Classification of Acetabular Defects: The most popular classification of acetabular defects is the Harrington four-grade grading system: Type I: The anterior and posterior columns, the superior acetabular dome and the internal wall of the acetabulum are intact, and only the lower part of the acetabulum is damaged and defective. Type II: a defect in the medial wall of the acetabulum, with the lesion potentially or already metastasizing into the pelvis through the medial wall of the acetabulum. Type III: the most challenging, as the defect involves the medial wall, lateral margins, and superior vault of the acetabulum. It also often involves one or both columns. Type IV: the defect is rare and is an isolated lesion capable of en-bloc resection for therapeutic purposes.