Symptomatic Fatty Involution of a Simple Bone Cyst in the Proximal Humerus: A Rare Case Report

Introduction: Intraosseous lipomas and simple bone cysts are mesenchymal bone tumors sharing similar characteristics and a suspected common pathophysiologic basis. Fatty involution of simple bone cysts is rare, especially in the proximal humerus. This report highlights a symptomatic case of fatty transformation in the proximal humerus, emphasizing diagnostic challenges and a novel surgical management approach. Case Report: A 36-year-old male presented with progressive left shoulder pain. Imaging revealed a lytic lesion in the proximal humeral metaphysis. The patient underwent extended curettage, bioabsorbable antibiotic-loaded cement bead application, and autologous bone grafting. Histopathology confirmed fibroadipose tissue with fatty involution. The patient resumed daily activities within 2 weeks, showing significant improvement with disabilities of the arm, shoulder, and hand scores improving from 35 at 2 weeks to 5 at 4 weeks postoperatively. Conclusion: Extended curettage with bio-absorbable antibiotic-loaded cement beads and autologous bone grafting is an effective option for managing symptomatic fatty involution in the proximal humerus. It provides complete lesion removal and structural reinforcement, offering excellent functional outcomes. Symptomatology should guide treatment decisions rather than imaging characteristics alone.