The primary objective is to evaluate the analgesic efficacy of IV SHR8554 compared with morphine and placebo in patients with acute postoperative pain following orthopedic surgery.

Inclusion Criteria:

1. Able and willing to provide a written informed consent
2. Subjects requiring elective general anesthesia orthopedic surgery
3. Conform to the ASA Physical Status Classification

Exclusion Criteria:

1. Subjects with a history of difficult airway
2. Subjects with a history of reflux esophagitis
3. Subjects with a history of mental illness
4. Subjects with poor blood pressure control
5. Transcutaneous oxygen saturation (SpO2) <90%
6. Random blood glucose ≥11.1mmol/L
7. Subjects with abnormal liver function
8. allergies to opioids and other medications that may be used during the trial