Electrolysis in Patients With Chronic Plantar Fasciitis

Pain intensity

Participants will rate their pain intensity on an 11-point numeric rating scale (NPRS; 0 = no pain; 10 = worst possible pain). They will consider the pain intensity of their first step in the morning, the average pain intensity during the day, and the maximum pain experienced in the past week. The average of all these values will be used to calculate a pain intensity score for the primary analysis.

Foot function

Foot function will be assessed using the Foot Function Index (FFI), the most commonly used self-assessment tool for the foot. The FFI has been shown to be reliable, valid, and sensitive to change in individuals with chronic plantar heel pain. The Foot Function Index (FFI) consists of 23 self-reported questions divided into three subscales: pain (nine items), disability (nine items), and activity limitation (five items). Each item is rated on a 0-10 scale (0 = no pain or difficulty, 10 = worst possible pain or difficulty requiring help). Each subscale is scored as a percentage from 0% to 100%, with higher scores indicating lower function and poorer foot-related health-related quality of life. In this study, the total FFI score, calculated as the average of the three subscales, will be used for the primary analysis.

Pain threshold

Participants will avoid pain meds/muscle relaxants for 24 hours. PPT will be measured using an electronic algometer at 30 kPa/s, with 3 measurements per site and a 30-second interval. PPT will be assessed bilaterally at the calcaneus, adjacent muscles, tibialis anterior, and a pain-free site. Inter-rater reliability: 0.74-0.97.

Tolerance

Participants will rate the intensity of pain experienced during the intervention on an 11-point numeric rating scale (NPRS; 0 = no pain; 10 = worst possible pain).

Tissue stiffness

All images will be acquired using a General Electric Logiq P9 ultrasound system equipped with a linear 4-15 MHz probe, located in the Rehabilitation Department of the 12 de Octubre Hospital. Experienced researchers, with over 10 years of experience in musculoskeletal ultrasound and blinded to participant group assignment, will perform the imaging. Device parameters will be identical for all measurements (gain 55 dB, dynamic range 85, brightness 17, depth 4 cm, frequency 8 MHz). The plantar fascia image will be acquired in a longitudinal plane. Subsequently, shear wave elastography mode will be activated, and a region of interest 1 cm wide (corresponding to the width of the algometer head) and an appropriate height to analyze the entire thickness of the fascia will be marked. The ultrasound system will automatically calculate tissue stiffness parameters within the marked region (shear wave velocity and Young's modulus).