## **Core Concept**
Rheumatoid arthritis (RA) and ankylosing spondylitis (AS) are both chronic inflammatory rheumatic diseases but have distinct clinical and radiological features. RA primarily affects the small joints of the hands and feet, while AS mainly affects the axial skeleton, including the spine and sacroiliac joints. The question focuses on a complication or feature more commonly associated with RA than AS.

## **Why the Correct Answer is Right**
The correct answer, **rheumatoid nodules**, are a common extra-articular manifestation of RA. These are firm, painless collections of inflammatory cells that can be found under the skin, often near the joints, but also in other areas such as the lungs and heart. Rheumatoid nodules are a hallmark of RA and are not typically associated with AS.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is not specified, but if we consider common features of RA and AS, we can infer that some manifestations are more typical of one condition over the other.
- **Option B:** Similarly, without the specific content of Option B, we note that AS is more commonly associated with **bamboo spine** due to spinal fusion and syndesmophyte formation, a feature not characteristic of RA.
- **Option C:** Without details, we proceed with the understanding that certain features like **sacroiliitis** are more commonly seen in AS than RA.
- **Option D:** Assuming this is not the correct answer related to rheumatoid nodules, we recognize that **uveitis** is more commonly associated with AS, an inflammatory eye condition that can lead to severe vision problems if not treated.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that **rheumatoid nodules** are highly suggestive of RA, particularly in patients with a long-standing history of the disease. These nodules are not only a diagnostic criterion but also reflect the systemic nature of the disease. They are more common in patients with seropositive RA.

## **Correct Answer: C. Rheumatoid nodules.**