Pulsed Radiofrequency for Low back pain and Sciatica
Typically, low-back pain is described as discomfort, muscle tightness, or stiffness that is situated below the ribcage and above the lower boundary of the buttocks, and it may or may not be accompanied by leg pain, also known as sciatica.
Between 9.9% and 25% of individuals experience low-back pain accompanied by leg pain that extends below the knee on a yearly basis.
The cause of low-back pain remains unclear in approximately 90% of patients who experience symptoms in this area. The indication of nerve root problems serves as a potential sign of an underlying pathological condition.
The most prevalent cause of lumbar radicular pain is typically intervertebral disc herniation (DH), followed by failed back surgery (FBSS), and spinal stenosis (SS).
The use of medication, such as paracetamol, NSAIDs, and opioids, is a potential choice for managing radicular pain. However, there is insufficient evidence to favor the prescription of any specific medication.
Non-pharmacological interventions that do not involve invasive procedures, such as physical exercise (including biomechanical, aerobic, mind-body, or a combination of approaches) along with or without manual therapy (such as spinal manipulation, mobilization, and massage) or psychological therapy, often yield outcomes that are not durable in the long term.
For many years, epidural corticosteroid injection has been widely utilized in clinical settings. While it can provide short-term pain relief, it should not be relied upon for long-term effects.
The procedure carries a complication rate that ranges between 0% and 9.65%. Under radiological guidance, transforaminal injection (TFESI) appears to exhibit greater efficacy compared to epidural injection.
In cases where conservative treatment fails to yield positive results or significant neurological impairment is present, surgery (including discectomy, microdiscectomy, and other microsurgical techniques) is typically advised for carefully chosen patients with severe symptoms.
In terms of short-term pain relief, surgery offers superior results compared to long-term conservative care. However, no notable distinctions have been discovered between surgery and conservative treatment after one or two years. Furthermore, there are various adverse effects linked to surgery.
The utilization of pulsed radiofrequency (PRF) involves the intermittent delivery of high-frequency current. The key objective is to maintain the temperature below the critical threshold of 42°C to prevent potential harm to the neurons.
Hence, PRF operates based on a mechanism of action that differs from conventional continuous radiofrequency (CRF). Unlike CRF, which involves continuous administration leading to elevated temperatures and tissue heating, PRF employs intermittent delivery to avoid exceeding the critical threshold. This approach prevents thermal coagulation from occurring.
In various areas of application, PRF has demonstrated promising outcomes, encompassing diverse spinal pain conditions such as cervical radicular pain, posterior degenerative spinal disease, pathology related to discs, pain in the sacroiliac joint, spondylolisthesis, and infection.
Mechanisms of Action
For more than 30 years, CRF to DRG has been utilized as a well-established approach in the management of chronic pain. This procedure entails the ongoing electrical stimulation of specific nerves, resulting in increased temperature (typically ranging from 60°C to 80°C) surrounding the needle’s tip.
Consequently, the nerve fibers responsible for transmitting pain signals are eliminated. CRF has proven to be effective in treating diverse conditions, such as occipital neuralgia, cervicogenic headaches, cervical and lumbar radicular pain, discogenic pain, and pain associated with the sacroiliac joint.
With its intermittent delivery of high-frequency current, RF is a contemporary and minimally invasive procedure. This technique guarantees the dissipation of generated heat into the adjacent tissues, effectively avoiding temperature escalation beyond the critical threshold of 42°C. In practice, RF current, operating at a frequency of 50,000 Hz, is administered through 20 ms pulses at a frequency of 2 pulses per second over a 120-second timeframe.
Imaging guidance, such as fluoroscopy or CT scans, is typically essential during the PRF procedure. To target the specific dorsal root ganglion (DRG), a 20-22 G needle-electrode with an active tip is meticulously inserted and guided.
The activation of RF current relies on the accurate placement of the needle within an 8 mm range of the symptomatic DRG, as confirmed by imaging results. To ensure utmost safety, low-frequency electrical sensory stimulation is employed to verify the optimal positioning before the actual treatment.
Although local anesthesia is typically unnecessary, certain healthcare providers might choose to administer a 1-2% Lidocaine injection to alleviate localized pain.
Although the therapeutic principles of PRF are not entirely understood, there is still uncertainty surrounding the precise mechanism of action. Electron microscopy studies have shown minimal histological alterations in the tissues and no evidence of permanent thermal damage.
