This document provides an overview of avascular necrosis (AVN), also called osteonecrosis, which is the death of bone tissue due to interruption of the blood supply. It discusses early diagnosis, radiological evaluation, MRI findings, treatment algorithms, and management strategies depending on the stage of AVN. For pre-collapse cases, options include observation, core decompression, or free fibula grafting. For post-collapse cases, osteotomies or bone grafting may be considered if less than 30% involvement, otherwise joint replacement. The document emphasizes the importance of staging/quantification and presents several case studies demonstrating surgical outcomes.