**Core Concept**
Rheumatic fever is an autoimmune inflammatory process that occurs after a group A beta-hemolytic streptococcal infection. Subcutaneous nodules are a manifestation of this process, representing a localized area of inflammation and immune complex deposition.

**Why the Correct Answer is Right**
Subcutaneous nodules in Rheumatic fever are typically **non-tender**, firm, and painless, often found over bony prominences such as the elbows, knees, and wrists. They are a result of the deposition of immune complexes containing IgG and IgM antibodies against the streptococcal antigens, which accumulate in the dermal layer of the skin. This process leads to an inflammatory response, characterized by the presence of giant cells and granulomatous changes.

**Why Each Wrong Option is Incorrect**
* **Option A:** "Non tender" is the correct characteristic of subcutaneous nodules in Rheumatic fever, but the statement "Most common manifestation" is incorrect as the most common manifestation is actually carditis.
* **Option B:** "Most common manifestation" is incorrect as carditis is the most common manifestation of Rheumatic fever, not subcutaneous nodules.
* **Option C:** "Present in extensor surfaces" is incorrect as subcutaneous nodules are typically found over bony prominences, not necessarily in extensor surfaces.
* **Option D:** "Associated with arthritis" is incorrect as while arthritis is a manifestation of Rheumatic fever, subcutaneous nodules are not directly associated with arthritis.

**Clinical Pearl / High-Yield Fact**
Subcutaneous nodules in Rheumatic fever are often a sign of a more severe disease process, and their presence may indicate a higher risk of cardiac complications.

**Correct Answer:** .