Responders to Cervical Facet Platelet-Rich Plasma Demonstrate Synergistic Improvements in Pain and Isometric Strength in Chronic Whiplash-Associated Disorders: A Series of Mediation Analyses

Background/Objectives: Platelet-rich plasma (PRP) is emerging as a safe and effective treatment for facet-mediated pain. Studies have demonstrated reductions in pain and improvements in function, both in the short (3 months) and longer term (6 and 12 months). The mechanisms underlying clinical improvements are largely unknown. It is also unclear whether reported outcomes are due to the PRP administered or concurrently applied rehabilitation. Methods: A prospective case series was conducted in a single, multidisciplinary chronic pain centre. Forty-two participants with chronic WAD and cervical facet-mediated pain who received PRP (64% female; mean age (SD) 42.8 (11.6) years; median WAD duration [IQR] 23 [18,29] mths), attended rehabilitation, and reported successful outcomes 3 months post-PRP fulfilled the inclusion criteria. Measures of pain, cervical isometric strength, and range of motion were collected at baseline and 3 months post-PRP. Mediation analyses were performed to determine how these factors influenced disability. Results: Participants demonstrated clinically significant and relevant improvements in pain, disability, and isometric strength measures (all p < 0.01). Causative mediation analyses demonstrated independent direct, but not indirect, effects of both pain and strength on disability (both p < 0.001), with no direct or indirect effects of cervical ROM on disability.