The Underlying Mechanism of Spinal Manipulative Therapy and the Effect of Pain on Physical Outcome Measures

SMT is a common manual therapy for treating patients with mechanical low back pain (LBP). SMT is defined as a high velocity, low amplitude thrust technique. Specifically, the clinician stands beside a supine patient. The patient is passively side-bent towards the side to be manipulated. The clinician passively rotates the patient and then delivers a high velocity, low amplitude thrust to the anterior superior iliac spine in a posteroinferior direction. SMT is indicated for patients with LBP judged to have spinal hypomobility or malalignment. Recently, our collaborators have discovered that LBP subjects who benefit from SMT can be identified prior to treatment by a five-item clinical prediction rule. Compared to non-responders, those who respond to SMT have: 1) more than 30% decrease in the modified Oswestry Disability Index score, 2) a significant and immediate decrease in spinal stiffness, and 3) a concurrent change in lumbar multifidus muscle activity. Taken together, the physical changes experienced by SMT responders alone provide an unique opportunity to better understand the mechanisms underlying SMT.

Since spinal stiffness is an important physical indicator of SMT response, it is important to understand the causal relation between pain, paraspinal/trunk muscle activity and spinal stiffness. Although research has shown positive correlation between pain and muscle activity, and between paraspinal muscle activity and spinal stiffness, the causal relation between pain, paraspinal/trunk muscle activity and spinal stiffness remains unknown. Given this background, an induction of temporary benign experimental pain to asymptomatic individuals can help clarify such causal relation and improve our understanding of physical responses in responders following pain resolution by SMT.