Peri-implant Femoral Fracture: An Uncommon Presentation in a Patient with Hallermann-Streiff Syndrome - A Case Report and Review of the Literature.

Introduction: Hallermann-Streiff syndrome (HSS) is a globally rare congenital condition of unknown etiology, with approximately 200 cases reported worldwide. Although its skeletal morphological abnormalities are well recognized, traumatic and periprosthetic fractures have not been documented. These anatomical variations pose significant challenges for determining the optimal therapeutic approach, particularly in acute trauma settings. Case Report: We report the case of a 12-year-old male from Mexico who presented to the emergency department after a fall from standing height, sustaining direct trauma to the right hemibody. His medical history included a right femoral fracture 5 years earlier. Intraoperative findings revealed pronounced femoral shaft thinning, and open reduction and internal fixation (ORIF) with a low-profile plate was performed. The post-operative course was favorable, with satisfactory clinical and radiological progression at 6 months. This case illustrates the complex skeletal involvement associated with HSS and underscores the need for individualized surgical planning within a multidisciplinary framework. Conclusion: This case contributes valuable evidence to the limited literature on HSS by documenting a traumatic fracture requiring surgical management in a patient with this rare syndrome. Recognition of skeletal abnormalities and coordinated multidisciplinary care are essential for improving diagnosis, treatment, and follow-up in similar future presentations.