In total knee arthroplasty, the effectiveness of some peripheral nerve blocks in postoperative pain control has been investigated, with conflicting results reported. The primary aim of this study is to evaluate the effects of the suprainguinal fascia iliaca plane block, which is routinely performed in our clinic for postoperative pain management, and the adductor canal block in patients undergoing total knee arthroplasty under spinal anesthesia. Patients scheduled for total knee arthroplasty under spinal anesthesia will be randomly assigned using computer-generated randomization into two groups: the adductor canal block group (Group A) and the suprainguinal fascia iliaca plane block group (Group S). The nerve blocks will be performed by a single investigator according to the assigned group. Postoperative follow-up assessments will be conducted and recorded by a different investigator who is blinded to which nerve block was performed.