This study will compare the effect and safety of HSK16149 with placebo on perioperative analgesia in orthopedic surgery, and explore the dosage of HSK16149 capsules for orthopedic analgesia during perioperative period.

This study included patients who have orthopedic surgery under general anesthetic, with expected operation time ≤4h.

Subjects were given 40mg or 60mg of HSK16149 or placebo orally the night before surgery, 2h before surgery, 4h and 16h after surgery, for a total of 4 times during the whole treatment period.

Subjects will receive intravenous patient-controlled analgesia (PCA) morphine for pain in the immediate postoperative period. If PCA is insufficient, rescue analgesia of morphine may be given I.V. as determined by the investigator.

After the treatment period, the subjects will be followed up.

Inclusion Criteria:

1. Male or female between the ages of 18 and 75 years (included);
2. Elective orthopedic surgery under general anesthesia, expected operation time ≤4 hours and postoperative morphine analgesia time ≥24 hours;
3. 18kg/m^2≤BMI≤30 kg/m^2;
4. American Society of Anesthesiologists (ASA) grade I and II;

Exclusion Criteria:

1. Any of the following medical histories or conditions prior to screening:

   • Long history of chronic pain;
   • history of severe cardiovascular or respiratory disease;
   • history of neurological or psychiatric disorders;
   • history of acute poisoning with alcohol, hypnotics, analgesics or other drugs acting on the central nervous system;
   • major surgery within 3 months;
   • patients with high bleeding risk;
   • history of renal disease treated with dialysis within 28 days before surgery;
   • have active infection within the past 2 weeks;

2. Use of any of the following medications or treatments:

   • opioid analgesics for more than 10 consecutive days within 3 months prior to screening;
   • other analgesics before randomization if the last dose was taken less than 5 half-lives of the drug (according to the label);

3. Abnormal laboratory tests during screening:

4. Hypertension that is not adequately controlled by antihypertensive drugs (systolic blood pressure ≥160 mmHg and/or diastolic blood pressure ≥100 mmHg), or systolic blood pressure ≤90 mmHg during screening;

5. A history of drug abuse, and/or alcohol abuse in the 3 months prior to screening;

6. Participated in another clinical trial and received IMP within 30 days prior to screening;

7. Pregnant or lactating women;

8. Unwillingness to use reliable contraceptive methods from the time of screening until 28 days after the last dose of IMP;