A Mediation Analysis Investigating Dry Needling Treatment Mechanisms in a Chronic Low Back Pain Population

Pain intensity will be assessed using the Brief Pain Inventory's (BPI) pain intensity sub-scale. The BPI pain intensity sub-scale creates an average score of pain intensity by assessing four pain intensity domains of the current, best, and worst pain in the past twenty-four hours and pain on average, then adding these scores together and taking an average. The pain intensity domains are measured using the numeric pain rating scale (NPRS) anchored at "0" (no pain) and "10" (The worst pain imaginable).

The PROMIS-29 is a National Institute of Health-supported outcome measure that assesses multiple domains, including pain intensity with the NPRS an average of pain in the past seven days, physical function, fatigue, pain interference, ability to participate in social roles and activity, symptoms of anxiety, symptoms of depression, and sleep disturbance

The PGIC is a single-item, seven-point measure ranging from "Very much improved" to "Very much worse" and is responsive to change in chronic pain samples

The PII is a seven-item test of various ranges of motion (ROM) and strength measures specific to the low back. These seven tests include total flexion ROM, total extension ROM, average lateral flexion ROM, average straight leg raise ROM, spinal tenderness, bilateral active straight leg raise, and active sit-up. Each test is scored as a positive or negative, resulting in a "1" or "0" score for a total possible score of seven. A higher score indicates higher levels of impairment

Myotonometry measures global soft tissue biomechanical and viscoelastic properties. Myotonometry can be performed with handheld devices to quantify soft tissue properties. the MyotonPro handheld device will be used to collect myotonometry measurements. For this investigation, the MyotonPro (MyotonPro, Myoton Ltd.s., Tallinn, Estonia) will be used to collect myotonometry measurements of dynamic stiffness. The measure of dynamic stiffness is a measure of soft tissue resistance to deformation of its initial shape in response to internal or external forces. The measure of stiffness in newtons per meter will be collected at the spinal level of L4 on the side of the most tender trigger point

Pressure pain threshold testing will be measured at the lower back just medial to the posterior superior iliac spine (PSIS) and on the proximal anterior tibialis (approximately 5cm from Girdy's Tubercle) on the side of the most tender trigger point. Threshold testing will be performed using a digital pressure algometer (Wagner Instruments FPX 25, Greenwich, CT) with a 1 cm diameter rubber tip with pressure applied perpendicular to the testing area at a rate of 1 kgf/s. Participants will be instructed to verbally indicate when the sensation first changed from pressure to pain and the amount of pain intensity with the NPRS. The NPRS will be anchored at "0" (no pain) and "100" (The worst pain imaginable). Pressure pain threshold testing will be performed two times, with an average of the two measures used for analysis.

The PCS is a thirteen-item questionnaire in which participants rate each item from 0 to 4, with larger numbers indicating higher levels of pain catastrophizing. The PCS is extensively studied as an assessment of pain catastrophizing and has sound psychometric properties.