Schematic illustration of the study protocol.

<p>(<b>A</b>) The day before scheduled surgery patients completed the Spielberger's State-Trait Anxiety Inventory (STAI) and Beck's Depression Inventory (BDI); (<b>B</b>) Then patients underwent a conditioned pain modulation paradigm in which a baseline pressure pain threshold was measured at the quadriceps muscle followed by a conditioning painful stimulus induced by a cold pressor test (CPT) (i.e., hand immersion in an ice water bath for 120 seconds). After 120 seconds of hand immersion (or upon spontaneous hand removal) the pressure pain threshold at the quadriceps muscle was reassessed. The Situational Pain Catastrophizing Scale (S-PCS) was re-administered within five minutes after cold pressor test and patients were instructed to reference the cold pressor pain while answering; (<b>C</b>) From postoperative days 2–5 pain-related outcomes were assessed, including postoperative movement-evoked pain intensity, morphine consumption, and an integrated analgesic assessment score based on the aforementioned; (<b>D</b>) Persistent postoperative pain was assessed according to responses to the Brief Pain Inventory – Short Form (BPI) at six months.