Total hip arthroplasty (THA) is a commonly used treatment for hip lesions, but it is often accompanied by persistent pain after surgery, which obviously affects the quality of life of patients, so perfect postoperative analgesia is particularly important for the rapid recovery of patients. Peripheral nerve blocks are often used as postoperative analgesia for THA, and fascia iliaca compartment block (FICB) is the preferred nerve block for THA due to its good postoperative analgesic effect and fewer postoperative adverse reactions. However, the effect of nerve block with ropivacaine alone is short, and the postoperative analgesia time is limited, which seriously affects the patient's surgical recovery. Therefore, prolonging the postoperative analgesic time is an urgent problem to be solved by FICB, and some scholars recommend the combined use of local anesthetic adjuvants to prolong the block time, which is an effective and safe method. In this study, a long-acting analgesic drug, methylene blue, was selected as an adjuvant for ropivacaine for FICB, but there was no unified clinical standard for the postoperative analgesic concentration of methylene blue.

Inclusion Criteria:

• Hip replacement surgery is indicated
• ASA Class II - Class III
• No history of analgesic or local anesthetic allergy
• No history of alcohol abuse or narcotic drug abuse
• Patients and their families have given informed consent and signed the informed consent form

Exclusion Criteria:

• Patient or family refusal to participate in the study
• Severe coagulation abnormalities
• Local anesthetic allergy
• Severe psychiatric illness or other communication disorder
• There is an infection at the puncture site