (mJSW), lower limb physical functions and knee-specific patient-reported outcome (PRO) in patients with refractory mild-to-moderate knee OA.

Methods: Sixty refractory knee OA patients, aged 50 and older, with a pain score of 4 or higher were randomized to receive either PEMF or SHAM treatment for 30 min, 3 times a week over 8 weeks. Outcome measures, including muscle strength, lean muscle mass, cartilage thickness, mJSW, mobility and PRO were assessed at baseline, immediate post-intervention and 6- and 12-month post-intervention.

Results: Significant interactions were observed between PEMF therapy and time for both knee extension peak torque (p < 0.001) and knee flexion peak torque (p = 0.007). Post hoc analysis revealed that PEMF significantly increased extension peak torque compared to the SHAM group at 6-month post-intervention (p = 0.042). The PEMF group showed a 72% increase in knee extensor strength after 6 months from baseline, whereas the SHAM group only saw a 25% increase (p = 0.003). However, no significant difference in knee flexion peak torque was detected between the PEMF and SHAM treatments in the post hoc analysis. Nonetheless, the knee flexor strength in the PEMF group increased by 72% at 6 months from baseline, whereas the SHAM group showed only a 24% rise (p = 0.022). Additionally, there were no differences between the PEMF and SHAM groups in lean muscle mass, cartilage thickness, mJSW, the 6-m walk time and the number of repetitions of chair standing in 30 s and WOMAC (all p > 0.05).

Conclusions: An 8-week course of PEMF therapy significantly improved the knee extension strength in refractory patients with mild to moderate knee OA at 6-month post-intervention, suggesting its potential to address extensor weakness in this high-risk population. However, it did not significantly enhance knee flexion strength, lean muscle mass, cartilage thickness, mJSW, lower limb physical functions or PRO up to 12-month post-intervention. Further research is needed to identify treatment regimens that may promote structural and functional outcomes in knee OA patients.

Trial registration: ClinicalTrials.gov: NCT05442697.

Keywords: degenerative knee arthritis; electromagnetic fields; knee arthroses; knee osteoarthritis; knee osteoarthrosis; pulsed electromagnetic field therapy.