Can a sedative outlast a standard painkiller in spinal anesthesia?

This trial tests whether adding dexmedetomidine to the spinal anesthetic bupivacaine provides longer-lasting pain relief after lower limb orthopedic surgery than adding fentanyl. Sixty adults undergoing leg surgery under spinal anesthesia will be randomly assigned to receive one of the two combinations. After surgery, pain is measured hourly, and the time until a patient first needs rescue pain medication is recorded. The goal is to see if dexmedetomidine extends the duration of effective analgesia compared to fentanyl.