STEP Trial for Heel Fat Pad Syndrome

Participants verbally select a value that corresponds with the average intensity of pain that they experience in the past 24 hours. Participants verbally select a value that corresponds with the intensity of pain that they experience. "0" means "no pain" and "10" means "pain as bad as you can imagine" or "worst pain imaginable". The NPRS, an 11-point (i.e., 0-10) measure of pain intensity, is recommended as a core outcome measure in clinical trials of chronic pain treatments and has excellent reliability and validity for adults with chronic musculoskeletal pain.

The FHSQ is a self-administered questionnaire consisting of 13 items in 4 domains of foot pain (4 items), foot function (4 items), footwear (3 items), and general foot health (2 items). Each item is rated on a 5-point Likert scale from no (score =1) to severe (score = 5) pain, problems, or limitations. Responses to footwear questions are on a 5-point bipolar Likert scale from strongly disagree to strongly agree regarding shoe fit, discomfort wearing shoes, and shoewear available. Each domain score ranges from 0 (worst foot health) to 100 (optimal foot health). Higher scores indicate better foot health and quality of life. A validated Danish version of FHSQ is available. Good FHSQ test/retest and interrater/intrarater reliability and validity have been established for patients with foot disorders.

Another core outcome measure for chronic musculoskeletal pain is the GROC, a widely used single-item instrument that asks each participant to indicate whether and to what extent they perceive change has occurred pre vs. post-intervention. This global rating is unique because, unlike other self-reported outcomes, it allows each participant to decide what he/she considers most important and relevant change. In the proposed study, participants will be queried "With respect to your heel pain, how would you describe it after the intervention compared to before the intervention?" and quantify the perceived change on a 7-point visual analogue scale of -3 to +3, where "-3" indicates "much worse", "0" indicates "no change", and "+3" indicates "much improved". GROC has been demonstrated to be a reliable and valid tool for musculoskeletal conditions.

Pain sensitivity is quantified by measuring pressure pain thresholds (PPT) on the most painful spot on the heel fat pad, confirmed by palpation. Participants lay prone on the examination table, with the feet hanging freely over the edge of the table. The examiner places the 1-cm2 probe of a hand held mechanical pressure algometer perpendicular to the skin, and gradually increase the pressure at a rate of 30 kPa/s. Participants will report when the sensation changes from pressure, to the first onset of pain. This will be repeated three times, with a 30-second break between tests, and the average used for the analysis. The probe location will be marked on the skin to ensure placement consistency between pre- and post-intervention testing. The interrter and intrarater reliability of PPT assessment for patients with plantar heel pain was good at ICC 0.80-0.94 for intrarater and 0.75-0.92 for interrater.

An ultrasound unit with a 6-13 MHz transducer frequency will be used to measure the heel fat pad thickness. Participants lay prone on the examination table, with the feet hanging freely over the edge of the table. The plantar fat pad will be marked by a sagittal midline; the ultrasound transducer will be placed on the midline for a transverse scan to measure the largest distance between the calcaneus and the skin. The average of two sonographic measurements will be used for analysis. The intrarater and interrater sonographic assessment of heel fat pad thickness was excellent with the intraclass correlation coefficients (ICCs) ranging from 0.81 to 0.96.