**Core Concept**
Congenital syphilis is a condition that occurs when a baby is born with syphilis, a bacterial infection caused by *Treponema pallidum*. The condition can manifest with various symptoms, including joint effusions.

**Why the Correct Answer is Right**
The painless effusion in joints in congenital syphilis is known as Clutton's joints. This phenomenon is thought to occur due to the infiltration of lymphocytes and plasma cells into the synovium, leading to inflammation and joint effusion. Clutton's joints are a classic sign of congenital syphilis and can be a diagnostic clue in patients presenting with this condition.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it does not accurately describe the joint effusion associated with congenital syphilis.
* **Option B:** This option is incorrect because it is not a recognized term in the context of congenital syphilis.
* **Option D:** This option is incorrect because it is not a specific term related to joint effusion in congenital syphilis.

**Clinical Pearl / High-Yield Fact**
Clutton's joints are a classic sign of congenital syphilis and can be a diagnostic clue in patients presenting with this condition. It is essential to consider congenital syphilis in the differential diagnosis of joint effusions in children.

**Correct Answer: C. Clutton's joints.**