Validity, Sensitivity, and Responsiveness of the 11-Face Faces Pain Scale to Postoperative Pain in Adult Orthopedic Surgery Patients

• Pain is one of the most common complications in patients who underwent surgery.
• The face pain scale (FPS) is a highly reliable and validated assessment tool that uses a series of facial expressions (six, seven, nine, and eleven faces) to illustrate a spectrum of pain intensity in pediatric, adult, older, and cancer populations.
• The 11-face FPS demonstrated excellent concurrent validity.
• The 11-face FPS was sensitive to detect changes in postoperative pain intensity in response to pain medication.

Pain is common in patients after orthopedic surgery. The 11-face Faces Pain Scale has not been validated for use in adult patients with postoperative pain. To assess the validity of the 11-face Faces Pain Scale and its ability to detect responses to pain medications, and to determine whether the sensitivity of the 11-face Faces Pain Scale for detecting changes in pain intensity over time is associated with gender differences in adult postorthopedic surgery patients. The 11-face Faces Pain Scale was translated into Vietnamese using forward and back translation. Postoperative pain was assessed using an 11-point numerical rating scale and the 11-face Faces Pain Scale on the day of surgery, and before (Time 1) and every 30 minutes after (Times 2-5) the patients had taken pain medications on the first postoperative day. The 11-face Faces Pain Scale highly correlated with the numerical rating scale (r = 0.78, p < .001). When the scores from each follow-up test (Times 2-5) were compared with those from the baseline test (Time 1), the effect sizes were −0.70, −1.05, −1.20, and −1.31, and the standardized response means were −1.17, −1.59, −1.66, and −1.82, respectively. The mean change in pain intensity, but not gender–time interaction effect, over the five time points was significant (F = 182.03, p < .001). Our results support that the 11-face Faces Pain Scale is appropriate for measuring acute postoperative pain in adults.