PF is a prevalent worldwide public health issue. When noninvasive conservative treatment fails, which intervention is most beneficial for recalcitrant PF is still equivocal and controversial, especially during the whole rehabilitation period. Therefore, we proposed a novel combination strategy of ultrasound-guided percutaneous bipolar plasma RFA and CI for the treatment of recalcitrant PF. Our findings showed that the combination strategy can significantly improve the symptoms, function, and structural anomaly from the immediate postoperative to 1-year follow-up period. This combination strategy yielded comparable rapid pain relief to CI while sustaining a better efficacy at long-term follow-up. The present results may provide new insights for optimizing the treatment options for recalcitrant PF.

The exact definition of recalcitrant PF remained equivocal, and no widely accepted criteria have been established based on the duration and severity of symptoms. Generally, it is considered a condition that symptoms persist after 6–12 months of conservative treatment. Our results showed that continuous noninvasive conservative treatment showed significant improvements in pain relief and function for patients with recalcitrant PF at a 12-month follow-up. We believe this may be attributed to two major reasons. First, PF is a self-limiting disease, and its process may persist for months to years until recovery [4]. In this study, the median DOS of the control group was only 10 months, indicating a still hopeful and promising improvement subsequently. Besides, the efficacy of conservative treatment may be revealed gradually even up to 2 years. A prospective study evaluated the 2-year outcomes of patients with chronic PF treated by extracorporeal shock wave therapy and conventional conservative treatment and found a continuous reduction of VAS from 24 weeks to 2 years [25]. Second, a great portion of patients in the control group received individualized and standard education by experts during outpatient visits and adjusted to several alternative conservative treatment approaches subsequently in follow-up periods, which may be beneficial to the therapy. However, the present study found the general improvement of symptoms, function, and structural anomaly in continuous noninvasive conservative treatment was more inconspicuous than in intervention groups. A survey was conducted among surgeons in the American Orthopaedic Foot and Ankle Society in 2012 to investigate the preferred management of recalcitrant PF, and more than half (55%) of the members preferred surgery, especially open surgery like gastrocnemius recession, partial plantar fascia release, or nerve decompression, for patients with 10-month symptom duration [26]. With the rapid development of techniques and concepts in the last decade, a more optimal strategy for recalcitrant PF was desired to balance clinical outcomes and surgical trauma.

CI is prevalently used for recalcitrant PF after the failure of noninvasive conservative treatments, based on its corresponding effects including inhibition in fibroblast proliferation and ground substance protein expression [12]. Nonetheless, there is indelible concern about the serious adverse events related to CI including plantar fascia ruptures and injection site infections, despite being under-reported generally [27,28,29]. Besides, pooled data from meta-analysis indicated that CI showed exact short-term effects of pain relief for treating recalcitrant PF [12], even more, superior than autologous blood injection and foot orthoses [30]. However, the efficacy may not be sustained for the medium or long-term [12]. As an echo of such evidence, our results showed a recurrence of symptoms and disability from short-term to 1-year follow-up. Therefore, we believe that CI alone may not be the most ideal regimen for recalcitrant PF.

Percutaneous RFA, actually a specific pattern of microfasciotomy, is another alternative minimally invasive approach for treating recalcitrant PF. This technique was performed by implementing multipoint ablations in the plantar fascia area, stimulating angiogenesis and further degenerative tissue repair through several growth factors [21]. The idea was first proposed by Weil et al. in 2008 [16] and validated and modified in several studies subsequently [14, 15, 17, 22, 23]. However, a typical RFA procedure conducted in most studies included drawing a grid-like pattern mark at the area of maximum tenderness, followed by blind perpendicular multipoint punctures and ablations [14, 16, 17, 22, 23]. Such an approach cannot ensure precise guidance to the lesion area and may result in additional damage to the weight-bearing area of the plantar fat pad and plantar dermis. Although the technique gained satisfactory pain relief and functional improvement in the treatment of PF generally, there is still a lack of high-level evidence to report a persuasive efficacy and safety, especially at the early stage postoperatively. Sorensen et al. conducted a prospective study and found that only 33.3% of patients experienced satisfactory pain relief within 1 month after RFA treatment for recalcitrant PF [14]. Therefore, we proposed a novel RFA technique, based on a percutaneous oblique puncture longitudinally by ultrasound guidance. It can provide precise real-time navigation to lesions and minimize additional damages in the weight-bearing area, which may improve efficacy as well as safety and promote rapid recovery. As this procedure was a novel technique, all patients in this study were managed under inpatient care and performed in the operating room. However, it has the potential to apply in the outpatient department as the low-cost and convenient features of ultrasound and RFA.

Further, we proposed a combined strategy of ultrasound-guided percutaneous bipolar RFA and CI for the treatment of recalcitrant PF. This idea was inspired and supported by three main aspects below. First, although RFA was proven to result in rapid pain reduction by inducing the degeneration of the nerve fibers in rat models [31], this effect may be short-lived and insufficient. The symptom improvement in patients with PF treated with RFA seemed to be gradual [14,15,16,17]. Tasto et al. performed a prospective study to evaluate the effectiveness of RFA microtenotomy for treating chronic tendinosis and reported a reduction of the median VAS score from 8 to 3 (preoperative to postoperative 7–10 days). However, the median VAS score further decreased to 0.7 at 2 years postoperatively, and the ratio of patients who reported minimal to no pain (VAS ≤ 1) was 0 vs. 100% (postoperative 7–10 days vs. 2 years) [32]. They speculated the mechanism of pain relief switched from antinociceptive response to histological improvement including revascularization and reorganization of collagen, which occurs at least 2–3 weeks after RFA and contributed to longer-term and better symptom improvement [32]. Therefore, given the superiority of the short-term effects of CI for recalcitrant PF, complementing their strengths with a combined strategy was reasonable and attractive. Second, the procedure of the proposed combined strategy was similar to the combination therapy of CI and peppering technique, which has been proven to be effective in high-level evidence [18,19,20]. Third, we believe CI will not contribute to additional damage and burden on the routine RFA workflow. Based on the target point of needle placement, the CI modality can be divided into injections within or surrounding the plantar fascia [30]. We chose to mix the corticosteroid with local anesthetics, followed by an injection at the periphery of the plantar fascia. Collectively, the results showed that this combination strategy can significantly improve the symptoms, function, and structural anomaly from immediate postoperative to 1-year period. Furthermore, no obvious adverse effect or complication was observed during follow-up.

Our study had certain limitations. First, the study was subject to the retrospective and single-center design with a small sample size; thus, we could not exclude selection bias. Further validation with prospective, multicenter, and large sample size studies is required. Second, whether the superiority of pain relief at the early stage postoperatively was attributed to the modification of the RFA technique or the additional effect of corticosteroid could not be determined because we did not build a control group consisting of patients treated by modified RFA alone. We speculated that both the modified RFA technique and CI contributed to the immediate improvement postoperatively, yet it still needed to be proven by further well-designed studies. Finally, we did not collect the detail of nonsteroidal anti-inflammatory drugs use of the study individuals during the treatment course, which may cause unexpected bias.