Comparison of IntraArticular Platelet-Rich-Plasma to Corticosteroid Injections for Patients With Zygapophyseal Joint (Z-Joint) Low Back Pain Confirmed by Dual Intra-Articular Local Anesthetic Injections

Inclusion Criteria: * \- 40 years old or more; given the low prevalence of facet pain in younger adults * LBP present for more than six months, with an axial predominance * Persistent LBP after three months of non-interventional treatment * Pretreatment ODI score of at least 30/100 (moderate disability associated with LBP) * Pretreatment LBP VAS of at least 4/10 * 80% LBP reduction 30 minutes after 2 intra-articular diagnostic blocs with Xylocaine and Marcaine * Radiological signs of facet joint degeneration (on X-rays, CT Scan or MRI) * Absence of neurological deficit * Sufficient knowledge of French or English to complete the questionnaires Exclusion Criteria: * \- Less than 40 years old * Failure to achieve intra-articular diagnostic block * Intra-articular injection of CS 3 months or less before recruitment * Oral corticosteroid use in the last two weeks * Inflammatory disease * Systemic infection * Infection at injection site * Vertebral fracture * Spine tumour * Surgical intervention at injection site prior to the study or planned * Cognitive disorder that impairs the ability to answer the questionnaires * Pregnancy * Breastfeeding * Coagulopathy affecting platelets * Drug affecting platelets that cannot be stopped (except acetylsalicylic acid) * Intolerance or allergies to local anesthetics, contrast agent, CS, and blood products