## Acetabular Anatomy and Bone Contributions **Key Point:** The acetabulum is a triradiate structure formed by the fusion of the ilium, ischium, and pubis at the acetabular fossa. Each bone contributes a specific anatomical region. ### Anatomical Contributions | Bone | Contribution | Anatomical Region | Percentage | |------|--------------|-------------------|------------| | **Ilium** | Superolateral portion | Forms the roof and lateral wall | ~60% | | **Ischium** | Inferoposterior portion | Forms the posterior and inferior margin | ~25% | | **Pubis** | Anteromedial portion | Forms the anterior and medial margin | ~15% | ### Mnemonic **"IIP"** — **I**lium (superolateral), **I**schium (inferoposterior), **P**ubis (anteromedial) Alternatively: **"SIP"** — **S**uperolateral (Ilium), **I**nferoposterior (Ischium), **P**ubis (anteromedial) ### Clinical Significance **High-Yield:** The acetabular roof (formed primarily by the ilium) is the weight-bearing portion of the acetabulum. Damage to this region is clinically significant in hip osteoarthritis and acetabular fractures. **Clinical Pearl:** Acetabular fractures are classified by which bone(s) are involved: - Iliac fractures → superior/roof fractures (weight-bearing) - Ischial fractures → posterior wall fractures - Pubic fractures → anterior column fractures ### Anatomical Landmarks - **Acetabular fossa:** Central depression where the three bones meet - **Lunate surface:** Articular cartilage-covered crescent-shaped area - **Acetabular notch:** Inferiorly located gap between ischium and pubis - **Acetabular labrum:** Fibrocartilaginous rim that deepens the socket 
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