The mechanism of back pain relief by spinal manipulation relies on decreased temporal summation of pain

The aim of the present study was to determine whether thoracic spinal manipulation (SM) decreases temporal summation of back pain. The study comprised two controlled experiments including 16 and 15 healthy participants, respectively. Each study included six sessions during which painful or non-painful electrical stimulations were delivered in three conditions: (1) control (2) light mechanical stimulus (MS) or (3) SM. Electrical stimulation was applied on the thoracic spine (T4), in the area where SM and MS were performed. In Experiment 1, electrical stimulation consisted in a single 1-ms pulse while a single or repeated train of ten 1-ms pulses was used in Experiment 2. SM involved articular cavitation while MS was a calibrated force of 25 N applied manually for 2 s. For the single pulse, changes in pain or tactile sensation in the SM or MS sessions compared with the CTL session were not significantly different (all p's > 0.05). In contrast, temporal summation of pain was decreased in the SM session compared with the CTL session for both the single and repeated train (p's < 0.05). Changes were not significant for the MS sessions (all p's > 0.05) and no effect was observed for the tactile sensation (all p's > 0.1). These results indicate that SM produces specific inhibitory effects on temporal summation of back pain, consistent with the involvement of a spinal anti-nociceptive mechanism in clinical pain relief by SM. This provides the first mechanistic evidence of back pain relief by spinal manipulation.