Background: Isolated subtalar joint dislocations without associated fractures are rare in the medical literature. They occur when the talus bone remains in place while the calcaneus and navicular bones shift out of place. These dislocations account for about 15% of talus bone injuries and 1 to 2% of all joint dislocations. They are more common in young men following inversion trauma. Objective: This study aims to improve the understanding of diagnosis, treatment, and management of these rare injuries for better patient care. Case presentation: 17-year-old male patient with type 1 diabetes mellitus presented to the emergency department with severe ankle pain and swelling following an inversion injury, which rendered him unable to walk or stand. Despite his chronic condition, he was hemodynamically stable, with no neurovascular deficits but an apparent deformity in the left ankle. Treatment involved pain management with morphine, successful closed reduction under ketamine sedation, and immobilization. Follow-up radiographs and a CT scan revealed no fractures but indicated soft tissue edema, joint effusion, and subsequent osteopenia. At a three-month follow-up, the patient experienced ongoing pain and weight-bearing difficulties, diagnosed as complicated pain syndrome requiring further physiotherapy and rehabilitation. Conclusion: This case highlights the clinical challenges and complications in managing isolated subtalar joint dislocations, particularly in patients with systemic health issues, and contributes valuable insights to the sparse literature on this topic.