Chronic musculoskeletal pain of non-specific origin affects approximately 30% of the global population. Beyond its prevalence, it represents a serious health and socioeconomic problem. It is considered the leading cause of years lived with disability and is characterized by persistent functional limitation, deterioration of quality of life, and poorer mental health, with a high comorbidity of depression, anxiety, and sleep disorders, as well as a greater risk of suicidal ideation and behavior.
From a socioeconomic perspective, chronic pain entails an impact of up to USD 635 billion annually just in United States (USA). In fact, spinal pain alone represents the condition with the highest direct costs (around USD 134.5 billion in USA) and additional indirect costs due to absenteeism and presenteeism, which impair productivity and work performance. These figures are expected to be substantially higher when considered at a global scale.
One of the main aggravating factors of this condition is that in up to 90% of patients experiencing pain there is no identifiable anatomopathological substrate that reliably explains the symptoms (non-specific pain). Radiological findings are extremely common in asymptomatic populations, and making diagnostic or therapeutic decisions based on such findings, promotes overdiagnosis and low-value clinical cascades. It is estimated that up to 50% of imaging requests and 60% of spinal surgeries6 are unnecessary or unjustified. For this reason, Clinical Practice Guidelines recommend prioritizing interventional diagnostic techniques based on functional criteria over the interpretation of radiological findings, as they allow for more sensitive and specific identification of nociceptive sources (with a recommendation grade I-II).
In this context, the motivation of the project is to study PENS as a non-pharmacological, safe, and transferable alternative to nerve blocks, reducing the risk of complications associated with the use of local anesthetics/corticosteroids and large-gauge needles. According to recent systematic reviews and meta-analyses confirming immediate analgesic responses, PENS could be a feasible alternative that maintains functional diagnostic and therapeutic value with a generally mild adverse-event profile and lower cost.
Participants with chronic LBP lasting at least three months and clinical suspicion of facet joint pain.
A balanced sex distribution and a wide range of body mass index (BMI) will be promoted to allow subgroup analyses and to explore potential associations between obesity and procedural complications, thus strengthening the external validity of the study. This demographic selection is justified by prevalence patterns reported in the literature and by the need to capture clinically relevant effect modifiers in real clinical environments.
The suspicion of facet joint pain will be based on a compatible axial clinical pattern and the absence of objective neurological deficit, considering that neither physical examination nor imaging tests provide sufficient specificity. Therefore, diagnostic confirmation will be performed functionally through ultrasound-guided medial branch diagnostic blocks, which are the most reliable tool for attributing pain to the facet joint. The dual innervation of each lumbar facet joint will be considered; thus, two adjacent levels will be blocked per joint (the medial branch at the affected level and the one immediately above).
Eligible patients will be those with a positive functional screening in two independent medial branch diagnostic blocks performed with anesthetics of different duration, in separate sessions, to reduce false positives.
Exclusion criteria will include red flags or specific etiologies such as infection, neoplasm, fracture, or cauda equina syndrome, as well as patients with progressive motor radiculopathy or another demonstrated neuropathic pain source other than facet origin.
Individuals who have undergone prior procedures that could compromise response interpretation such as recent radiofrequency denervation, cryoneurolysis or intra-articular corticosteroid injections within a period that could extend analgesic effects.
Parallel
Nerve block with Lidocain
DrugTwo adjacent levels per joint will be blocked in a single session. After minimal intradermal infiltration for local anesthesia, a sterile 25G-22G needle will be inserted in-plane toward the target under continuous visualization. Before administering the drug in opaque syringes, negative aspiration and fractional injection will be performed, confirming the absence of abnormal resistance or radiating pain. The diagnostic injectate will be a local anesthetic without corticosteroid (1% lidocaine) with low volumes of 0.5 ml per branch to limit diffusion
Percutaneous electrical nerve stimulation
DeviceA single ultrasound-guided session will be applied using fine solid needles (0.32 mm diameter), accounting for dual innervation. Electrical parameters will be fixed within recommended ranges (10 Hz, 250 µs, current intensity sufficient to produce a strong but tolerable sensation below the motor threshold using a standardized ramp, and session duration of 15-20 minutes)
Sham Block
Other interventionThe full ritual of the nerve block will be reproduced. However, in this group, no active drug will be administered (a minimal volume of inert solution will be injected into the subcutaneous/superperiosteal plane to mimic the injection sensation without depositing perineural anesthetic)
Pain intensity
The primary variable will be immediate analgesic response, defined as a ≥50% reduction in the Numerical Pain Rating Scale (NPRS, 0-10). Lower scores indicate less pain intensity.
Pain during specific movements
Participants will be asked to rate, using the Numerical Pain Rating Scale (NPRS) from 0-10 (lower scores indicate less pain intensity), their pain during lumbar flexion, rotation, extension and inclination
Pressure pain threshold
An algometer will be used to determine the mechanosensitivity over the projection of the symptomatic facet joint.
Analgesic drug consumption
A record will be used.
Participants' satisfaction
Patients will be asked to rate in a 0-10 scale their satisfaction with the intervention.
Record of local and systemic adverse events
Any adverse events or sequelae (defined as short-medium term symptoms perceived as unacceptable by the patient or that required further treatment) experienced during or 7 days after the interventions
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Universidad Complutense de Madrid
Lead sponsor
Universidad Francisco de Vitoria
Collaborator
Medical University of Warsaw
Collaborator
Jagiellonian University
Collaborator
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