No evidence for generalized increased postoperative responsiveness to pain: a combined behavioral and serial...

Although it is generally accepted that increased pain responsiveness and central sensitization develop after major tissue injury, this claim has not been tested using brain imaging methods in a clinical pain setting. We tested this hypothesis using a postoperative pain model, in conjunction with serial functional magnetic resonance imaging (fMRI).

We studied brain and subjective pain responses to innocuous and noxious heat in seven patients before and after total knee arthroplasty. Noxious and innocuous thermal stimuli were applied to the upper leg, proximal to the surgical area and to the lower forearm, a site remote from the surgical area. A group of eight age- and sex-matched control subjects underwent the same two-test procedure except that they were not submitted to an orthopedic surgical intervention.

Subjective pain and brain responses to innocuous and noxious stimulation were not increased postoperatively. Actually, responses in primary and secondary somatosensory cortex for stimulation of the operated leg were significantly smaller after surgery. Brain responses in the control group did not differ significantly across the two sessions.

These data argue against the development of an overall increased pain responsiveness after a major surgical trauma. The data are in contrast with results from animal studies and from brain imaging studies using surrogate models of clinical pain, which have shown increased central responsiveness in the area around the insult, thereby calling into question the clinical implications of acute postinjury sensitization.