The potency of ropivacaine compared with bupivacaine in regional anesthesia remains controversial. Therefore, we compared the pharmacodynamics of equal concentrations of bupivacaine and ropivacaine in combined sciatic and femoral nerve blocks for patients undergoing knee arthroplasty. Fifty patients received 40 mL of either 0.5% bupivacaine (n = 25) or 0.5% ropivacaine (n = 25) divided between the sciatic (15 mL) and the femoral (25 mL) nerves before induction of anesthesia. Loss and recovery of sensory (% of cold sensation compared to opposite side) and motor (no contraction or normal muscle force) functions were recorded in the distribution of the femoral, saphenous, common peroneal, and tibial nerves. Pain scores and morphine consumption over 48 h were also evaluated. There were no difference between bupivacaine and ropivacaine in terms of onset of sensory and motor blockade. However, resolution of sensory and motor function was faster in the ropivacaine group but only significantly so for the sciatic nerve and between 24 to 28 h for sensory resolution and 12 to 20 h for motor function. Overall, pain scores and morphine consumption were similar. In conclusion, we showed that block resolution is different between bupivacaine and ropivacaine when administered for combined sciatic and femoral nerve blocks. A new systematic method to assess sciatic and femoral nerve blockade is proposed.