A medial condyle fracture of the humerus with preexisting fishtail deformity and lateral condyle nonunion is very rare, and there have been few reports describing favorable treatment options. We herein report the case of an 83-year-old woman who sustained a medial condyle fracture of her elbow with a comorbidity of long-lasting limited elbow motion with a history of elbow trauma in childhood. After conservative treatment with casting for four weeks, unstable medial condyle fracture in the presence of fishtail deformity and lateral condyle nonunion remained. Due to persistent pain, the patient underwent surgical treatment with semiconstrained total elbow arthroplasty (TEA) through the triceps-on approach. At the 12-month follow-up examination, the patient had no pain and achieved satisfactory functional outcomes. This case report demonstrated the efficacy of TEA for deteriorated stability due to bilateral condyle fracture/nonunion with fishtail deformity of the humerus.