Objective: During spinal anaesthesia, intrathecal adjuvants like fentanyl and dexmedetomidine are used to boost the effects of bupivacaine. The purpose of this research is to evaluate the safety and effectiveness of intrathecal fentanyl and dexmedetomidine in conjunction with bupivacaine for patients having lower limb orthopaedic surgery. Method: Three groups of thirty patients each were used in this randomized controlled study. 25 µg of fentanyl and 15 mg of 0.5% hyperbaric bupivacaine were given to Group 1, 5 µg of dexmedetomidine and 15 mg of 0.5% hyperbaric bupivacaine was given to Group 2, and 15 mg of bupivacaine was given to Group 3. The features of the motor and sensory blocks, hemodynamic parameters, postoperative pain (VAS), time to first analgesic request, and side effects were noted and compared across the groups. Results: There was no significant difference in the groups' surgery times or demographic makeup. In comparison to the fentanyl and control groups, dexmedetomidine substantially extended both sensory block (120 ± 23.5 min) and motor block regression (242 ± 22 min) (P < 0.001). The dexmedetomidine group had a longer time to first analgesic request (245 ± 3.6 min) than the fentanyl and control groups (P < 0.001). The group that received dexmedetomidine consumed considerably fewer postoperative analgesics. All groups maintained hemodynamic stability, and there were no significant variations in the incidence of bradycardia, hypotension, or nausea, among other adverse effects. Conclusion: Compared to fentanyl, the addition of 5 µg dexmedetomidine to intrathecal bupivacaine considerably prolongs the duration of sensory and motor block and decreases the requirement for postoperative analgesia. Dexmedetomidine is an excellent adjuvant for spinal anaesthesia in lower limb procedures as it also offers steady hemodynamics with few adverse effects.