Background <p>The Clinical Frailty Scale (CFS) is a tool to assess the overall health of older adults. There are few reports of CFS and prognosis of ankle fracture. The objective of this study was to determine the predictive power of the CFS for adverse clinical and radiographic outcomes after surgery in elderly patients with trimalleolar fractures.</p> Method <p>All patients aged 65 and older underwent open reduction and internal fixation for trimalleolar fractures between January 2015 to January 2023 were selected. Follow-up time was at least 1 year. Patients with post-traumatic osteoarthritis, bone tumors, bone infection, and other diseases before surgery were excluded. According to the CFS score, the patients were divided into three groups: not frail, vulnerable, and frail. Multivariate logistic regression analysis was used to evaluate the effect of the clinical frailty scale on postoperative complications.</p> Result <p>Excluding 3 cases of death during the follow-up process, and 4 cases lost to follow-up, the study included a total of 146 patients, who were grouped based on their degree of frailty: the Healthy Group (CFS = 1–3, <i>n</i> = 69), the Vulnerable Group (CFS = 4, <i>n</i> = 50), and the Frail Group (CFS = 5–9, <i>n</i> = 47). In comparison with the not frail group, frail (CFS 5–9) emerged as an independent predictor of any complications (OR = 6.90, CI: 1.43–11.56, <i>P</i> = 0.009), adverse discharge destination (OR = 7.53, CI: 2.06–77.50, <i>P</i> = 0.006), and post-traumatic osteoarthritis (OR = 8.90, CI: 1.94–24.66, <i>P</i> = 0.003).</p> Conclusions <p>The frailty assessed by the CFS is associated with adverse discharge destination, any complications, and post-traumatic osteoarthritis in elderly patients undergoing open reduction and internal fixation for trimalleolar fractures.</p>