Open-label milnacipran for patients with persistent knee pain 1 year or longer after total knee arthroplasty: a pilot study.

Objective: The current study investigates whether milnacipran is effective in reducing pain and improving function in patients with persistent pain ≥ 1 year after total knee arthroplasty.

Method: This was a 12-week open-label study of flexibly dosed milnacipran in patients (N = 5) experiencing chronic persistent knee pain ≥ 1 year following total knee arthroplasty in the absence of new injury, infection, or implant failure. Subjects were identified from October 2010 to August 2011 through the Duke University Medical Center orthopedic clinic (Durham, North Carolina), typically during 1-year postoperative follow-up visits, and were referred by their orthopedic surgeon.

Results: Milnacipran treatment was associated with reduction in pain according to the primary outcome measure of the visual analog scale (VAS) score for pain (effect size of 1.15) and secondary outcome measures of Knee Society Score (KSS) evaluation subscale score (effect size of 1.37) and Medical Outcomes Study 36-item Short-Form Health Survey (SF-36) bodily pain subscale (effect size of 1.16) at week 12. Secondary outcome measures of functional change were mixed in such that, at week 12, the SF-36 physical functioning subscale showed improvement (effect size of 1.16), but the KSS function subscale score was just below the threshold for meaningful effect size (0.98).

Conclusions: Open-label milnacipran demonstrated reduced pain and some evidence of functional improvement in this small sample of patients with chronic persistent pain 1 year or more after total knee arthroplasty such that well-powered studies are warranted.