Boutonniere deformity involves –
**Core Concept**
Boutonniere deformity is a deformed position of the finger, characterized by flexion of the proximal interphalangeal (PIP) joint and hyperextension of the distal interphalangeal (DIP) joint. This condition is often associated with **rheumatoid arthritis** and **trauma**. The deformity results from an imbalance of the extensor tendons.
**Why the Correct Answer is Right**
The correct answer is related to the imbalance of the extensor tendons, specifically the **central slip** of the extensor tendon. When the central slip is disrupted, the lateral bands of the extensor tendon slip volarly, causing flexion of the PIP joint. The DIP joint hyperextends due to the unopposed action of the **terminal tendon**.
**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because it does not accurately describe the joint involvement in Boutonniere deformity.
**Option B:** Incorrect as it is more related to swan neck deformity.
**Option C:** Incorrect because it is associated with a different type of deformity.
**Option D:** Incorrect as it is not directly related to the pathophysiology of Boutonniere deformity.
**Clinical Pearl / High-Yield Fact**
Boutonniere deformity is a common complication of rheumatoid arthritis, and early recognition is essential for effective management. The deformity can be treated with splinting or surgery, depending on the severity.
**Correct Answer:** D. Proximal interphalangeal joint flexion and distal interphalangeal joint hyperextension.