Background: To evaluate the clinical efficacy and safety of unilateral spinal anaesthesia with 0.66% hyperbaric ropivacaine compared with 0.5% hyperbaric bupivacaine for arthroscopic knee surgery. 

Patients and methods: Forty patients with American Society of Anesthesiology physical status grade I-II were randomly and double blindly allocated to one of two groups. Spinal anaesthesia was performed from the L3-4 or L4-5 interspace with the patient in the lateral decubitus position and with the operative side below. Group B (n = 20) received 7.5mg of 0.5% hyperbaric bupivacaine and group R (n = 20) received 10mg of 0.66% hyperbaric ropivacaine. Patients stayed in the lateral decubitus position for 10 minutes and were then turned to the supine position. The characteristics of spinal block, intraoperative quality of spinal anaesthesia, adverse effects and recovery times were recorded. 

Results: The onset of sensory block and motor block were significantly earlier in group B compared with group R (p < 0.05). The duration of sensory block and motor block were significantly shorter for group R compared with group B (p < 0.05). Bilateral sensory block occurred in 85% of patients in group B and in 40% of patients in group R (p < 0.05). Bilateral motor block occurred in 70% of patients in group B and in 25% of patients in group R (p < 0.05). 

Conclusion: For outpatient knee arthroscopy, 10mg of 0.66% hyperbaric ropivacaine is preferred to 7.5mg of 0.5% hyperbaric bupivacaine because it provides a more selective unilateral block and a faster recovery.