Investigation des mécanismes qui sous-tendent les effets cliniques de la manipulation vertébrale dans la prise en charge des douleurs chroniques non spécifiques au rachis: rôle des réponses neuromécaniques et de la rigidité vertébrale

Chronic nonspecific back pain poses an important socioeconomic burden for society and has serious implications on patients’ quality of life. Spinal manipulation therapy (SMT) is now a therapeutic modality recommended by numerous practice guidelines. It is suggested that SMT clinical effects are, at least partly, associated to the neuromechanical responses (muscle response and vertebral displacement) characterizing this therapy. These responses have been shown to be dependent of the therapy characteristics. Moreover, an immediate decrease in spinal stiffness could help identify patients that are most likely to improve following few treatment sessions involving SMTs. Despite such evidence, associations between SMT characteristics and neuromechanical responses, spinal stiffness modulation, and the clinical evolution of patients with chronic nonspecific back pain remain unknown.   The main objective of this thesis is to investigate, through an apparatus using a servocontrolled linear actuator motor, the mechanisms underlying the clinical effects of SMT in the management of chronic nonspecific back pain. Specifically, the relationship between SMT characteristics (peak force and rate of force application) and the amplitude of the lumbar paraspinal muscle response were compared between healthy participants and participants with chronic nonspecific low back pain (study 1). Considering that the fourth study would required the palpation of the thoracic transverse processes, a palpation method was developed and validated (study 2). Spinal stiffness was then compared between participants with and without chronic nonspecific thoracic pain and the measurement reliability was assessed (study 3). Finally, relationships between SMT characteristics, changes in spinal stiffness, and the clinical evolution of participants with chronic nonspecific thoracic pain, at one week following three treatment sessions, were evaluated and predictors of short-term improvement were also identified (study 4).  First study results showed that the amplitude of the muscle response increases with the increase in the SMT peak force (and rate of force application) in participants with and without chronic low back pain. In the third study, spinal stiffness was shown to be reliable and lower spinal stiffness was observed in participants with chronic thoracic pain. The fourth study results revealed no significant differences in the clinical and biomechanical outcomes of the four groups of participants: three specific SMT doses and one control group not receiving SMT. Participants showed, at the fourth session, a decrease in pain intensity, disability, spinal stiffness and tenderness during spinal stiffness measurement. An improvement was associated with a decrease in tenderness and pain intensity.  In conclusion, the thesis results suggest that, in this experimental setting, SMT characteristics and therefore, the neuromechanical responses to SMT, do not greatly influence this therapy clinical effects. Studies are still required to identify the mechanisms underlying the clinical effects of SMT

Keyphrases: Chiropractic, Chronic low back pain, Chronic mid-back pain, Clinical effect, Complementary and alternative medicine, Dose-response relationship, Electromyography, Manual therapy, Neuromechanical response, Non-specific pain, Spinal manipulation, Spinal stiffness