One proposed theory is that PRF may exert a neuromodulatory effect by modifying nerve activity in specific areas. PRF applied to the DRG results in the activation of the early gene c-Fos, indicating neuronal activity in the dorsal horn, and an increase in ATF3, which indicates cellular stress.
It is noteworthy that this effect appears to specifically target small-diameter axons, particularly C and A delta fibers. Research conducted on animals has indicated that PRF exhibits the capacity to mitigate mechanical allodynia and augment the inhibitory pathways responsible for transmitting pain signals through the bulbospinal descending pathway.
Based on the current literature, PRF performed near the DRG has shown a favorable safety profile, with only a few minor side effects reported as the most commonly encountered complications, including headache or procedural discomfort.
Most of the evidence concerning the effectiveness of PRF primarily comes from retrospective studies that include limited and varied groups of patients, with relatively short periods of follow-up.
Furthermore, there is a lack of agreement regarding the parameters of PRF, including the ideal duration for delivering pulses. While some studies adhere to a 120-second duration, others employ longer durations in their procedures.
In addition, the lack of standardized criteria for assessing the clinical effectiveness of PRF treatment results in a wide range of reported outcomes across different studies.
Commonly used measures to assess pain relief and functional improvement include the Visual Analogue Scale (VAS), Numerical Rating Scale (NRS), Oswestry Disability Index (ODI) score, and Global Perceived Effect (GPE).
Only one randomized, double-blind, sham-controlled study on PRF for chronic lumbar radicular pain was found. The study did not show a statistically significant difference between PRF and sham treatment.
Although the PRF group had slightly better VAS and ODI scores at different follow-up time points, the clinical difference, calculated as a 50% reduction in pain, was small. The limited sample size of 32 patients, with some lost to follow-up, may have contributed to the absence of significant results.
The reported success rate in other studies ranges from approximately 30% to 60%. heterogeneous selection criteria may contribute to the conflicting results. A retrospective analysis of 54 patients with radicular pain showed a significant reduction in the NRS score for patients with specific conditions, but not for those with a different condition.
A prospective study with stricter inclusion criteria reported a higher success rate, particularly for patients with neuropathic pain.
Randomized trials reported by literature have compared PRF and TFESI efficacy. PRF was found to be as effective as TFESI for treating persistent pain after the initial TFESI in patients with cervical or lumbar radicular pain due to disc herniation.
In a recent trial for chronic lumbar radicular pain, PRF demonstrated significant improvements in NRS scores at 3 and 6 months, while no notable differences were observed in ODI scores between the two groups.
TFESI provides only short-term pain relief for chronic lumbar radicular pain. PRF, either alone or combined with TFESI, offers a more prolonged period of pain relief.
In a retrospective study, patients treated with PRF alone or PRF combined with TFESI experienced longer-lasting pain relief compared to TFESI alone.
Similarly, a randomized trial showed better pain relief with PRF followed by TFESI compared to TFESI alone, although statistical significance was not reached due to a small sample size and stricter criteria for successful treatment.
In a randomized prospective study reported by literature with 76 patients, no significant difference was found in the duration of pain relief between those treated with a combination of PRF and continuous RF versus PRF alone. Both groups had similar rates of successful response, with pain relief lasting around 3 to 4 months.
PRF is a safe and effective procedure for cervical radicular pain, with compelling evidence. It also provides intermediate-term pain relief for lumbar radicular pain without complications. PRF is thought to have a neuromodulatory effect on the DRG, influencing gene expression in nerve fibers and enhancing the activity of antinociceptive systems. Unlike traditional RF, PRF does not cause thermal damage, making it a safer option.
To avoid potential side effects associated with steroid injections, which can have a complication rate ranging from 0% to 9.65%, including rare catastrophic complications, PRF can be considered as an alternative to TFESI for patients with contraindications to steroid administration or when TFESI does not provide adequate pain relief duration.
PRF can be used in combination with steroid injections for effective and longer-lasting relief of radicular pain. It also offers an alternative to CRF, avoiding potential side effects associated with continuous current administration.
However, further well-designed clinical trials are needed to define PRF indications, contraindications, and standardized parameters. Precise patient selection and proper imaging guidance are essential for reliable data comparison.