The METRIC Study Protocol

The METRIC Study Protocol: an Explanatory Randomized Controlled Trial Investigating the Neurophysiological Mechanisms Underlying the Therapeutic Effects of Spinal Manipulative Therapy for Chronic Primary Low Back Pain

The goal of this clinical trial is to test the effects of spinal manipulative therapy in individuals with chronic primary low back pain and determine the neurophysiological mechanisms underlying pain relief. The main questions it aims to answer are: • Is pain relief produced by spinal manipulative therapy in patients with chronic primary low back pain caused by a reduction of C-fiber-related nociceptive processing? • Are these effects greater when spinal manipulative therapy is applied to the whole spine where it is clinically indicated compared with lumbar spine only? • Are these effects greater after 36 treatments over 3 months compared with 12 treatments over 1 month. Participants will receive spinal manipulative therapy (all clinically indicated spine segments or back only) or a control intervention. A group of healthy volunteers will be recruited to assess secondary outcome measures over the same time period, as reference data for comparisons. Researchers will compare the two groups receiving spinal manipulative therapy to the group receiving the control intervention to see if clinical pain relief and the reduction of temporal summation of second pain (produced experimentally) is significantly greater with spinal manipulative therapy.

Inclusion Criteria:

• Duration of current low back pain (LBP) episode ≥ 6 months;
• Average LBP intensity during the last 7 days ≥ 3/10;
• (For healthy volunteers only) To be of the same sex and age (± 1 year) as a participant with low back pain.

Exclusion Criteria:

• Diagnosis of back conditions other than chronic primary LBP e.g., failed back surgery syndrome, spondylosis, spondylolisthesis, spinal stenosis, herniated disc, infection, etc.;
• Presence of pain in another body location that is more severe than the pain in the lower back;
• Presence of a neurological deficit i.e., sensation loss, muscle weakness, decreased deep tendon reflexes;
• Presence of contraindications to spinal manipulative therapy e.g., recent fracture, history of spinal surgery, cauda equina syndrome, inflammatory arthritis, taking anticoagulant medication, active cancer, moderate to severe osteoporosis, abdominal aortic aneurysm;
• Underwent surgery in the last 3 months;
• Pregnancy, ≤ 3 months post-partum or planning to get pregnant in the next 12 months;
• History of spinal manipulative therapy in the past 12 months;
• Scoliosis ≥ 20°;
• BMI ≥ 40;
• Insufficient language skills in French to complete the questionnaires;
• Open or pending litigation for LBP or seeking/receiving disability compensation;
• Diagnosis of an illness affecting the sensorimotor functions e.g., diabetes, multiple sclerosis, amyotrophic lateral sclerosis;
• Diagnosis of mental health disorders (with the exception of anxiety and depression);
• Current drug or alcohol dependence;
• Skin of type I on the Fitzpatrick scale;
• (For healthy volunteers only) Regular use of pain medication or usage in the 48 h prior to data collection;
• (For healthy volunteers only) History of chronic pain;
• (For healthy volunteers only) Acute pain on the days of data collection.