Table 2 Main inclusion and exclusion criteria

Patients with acute pain caused by manual treatment after anterior ligament reconstruction

Patients with mental disorder or altered mental status have difficulty in reporting pain

Age ≥ 18 years old

Patients who have undergone other surgical operations on the knee except for ACL

Willing to participate in the trial and sign informed consent

Drug dependence or abuse

Background worst pain (during Manual therapy) reported being 4 or higher (on a visual analogue scale (VAS) of 0 to 10 cm)

Contraindications to N₂O (suspected bowel obstruction, air embolism, pneumothorax, epilepsy, chronic obstructive pulmonary disease, and acute respiratory infection, pregnancy, pharmaceutical or pathological pulmonary fibrosis, maxillofacial injuries, disease involving ear, nose, larynx)

Without postoperative complication