Two hundred thirty-one patients with lower-limb fractures were randomized to bupivacaine alone (B; n=78), bupivacaine+5 µg sufentanil (BS1; n=85), or bupivacaine+10 µg sufentanil (BS2; n=84). The primary outcomes were postoperative NRS pain scores and rescue analgesic use across postoperative days (POD) 1–3. Secondary outcomes included block characteristics and adverse events. Outcomes were assessed repeatedly up to 72 hours. Overall, the results showed lower POD2 pain scores (BS1 and BS2 vs B) and reduced rescue analgesic use (POD2 for BS1 and BS2; POD3 for BS2), along with longer motor block durations when sufentanil was added. In short, intrathecal bupivacaine+sufentanil improved analgesia and decreased opioid requirements, with 10 µg showing the most sustained effect but more pruritus and early hypoxemia.