Pain Compared Between the First and the Second Surgery in Staged BTKA

Inclusion Criteria: * patients undergoing elective bilateral staged total knee arthroplasty at a 1-week interval under spinal anesthesia, * age \<=85 * American Society of Anesthesiologists physical status of I to II Exclusion Criteria: any contraindication to spinal anesthesia or femoral nerve block such as coagulopathy; conversion to general anesthesia; preexisting pain syndrome; abnormal liver function or renal test results; severe heart, liver, or renal disease; history of stroke or neurologic deficits; psychiatric disorder; chronic opioid use; drug dependency; allergy to study medications; inflammatory joint disease; previous surgery on or trauma of the knee; difference in preoperative VAS score of ≥ 20 (at rest and at maximum knee flexion) between each side of the knee; body mass index of ≥ 40 kg/m2; and inability to comprehend the VAS or to use patient-controlled analgesia (PCA.