The purpose of this study is to evaluate the adequate dose of intrathecal hydromorphone injection for postoperative pain relief after knee arthroscopic surgery.

Sixty patients who were undergoing unilateral knee arthroscopy randomly received unilateral spinal anesthesia with 0.5% hyperbaric bupivacaine 6 mg combined with normal saline 0.05 mL or hydromorphone 2.5, 5 or, 10 μg/0.05 mL. The verbal numerical rating scale (VNRS) pain scores were measured at 30 minutes and 2, 4, 6, 12 and 24 hours postoperatively, and the side effects of hydromorphone were recorded.

Inclusion Criteria:

• ASA class I-II (age range: 18-72 years)
• Informed consent obtained patients

Exclusion Criteria:

• The exclusion criteria included evidence of neurological or neuromuscular disease, respiratory or cardiac disease, diabetes mellitus or peripheral neuropathy, as well as those patients who were receiving chronic analgesic therapy or who had infection at the intended site of spinal needle insertion or who had hypersensitivity to amide local anesthetics or opioids