RESUMEN
BACKGROUND: We aimed to appraise the evidence relating to the measurement properties of unidimensional tools to quantify pain after surgery. Furthermore, we wished to identify the tools used to assess interference of pain with functional recovery. METHODS: Four electronic sources (MEDLINE, Embase, CINAHL, PsycINFO) were searched in August 2020. Two reviewers independently screened articles and assessed risk of bias using the COnsensus-based Standards for the selection of health Measurement INstruments (COSMIN) checklist. RESULTS: Thirty-one studies with a total of 12 498 participants were included. Most of the studies failed to meet the methodological quality standards required by COSMIN. Studies of unidimensional assessment tools were underpinned by low-quality evidence for reliability (five studies), and responsiveness (seven studies). Convergent validity was the most studied property (13 studies) with moderate to high correlation ranging from 0.5 to 0.9 between unidimensional tools. Interpretability results were available only for the visual analogue scale (seven studies) and numerical rating scale (four studies). Studies on functional assessment tools were scarce; only one study included an 'Objective Pain Score,' a tool assessing pain interference with respiratory function, and it had low-quality for convergent validity. CONCLUSIONS: This systematic review challenges the validity and reliability of unidimensional tools in adult patients after surgery. We found no evidence that any one unidimensional tool has superior measurement properties in assessing postoperative pain. In addition, because promoting function is a crucial perioperative goal, psychometric validation studies of functional pain assessment tools are needed to improve pain assessment and management. CLINICAL TRIAL REGISTRATION: PROSPERO CRD42020213495.