Agreement Between Patient-Reported Pain, Observer-Rated Pain Behavior, and Analgesic Request After Total Knee Arthroplasty

Postoperative pain is a major determinant of recovery after total knee arthroplasty (TKA), affecting patient satisfaction, early mobilization, and rehabilitation. The Numeric Rating Scale (NRS) is among the most widely used tools for postoperative pain assessment and frequently guides analgesic decisions. However, pain is a subjective and multidimensional experience, and patients with similar NRS scores may display different levels of pain behavior and analgesic need. Although patient-reported pain intensity, observed pain behavior, and analgesic request have each been studied, few studies have evaluated these three components simultaneously in the early postoperative period.

This single-center, prospective observational study will be conducted at Sincan Training and Research Hospital, Ankara, Turkey. No intervention, randomization, or change in anesthesia or analgesia protocol will be made; all procedures follow routine clinical practice. Written informed consent will be obtained preoperatively.

Adult patients (18 years or older, ASA physical status I-III) undergoing elective primary TKA under spinal anesthesia will be included. Demographic data (age, sex, height, weight), ASA physical status, comorbidities, and perioperative clinical data will be recorded on standardized case report forms.

At postoperative hours 2, 6, and 24:

1. Patient-reported pain intensity will be assessed with the NRS (0 = no pain, 10 = worst pain imaginable).
2. Observer-rated pain behavior will be scored with a standardized behavioral pain assessment developed by the investigators, adapted from established behavioral scales (CPOT, FLACC). Facial expression, body movements, and vocal expressions are each scored 0-2 (total score 0-6; higher scores indicate more pronounced pain behavior).
3. Patients will be asked whether they feel the need for additional analgesia (analgesic request: yes/no).

All patients will receive the institution's standard postoperative multimodal analgesia protocol. Routine analgesics, rescue analgesic administrations, their timing, and total analgesic consumption over the first 24 postoperative hours will be recorded.

Sample size: Based on a power of 90% and a type I error of 5% (G*Power 3.1), assuming a medium effect size, a minimum of 112 patients is required. Allowing for data loss and incomplete records, at least 120 patients will be enrolled.

Statistical analysis: Analyses will be performed with IBM SPSS Statistics. Relationships between NRS, observer-rated pain behavior score, and analgesic request will be analyzed using appropriate parametric or non-parametric tests, including Pearson or Spearman correlation, and chi-square or Fisher's exact test. A p value < 0.05 will be considered statistically significant.

The findings are expected to clarify the clinical validity of numeric pain scores and support a more comprehensive approach to postoperative pain assessment and analgesic decision-making.