The purpose of this study is to compare the efficacy, duration of motor block until return to normal function in the non-operated leg after the start of injection, of ropivacaine 5 mg/ml and bupivacaine 5 mg/ml when used for spinal anaesthesia in patients undergoing unilateral lower limb surgery.

Inclusion Criteria:

• Provision of written informed consent
• Men or women, 18 years £ age £ 70 years
• Patient scheduled for unilateral lower limb surgery with an estimated duration < 2 hours under spinal anaesthesia
• ASA category I ~ II
• 18.5 ≤ BMI ≤ 23.9

Exclusion Criteria:

• Contraindications to spinal anaesthesia, such as local infections, generalised septicaemia, platelet and clotting factor abnormalities, significant neurological disease with motor or sensory deficit, diagnosed increased intracranial pressure
• A known history of allergy, sensitivity or any other form of reaction to local anaesthetics of amide type
• Suspected inability to comply with the study procedures, including language difficulties or medical history and/or concomitant disease, as judged by the investigator
• Psychiatric history or any other concomitant disease which may lead to unreliability in clinical assessments, as judged by the investigator
• Significant alcohol, drug or medication abuse, as judged by the investigator
• Women who are pregnant or lactating or women of child bearing potential who are not practising adequate contraception or have positive urine pregnancy test (a urine Human chorionic gonadotropin [HCG] analysis)
• Involvement in the planning and conduct of the study (applies to both AstraZeneca staff or staff at the study site)
• Previous enrolment in the present study
• Participation in a clinical study during the last 3 months
• Serious or unstable medical or psychological conditions that, in the opinion of the investigator, would compromise the subjects' safety or successful participation in the study.