Adult Proximal Humeral Aneurysmal Bone Cyst: Radical Resection and Reconstruction with Osteoconductive Allograft & Reverse Arthroplasty— Ecuador's First Reported Case and Functional Outcomes

Gabriel Gamecho Arteaga¹Henry Hernández¹Chrystian X. Mestanza¹Jaime Zurita¹Marlon Arias-Intriago²Juan S. Izquierdo-Condoy^3*

• ¹Hospital Carlos Andrade Marin, Quito, Ecuador
• ²Hospital Oncologico Solca Nucleo de Quito, Quito, Ecuador
• ³Universidad de Las Americas, Quito, Ecuador

Abstract Introduction: Aneurysmal bone cysts (ABCs) are rare benign lesions, with adult cases being exceptionally uncommon. This report details a multidisciplinary approach for managing a proximal humeral ABC in an adult, emphasizing functional restoration. Case Presentation: A 36-year-old male presented with progressive pain, swelling, and restricted shoulder mobility. Imaging revealed an expansile lytic lesion with "soap-bubble" morphology. Histopathology confirmed a primary ABC. After failed conservative management, radical en bloc resection was performed, followed by single-stage reconstruction using osteoconductive allograft, reverse shoulder arthroplasty, and rotator cuff repair. Conclusion: This case demonstrates the efficacy of aggressive, single-stage reconstruction in adult ABCs, combining advanced orthopedic and oncologic principles. It advocates for molecular diagnostics to confirm primary lesions and supports hybrid graft-prosthesis strategies to optimize outcomes. The success of this approach provides a framework for managing rare, large ABCs in adults, encouraging further exploration of tailored surgical innovations in orthopedic oncology.