Real-World Clinical Outcomes of Polydioxanone Filament Insertion into the Vastus Medialis Obliquus for Knee Osteoarthritis: A Retrospective Observational Study

Purpose: MEST (Muscle Enhancement and Support Therapy) is a device for intramuscular placement of bidirectional barbed polydioxanone filaments. Placement of these filaments into the vastus medialis obliquus has been reported to reduce knee pain and improve quadriceps function in patients with knee osteoarthritis. However, clinical evidence remains limited and is based primarily on a small number of controlled trials in selected populations. This study evaluated the real-world clinical outcomes and safety of the MEST procedure across Kellgren–Lawrence (KL) grades I–IV. Patients and Methods: In this retrospective study, 62 patients with knee osteoarthritis who underwent the MEST procedure between March 2025 and February 2026 were analyzed. Pain intensity, functional outcomes, patient-reported overall improvement, effusion grade, and adverse events were assessed at 4, 8, and 12 weeks. The primary outcome was the change in numeric rating scale (NRS) pain score from baseline to 8 weeks. Factors associated with treatment response, defined as ≥ 2-point NRS reduction at 8 weeks, were also evaluated by logistic regression. Results: NRS scores decreased from 5.8 ± 1.7 at baseline to 2.5 ± 2.4 at 8 weeks ( Padj < 0.001), and 50 patients (80.6%) achieved a ≥ 2-point reduction. At 8 weeks, walking and stair climbing improved in 54 (87.1%) and 38 patients (61.3%), respectively, and 55 patients (88.7%) rated the procedure as effective or very effective. In multivariable analysis, moderate-to-severe baseline effusion was associated with a lower response likelihood (odds ratio, 0.22; 95% confidence interval, 0.05– 0.94; P = 0.041). No serious adverse events occurred. Conclusion: The MEST procedure was associated with clinically meaningful pain reduction and favorable patient-reported outcomes across KL grades I–IV, with no serious adverse events. In an exploratory analysis, moderate-to-severe baseline effusion grade was associated with a lower likelihood of response, suggesting that baseline effusion warrants further investigation as a potential marker of treatment response. Keywords: osteoarthritis, knee, muscle enhancement and support therapy, polydioxanone, quadriceps muscle, hydrarthrosis, chronic pain