1965: Two-Year Outcomes of Microwave Ablation for Recurrent Monoarthritis with Synovial Hypertrophy Resistant to Medical Treatment: Expanded Cohort and Long-Term Follow-Up Results

Background/Purpose: Recurrent monoarthritis (RM) is a significant therapeutic challenge in rheumatology, often persisting despite NSAIDs, corticosteroids (CS), DMARDs, and biologic therapies. Local interventions like intra-articular aspiration (IAA) and CS injections offer transient relief and are limited by high recurrence rates. Surgical and chemical synovectomy have largely been abandoned due to poor efficacy and high complication rates. Microwave ablation (MWA) is a well-known technique in the treatment of benign or malign lesions of different etiologies. Building upon our initial findings using MWA in RM sucessfully, we present long-term outcomes from a larger cohort of medical treatment-resistant RM, providing real-world data on the efficacy and safety of MWA.

Methods: Patients with RM associated with various inflammatory diseases were included. MWA was performed after measuring the size of synovial hypertrophy (SH) with 15 or 20-watt power and different durations until microbubbles were shown indicating necrosis (Figure 1). Both clinical and radiologic data were recorded baseline and prospectively.

Results: We applied MWA to a total of 43 knee joints in 37 patients (18 female and 19 male) aged between 22 and 71 years. The median number of IAA required in the 6 months prior to MWA was 5 (0–15). Three patients had previously undergone surgical synovectomy. In 3 knees of 2 patients, the number of IAAs in the last 6 months was 0; these patients had persistent synovial effusion and abundant synovial hypertrophy but declined IAA. A 2nd MWA session was required in 5 patients, and 1 patient underwent a 3rd. The median follow-up period was 15 months (5–25). The IAA frequency dropped dramatically from 207 over 258 patient-months (0.81/month) before MWA to just 21 over 624 patient-months post-MWA (0.03/month; p < 0.001). Short-term, Lowe dose CS therapy was administered in 14 patients (16 knees) with all anti-inflammatory treatments maintained unchanged during the first 6 months post-procedure.


CS reduction or cessation was achieved in 16 patients. Functional disability and pain scores showed significant improvement, with the median score decreasing from 9 to 1 (p < 0.0001 for both, Figure 2). No complications were observed during the procedure or follow-up. While both SH and effusion persisted to varying degrees at the 1st and 3rd months on USG and MRI, IAA was deferred unless symptoms developed. Significant regression in SH was demonstrated on MRI at the 6th month (Figure 3). A discordance between clinical improvement and radiological findings was observed in a small subset of the cohort.

Conclusion: MWA is a safe, effective, and minimally invasive adjunctive option for managing RM with SH. It significantly reduces arthritis flares frequency, CS dependecy, and the need for IAAs while improving functional outcomes and pain. Although early imaging may show persistent effusion and SH, significant regression by six months correlates with sustained clinical improvements. These long-term results support MWA as a promising alternative to surgical interventions in RM resistant to conventional medical therapies.