Randomization
Using computer-generated random sequence tables and sealed envelopes, patients were randomized to one of two groups: 0.1% ropivacaine or 0.2% ropivacaine. The envelopes, which contained the prepared local anaesthetics for FNB and a computer-generated number, were opened just before the surgery when the patients arrived in the operating room. The patients, anaesthesiologists, orthopaedists, and research assistants were not informed about the concentration of ropivacaine used for FNB.