## Autopsy Findings: Entrance Wound Identification ### Clinical Scenario Analysis **Key Point:** In this case, the combination of inward bone beveling and an abrasion collar definitively identifies this as an entrance wound. These two features together are pathognomonic for bullet entry. ### The Abrasion Collar: Mechanism and Reliability The abrasion collar forms when the bullet's forward motion scrapes and abrades the epidermis as it penetrates the skin. This creates a visible rim of abraded tissue that: - Is present in ~95% of entrance wounds - Is virtually never present in exit wounds - Persists even with decomposition - Is independent of projectile velocity or caliber **High-Yield:** The abrasion collar is the single most reliable naked-eye finding for identifying entrance wounds at autopsy. ### Bone Beveling: The Shock Wave Effect **Mnemonic:** **IBO** = **I**nward beveling = **B**ullet **O**rigin (entrance) When a bullet penetrates bone: 1. The projectile creates a primary wound cavity along its trajectory 2. The shock wave propagates radially outward from the bullet's path 3. This shock wave preferentially fractures bone on the side opposite entry 4. **Result:** Inward (internal) beveling at entrance, outward (external) beveling at exit ### Distinguishing Features: Entrance vs Exit (Rib Fracture Pattern) | Feature | Entrance Wound | Exit Wound | | --- | --- | --- | | **Bone beveling** | Inward (internal cone) | Outward (external cone) | | **Abrasion collar** | Present (95%) | Absent | | **Fracture pattern** | Radial from wound center | Irregular, explosive | | **Tissue damage** | Localized | Extensive, stellate | | **Soot/tattooing** | May be present | Never present | ### Why This Combination is Definitive **Clinical Pearl:** Inward bone beveling + abrasion collar = entrance wound with near 100% certainty. This combination is not found in exit wounds. [cite:Reddy Forensic Medicine 33e Ch 8]
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