The evolution of primary hyperalgesia in orthopedic surgery: quantitative sensory testing and clinical evaluation before and after total knee arthroplasty.

BACKGROUND Quantitative sensory testing (QST) allows precise characterization of sensory deficits and painful symptoms and may offer additional information on the pathophysiology of postoperative pain. METHODS We evaluated 20 patients scheduled for total knee arthroplasty clinically and with QST before surgery, at 1 and 4 days after surgery, and at 1 and 4 mo after surgery. The clinical evaluation included preoperative pain and inflammation of the operative knee, postoperative assessment of pain at rest and during movement (Visual Analog Scale score), cumulative morphine consumption, and circumference and temperature of both knees. QST included thermal and mechanical (pressure) pain threshold measurements and assessment of responses to suprathreshold stimuli. Brush-evoked allodynia was also evaluated. Measurements were taken on the operative knee, contralateral knee, and on the hand as a control site. RESULTS All patients had prolonged and severe pain before surgery and inflammation of the operative knee. Preoperative QST provided evidence of heat hyperalgesia in the inflammatory area on the operative knee, but absence of punctate or brush-evoked allodynia in the adjacent noninflamed area. Patients had intense postoperative pain, mostly induced by movement. Primary heat hyperalgesia was present on the operative knee on the first and fourth day after surgery, and was associated with punctate mechanical allodynia in the inflammatory area, but not in the adjacent noninflamed area. Postoperative morphine consumption was correlated with preoperative heat hyperalgesia (r = 0.63; P = 0.01). QST returned to baseline at the 4-mo evaluation. Only four patients had moderate knee pain induced by movement at that time. CONCLUSION Heat hyperalgesia was the predominant QST symptom associated with perioperative pain after total knee arthroplasty, and was predictive of postoperative morphine consumption.