Perioperative oxidative stress predicts subsequent pain-related outcomes in the 6 months following total knee arthroplasty.

Total knee arthroplasty (TKA) is effective for pain reduction in most patients, but 15% or more report unsatisfactory long-term pain outcomes. We tested whether oxidative stress (OS) related to extended tourniquet application during TKA and subsequent ischemic reperfusion contributed to adverse post-TKA pain outcomes. Blood samples were obtained in 91 osteoarthritis patients (63% female) undergoing TKA prior to tourniquet placement (T1), 45 minutes after tourniquet inflation (T2), and 15 minutes following tourniquet removal (T3). Plasma levels of F2-isoprostanes and isofurans, the most specific measures of in vivo OS, were quantified. Pain intensity and function were assessed at baseline and again at 6 weeks and 6 months following TKA. Results indicated that higher Combined OS (F2-isoprostanes+Isofurans/2) at T1 baseline as well as larger increases in Combined OS from T1 to T2 were associated with higher baseline-corrected past 24-hour worst and average pain intensity (numeric rating scale) and higher past week McGill Pain Questionnaire-2 total scores at 6-month follow-up (p's <.05). Increases in Combined OS from T1 to T3, which should most directly capture OS and ischemic reperfusion injury related to tourniquet use, were not associated with short-term or long-term post-TKA pain outcomes. Longer ischemia duration was unexpectedly associated with lower baseline-corrected pain intensity at 6-month follow-up. Combined OS was not linked to functional outcomes at either follow-up. Elevated perioperative OS appears to exert small but significant adverse effects on long-term post-TKA pain outcomes, although this OS appears unrelated to ischemic reperfusion injury associated with extended tourniquet use.