• D A Rice, M T Kluger, P J McNair, G N Lewis, A A Somogyi, R Borotkanics, D T Barratt, and M Walker.
• Health and Rehabilitation Research Institute, Auckland University of Technology, Auckland, New Zealand; Waitemata Pain Services, Waitemata District Health Board, Auckland, New Zealand. Electronic address: david.rice@aut.ac.nz.
• Br J Anaesth. 2018 Oct 1; 121 (4): 804-812.

BackgroundPersistent postoperative pain (PPP) is common after total knee arthroplasty (TKA). The primary aim of this prospective cohort study was to identify important predictors of moderate to severe PPP 6 and 12 months after TKA.MethodsConsenting patients (n=300) undergoing primary unilateral TKA attended a preoperative session to collect clinical information (age, gender, BMI, preoperative knee pain, comorbid pain, likely neuropathic pain) and psychological variables (depression, anxiety, catastrophising, expected pain). Quantitative sensory testing (pressure pain thresholds, temporal summation, conditioned pain modulation) was performed, and blood samples were obtained for subsequent genotyping of OPRM1 and COMT. Acute postoperative pain was measured at rest and during movement. Surgical factors (surgery time, patella resurfacing, anaesthetic type) were collected after operation. Follow-up questionnaires were sent 6 and 12 months after surgery. Multivariate logistic regression was used to identify predictors of PPP.ResultsThe prevalence of moderate to severe PPP was 21% (n=60) and 16% (n=45) 6 and 12 months after surgery, with 55% (n=33) and 60% (n=31) of PPP likely neuropathic in nature. At 6 months, a combination of preoperative pain intensity, expected pain, trait anxiety, and temporal summation (Akaike information criterion, 309.9; area under receiver operating characteristic (ROC) curve, 0.70) was able to correctly classify 66% of patients into moderate to severe PPP and no to mild PPP groups. At 12 months, preoperative pain intensity, expected pain, and trait anxiety (Akaike information criterion, 286.8; area under ROC curve, 0.66) correctly classified 66% of patients.ConclusionsFindings from this study highlight several factors that may be targeted in future intervention studies to reduce the development of PPP.Trial Registry NumberACTRN12612001089820.Copyright © 2018 British Journal of Anaesthesia. Published by Elsevier Ltd. All rights reserved.

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