*4.6. Study Limitations*

There were some limitations in this study. First, our study had a selection bias in relation to the retrospectively evaluated characteristics. RNB use was decided by the anesthesiologists, and there was no clear criterion. Future prospective studies with randomization are needed. Second, the types of nerve block used varied. FICB, LSPB, and PENG block were used herein, which might have confounded the results. Third, the severity of delirium was not considered. Some patients only demonstrated temporary inattention; however, other patients demonstrated irritability that needed restraint. We classified these demonstrations as delirium. Subgroup analyses according to the severity of delirium will be helpful in the evaluation of the effects of RNB. Despite these limitations, our study provided evidence that RNB can reduce the incidence of delirium, and we believe that its use can help improve the prognosis of elderly patients with hip fracture.
