Question 1: A patient presents with a forefinger injury from glass, with suspicion of a retained foreign body. What is the initial investigation of choice?
- A. MRI
- B. CT scan
- C. Plain radiograph (Correct Answer)
- D. Ultrasonography
Explanation: **Explanation:**
The initial investigation of choice for a suspected retained foreign body (FB) in the extremities is a **Plain Radiograph (X-ray)**.
1. **Why Plain Radiograph is Correct:** Most foreign bodies encountered in trauma, such as glass, metal, and stone, are **radiopaque**. Glass, regardless of its lead content, is visible on X-rays in over 90% of cases if it is at least 2mm in size. X-rays are inexpensive, widely available, and highly effective at screening for these materials. Two orthogonal views (Anteroposterior and Lateral) are mandatory to localize the object accurately.
2. **Why other options are incorrect:**
* **Ultrasonography (USG):** This is the investigation of choice for **radiolucent** foreign bodies (e.g., wood, thorns, plastic) that do not show up on X-ray. It is also excellent for guiding removal but is usually the second step after a negative X-ray.
* **CT Scan:** While highly sensitive, it is not the "initial" choice due to higher radiation dose and cost. It is reserved for deep-seated foreign bodies in complex anatomical areas.
* **MRI:** This is generally **contraindicated** as an initial step because if the foreign body is metallic, the magnetic field can cause it to migrate, leading to further tissue or neurovascular injury.
**High-Yield Clinical Pearls for NEET-PG:**
* **Radiopaque FBs (Visible on X-ray):** Metal, Glass, Stone, Pencil lead (graphite).
* **Radiolucent FBs (Invisible on X-ray):** Wood, Thorns, Plastic, Cactus spines.
* **Gold Standard for Wood/Organic matter:** Ultrasonography.
* **Rule of Thumb:** If the history suggests glass or metal, start with an **X-ray**. If the history suggests wood or the X-ray is negative but clinical suspicion remains high, proceed to **USG**.
